SYNTHESIS OF PROTEINS DURING THE DEVELOPMENT OF THE 1ST LEAF OF OAT (AVENA-SATIVA)

Distal segments of the first leaf of intact oat (Avena sativa L. cv. Victory) plants at different stages of development were labelled with S-35-methionine. During 12-h labelling periods similar amounts of label were retained in the segments, but incorporation into protein decreased from 28% in 7-day- to 3% in 27-day-old plants. Two-dimensional polyacrylamide gel electrophoretic analysis of the proteins revealed that even at a late stage of senescence a great many proteins are still being synthesized. Synthesis of ribulosebisphosphate carboxylase and other chloroplast-associated proteins declined more rapidly than general protein synthesis. With increasing leaf age, two sets of proteins with a relatively high molecular weight around 67 kDa and isoelectric points between 6.5 and 6.8 became the most prominently synthesized proteins. Since these proteins were hardly visible upon silver-staining, they seem to be subject to rapid turnover. An involvement of these proteins in senescence might explain the requirement of protein synthesis for senescence to proceed.