Characterization of Cytoplasmic and Nuclear Mutations Affecting Chlorophyll and Chlorophyll-Binding Proteins during Senescence in Soybean

GUIAMET JJ; E. SCHWARTZ; E. PICHERSKY; L. D. NOODEN

PLANT PHYSIOLOGY.

AMER SOC PLANT BIOLOGISTS

Lugar: Rockville; Año: 1991 vol. 96 p. 227 - 231

0032-0889

Soybean plants (Glycine max [L.] Merr. cv Clark) carrying nuclear and cytoplasmic "stay-green" mutations, which affect senescence, were examined. Normally, the levels of chlorophyll (ChI) a and b decline during seedfill and the Chi a/b ratio decreases during late pod development in cv Clark. Plants homozygous for both the di and d2 recessive alleles, at two different nuclear loci, respectively, retained most (64%) of their Chi a and b and exhibited no change in their Chi a/b ratio. Combination of G (a dominant nuclear allele in a third locus causing only the seed coat to stay green during senescence) with did2 further inhibited the loss of Chi in the leaf. Whereas the thylakoid proteins seem to be degraded in normal Clark leaves during late pod development, they were not substantially diminished in did2 and Gd1d2 leaves. In plants carrying a cytoplasmic mutation, cytG, Chi declined in parallel with normal cv Clark; however, the cytG leaves had a much higher level of Chi b, and somewhat more Chi a, remaining at abscission, enough to color the leaves green. In cytG, most thylakoid proteins were degraded, but the Chi a/bbinding polypeptides of the light-harvesting complex in photosystem 11 (LHCII), and their associated Chi a and b molecules, were not. Thus, the combination of d1 and d2 causes broad preservation of the thylakoid proteins, whereas cytG appears to selectively preserve LHCII. The cytG mutation may be useful in elucidating the sequence of events involved in the degradation of LHCII proteins and their associated pigments during senescence.