Natural Products for Pest Management - American Chemical Society

SLA and a highly significant decrease in stomatal density (SD). This could be a new indication about a major ability of Salt-treated plants to tolerat...
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Downloaded by PENNSYLVANIA STATE UNIV on July 6, 2012 | http://pubs.acs.org Publication Date: May 25, 2006 | doi: 10.1021/bk-2006-0927.ch004

Physiological Effects of 2-Benzoxazolinone on Lettuce Manuel J. Regiosa and Adela M. Sánchez-Moreiras Department of Plant Biology and Soil Science, University of Vigo, As Lagoas, Marcosende, s/n, Vigo 36310, Spain

The authors have proposed a general mode of action for 2benzoxazolinone (BOA), including several primary effects and their relation to general stress pathways, including sencescence and oxidative damage. Experiments were performed using whole plants with the addition of B O A , B O A + NaCl and NaCl alone to elucidate the validity of this mode of action. Results partially support the proposed mode of action.

Primary and Secondary Effects of 2-Benzoxazolinone Allelopathic properties of 2-benzoxazolinone (BOA) have been studied for the past few years in our laboratory (7). B O A has been shown to produce several primary and secondary effects in laboratory conditions: it slows root cell cycle (7), depresses germination (2), deorganizes cell membranes (5) and changes gene expression (7). According to those physiological effects, a general multiple mode of action model has been proposed (7). In this work we try to validate the effects at the whole plant level using combination of abiotic (salt) and biotic stress, considering that the proposed model suggests that the effects of B O A are 48

© 2006 American Chemical Society In Natural Products for Pest Management; Rimando, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.

49 correlated partially to the stress response and that it is probable to have some kind of synergy between allelopathic and non-allelopathic stresses (4). Therefore, we selected the occurrence of salt stress by its common and increasing presence in limiting plant productivity in several agricultural lands (5).

Downloaded by PENNSYLVANIA STATE UNIV on July 6, 2012 | http://pubs.acs.org Publication Date: May 25, 2006 | doi: 10.1021/bk-2006-0927.ch004

Experimental designs Lettuce seeds (Lactuca sativa cv. Great Lakes, California) were germinated in plastic trays with a 5-cm deep layer perlite and filled every other day with 500 mL 1:1 Hoagland's solution (6). Seedlings were germinated in a controlled environment chamber with 20 °C temperature (in dark). For seedling growth the environmental conditions were: 12 h-photoperiod, 18:8 °C day-night temperature, 60 ± 5% relative humidity, and 200 nmol ~ s" irradiance. One month after germination, plants were transferred to pots containing perlite. One week later, roots were exposed to four different treatments for 15 days: control (i.e. Hoagland's solution 1:1), 1 m M B O A , 60 m M NaCl, and a combined treatment of 1 m M B O A + 60 m M NaCl. Photosynthesis and transpiration, recorded with an infrared gas analyser LI6400 (Li-Cor model 6400, Lincoln, USA), were measured on the first wellexpanded leaf in six replicates per treatment and pulse-modulated and continuous fluorescence measurements, recorded with a Plant Efficiency Analyser (Hansatech Instruments Ltd.). Fresh and oven dry plant weight, relative water content (RWC), water potential 0F ), and leaf osmotic potential were also determined in eight replicates per treatment. Total leaf C, N , H and S were determined using an elemental C H N S analyser (EA 1110 Automatic Elemental Analyser; Fisons EA-1108). Plant extracts were obtained for the measurement of superoxide dismutase (SOD) and peroxidase (POD) activities. Five replicates per treatment were used for leaf as well as root analyses. Superoxide dismutase (SOD) activity was measured by the nitroblue tetrazolium reaction (7). Peroxidase (POD) activity was measured using guaiacol as hydrogen donor (8). The level of lipid peroxidation was measured by the thiobarbituric acid reaction (9) with slight modifications (10). Leaves and roots from five replicates per treatment were employed in these measurements. Sulfhydryl groups were determined in roots from five living plants per treatment (77). ATPase activity was measured (72, 13) in leaf and root microsomal fractions from five plants per treatment. Microsomal fractions were obtained (14). Protein content of this fraction was assayed by modified Bradford method (75, 16). Total, plasma membrane, vacuolar, mitochondrial, and organular ATPase activities were measured using inhibitors. Six repetitions were tested for m

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In Natural Products for Pest Management; Rimando, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.

50 each case. After hydrolysis, released inorganic phosphate was measured (77). Leaves from five replicates per treatment were used for free proline content determination (75). Soluble polyamines were determined (79,20).

Downloaded by PENNSYLVANIA STATE UNIV on July 6, 2012 | http://pubs.acs.org Publication Date: May 25, 2006 | doi: 10.1021/bk-2006-0927.ch004

Results and discussion Plants treated with 1 m M B O A ( B O A from now on), 60 m M NaCl (Salt from now on) and a combination of both treatments: I m M B O A + 60 m M N a C l (BOA+Salt from now on) were less developed than control plants after 15 days exposition. These effects were reflected in the analysis of biometric data, where all treatments showed significant differences on plant height when compared to its corresponding control (Figure 1).

Control

BOA

BOA+Salt

Salt

Plant height

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b ***

b ***

b **

Root length

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b *

b *

a n.s.

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Control •

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BOA Plant Height

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BOA+Salt X

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Salt

Root length

Figure 7. Height and root length (cm) of lettuce plants treated for 15 days with Hoagland's solution (control); 1 mM BOA (BOA), 60 mM NaCl (Salt), and 1 mM BOA + 60 mMNaCl (BOA+Salt). In the table, asterisks show significant differences when compared to control, whilst letters show significant differences between treatments (***P