EFFECT OF HIGH-TEMPERATURE ON GERMINATING PEA-SEEDS

The effects of prolonged high temperature on radicle emergence, growth of axes, early proteolysis, and protein synthesis in the embryonic ax es of germinating pea (Pisum sativum L.) seeds were studied. A tempera ture of 28 degrees C was shown to be best for radicle emergence and fu rther growth of axes; these processes were retarded at 34 and 36 degre es C and substantially or completely inhibited at 38 and 40 degrees C. The maximum temperature permitting germination of 50% of the seeds wa s between 36 and 38 degrees C. Intact seeds were more sensitive to hea ting than their embryos, and radicle emergence was less sensitive than the further growth of axes. Initial imbibition at 40 degrees C retard ed the subsequent germination at 28 degrees C. During imbibition at 40 degrees C, loss of viability occurred in 10-25 h, depending on pea cu ltivar. Partial proteolysis in the axes occurred before and during rad icle emergence; it did not depend on the presence of a seed coat or co tyledons and was completely inhibited at 40 degrees C. The inhibitor o f plant proteases, phenylmethylsulfonyl fluoride (1-5 mM), depressed b oth proteolysis and germination. Long-term heating (17-20 h at 40 degr ees C) inhibited protein synthesis by 50-60%, but was not critical for germination. Proteins synthesized by the axes at the moment of radicl e emergence differed from those synthesized at the same time after hea ting at 40 degrees C. The roles of protein mobilization in the axes an d the changes in gene expression during the period preceding radicle e mergence are referred to as conceivable mechanisms of the adverse acti on of high temperature on germination.