CHANGES IN POLYPEPTIDES IN PHARBITIS COTYLEDONS DURING THE 1ST FLOWER-INDUCTIVE PHOTOPERIOD

Two-dimensional (2-D) gel electrophoresis was used to determine qualitative and quantitative changes in polypeptides in cotyledons of Pharbitis nil Choisy cv. Violet under different photoperiodic conditions. Seedlings cultured under continuous light were subjected to short-day (SD, flower-inductive condition), night-break (NB, non-inductive condition) or long-day (LD, non-inductive condition) treatment. Total proteins labeled in vivo with [S-35]methionine were extracted from cotyledons at various times during the first cycle of the different photoperiods. There were no qualitative differences among the three photoperiods. However, the intensity of one polypeptide spot (molecular mass, 22 kDa; pl, 7.5) increased during SD treatment as compared to those of NB and LD treatments. A peptide-mapping experiment revealed that the protein in the spot that was detected by staining of the gel at the same position as that of the radioactively labeled 22-kDa polypeptide was identical to the radioactively labeled 22-kDa polypeptide. By measuring the intensity of protein spots on the stained gel, we found that the total amounts of this polypeptide under the three sets of photoperiodic conditions were the same at the end of the various photoperiods. The likelibood of turnover of this protein is discussed.