Effect of benzyladenine on the polypeptide pattern of plastids in excised watermelon cotyledons

Abstract

We have shown in a previous paper that plastids of watermelon (Citrullus vulgaris Schrad., cv. Fairfax) cotyledons differentiate into amyloplasts when the cotyledons are grown in water and into prochloroplasts when they are grown in benzyladenine (BA) solution. In the present work we have tested whether this large difference in development of the plastids is accompanied by equally conspicuous changes in their polypeptide pattern. Cotyledons were grown for 4 days in the dark either on distilled water or on 10−5M BA. Alternatively they were transfered to 10−5M BA after 4 days of growth in water.Plastids of control cotyledons had a rather simple polypeptide pattern. The only prominent protein bands were the two subunits of ribulose bisphosphate carboxylase (EC 4.1.1.39). Contamination with storage protein was present. Plastids from BA‐treated cotyledons had a much more complex polypeptide pattern. No storage protein contamination was observed. Polypeptide bands present only as traces in the control and having molecular weights of 32, 44, 48 and 49 kDa increased in intensity after an exposure of only 6 h to BA. The 32‐kDa band seemed to be most dependent on the presence of the hormone. Contrary to what was observed in plastids, BA seemed to have no influence on the polypeptide pattern of mitochondria.