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 vulgar is. Impaired yellowing in these genotypes was accompanied by abnormal retention of thylakoid membrane proteins including the light-harvestin g chlorophyll-binding protein of photosystem II, the 33 kDa polypeptid e of the oxygen-evolving complex, cytochrome f and the psaF protein of photosystem I. On the other hand, ribulose bisphosphate carboxylase w as somewhat more labile in the mutant than the wild-type. The stay-gre en character was not associated with unusual persistence of chlorophyl l biosynthesis enzymes. During senescence, normal leaf tissue accumula ted an array of fluorescent (FCC) and non-fluorescent (NCC) compounds with chromatographic and spectrophotometric properties similar to thos e of chlorophyll catabolites previously identified in other species. W ith the exception of one prominent NCC and a trace of one FCC, these c onstituents were absent from extracts of stay-green genotypes, strongl y supporting the proposal that they are indeed products of chlorophyll breakdown. The kinetics of their accumulation during senescence was c onsistent with a primary or intermediary role for FCCs in the cataboli c pathway whereas NCCs seem to be final products. The complement of FC Cs and NCCs in Phaseolus vulgaris was as distinct from that of the pre viously-studied species barley and rape as the latter are from each ot her. Genotypic and interspecific variations in the biochemistry of sen escence are discussed in relation to genetic regulation of the process .