Comparative Study of the Effects of Methyl Jasmonate and Abscisic Acid on Rna and Protein Synthesis in Excised Cotyledons of Cucurbita

The effects of methyl jasmonate and abscisic acid on the polypeptide pattern of soluble proteins as well as in vivo protein and RNA synthesis and endogenous nuclear RNA polymerase activity were compared in excised marrow cotyledons grown in the light. Treatment of cotyledons with MeJA resulted in the induction of two abundant polypeptide bands with Mr 43 and 60 kDa and a significant accumulation of a polypeptide band with Mr 97.4 kDa as analysed by SDS–PAGE. In contrast to MeJA, ABA did not cause the formation of these specific polypeptide bands. Furthermore, the inhibitory effect of ABA on protein and RNA biosynthesis as well as the activity of total endogenous RNA polymerases was much stronger than the effect of MeJA. It is suggested that in excised marrow cotyledons MeJA and ABA act by different mechanisms in the regulation of cotyledon growth and development during the earlier stages of germination.