SHORT CHAIN FATTY ACIDS AS NATURAL PLANT GROWTH REGULATORS

摘要

Although short chain fatty acids undoubtedly function as food reserves in many seeds, there is increasing evidence that they may also act as modulators of seed dormancy, particularly in cases where large quantities of free acids accumulate. In some dormant seeds, butyric, pentanoic, or hexanoic acid reach the level of milligrams per gram of tissue extracted. The level apparently falls with radicle protrusion, and there is evidence that these acids are concentrated outside the embryonic axis. In wild oats, another lab has shown that a decline in free acids accompanies after-ripening.;Short (3 - 8 C) straight-chain fatty acids inhibit radicle emergence and root growth when nondormant seeds are exposed to millimolar solutions directly or to a gas phase in equilibrium with millimolar solutions. Using direct contact with solutions, it can be shown that the threshold molarity for reduction of root growth is 0.5 mM, while that for inhibition of radicle emergence is 3 mM or higher. Inhibition of radicle emergence increases as chain length of the acid increases; in lettuce, this inhibition can be reversed by irradiation with red light or by simultaneous treatment with gibberellic acid or kinetin. In contrast, inhibition of root growth is independent of chain length, and treatment with red light, kinetin, gibberellic acid, or indoleacetic acid does not alter the effect of representative acids. Neither type of inhibition is accompanied by depression of respiration. No special involvement of CO(,2) or ethylene has been detected. The decreased rate of elongation of a root exposed to subtoxic amounts of one of these acids remains constant for at least 72 h, and rapidly improves once exposure is terminated.;Hypocotyl elongation is less sensitive to short chain fatty acids than root growth, inhibition increasing with chain length. Inhibition of turnip hypocotyl elongation is not accompanied by a decrease in anthocyanin or chlorophyll levels.;Short (3 - 8 C) chain alcohols also inhibit root growth but, unlike acids, produce stronger inhibition with increasing chain length. Acids and alcohols are similar in their effect on radicle emergence; from 3 to 8 C, inhibition at 3 mM rises from 0 to about 60%.;Thus, the impetus for further study of the role of these acids in plant systems is two-fold: first, they appear to act as natural regulators in seed dormancy, and second, there are obvious ecological and commercial implications of the effects of microbially-generated short chain fatty acids on crop productivity.