Photosynthetic apparatus in chilling-sensitive plants

Proteins of fresh, cold and dark-stored and illuminated tomato leaves were fractionated by SDS electrophoresis. The total soluble proteins extracted from fresh leaves were separated into 5 main fractions with MWs of 54,000, 45,000, 32,000, 23,000 and 14,000. The cold and dark storage of the leaves causes a marked reduction mainly in the fraction with MW of 45,000 which increased with the illumination of the cold and dark-storaged leaves. The polypeptides with MWs of 54,000 and 14,000 (probably large and small subunits of ribulose, bisphosphate carboxylase) were stable under these conditions. In contrast, the polypeptides with MWs of 54,000 and 14,000 are decreased following the storage of tomato leaves in the dark at room temperature. Chloroplast soluble proteins were seperated by SDS electrophoresis into fractions with MWs of 64,000, 54,000, 20,000 and 14,000. The same fractions in similar proportions were observed in soluble-chloroplast proteins from fresh as well as coold and dark-stored and illuminated leaves. No drastic changes in structural polypeptides were observed following cold and dark-storage and illumination of the leaves. The results indicated that the main protein fraction, which degradated following cold and dark storage of tomato leaves and synthetized during illumination, is the fraction of cytoplasmic protein which in SDS electrophoresis gives polypeptides of about 45,000 MW. The fractions of chloroplast proteins were stable under such conditions.Abbreviations DCIP 2,6-dichlorophenolindophenol - FFA free fatty acid - MW molecular weight - RuBP carboxylase ribulose 1,5-bisphosphate carboxylase - SDS sodium dodecyl sulphate - TCA trichloroacetic acid