The Development of Agricultural Antibiotics - ACS Symposium Series

10 The Development of Agricultural Antibiotics TOMOMASA MISATO

Downloaded by UNIV OF ARIZONA on May 26, 2017 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

The Institute of Physical and Chemical Research, Wako-shi, Saitama 351, Japan

Introduction The successful use of a n t i b i o t i c s against b a c t e r i a l diseases of human beings has led to a large scale screening of a n t i b i o t i c s effect for plant disease control in the world. Many a n t i b i o t i c s developed for medical purposes were investigated for a c t i v i t y against plant pathogens. Furthermore screening of soil organisms for production of a n t i b i o t i c substances was started with the prime purpose of plant disease c o n t r o l . However, the results obtained with a n t i b i o t i c s and a n t i b i o t i c containing culture broth did not fulfil the high expectations. Many of them were too unstable under field conditions or showed toxic side effects on plants. Most a n t i b i o t i c s were rather expensive, even when used as a crude product. In western countries only a few a n t i b i o t i c s have been developed for p r a c t i c a l use. These are streptomycin, tetra cycline, cycloheximide and g r i s e o f u l v i n . Streptomycin, the first a n t i b i o t i c introduced in a g r i c u l t u r e , was used in the United States for the control of pear f i r e b l i g h t . This a n t i b i o t i c and a mixture of streptomycin and tetracycline have been used for the control of b a c t e r i a l plant diseases, while cycloheximide and griseofulvin have been used for the control of fungal plant diseases. Cycloheximide is a very powerful fungicide, but unfor tunately, highly toxic to plants, which r e s t r i c t s its use against plant diseases. Griseofulvin i s a much less phytotoxic systemic fungicide, but its use is also restricted, because the r e l a t i o n of its manufacturing cost to its performance under field condition is not quite satisfactory. In Japan, these four a n t i b i o t i c s had been used only on a very l i m i t e d scale for p r a c t i c a l control of plant diseases, u n t i l the curative effect of blasticidin S on r i c e blast was discovered by the author's research group i n 1958. The successful application of blasticidin S against r i c e blast has stimulated the development of a g r i c u l t u r a l a n t i b i o t i c s and led to the discovery of several excellent a n t i b i o t i c s , such as kasuga mycin, polyoxins and validamycin etc. Nowadays, blasticidin S and kasugamycin have been in p r a c t i c a l use for r i c e blast control instead of mercuric fungicides, and polyoxins and validamycin have ;

170

Plimmer et al.; Pesticide Chemistry in the 20th Century ACS Symposium Series; American Chemical Society: Washington, DC, 1977.


1974

1968

1964

1964

1957

1972

1970

1967

1965

1961

1959

1959

Registration

Insecticidal Antibiotics Tetranactin

ANTIBACTERIAL ANTIBIOTICS Streptomycin (Wettable Powder) Cellocidin (Wettable Powder) Chloramphenicol +Basic copper (Wettable Powder) Novobiocin (Solution)

ANTIFUNGAL ANTIBIOTICS Cycloheximide (Wettable Powder) Griseofulvin (Paste) Blasticidin S (Dust) (Wettable Powder) (Solution) Kasugamycin (Dust) (Wettable Powder) (Solution) Polyoxins (Dust) (Wettable Powder) (Solution) Ezomycin (Wettable Powder) Validamycin (Dust) (Wettable Powder)

Antibiotics

Blight

Insects Carmine Mite of F r u i t s and Tea

B a c t e r i a l Canker of Tomatoes

B a c t e r i a l Diseases of F r u i t s and Vegetables Rice B a c t e r i a l Leaf B l i g h t Rice B a c t e r i a l Leaf B l i g h t

Rice Sheath

Stem Rot of Kidney Bean

Rice Sheath B l i g h t Fungal Diseases of F r u i t s and Vegetables

Rice Blast

Rice B l a s t

Onion Downy Mildew Shoot B l i g h t of Japanese Larch Fusarium W i l t of Melon

Diseases

0

10

0

349

3,893 94

0

387 418 34

7,930 265 10

1,250 3 152

2

17

(ton)

(10

0

33,130

0

692,086

513,876 143,256

0

32,121 960,982 38,216

507,762 221,805 8,820

75,000 2,547 102,426

4,700

3

(1974)

35,020

Amounts used i n Japan

Table I . A g r i c u l t u r a l A n t i b i o t i c s used i n Japan


yen)

PESTICIDE C H E M I S T R Y


172

IN T H E 2 0 T H

CENTURY

been used t o c o n t r o l t h e s h e a t h b l i g h t o f r i c e p l a n t i n s t e a d o f arsenic fungicides. The amount o f a n t i b i o t i c s u s e d i n J a p a n i s shown i n T a b l e I . The d e v e l o p m e n t o f a g r i c u l t u r a l a n t i b i o t i c s has n o t b e e n l i m i t e d o n l y f o r c o n t r o l l i n g p l a n t d i s e a s e s , b u t h a s e x t e n d e d w i d e r and more a c t i v e l y o v e r v a r i o u s a r e a s s u c h a s u t i l i z a t i o n o f i n s e c t i c i d e s , h e r b i c i d e s and p l a n t r e g u l a t o r s i n J a p a n . As shown i n T a b l e I I , many compounds o f m i c r o b i o l o g i c a l o r i g i n a r e a l r e a d y u s e d as p e s t i c i d e s o r show p r o m i s e f o r practical application. B l a s t i c i d i n S; e t c . as a n t i f u n g a l a n t i b i o t i c s , s t r e p t o m y c i n , e t c . as a n t i b a c t e r i a l a n t i b i o t i c s , t e t r a n a c t i n as a m i t i c i d e , and g i b b e r e l l i n s as p l a n t g r o w t h r e g u l a t o r s a r e p r a c t i c a l l y u s e d . A a b o m y c i n as an a n t i v i r a l a n t i b i o t i c , a p r o d u c t o f B a c i l l u s t h u r i n g e n s i s as a i n s e c t i c i d a l a n t i b i o t i c and a n i s o m y c i n d e r i v a t i v e s as h e r b i c i d e s h a v e b e e n t e s t e d f o r p r a c t i c a l use i n the f i e l d s . Table I I .

Pesticidal

compounds o f m i c r o b i o l o g i c a l

[Fungicide] * Antifungal antibiotics * Antibacterial antibiotics Antiviral antibiotics [insecticide] * Miticidal antibiotic * Bacterial toxin [Herbicide] Herbicidal antibiotic [Growth r e g u l a t o r ] * Fungal product

: : :

B l a s t i c i d i n S, e t c . Streptomycin, e t c . Aabomycin, e t c .

:

Tetranactin

:

Bacillus

:

Anisomycin

: *

origin

thuringensis

Gibberellins

P r a c t i c a l l y u s e d as p e s t i c i d e s

R e v i e w s on many a n t i b i o t i c s i n c l u d i n g c y c l o h e x i m i d e , g r i s e o f u l v i n and s t r e p t o m y c i n t e s t e d f o r t h e p u r p o s e o f a g r i c u l t u r a l use i n w e s t e r n c o u n t r i e s have been p u b l i s h e d ( 1 - 6 ) . I ti s the purpose o f t h i s paper t o d i s c u s s t h e p r e s e n t s t a t u s o f a n t i b i o t i c s a s p l a n t d i s e a s e c o n t r o l a g e n t s . The d i s c u s s i o n w i l l m a i n l y be l i m i t e d t o a n t i b i o t i c s w h i c h a r e p r a c t i c a l l y u s e d a s new p e s t i c i d e s i n J a p a n . F o r t h e o t h e r l i t e r a t u r e , t h e r e a d e r may r e f e r t h e r e v i e w s m e n t i o n e d above. Antifungal

antibiotics

B l a s t i c i d i n S. B l a s t i c i d i n S i s t h e f i r s t s u c c e s s f u l a g r i c u l t u r a l a n t i b i o t i c developed i n Japan. I t was i s o l a t e d f r o m t h e c u l t u r e f i l t r a t e s o f Streptomyces griseochromogenes by T a k e u c h i e t a l . ( 7 ) , and t h e p o t e n t c u r a t i v e e f f e c t o f b l a s t i c i d i n S on r i c e b l a s t was f o u n d b y M i s a t o elt a l . ( 8 ) . T h e r e a f t e r t h e b e n z y l aminobenzene s u l f o n a t e o f b l a s t i c i d i n S was r e p o r t e d t o be l e a s t phytotoxic to the host plant without reducing antifungal a c t i v i t y a g a i n s t P y r i c u l a r i a o r y z a e , t h e p a t h o g e n o f r i c e b l a s t ( 9 ) , and


MisATO

10.

Agricultural

173

Antibiotics

t h i s s a l t has been i n d u s t r i a l l y produced f o r a g r i c u l t u r a l use. 1) C h e m i s t r y a n d mode o f a c t i o n : The c h e m i c a l s t r u c t u r e o f b l a s t i c i d i n S has been s t u d i e d e x t e n s i v e l y by Yonehara and h i s c o - w o r k e r s a n d t h e f i n a l s t r u c t u r e a s s i g n e d b l a s t i c i d i n S i s 1(l -cytosinyl)-4-[L-3 -amino-5 -(l -N-methylguandidino)-valerylamino]-!,2,3,4-tetradeoxy-B-D-erythro-hex-2-eneuronic a c i d as shown i n F i g u r e 1 ( 1 0 , 1 1 ) . S e t o e t a l . (12,13) s t u d i e d t h e b i o s y n t h e s i s o f b l a s t i c i d i n S by the p r o d u c i n g organism u s i n g Relabeled suspected precursors. The r e s u l t s o b t a i n e d w e r e t h a t t h e p y r i m i d i n e r i n g o f t h e a n t i b i o t i c came f r o m c y t o s i n e d i r e c t l y a n d sugar moiety from g l u c o s e ; a r g i n i n e s e r v e d as t h e p r e c u r s o r f o r b l a s t i d i c a c i d , and t h e N - m e t h y l group o f b l a s t i d i c a c i d a r o s e from m e t h i o n i n e . M i s a t o and h i s co-workers have s t u d i e d t h e b i o c h e m i c a l p r o p e r t i e s o f b l a s t i c i d i n S on _P. o r y z a e . They f o u n d t h e c u r a t i v e e f f e c t o f b l a s t i c i d i n S on r i c e b l a s t due t o a s t r o n g i n h i b i t o r y a c t i o n on m y c e l i a l g r o w t h o f t h e p a t h o g e n , and r e p o r t e d t h a t t h e a n t i b i o t i c m a r k e d l y i n h i b i t e d t h e i n c o r p o r a t i o n o f Rel a b e l e d amino a c i d i n t o p r o t e i n i n t h e c e l l - w a l l s y s t e m o f ]?. o r y z a e ( 1 4 ) , w h i l e m e t a b o l i c pathways i n c l u d i n g g l y c o l y s i s , s u c c i n i c d e h y d r o g e n a s e s y s t e m , e l e c t r o n t r a n s p o r t s y s t e m , and o x i d a t i v e p h o s p h o r y l a t i o n s y s t e m o r i n c o r p o r a t i o n o f ^2p i n t o t h e n u c l e i c a c i d w e r e n o t i n h i b i t e d b y b l a s t i c i d i n S ( 1 5 , 1 6 ) . The mode o f a c t i o n o f t h i s a n t i b i o t i c on t h e m o l e c u l a r b a s i s i n d e t a i l i s n o t known s o f a r w i t h any c e r t a i n t y , b u t c e r t a i n p r o c e s s e s r e l a t e d t o p e p t i d y l transferase a c t i v i t y a r ei n h i b i t e d by b l a s t i c i d i n S (17,18).


1

1

1

! !

2) Biological properties: B l a s t i c i d i n S has a wide range of b i o l o g i c a l a c t i v i t i e s . Besides i t s s i g n i f i c a n t i n h i b i t o r y e f f e c t s on t h e g r o w t h o f ]?. o r y z a e , i t a l s o e x h i b i t s o t h e r a n t i m i c r o b i a l ( 7 ) , and a n t i - v i r a l (19) a s w e l l a s a n t i - t u m o r a c t i v i t i e s ( 2 0 ) , t h o u g h t h e m e d i c i n a l a p p l i c a t i o n s a r e impeded b y i t s toxic properties. I n t h e case o f spraying i n t h e f i e l d t o pro tect r i c e b l a s t , thee f f e c t i v e concentration of b l a s t i c i d i n S i s u s u a l l y 10 t o 20 ppm ( 1 - 3 g b l a s t i c i d i n S / 1 0 a ) , b u t i t o c c a s i o n a l l y c a u s e s c h e m i c a l i n j u r y on r i c e l e a v e s when s p r a y e d b e y o n d t h e c o n c e n t r a t i o n d e s c r i b e d above. The a p p l i c a t i o n b y d u s t i n g o c c a s i o n a l l y causes c o n j u n c t i v i t i s i f i t a c c i d e n t a l l y c o n t a c t s t h e eyes, a l t h o u g h no a c c i d e n t has been r e p o r t e d i n t h e c a s e o f t h e s p r a y o f w e t t a b l e powder o r s o l u t i o n . Such t o x i c e f f e c t on mammals i s t h e most u n f a v o r a b l e c h a r a c t e r i s t i c o f b l a s t i c i d i n S. Many a t t e m p t s h a v e b e e n made t o remedy t h i s d e f e c t o f b l a s t i c i d i n S. S u g i m o t o (21) f o u n d a s i m p l e method t o a l l e v i a t e e y e i r r i t a t i o n c a u s e d b y b l a s t i c i d i n S; t h e a d d i t i o n o f calcium acetate t o b l a s t i c i d i n S dust (5% a d d i t i o n ) s p e c i f i c a l l y r e d u c e d t h e e y e t r o u b l e w i t h o u t i n f l u e n c e on a n t i b l a s t e f f e c t , t h o u g h o t h e r mammalian t o x i c i t y o r p h y t o t o x i c i t y o f t h e a n t i b i o t i c are also not affected. T h i s i m p r o v e d d u s t i s now u s e d p r a c t i c a l l y f o r a g r i c u l t u r a l use. The b e h a v i o r a n d f a t e o f b l a s t i c i d i n S i n t h e environment were i n v e s t i g a t e d u s i n g r a d i o -



PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

Figure 2.

Structure of kasugamycin



10.

MisATO

Agricultural

Antibiotics

175

a c t i v e compounds p r e p a r e d b i o s y n t h e t i c a l l y f r o m C - c y t o s i n e and C - L - m e t h i o n i n e ( 2 2 ) . The s p r a y e d a n t i b i o t i c was l o c a t e d on t h e s u r f a c e o f t h e r i c e p l a n t a n d l i t t l e was d i f f u s e d o r t r a n s p o r t e d i n t o t h e t i s s u e . From t h e wound o r i n f e c t e d p a r t , however, t h e compound was i n c o r p o r a t e d and t r a n s l o c a t e d m a i n l y t o u p p e r p a r t . The compound l o c a t e d a t t h e p l a n t s u r f a c e was decomposed b y s u n l i g h t a n d gave r i s e t o c y t o s i n e a s t h e m a i n d e g r a d a t i o n product. A considerable quantity o f b l a s t i c i d i n S sprayed f e l l t o t h e g r o u n d a n d was a d s o r b e d on t h e s o i l s u r f a c e t i g h t l y . Further more, s i g n i f i c a n t g e n e r a t i o n o f - ^ C - c a r b o n d i o x i d e f r o m t h e - ^ C i b l a s t i c i d i n S t r e a t e d s o i l was o b s e r v e d , and s e v e r a l m i c r o b e s u s u a l l y i n h a b i t i n g t h e paddy f i e l d w e r e f o u n d t o make t h e b i o l o g i c a l a c t i v i t y o f b l a s t i c i d i n S lower. From t h e r e s u l t s o b t a i n e d , Y a m a g u c h i et_ a l . s u p p o s e d t h a t a f t e r a p p l i c a t i o n t o t h e c r o p a t very low c o n c e n t r a t i o n , t h e a n t i b i o t i c might be r a p i d l y broken down i n t h e e n v i r o n m e n t , s o t h a t t h e r e may b e no d a n g e r o f e n v i r o n m e n t a l p o l l u t i o n and food contamination. Kasugamycin. K a s u g a m y c i n i s a w a t e r - s o l u b l e and b a s i c a n t i b i o t i c produced by Streptomyces kasugaensis (23). F o l l o w i n g t h e d e v e l o p m e n t o f b l a s t i c i d i n S, k a s u g a m y c i n h a s b e e n u s e d a s a n a g r i c u l t u r a l a n t i b i o t i c f o r r i c e b l a s t c o n t r o l i n Japan s i n c e 1965. This a n t i b i o t i c controls r i c e b l a s t disease a t a concentra t i o n a s l o w a s a b o u t 20 ppm. I t c a n b e s a f e l y u s e d w i t h o u t a n y t o x i c i t y on c r o p s , and w i t h v e r y l o w t o x i c i t y t o mammals. These advantages a r e t h e main r e a s o n s t h a t b l a s t i c i d i n S i s l o s i n g ground t o kasugamycin. However, r e c e n t l y , t h e v i r u l e n c e o f kasugamycin-resistant s t r a i n i n paddy f i e l d h a s r a i s e d a s e r i o u s problem i n r i c e b l a s t c o n t r o l by kasugamycin. 1) C h e m i s t r y and mode o f a c t i o n : The c h e m i c a l s t r u c t u r e o f k a s u g a m y c i n was s t u d i e d b y S u h a r a elt a l . (24,25) b y c h e m i c a l methods a n d b y I k e k a w a e t a l . (26) b y X - r a y d i f f r a c t i o n a n a l y s i s . As shown i n F i g u r e 2, t h e m o l e c u l e o f k a s u g a m y c i n c o n s i s t s o f t h r e e m o i e t i e s w h i c h a r e D - i n o s i t o l , kasugamine (2,3,4,6-tetrad e o x y - 2 , 4 - d i a m i n o h e x o p y r a n o s e ) and an i m i n o a c e t i c a c i d s i d e c h a i n . N a k a j i m a and h i s a s s o c i a t e s s t u d i e d t h e s y n t h e s i s o f k a s u g a m y c i n , and s u c c e e d e d i n s y n t h e s i z i n g k a s u g a n o b i o s a m i n e and r e l a t e d com pounds ( 2 7 , 2 8 ) ; t h a t means t h e t o t a l s y n t h e s i s o f k a s u g a m y c i n b y t h e i n t r o d u c t i o n o f t h e o x a l i m i d y l group i n t o k a s u g a n o b i o s a m i n e . K a s u g a m y c i n e n t e r s i n t o t h e p l a n t t i s s u e , a n d shows b o t h p r o t e c t i v e and c u r a t i v e a c t i o n . I t does n o t i n h i b i t s p o r e g e r m i n a t i o n even a t a c o n c e n t r a t i o n o f 120 ug/ml. I t s effect against £.· o^yzae comes o n l y t o e x p r e s s i o n i n t h e p l a n t a n d i n v i t r o a t l o w pH ( 2 9 ) . T a n a k a jet a l . (30) r e p o r t e d t h a t k a s u g a m y c i n i n h i b i t e d p r o t e i n s y n t h e s i s i n c e l l f r e e s y s t e m s o f ]?. o r y z a e . Kasugamycin i n h i b i t s p r o t e i n s y n t h e s i s i n E s c h e r i c h i a c o l i b y i n t e r f e r i n g w i t h t h e b i n d i n g o f a m i n o a c y l - t R N A t o mRNA-30 S r i b o s o m a l s u b u n i t complex. The compound does n o t c a u s e m i s c o d i n g .


PESTICIDE C H E M I S T R Y IN

176

THE

20TH

CENTURY

2) B i o l o g i c a l p r o p e r t i e s : K a s u g a m y c i n s e l e c t i v e l y i n h i b i t e d t h e g r o w t h o f P. ovyzae and some b a c t e r i a i n c l u d i n g Pseudomonas s p e c i e s , and showed l i t t l e o r no a c t i v i t y a g a i n s t o t h e r f u n g i tested. The a n t i b i o t i c d i d n o t show a c u t e o r c h r o n i c t o x i c i t y t o m i c e , r a t s , r a b b i t s , d o g s , monkeys and human b e i n g s . The o r a l LD f o r m i c e was 2 g/kg. A t a c o n c e n t r a t i o n o f 1,000 ppm t h e r e was no t o x i c i t y t o f i s h . K a s u g a m y c i n i s now u s e d i n a l a r g e scale against r i c e blast. I t c o n t r o l s r i c e b l a s t when s p r a y e d a t a b o u t 20 - 40 ppm aqueous s o l u t i o n . For p r a c t i c a l disease c o n t r o l k a s u g a m y c i n i s m a i n l y a p p l i e d a s a d u s t , c o n t a i n i n g 0.3 % o f a c t i v e i n g r e d i e n t . No i n j u r y was o b s e r v e d t o many o t h e r p l a n t s . The d e v e l o p m e n t o f r e s i s t a n c e i n f u n g i t o k a s u g a m y c i n has been r e p o r t e d from l a b o r a t o r y experiments, but not i n the f i e l d s f o r some y e a r s a f t e r a p p l i c a t i o n o f t h e a n t i b i o t i c . However, s i n c e 1971, t h e d e v e l o p m e n t o f a k a s u g a m y c i n - r e s i s t a n t s t r a i n o f r i c e b l a s t f u n g u s i n t h e f i e l d s has become a s e r i o u s p r o b l e m ( 3 1 ) . A f t e r k a s u g a m y c i n r e s i s t a n t s t r a i n s had b e e n d e t e c t e d i n t h e f i e l d , t h e c o m b i n e d f o r m u l a t i o n s o f k a s u g a m y c i n and c h e m i c a l s w i t h d i f f e r e n t a c t i o n mechanisms h a v e b e e n p r a c t i c a l l y u s e d .


5 0

Polyoxins. The p o l y o x i n s , a new g r o u p o f p e p t i d y l - p y r i m i d i n e n u c l e o s i d e a n t i b i o t i c s , a r e p r o d u c e d by Streptomyoes oaoaoi v a r . asoensis (32,33). P o l y o x i n s a r e composed o f t h i r t e e n components (A - M) o f some c l o s e l y r e l a t e d " p e p t i d i c n u c l e o s i d e s " as r e f e r r e d by I s o n o and S u z u k i ( 3 4 ) . They c a n be s a f e l y u s e d w i t h no t o x i c i t y t o man, l i v e s t o c k , f i s h and p l a n t . Such e x c e l l e n t c h a r a c t e r i s t i c s may be due t o t h e f a c t t h a t p o l y o x i n s s e l e c t i v e l y i n h i b i t the s y n t h e s i s of c e l l w a l l c h i t i n of s e n s i t i v e f u n g i , as was r e p o r t e d by M i s a t o and h i s c o - w o r k e r s ( 3 5 - 3 8 ) . P o l y o x i n s have b e e n w i d e l y u s e d f o r t h e p r o t e c t i o n a g a i n s t some p a t h o g e n i c f u n g i

s u c h a s Altemaria miyabeanus

kikuohiana,

i n Japan s i n c e

Pellioularia

sasakii, and

Coehlibolus

1967.

1) C h e m i s t r y and mode o f a c t i o n : S t r u c t u r e s o f a l l p o l y o x i n s were g i v e n by I s o n o et al. (39) a s d e p i c t e d i n F i g u r e 3. Among p o l y o x i n s , C component i s t h e s m a l l e s t , and t h o u g h i t l a c k s a n t i f u n g a l a c t i v i t y i t was a k e y compound t o e l u c i d a t e t h e s t r u c t u r e of p o l y o x i n s s i n c e h y d r o l y t i c degradation of a l l the p o l y o x i n s afforded p o l y o x i n C or i t s analogues. I s o n o and S u z u k i (40) assigned the s t r u c t u r e , l-ft-iS'-amino-S'-deoxy-D-allofuranuronosyl) - 5 - h y d r o x y m e t h y l u r a c i l t o p o l y o x i n C by c h e m i c a l and p h y s i c a l t e c h n i q u e s , and a s i n g l e - c r y s t a l X - r a y d i f f r a c t i o n a n a l y s i s o f Nb r o s y l p o l y o x i n C c o n f i r m e d the s t r u c t u r e (41). T h i s prompted the t o t a l s y n t h e s i s o f p o l y o x i n J by K u z u h a r a et al. ( 4 2 ) . In s t u d y i n g t h e mechanism o f f u n g i c i d a l a c t i o n o f p o l y o x i n s , E g u c h i et al. (43) o b s e r v e d a s p e c i f i c p h y s i o l o g i c a l a c t i o n a g a i n s t Altevnaria spp. i n i n h i b i t i n g i t s g r o w t h ; p o l y o x i n s c a u s e d m a r k e d a b n o r m a l b u l b o u s phenomenon on germ t u b e s o f s p o r e and h y p h a l t i p s o f t h e p a t h o g e n a t l o w c o n c e n t r a t i o n , and t h i s a b n o r m a l l y s w o l l e n s p o r e became n o n - i n f e c t i o u s . I t was a l s o r e p o r t e d t h a t t h e


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Agricultural

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Ri


Polyoxin

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Structure of polyoxins


178


THE

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lz

i n c o r p o r a t i o n of *C-glucosamine i n t o c e l l w a l l c h i t i n of Coohliobolus miyabeanus was m a r k e d l y i n h i b i t e d by p o l y o x i n D, w i t h o u t i n h i b i t o r y e f f e c t on r e s p i r a t i o n and s y n t h e s i s o f m a c r o m o l e c u l e s s u c h as p r o t e i n o r n u c l e i c a c i d s ( 4 4 ) . Endo and M i s a t o (36) showed i n t h e i r k i n e t i c s t u d i e s o f t h e c e l l - f r e e s y s t e m o f Neurospora arassa t h a t p o l y o x i n D s t r o n g l y i n h i b i t s t h e i n c o r p o r a t i o n of N - a c e t y l g l u c o s a m i n e (GlcNAc) i n t o c h i t i n i n c o m p e t i t i v e manner b e t w e e n UDP-GlcNAc and p o l y o x i n D. More r e c e n t l y H o r i et at. (38) r e p o r t e d t h e r e l a t i o n b e t w e e n p o l y o x i n s t r u c t u r e and i n h i b i t o r y a c t i v i t y on c h i t i n s y n t h e t a s e . According to t h e i r k i n e t i c a n a l y s i s , the carbamoyl polyoxamic a c i d moiety of p o l y o x i n s w o u l d h e l p t o s t a b i l i z e t h e p o l y o x i n enzyme c o m p l e x and the p y r i m i d i n e n u c l e o s i d e moiety of the a n t i b i o t i c s would a l s o f i t i n t o b i n d i n g s i t e of the p r o t e i n . Therefore the e x c e l l e n t c h a r a c t e r i s t i c s o f p o l y o x i n s may be due t o t h e f a c t t h a t t h e a n t i b i o t i c s i n h i b i t the c e l l w a l l s y n t h e s i s of s e n s i t i v e f u n g i but have no i n f l u e n c e on o t h e r o r g a n i s m s i n c l u d i n g mammals, s i n c e t h e r e e x i s t no c e l l w a l l s i n a n i m a l c e l l s . 2) B i o l o g i c a l p r o p e r t i e s : P o l y o x i n s i n h i b i t t h e g r o w t h o f some f u n g i b u t a r e i n a c t i v e a g a i n s t b a c t e r i a and y e a s t . A l l the p o l y o x i n s e x c e p t C and I showed s e l e c t i v e a n t i f u n g a l a c t i v i t y a g a i n s t v a r i o u s p l a n t p a t h o g e n i c f u n g i ( 4 5 ) . Among p o l y o x i n s , p o l y o x i n D was most e f f e c t i v e f o r r i c e s h e a t h b l i g h t p a t h o g e n , Pellicularia sasakii, w h e r e a s Β and L w e r e e f f e c t i v e f o r p e a r s p o t f u n g u s and a p p l e c o r k s p o t f u n g u s a t 50 t o 100 ppm. Polyoxin c o m p l e x has b e e n u s e d i n p r a c t i c e i n d u p l i c a t e f o r m s ; p o l y o x i n D r i c h f r a c t i o n f o r t h e s h e a t h b l i g h t c o n t r o l , and Β r i c h f r a c t i o n f o r d i s e a s e s c a u s e d by Altemaria spp. As f o r i t s t o x i c i t y , o r a l a d m i n i s t r a t i o n a t 15 g/kg and i n j e c t i o n a t 800 mg/kg t o m i c e d i d n o t c a u s e any a d v e r s e e f f e c t , n o r i s i t t o x i c t o f i s h d u r i n g 72 h o u r s p e r i o d o f e x p o s u r e a t 10 ppm. M o r e o v e r , f o l i a r s p r a y s o f 200 ppm p o l y o x i n s have p r o d u c e d no p h y t o t o x i c i t y on most c r o p s , and e s p e c i a l l y on r i c e p l a n t no i n j u r y was o b s e r v e d e v e n a t 800 ppm a p p l i c a t i o n ( 3 3 , 4 6 ) . R e c e n t l y , N i s h i m u r a et at. (47) h a v e r e p o r t e d t h e d i s c o v e r y o f p o l y o x i n r e s i s t a n t s t r a i n s o f A. kikuohiana i n some o r c h a r d s o f T o t t o r i P r e f e c t u r e , J a p a n . H o r i et al. (48) s u g g e s t e d t h a t t h e r e s i s t a n c e i s c a u s e d by a l o w e r e d p e r m e a b i l i t y o f t h e a n t i b i o t i c t h r o u g h t h e c e l l membrane i n t o t h e s i t e o f c h i t i n s y n t h e s i s . M i t a n i and I n o u e (49) f o u n d t h a t t h e i n h i b i t i o n o f m y c e l i a l g r o w t h o f P. sasakii, by p o l y o x i n s was p r o t e c t e d by g l y c y l - L a l a n i n e , g l y c y l - D , L - v a l i n e and D , L - a l a n y l g l y c i n e . T h e r e f o r e , t h e p e p t i d e s may a c t a s a n t a g o n i s t s t o t h e i n c o r p o r a t i o n o f p o l y o x i n s i n t o the c e l l of the fungus. Validamycin. V a l i d a m y c i n A (VM-A) i s a new a n t i f u n g a l a n t i b i o t i c r e c e n t l y developed i n Japan f o r the c o n t r o l of r i c e sheath b l i g h t (50-52). I t was i s o l a t e d f r o m t h e c u l t u r e f i l t r a t e o f Streptomyaes hygroscopicus v a r . limoneus, w h i c h a l s o p r o d u c e d f i v e


10.

MisATO

Agricultural

Antibiotics

179


a d d i t i o n a l components d e s i g n a t e d v a l i d a m y c i n Β t o F, t o g e t h e r w i t h v a l i d o x y l a m i n e A and Β (52,53). VM-A c a n be u s e d w i t h o u t i n j u r y t o p l a n t s , and w i t h v e r y l o w t o x i c i t y t o mammals ( 5 4 ) . A l m o s t no t o x i c i t y was a l s o o b s e r v e d f o r b i r d s , f i s h and i n s e c t s . 1) C h e m i s t r y and mode o f a c t i o n : The c h e m i c a l s t r u c t u r e o f v a l i d a m y c i n A was d e t e r m i n e d b y H o r i i , Kameda and t h e i r c o - w o r k e r s t o be N - [ ( l s ) - ( l , 4 , 6 / 5 ) - 3 - h y d r o x y m e t h y l - 4 , 5 , 6 - t r i h y d r o x y c y c l o h e x - 2 enyl][Ο-β-D-glucopyranosyl-(l->3 ) - ( l s ) - ( l , 2 , 4 / 3 , 5 ) - 2 , 3 , 4 - t r i h y d r o x y - 5 - h y d r o x y m e t h y l c y c l o h e x y l ] amine a s shown i n F i g u r e 4 (53,55,56,57). As f o r mode o f a c t i o n o f v a l i d a m y c i n A, Wakae and M a t s u u r a ( 5 8 ) showed t h a t VM-A i n h i b i t s b i o s y n t h e s i s o f i n o s i t o l i n P . sasakii, and t h e y s u p p o s e d t h a t i n o s i t o l may be i n d i s p e n s a b l e f o r t h e n o r m a l g r o w t h and p a t h o g e n i c a c t i v i t y o f t h e f u n g u s . A l t h o u g h r e d u c t i o n o f p a t h o g e n i c i t y i n d u c e d b y VM-A was remarkably r e c o v e r e d by t h e p r e m i x i n g o f i n o s i t o l i n t h e i r e x p e r i ment, f u r t h e r i n v e s t i g a t i o n w i l l be r e q u i r e d t o s o r t o u t t h e s p e c i f i c s i t e a n d t y p e o f a c t i o n o f VM-A. 2) B i o l o g i c a l p r o p e r t i e s : A n t i m i c r o b i a l a c t i v i t y o f VM-A a g a i n s t a b o u t 3,000 s p e c i e s o f f u n g i and b a c t e r i a was n o t d e t e c t e d w i t h o r d i n a r y methods ( 5 1 , 5 9 ) , a n d a l s o d i s t u r b a n c e o f m i c r o f l o r a on r i c e p l a n t a n d c r o p f i e l d was n o t o b s e r v e d ( 5 8 ) . Wakae a n d M a t s u u r a (60) f o u n d no p h y t o t o x i c i t y o n o v e r 150 s p e c i e s o f p l a n t s s p r a y e d w i t h VM-A e v e n a t a c o n c e n t r a t i o n o f 1,000 ppm. Further more, a c u t e a n d s u b a c u t e t o x i c i t i e s t o mammals w e r e m a r k e d l y l o w ; i n o r a l a d m i n i s t r a t i o n o f v a l i d a m y c i n A a t t h e d o s e o f 10 g/kg t o m i c e and r a t s , o r i n s u b c u t a n e o u s and i n t r a v e n o u s a d m i n i s t r a t i o n a t t h e d o s e o f 2 g/kg t o m i c e , a l l a n i m a l s e x a m i n e d s u r v i v e d w i t h o u t any change f o r 7 days ( 5 1 ) . VM-A i s a m a i n component o f v a l i d a m y c i n c o m p l e x and i s s p e c i f i c a l l y e f f e c t i v e a g a i n s t c e r t a i n p l a n t d i s e a s e s c a u s e d b y Rhizoctonia s p p . , s u c h a s web b l i g h t , b u d r o t , d a m p i n g - o f f s e e d d e c a y , r o o t r o t and b l a c k s c u r f o f s e v e r a l c r o p s and s o u t h e r n b l i g h t o f v e g e t a b l e s a s w e l l a s s h e a t h b l i g h t o f r i c e p l a n t ( 5 8 ) . Though t h e a n t i b i o t i c showed n e i t h e r c i d a l n o r s t a t i c a c t i o n o f Rhizoctonia s p p . , i t c a u s e d an a b n o r m a l b r a n c h i n g a t t h e t i p s o f hyphae o f t h e p a t h o g e n , f o l l o w e d b y c e s s a t i o n o f f u r t h e r d e v e l o p m e n t ( 5 1 ) . When i t was a p p l i e d i n t h e e a r l y l o g a r i t h m i c p h a s e o f l e s i o n e x p a n s i o n on r i c e p l a n t , s u f f i c i e n t c o n t r o l was a c h i e v e d b y one s p r a y i n g o f 30 ppm VM-A s o l u t i o n ( 6 0 ) . VM-A h a s b e e n c o m m e r c i a l l y u s e d upon s h e a t h b l i g h t d i s e a s e s i n c e 1973. V a l i d a m y c i n s h a v e b e e n shown t o be s u s c e p t i b l e t o m i c r o b i a l a t t a c k and t h e i r a d d i t i o n t o s o i l r e s u l t ed i n c o m p l e t e l o s s o f b i o l o g i c a l a c t i v i t y b y s o i l m i c r o b e s . I t s h a l f - l i f e i n s o i l was l e s s t h a n 4 h o u r s . M i c r o b i a l degrada t i o n o f VM-A b y Pseudomonas denitrificans gave r i s e t o D - g l u c o s e and v a l i d o x y l a m i n e A, w h i c h was f u r t h e r decomposed i n t o v a l i e n a m i n e , v a l i d a m i n e and o t h e r l o w e r compounds ( 6 1 ) . V a l i d a m y c i n A has been p r a c t i c a l l y used t o p r o t e c t sheath b l i g h t o f r i c e p l a n t i n t h e f o r m u l a t i o n s o f 3 % s o l u t i o n o r 0.3 % d u s t .


180



Figure 5.

Structure of ezomycin


10.

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Agricultural

181

Antibiotics


R e s i d u e s i n r i c e g r a i n s and s t r a w s w e r e l e s s t h a n e a c h l i m i t by gas c h r o m a t o g r a p h y ( 6 2 ) .

detectable

Ezomycins. E z o m y c i n s a r e a n t i f u n g a l a n t i b i o t i c s p r o d u c e d by a s t r a i n o f Streptomyces v e r y s i m i l a r t o S. kitazawaensis. T a k a o k a et al. (63) i s o l a t e d a c o m p l e x o f t h e a n t i b i o t i c s f r o m t h e c u l t u r e f i l t r a t e o f t h e p r o d u c i n g o r g a n i s m and r e p o r t e d t h a t t h e c o m p l e x has u n i q u e b i o l o g i c a l a c t i v i t y i n s u p p r e s s i n g the g r o w t h o f v e r y l i m i t e d s p e c i e s o f p h y t o p a t h o g e n i c f u n g i , s u c h as Sclerotica and Botrytis spp. S i n c e t h e c o m p l e x showed r e m a r k a b l e a n t i m i c r o b i a l a c t i v i t y a g a i n s t Sclerotinia sclerotiorvm de B a r y t h a t c a u s e s s t e m r o t i n k i d n e y b e a n p l a n t s (Phaseolus vulgaris L.), i s o l a t i o n and c h a r a c t e r i z a t i o n o f e a c h component o f e z o m y c i n s w e r e c a r r i e d o u t by S a k a t a et al. (64). According to Sakata et al. e z o m y c i n s a r e new p y r i m i d i n e n u c l e o s i d e s , and t h e p r e s e n c e of L - c y s t a t h i o n i n e i n ezomycin molecule i s r e s p o n s i b l e f o r specific antifungal activity. Recently they e l u c i d a t e d the c h e m i c a l s t r u c t u r e o f a l l t h e e z o m y c i n s (65-67) ; F i g u r e 5 shows t h e c h e m i c a l s t r u c t u r e o f e z o m y c i n A. T h i s a n t i b i o t i c was registered a s an a g r i c u l t u r a l a n t i b i o t i c f o r t h e c o n t r o l o f s t e m r o t o f k i d n e y b e a n i n 1970, b u t has s c a r c e l y b e e n on t h e m a r k e t since then. 9

Antibacterial

antibiotic

Cellocidin. C e l l o c i d i n i s an a n t i b i o t i c p r o d u c e d f r o m Streptomyces chibaensis (68,69). I t i s an a c e t y l e n e d i c a r b o x y a m i d e c o n t a i n i n g o n l y f o u r c a r b o n atoms as shown i n F i g u r e 6. As i t s c h e m i c a l s t r u c t u r e i s so s i m p l e , i t i s e a s y t o s y n t h e s i z e chemically. T e c h n i c a l grade c e l l o c i d i n f o r commercial formula t i o n s i s now s y n t h e s i z e d f r o m f u m a r i c a c i d o r b u t y n e d i o l . C e l l o c i d i n shows an e x c e l l e n t p r e v e n t i v e e f f e c t a g a i n s t r i c e bacterial l e a f b l i g h t when s p r a y e d on r i c e p l a n t s a t 100 t o 200 ppm ( 7 0 ) . I t s t o x i c i t y when i n j e c t e d i n t r a v e n o u s l y i s h i g h ( L D o t o m i c e , l l m g / k ^ ) , b u t i n o r a l a d m i n i s t r a t i o n and s k i n a p p l i c a t i o n i t i s n o t so h i g h l y t o x i c ( L D t o m i c e , 89.2 - 125 mg/kg and L D o t o m i c e , 667 mg/kg r e s p e c t i v e l y ) . C e l l o c i d i n has b e e n p r a c t i c a l l y u s e d s i n c e 1964. However, i t s c o n s u m p t i o n has b e e n r e m a r k a b l y d e c r e a s e d due t o i t s p h y t o t o x i c i t y . The a n t i b a c t e r i a l a c t i o n o f c e l l o c i d i n was a n t a g o n i z e d by c y s t e i n e o r g l u t a t h i o n e , w h i c h i n d i c a t e s i n t e r a c t i o n w i t h SH-groups. A s t u d y of s e v e r a l m e t a b o l i c s y s t e m s f r o m Xanthomonas oryzae r e v e a l e d that c e l l o c i d i n s e l e c t i v e l y i n h i b i t e d N A D - r e q u i r i n g d e h y d r o g e n a s e , and e s p e c i a l l y i n t h e p a t h w a y f r o m α-ketoglutamic a c i d t h r o u g h s u c c i n y l Co A t o s u c c i n i c a c i d a t t h e minimum g r o w t h i n h i b i t o r y c o n c e n t r a t i o n o f 10 ppm (71). 5

5 0

Insecticidal

5

antibiotic

Tetranactin.

T e t r a n a c t i n , a new

miticidal antibiotic,


was

PESTICIDE

C H E M I S T R Y I N T H E 20TH

C —CONH,

111

C —C0NH

Structure of cellocidin


Figure 6.

2

Figure 7.

Structure of tetranactin


CENTURY

10.

MisATO

Agricultural

Antibiotics

183


i s o l a t e d as c r y s t a l l i n e rhombic prisms from the f i l t e r cake o f t h e f e r m e n t e d b r o t h o f Streptomyces aureus s t r a i n S-3466 ( 7 2 ) . The a n t i b i o t i c exerted remarkable p e s t i c i d a l a c t i v i t y s p e c i f i c a l l y a g a i n s t t h e a d u l t s o f c a r m i n e m i t e a n d showed v e r y weak t o x i c i t y to a warm-blooded a n i m a l . A l s o i t showed no p h y t o t o x i c i t y t o a p p l e , m a n d a r i n o r a n g e a n d t e a , when s p r a y e d a t h i g h c o n c e n t r a t i o n (73) . The m i t i c i d a l p r o p e r t y o f t e t r a n a c t i n i n t h e f i e l d s o f a p p l e a n d t e a h a d b e e n e v a l u a t e d i n J a p a n s i n c e 1968, a n d t e t r a n a c t i n h a s been used a s a m i t i c i d e f o r p l a n t s s i n c e 1974. 1) C h e m i s t r y a n d mode o f a c t i o n : Ando et al. (72) i s o l a t e d the a c t i v e p r i n c i p l e i n c r y s t a l l i n e form by e x t r a c t i n g t h e m y c e l i a l c a k e o f S. aureus w i t h acetone followed by s i l i c a g e l c o l u m n c h r o m a t o g r a p h y . They a l s o showed t h a t S. aureus produces, a l o n g w i t h t e t r a n a c t i n , two o t h e r s t r u c t u r a l l y r e l a t e d m a c r o t e t r o l i d e a n t i b i o t i c s , i . e . , d i n a c t i n and t r i n a c t i n , i n minor amount. From t h e s t u d i e s o n t h e c h e m i c a l c h a r a c t e r i s t i c s o f t e t r a n a c t i n , i t was f o u n d t h a t t h e a n t i b i o t i c a l s o b e l o n g s t o t h e c l a s s o f m a c r o t e t r o l i d e a n t i b i o t i c and i s a c y c l i c p o l y e s t e r composed o f f o u r u n i t s o f h o m o n o n a c t i c a c i d , a s shown i n F i g u r e 7 (74) • The s t e r e o c h e m i c a l s t r u c t u r e was c l a r i f i e d w i t h t h e u s e o f X - r a y c r y s t a l l o g r a p h y b y I i t a k e et al. (75). A s f o r mode o f a c t i o n o f t e t r a n a c t i n , Ando et al. (76) o b s e r v e d t h a t t e t r a n a c t i n i s an u n c o u p l e r i n c o c k r o a c h m i t o c h o n d r i a and supposed t h a t t h e a n t i b i o t i c caused t h e leakage o f a l k a l i c a t i o n s such as K through t h e l i p i d l a y e r o f t h e biomembrane i n m i t o c h o n d r i a , f o l l o w e d b y uncoupling. +

2) B i o l o g i c a l p r o p e r t i e s : S p e c i f i c i t y i n b i o l o g i c a l a c t i v i t y i s a unique property o f t e t r a n a c t i n ; i t exerted potent p e s t i c i d a l a c t i v i t y a g a i n s t the a d u l t s o f a carmine s p i d e r m i t e a l o n e , L D o f o r w h i c h i s 4.8 y g / m l w i t h t h e s p r a y method ( 7 7 ) . A z u k i b e a n w e e v i l and l a r v a o f m o s q u i t o were m o d e r a t e l y s e n s i t i v e to the a n t i b i o t i c , w h i l e o t h e r p e s t s such a s house f l y and c o c k r o a c h w e r e i n s e n s i t i v e . I n a d d i t i o n , i t was o b s e r v e d t h a t t h e o v i c i d a l a c t i v i t y o f the a n t i b i o t i c a g a i n s t t h e s e n s i t i v e m i t e s i s n o t s o s i g n i f i c a n t , w h i c h a p p e a r e d t o b e one o f t h e weak p o i n t s o f tetranactin. The m i t i c i d a l a c t i v i t y , h o w e v e r , was c o n f i r m e d i n the t r i a l s . T e t r a n a c t i n s u s p e n s i o n s were s p r a y e d on a p p l e t r e e s on w h i c h l e a v e s Kanzawa s p i d e r and European r e d m i t e were n a t u r a l l y p a r a s t i c ; p r o l i f e r a t i o n o f b o t h m i t e s were c o m p l e t e l y retarded d u r i n g 32 d a y s o f t h e e x p e r i m e n t . Another c h a r a c t e r i s t i c o f tetranactin i s i t s safety. Ando et al. (72) r e p o r t e d t h a t m i c e t o l e r a t e d a n i n t r a p e r i t o n e a l a d m i n i s t r a t i o n o f 300 mg/kg a n d a n o r a l a d m i n i s t r a t i o n o f 15 g/kg. They a l s o o b s e r v e d t h a t a c u t e t o x i c i t y o f t h e a n t i b i o t i c i s v e r y l o w ; t h e o r a l L D s o ' s a r e more t h a n 2 g/kg t o r a t s , g u i n e a p i g s , q u a i l s a n d r a b b i t s ( 7 6 ) . They suggested that t h e low t o x i c i t y i s p a r t l y a t t r i b u t a b l e t o t h e poor a b s o r p t i o n by a n i m a l s . When C - t e t r a n a c t i n p r e p a r e d b y b i o s y n t h e s i s was a d m i n i s t e r e d o r a l l y t o m i c e , i t was r e v e a l e d t h a t 5

1 4


184


THE

20TH

t h e a n t i b i o t i c i s l i t t l e a b s o r v e d so t h a t t h e d i s t r i b u t i o n v a r i o u s o r g a n s was n e g l i g i b l e and a l m o s t a l l r a d i o a c t i v i t y r e c o v e r e d i n f e c e s 72 h o u r s a f t e r a d m i n i s t r a t i o n ( 7 6 ) . Other promising

CENTURY

in was

antibiotics


1. H e r b i c i d a l a n t i b i o t i c M e t h o x y p h e n o n e (An a n i s o m y c i n a n a l o g u e ) . Yamada et αϊ· (78) f o u n d a s t r a i n o f Streptomyoes t o p r o d u c e two p l a n t - r e g u l a t i n g s u b s t a n c e s , w h i c h w e r e l a t e r i d e n t i f i e d as a n i s o m y c i n (79) and toyokamycin (80). They o b s e r v e d t h a t a n i s o m y c i n e x e r t e d s t r o n g g r o w t h - i n h i b i t o r y a c t i v i t y on t h e r o o t s and s h o o t s o f a l l t h e p l a n t s t e s t e d ( r i c e , b a r n y a r d g r a s s , c r a b g r a s s , l u c e r n e and t o m a t o ) a t 12.5 and 50 ppm, r e s p e c t i v e l y . T h e s e r e s u l t s l e d t o t h e i n v e s t i g a t i o n o f compounds h a v i n g p - m e t h o x y p h e n y l groups(pa n i s o l e d e r i v a t i v e s ) on p l a n t g r o w t h - r e g u l a t i n g a c t i v i t y , and many a n i s o l e d e r i v a t i v e s w e r e s y n t h e s i z e d and t h e i r a c t i v i t i e s w e r e t e s t e d (81). T h i s r e s u l t e d i n the f i n d i n g of i n t e r e s t i n g p l a n t g r o w t h - r e g u l a t i n g a c t i v i t i e s o f p - m e t h o x y d i p h e n y l m e t h a n e s and p-methoxybenzophenones. E s p e c i a l l y , r e m a r k a b l e h e r b i c i d a l a c t i v i t y was c o n f i r m e d f o r 3 , 3 - d i m e t h y l - 4 - m e t h o x y b e n z o p h e n o n e (methoxyphenone) i n t h e paddy f i e l d t e s t s . M e t h o x y p h e n o n e c o m p l e t e l y i n d u c e d c h l o r o s i s i n b a r n y a r d g r a s s and p r o v i d e d a s a t i s f a c t o r y h e r b i c i d a l e f f e c t a t 4 kg/ha a p p l i c a t i o n , a l t h o u g h weak c h l o r o s i s was o c c a s i o n a l l y o b s e r v e d i n r i c e s t e m a t 6 k g / h a (82). A c c o r d i n g t o I s h i d a et al., methoxyphenone i s q u i t e a s t a b l e s u b s t a n c e , b u t i s g r a d u a l l y decomposed by s u n l i g h t . In paddy f i e l d , i t a l s o seems t o be s u s c e p t i b l e t o m i c r o b i a l a t t a c k ; c o n c e n t r a t i o n o f methoxyphenone i n t h e s o i l r e a c h e d a max 2.16 ppm 7 days a f t e r a p p l i c a t i o n , b u t d e c r e a s e d t o 0.018 ppm a f t e r 30 d a y s and t o b e l o w 0.004 ppm a f t e r 60 d a y s . W h i l e t h e m e t a b o l i c f a t e o f methoxyphenone i n t h e e n v i r o n m e n t i s p r e s e n t l y u n d e r i n v e s t i g a t i o n , t h i r t e e n m e t a b o l i t i e s h a v e so f a r b e e n i d e n t i f i e d ; t h e m e t h o x y g r o u p was t r a n s f o r m e d i n t o t h e h y d r o x y g r o u p and t h e b e n z o p h e n o n e s k e l e t o n was decomposed t o w - t o l u i c a c i d and 4-hydroxy-/7?-toluic a c i d . I n a d d i t i o n , the acute t o x i c i t y of methoxyphenone t o m i c e and r a t s was f o u n d t o be more t h a n 4 g/kg independent of the a d m i n i s t r a t i o n routes (82). Therefore, m e t h o x y p h e n o n e i s c o n s i d e r e d t o be a p r o m i s i n g h e r b i c i d e w i t h a h i g h l e v e l o f s a f e t y f o r use i n the e n v i r o n m e n t . 1

2. A n t i v i r a l a n t i b i o t i c s One o f t h e most s e r i o u s p r o b l e m s on p l a n t d i s e a s e c o n t r o l i s the v i r u l e n c e of v i r u s d i s e a s e s . T r i a l s to develop a n t i v i r a l a n t i b i o t i c s h a v e b e e n e n t h u s i a s t i c a l l y c o n d u c t e d by many w o r k e r s . C o n s e q u e n t l y , many a n t i b i o t i c s h a v e b e e n r e v e a l e d t o be e f f e c t i v e on i n h i b i t i n g t h e m u l t i p l i c a t i o n o f s e v e r a l p l a n t v i r u s e s by in vitro t e s t and p o t t e s t . They a r e b l a s t i c i d i n S, l a u r u s i n , b i h o r o m y c i n , m i h a r a m y c i n , c i t r i n i n and a a b o m y c i n A e t c . However,


10.

MisATO

Agricultural

Antibiotics

t h e r e i s no a n t i b i o t i c virus diseases. A a b o m y c i n A. Streptomyces

hygros

185

used p r a c t i c a l l y for c o n t r o l l i n g any p l a n t

A a b o m y c i n A was i s o l a t e d f r o m c u l t u r e b r o t h o f copious

v a r . aabomyoeticus

by

Aizawa

et

at.


( 8 3 ) . By Y a m a g u c h i et al. (84) w i t h l e a f d i s c d i p p i n g method, a a b o m y c i n A showed a b o u t 80 % i n h i b i t i o n o n TMV m u l t i p l i c a t i o n i n tobacco t i s s u e s . Aabomycin A i s n o t o n l y e f f e c t i v e t o i n h i b i t t h e d i s e a s e d e v e l o p m e n t o f TMV, b u t a l s o e f f e c t i v e t o i n h i b i t t h a t o f CMV a n d AMV e t c . , w i t h p o t t e s t . Future prospects One o f t h e g r e a t e s t needs i n t h e p r e s e n t w o r l d i s p r o d u c t i o n o f food f o r b i l l i o n s o f people. A t p r e s e n t , such p r o d u c t i o n r e q u i r e s the use o f p e s t i c i d e s , b u t i n t u r n , t h i s u s e b r i n g s about t h e p o s s i b i l i t y o f environmental p o l l u t i o n . Environmental hazards caused by c o n v e n t i o n a l a g r i c u l t u r a l chemicals a r e c l a s s i f i e d i n t o two c a t e g o r i e s ; a. n o n - s e l e c t i v e t o x i c i t y ( p a r a t h i o n ) a n d b. c o n c e n t r a t i o n a n d a c c u m u l a t i o n o f t o x i c compounds i n t h e e n v i r o n ment (DDT a n d BHC). P o l l u t i o n f r e e p e s t i c i d e s , t h e r e f o r e , s h o u l d have s e l e c t i v e t o x i c i t y t o t a r g e t o r g a n i s m s a n d b e s e n s i t i v e f o r p h o t o l y s i s a n d d e g r a d a t i o n b y s o i l m i c r o o r g a n i s m s . From t h e s e v i e w p o i n t s , a n t i b i o t i c s may b e presumed t o b e u s e f u l b i o d e g r a d a b l e pesticides. As i s t r u e f o r every s c i e n t i f i c technique, t h e use of a g r i c u l t u r a l a n t i b i o t i c s a l s o has i t s advantages and limitations. The a d v a n t a g e s . 1) S e l e c t i v e t o x i c i t y t o t a r g e t o r g a n i s m s : S i n c e most a n t i b i o t i c s have s e l e c t i v e t o x i c i t y t o t a r g e t organisms and l o w t o x i c i t y t o mammals a s shown i n T a b l e I I I , t h e y c a n b e s a f e l y u s e d w i t h o u t h a r m i n g man, l i v e s t o c k , f i s h a n d c r o p s . Mode o f a c t i o n o f a g r i c u l t u r a l a n t i b i o t i c s a r e summarized i n T a b l e ÏV. Table I I I . Antibiotic

T o x i c i t y o f a n t i b i o t i c s t o animals Animal

Acute o r a l t o x i c i t y ( L D o mg/kg) 5

Blasticidin S Kasugamycin Polyoxins Validamycin Tetranactin

Rat Mouse Mouse Mouse Mouse

53.3 20,900 15,000 10,000 15,000


PESTICIDE C H E M I S T R Y IN T H E 2 0 T H

186

Table IV.

Mode o f a c t i o n o f a n t i b i o t i c Primary action

Antibiotic


Polyoxins Tetranactin Validamycin Blasticidin S Kasugamycin Cycloheximide Streptomycin Cellocidin Griseofulvin

CENTURY

site

C h i t i n synthesis of c e l l w a l l C a t i o n leakage from m i t o c h o n d r i a Biosynthesis of i n o s i t o l

• Protein synthesis * -ι j

DNA s y n t h e s i s

2) E a s y d e g r a d a t i o n b y s o i l m i c r o o r g a n i s m s : A n t i b i o t i c s p r o d u c e d b y m i c r o o r g a n i s m s w o u l d be r a p i d l y d e g r a d e d b y s o i l microorganisms. A f t e r a p p l i c a t i o n t o the crop, a n t i b i o t i c s might be r a p i d l y b r o k e n down i n t h e e n v i r o n m e n t , so t h a t t h e r e may be no d a n g e r o f e n v i r o n m e n t a l p o l l u t i o n and f o o d c o n t a m i n a t i o n . 3) S m a l l amount o f compound u s e d i n a u n i t a r e a : S i n c e a g r i c u l t u r a l a n t i b i o t i c s a r e sprayed a t v e r y l o w c o n c e n t r a t i o n as shown i n T a b l e V, t h e amount o f compounds s p r a y e d i n a u n i t a r e a i s f a r l e s s (1/10 - 1/100) t h a n t h a t o f o t h e r c o n v e n t i o n a l p e s t i c i d a l c h e m i c a l s . A l s o a n t i b i o t i c s w o u l d be r a p i d l y d e g r a d e d by s o i l m i c r o o r g a n i s m s . T h e r e f o r e , i t i s expected t h a t the use of a g r i c u l t u r a l a n t i b i o t i c s does n o t b r i n g about t h e p o s s i b i l i t y o f environmental p o l l u t i o n . T a b l e V.

The c o n c e n t r a t i o n o f a n t i b i o t i c f o r a p p l i c a t i o n

Antibiotic Cycloheximide Blasticidin S Kasugamycin Validamycin Tetranactin Polyoxins Streptomycin [Other f u n g i c i d e s ] O r g a n i c p h o s p h o r u s compounds O r g a n i c s u l f u r compounds I n o r g a n i c s u l f u r compounds B o r d e a u x m i x t u r e (CuSO/,)

Concentration 2 10 20 30 100 100 100

(ppm)

- 3 - 20 - 40 - 50 - 130 - 200 - 200

500 1,000 - 1,500 2,000 4,000


10.

MisATO

Agricultural

Antibiotics

187

4) M a n u f a c t u r e o f b i o - a c t i v e compounds w i t h c o m p l e x c h e m i c a l s t r u c t u r e s : N o v e l b i o - a c t i v e compounds w i t h v e r y c o m p l e x c h e m i c a l s t r u c t u r e s w h i c h a r e o u t s i d e t h e domain o f o r g a n i c s y n t h e s i s , c a n be i s o l a t e d a n d m a n u f a c t u r e d on a c o m m e r c i a l b a s i s .


5) F a v o r a b l e i n v e s t m e n t i n e q u i p m e n t : V a r i o u s a n t i b i o t i c s can be p r o d u c e d b y u s i n g a s i n g l e s e t o f e q u i p m e n t a n d f a c i l i t i e s . T h i s advantage b r i n g s about l o w i n i t i a l c o s t o f a n t i b i o t i c s . 6) U t i l i z a t i o n o f s o l a r e n e r g y : A n t i b i o t i c s a r e p r o d u c e d b y u t i l i z i n g a g r i c u l t u r a l products which are obtained from b i o l o g i c a l p h o t o s y n t h e t i c c o n v e r s i o n o f s o l a r e n e r g y . The p r o d u c t i o n o f a n t i b i o t i c s does n o t much consume t h e s t o r e d e n e r g y s u c h a s o i l and coal. The

limitations.

1) D i f f i c u l t y f o r a n a l y s i s i n m i c r o - s c a l e : A n t i b i o t i c s a r e g e n e r a l l y m i x t u r e s o f v a r i o u s s t r u c t u r a l l y r e l a t e d components l i k e polyoxins. This complexity i s a d i f f i c u l t y for analysis i n micros c a l e a n d s a f e t y e v a l u a t i o n o f compounds. 2) R e s i s t a n t o f p l a n t p a t h o g e n s t o a n t i b i o t i c s : T o l e r a n c e or r e s i s t a n c e o f p a t h o g e n i c microorganisms t o a n t i b i o t i c s has occurred shortly after application of a n t i b i o t i c s for the control o f p l a n t d i s e a s e s a s shown i n T a b l e V I . I n order t o reduce o r a v o i d t h e emergence o f t o l e r a n t f u n g i a n d b a c t e r i a i n t h e f i e l d s , the a l t e r n a t e o r combined a p p l i c a t i o n o f c h e m i c a l s w i t h d i f f e r e n t mechanisms o f a c t i o n i s recommended. Table VI. Antibiotic Blasticidin S Kasugamycin Polyoxins Streptomycin

Resistance to a n t i b i o t i c Where n o t e d Laboratory F i e l d and l a b . F i e l d and l a b , F i e l d and l a b .

Major organism Pyricularia Vyricularia Altemaria Xanthomonas

oryzae oryzae kikuchiana oryzae

P u b l i c h e a l t h a s p e c t s . A l i m i t e d number a n d a r e l a t i v e l y s m a l l q u a n t i t y o f m e d i c a l a n t i b i o t i c s have b e e n i n t r o d u c e d i n a g r i c u l t u r a l u s e a s shown i n T a b l e I . M o s t a g r i c u l t u r a l a n t i b i o t i c s have been used o n l y f o r p l a n t p r o t e c t i o n purposes and n o t used i n m e d i c a l treatment. T h e r e f o r e , the p u b l i c ' s concern f o r t h e e n v i r o n m e n t a l p r o b l e m o f a n t i b i o t i c s must b e d i f f e r e n t i n t h e two a r e a s where a n t i b i o t i c s a r e u s e d . A g r i c u l t u r a l a n t i b i o t i c s do not i n v o l v e p r i m a r i l y the h e a l t h o f t h e i n d i v i d u a l , b u t t h e i r u s e has m a c r o e n v i r o n m e n t a l c o n s e q u e n c e s . M o s t human i n f e c t i o u s d i s e a s e s a r e caused by b a c t e r i a and v i r u s e s , w h i l e p l a n t pathogens


188



a r e m o s t l y c l a s s i f i e d a s f u n g i . A c c o r d i n g l y , most m e d i c a l a n t i b i o t i c s a r e e f f e c t i v e a g a i n s t b a c t e r i a , whereas a g r i c u l t u r a l antibiotics aregenerally fungicidal. S e l e c t i v i t y of a g r i c u l t u r a l a n t i b i o t i c a c t i o n can eradicate fungi responsible f o r the target p l a n t d i s e a s e without harming other microorganisms such as b a c t e r i a p a r a s i t i c on humans. A p p l i c a t i o n o f a n t i b i o t i c s f o r the c o n t r o l o f p l a n t p e s t s i s never concerned i n t h e development of r e s i s t a n t microorganisms t o medical a n t i b i o t i c s . Some a n t i b i o t i c s c a n be s y n t h e s i z e d c h e m i c a l l y . I n t h i s respect there i s no d i f f e r e n c e b e t w e e n a n t i b i o t i c s a n d s y n t h e t i c c h e m i c a l s . The problem i s whether an a n t i b i o t i c i s used i n a g r i c u l t u r a l o r i n m e d i c a l use. I t makes no d i f f e r e n c e w h e t h e r i t i s p r o d u c e d b y microorganisms o r synthesized chemically. In t h i s a r t i c l e thepresent status o f a g r i c u l t u r a l a n t i b i o t i c s h a s been d e s c r i b e d . T h e i r development i n Japan h a s b r o u g h t a b o u t s u c c e s s f u l d i s c o v e r i e s o f b l a s t i c i d i n S, k a s u g a m y c i n , p o l y o x i n s and v a l i d a m y c i n . R e c e n t l y , s t u d i e s on a g r i c u l t u r a l a n t i b i o t i c s have n o t been l i m i t e d o n l y t o c o n t r o l l i n g p l a n t p a t h o g e n i c m i c r o o r g a n i s m s , b u t e x t e n d e d w i d e r a n d more a c t i v e l y over the v a r i o u s s u b j e c t s such as u t i l i z a t i o n as a n t i v i r a l agents, i n s e c t i c i d e s , h e r b i c i d e s and p l a n t r e g u l a t o r s . I t i s expected t h a t many p o t e n t i a l a n t i b i o t i c s w i l l be d e v e l o p e d a n d a p p l i e d i n a g r i c u l t u r e i n t h e near f u t u r e .

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