PROSPECTS IN FUTURE UTILIZATION OF PLANT GROWTH REGULATORS

The classical theories on the diversity and often conflicting effects of PGR were based mainly on the modulation of the regulators levels and their interaction with each other. Recently attention is being drawn to the central rold of the change in sensitivity to the various PGR in regulating their action. Very little is known on the physiological, biochemical, or molecular background underlying the change in sensitivity to environmental or hormonal signals. Sensitivity to PGR may involve the availability of specific receptors and/or the presence of certain "second messengers" involved in signal transduction. There is growing evidence to the rold of small oligosaccarides and fatty acids as well as calcium ions and chemicals modulating the cytosolic pH and CA⁺² level, in signal perception and transduction. Future work on modulating the action of PGR may pay special attention to changing the tissues sensitivity to the regulators.

Another novel approach to modulating the action of phytohormones is by manipulation at the molecular level. A variety of mutants with modifiied production or sensitivity to all the five phytohormones has been described. Transformed plants with antisence ACC-synthase genes blocking ACC production, or with a gene encoding an enzyme that enhance ACC breakdown, has been reported recently in tomatoes, resulting in much reduced enthylene production and delayed fruit ripening. Similar technologies will certainly be used in the future to modify production, transport, degradation and activity of PGR.

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