Inhibition of the degradation of chioropiast membranes during senescence in nuclear *stay green' mutants of soybean

GUIAMET J.J.; M. CRISTINA GIANNIBELLI

PHYSIOLOGIA PLANTARUM

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 1994 vol. 91 p. 395 - 402

0031-9317

Near-isogenic lines of soybean (Glycitie max [L.] Merr.) cv. Clark carrying nuclear ´stay green´ genes were examined to determine the effects of these genes on the breakdown of thylakoid membranes during senescence. In order to accelerate their senescence, matare leaves were excised and incubated in darkness for 7 days. The homozygous combination of the reces.sive alleles d! and d2 (at two different nuclear loci), with or without G (a dominant allele in another locus that causes green seed coat) inhibited the loss of chlorophyll and thylakoid proteins during senescence. Electi´on micrographs of leaves of cv. Clark during the yellowing process showed chloroplasts in various stages of disintegration; their thylakoid network was disrupted and abundant osmiophilic glohuli formed. These senescent leaves also showed evident signs of deterioration of the plasma membrane, including discontinuities, invaginations and membrane "whorls". In contrast, leaves carrying dldld2d2 and GGdldld2d2 did not show signs of plasma membrane degradation, and their chloroplasts appeared intact, with a continuous, unbroken thylakoid network and tightly stacked grana. Exogenous applications of abscisic acid (1 and 10 pM), methyl jasmonate (10 pJVf) or ethylene (1 and 10 JJLI V) accelerated chlorophyll degradation in cv. Clark, but had no appreciable effect in dldld2d2 and GGdIdld2d2, which indicates that their phenotypes are not due to a deficiency in any of these homnones. The nuclear ´stay green´ genotypes dldld2d2 and GGdldld2d2 exhibit a general incompetence for the degradation of chioropiast membranes and, thus, they may constitute Dsefnl tools in the study of the biochemistry and regulation of leaf senescence.