Chapter 26
Purine Alkaloids in Tea Seeds During Germination Takeo Suzuki and George R. Waller 1
2
Faculty of Textile Science, Kyoto Kogei-Sen-i University, Matsugasaki, Kyoto 606, Japan Department of Biochemistry, Oklahoma Agricultural Experiment Station, Oklahoma State University, Stillwater, OK 74078
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1
2
During imbibition of whole tea seeds (6 days) two purine alkaloids, caffeine and theobromine, did not decrease in the seed coats and there was no increase in the seeds. In parallel with and after the breaking seed coats there was a gradual release of caffeine from coats of germinating seeds. By contrast, when the seed was freed from the outer seed coat and soaked, imbibition of the seed required only two days and simultaneously caffeine was released from the inner seed coat. In such seeds, but not in whole seeds, growth of embryonic tissues (roots and shoots) was inhibited after the breaking of the inner seed coats. Nevertheless, caffeine increased more in such roots of the seedlings of decoated seeds than in roots of normal seedlings. Studies of caffeine (1,3,7-trimethylxanthine; Figure 1) in the coffee plant have shown that it undergoes a variety of metabolic changes (1-31 and has an ecological role rather than one as a nitrogen reserve (éz2.)> We (10) reported that two purine alkaloids, caffeine and theobromine (3,7-dimethylxanthine; Figure 1), in leaves and shoots of tea (Camellia sinensis) decreased significantly in August, October, and November in Japan. This suggests that the alkaloids have no role in the storage of nitrogen in tea leaves during winter months. The biosynthesis of caffeine in coffee and tea plants proceeds through the steps: purine nucleotides in the nucleotide pool (AMP and/or GMP) —> X M P —> xanthosine —> 7methylxanthosine —» 7-methylxanthine -» theobromine —» caffeine (3.11.12). In contrast with the seed caffeine of Coffea species, relatively little attention has been paid to that of tea. This is in part because the fruit of tea, including the seeds, is of minor economic importance compared with that of coffee; moreover earlier studies revealed little caffeine in the tea seed (13.14). Recently we (15) found that the pericarp contains the greatest concentrations of alkaloids in the dry fruit of tea, and that appreciable amounts occur in the seeds, especially in the coats. Thus, from physiological and ecological viewpoints, our concerns are the roles of purine alkaloids and seed coats of tea during fruit development (seed formation) and seed germination. Caffeine in Coffea arabica seed is synthesized in the pericarp, transported to the seed, and accumulated there during fruit 0097-6156/87/0330-0289$06.00/0 © 1987 American Chemical Society
In Allelochemicals: Role in Agriculture and Forestry; Waller, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
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ALLELOCHEMICALS: ROLE IN AGRICULTURE AND FORESTRY
development (16). whereas the caffeine i n both the pericarp and seed coats o f tea is synthesized and accumulated i n the same tissues (15). Allelopathic reactions o f coffee seeds and fruits containing these alkaloids have been described (7.17.18). The behavior o f two purine alkaloids i n tea during germination, and their physiological and ecological functions are described.
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Materials and Methods Seeds of tea (Camellia sinensis L.) were surface-sterilized in a saturated solution of calcium hypochlorite for 30 min, and soaked for 30 min i n running water. The whole seeds, or else seed that had been decorticated, i.e. removed from the hard testae, were sown in moist sea sand and allowed to germinate and grow i n dark at 28 °C. The mixture o f alkaloids present was extracted and analyzed as described previously (2.3). Results After the flowering i n October, fruit growth o f tea is almost unchanged until spring, and then proceeds progressively until the fruit is full-ripened and dried (15). The seeds are then shed i n November, and lose viability after several months. The contents o f purine alkaloids in the seeds of coffee and tea plants are given in Table I. W h e n the whole tea seed was used, imbibition required about 6 days, and then the seed broke out o f the outer seed coat 6-10 days after soaking (Figures 2 & 3). During imbibition alkaloid concentrations were unchanged i n the seed coat although caffeine is readily water-soluble (Figure 4). D u r i n g and after the breaking o f seed coats caffeine was gradually released from the coats o f germinating seeds (Figure 3). B y contrast, when the seed was removed from the outer seed coat and soaked, imbibition required only 2 days, and concurrently caffeine was released from the inner seed coat (Figures 2 & 3). In such seeds, but not i n whole ones, growth inhibition o f embryonic tissues (roots and shoots) occurred after the breaking o f the inner seed coats. Nevertheless, caffeine increased more in roots o f the decoated seed than i n normal seedling roots. Table II shows results on growth inhibition and increments o f caffeine in the roots o f 5week-old tea seedlings, when the seeds were freed from the outer seed coats, allowed to imbibe, and incubated i n water extracts from seed coats. Discussion F r o m these studies and the work o f others (4-9.17.18). we conclude that caffeine found in the seed coats of tea seeds (Table I) has no nutritive function and that it is phytotoxic and autotoxic i.e., inhibits growth o f germinating tea seedlings (Table II). T h e seed coats are the barriers between the embryo and its immediate environment. A s dead tissues, the seed coats o f the mature seed protect the enclosed embryo. Equally important are the nutritive and regularatory functions of the living seed coats during embryo development (19-23). The developing tea seed has a more highly developed seed coat than the coffee seed (15). The coat functions as a good reservoir o f the toxic alkaloids (caffeine and theobromine) (Table I), but prevents autotoxic hazards from occurring during fruit development in the tea plant. The seed coat o f tea regulates imbibition o f tea seed (Figure 2) and releases caffeine during germination (Figure 3). These processes may be dependent upon
In Allelochemicals: Role in Agriculture and Forestry; Waller, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on September 27, 2015 | http://pubs.acs.org Publication Date: January 8, 1987 | doi: 10.1021/bk-1987-0330.ch026
26.
SUZUKI AND WALLER
Xanthine 1,3-Dimethylxanthine 3,7-Dime thy lx an thine 1,7-Dimethylxanthine 1,3,7-Trimethylxanthine
Pwrine Alkaloids
in Tea Seeds
Trivial name
Rl
Theophylline Theobromine Paraxanthine Caffeine
H CH H CH CH
R
291
R3
H CH CH H CH
3
3
3
3
3
3
3
Figure 1. Some Naturally Occurring Methylated Xanthines.
Table I. Caffeine (Cf) and Theobromine (Tb) Contents of Coffee and Tea Seeds
C , arabica seed
C . sinensis seed
a
Seed coat
Tb
Cf
Cf
b
Cotyledon
Tb
Cf
Tb
^g/g fresh wt.) 3893
54
2343
143
a
S u z u k i and Waller Q5).
b
F r o m the ripened dry fruits almost ready to drop.
100
