STAY-GREEN GENOTYPES OF PHASEOLUS-VULGARIS L - CHLOROPLAST PROTEINS AND CHLOROPHYLL CATABOLITES DURING FOLIAR SENESCENCE

Leaf senescence was analyzed in stay-green mutants of Phaseolus vulgaris. Impaired yellowing in these genotypes was accompanied by abnormal retention of thylakoid membrane proteins including the light-harvesting chlorophyll-binding protein of photosystem II, the 33 kDa polypeptide of the oxygen-evolving complex, cytochrome f and the psaF protein of photosystem I. On the other hand, ribulose bisphosphate carboxylase was somewhat more labile in the mutant than the wild-type. The stay-green character was not associated with unusual persistence of chlorophyll biosynthesis enzymes. During senescence, normal leaf tissue accumulated an array of fluorescent (FCC) and non-fluorescent (NCC) compounds with chromatographic and spectrophotometric properties similar to those of chlorophyll catabolites previously identified in other species. With the exception of one prominent NCC and a trace of one FCC, these constituents were absent from extracts of stay-green genotypes, strongly supporting the proposal that they are indeed products of chlorophyll breakdown. The kinetics of their accumulation during senescence was consistent with a primary or intermediary role for FCCs in the catabolic pathway whereas NCCs seem to be final products. The complement of FCCs and NCCs in Phaseolus vulgaris was as distinct from that of the previously-studied species barley and rape as the latter are from each other. Genotypic and interspecific variations in the biochemistry of senescence are discussed in relation to genetic regulation of the process.