Effect of Phenylmethylsulfonyl Fluoride – an Inhibitor of Proteases, on the Growth and Polypeptide Profile of Excised Cotyledons of Cucurbita Pepo L. (zucchini) after Treatment with Benzyladenine

Treatment of excised marrow (Cucurbita pepo L., zucchini) cotyledons in darkness with 45 μM BA caused a marked stimulation of the growth accompanied by a strong decrease in cotyledons relative dry weight. PMSF – a well known inhibitor of both thioland serine-type proteases, present in the aqueous solutions either alone or with the cytokinin, inhibited significantly the growth of cotyledons and hindered the decrease in cotyledons dry weight in all treatments. SDS-PAGE analysis of the protein profiles showed that PMSF suppressed the gradual decline in the quantity of the 20– 2 kDa polypeptide group and the low-molecular-weight polypeptide bands (below 15 kDa) both in the control and BA-treated cotyledons. On the other hand, the polypeptide bands migrating in the higher molecular weight zone of the profiles including the 97.4-kDa polypeptide and the LSU of Rubisco (55 kDa) decreased in quantity in the presence of PMSF. These results suggest that the inhibitory effect of PMSF on the breakdown of storage proteins in the excised marrow cotyledons may be due to an inhibition only of certain PMSF-sensitive proteases taking part in this process during germination.