TEMPORAL AND NUTRITIONAL FACTORS MODULATE RESPONSES TO ABSCISIC-ACID AND OSMOTICUM IN THEIR REGULATION OF STORAGE PROTEIN-SYNTHESIS IN DEVELOPING SEEDS OF ALFALFA (MEDICAGO-SATIVA L)

Storage protein synthesis during alfalfa (Medicago sativa L.) seed dev elopment displays a temporal pattern and is regulated both by ABA and low osmotic potentials, Deposition of the 2S, 7S and 11S storage prote ins occurs maximally at the mid- to late stages of development. Osmoti cum, but not ABA alone could effectively induce storage protein synthe sis at early stages of development in isolated alfalfa embryos placed on water for several days. Neither ABA nor osmoticum alone could maint ain storage protein synthesis in isolated late-stage embryos placed on water, On the other hand, isolated developing embryos cultured on a n utrient (Murashige and Skoog) medium could maintain storage protein sy nthesis in the presence of ABA and osmoticum, alone or in combination, for up to 14 d after being dissected from the pod, Of the components of this medium, the inorganic salts appeared to be the most important. The response to ABA and osmoticum varied with the time of isolation d uring development with the greatest enhancement of storage protein syn thesis in isolated embryos coinciding with the time of maximum synthes is within the seed when in planta. Addition of ABA and osmoticum after the time of maximum storage protein synthesis did not elevate the amo unt of synthesis, but rather prolonged the time over which it could ta ke place, Thus, while the amplitude of storage protein synthesis could be modified by ABA or osmoticum, the inherent temporal pattern, with maximum synthesis occurring only at mid- to late stages of embryo deve lopment, could not.