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

Abstract

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.

Regulation of Photosynthesis during Leaf Development in RbcS Antisense DNA Mutants of Tobacco

“…This is consistent with earlier findings on first fully expanded leaves of the mutant plants (Quick et al, 1991b;Hudson et al, 1992;Masle et al, 1993). Thus, the present findings are generally in accord with studies of stay-green senescence mutants of fescue grass (Hilditch et al, 1989;Thomas, 1992), Phaseolus (Ronning et al, 1991), and soybean (Guiamét et al, 1991) and emphasize the notion that leaf development is a coordinated series of events that are not obligatorily connected (parallel pathways).…”

The Senescence-Induced Staygreen Protein Regulates Chlorophyll Degradation

“…The nonfunctional type C stay-green mutants share a number of unusual features, such as the high stability of Chl binding thylakoid proteins among chloroplast proteins, especially LHCPII, and the persistence of unstacked thylakoid membranes in senescing leaf cells (Thomas, 1977(Thomas, , 1982Hilditch, 1986;Hilditch et al, 1989;Guiamé t et al, 1991;Thomas et al, 2002;Oh et al, 2003). Thus, we further examined the stabilities of thylakoid proteins and membranes in the senescing mesophyll cells of sgr.…”

“…Since the photosynthetic competence of sgr leaves decreases normally during that period, it is classified as one of the nonfunctional type C stay-green mutants. To date, type C mutants have been reported in several plants: the senescenceinduced deficiency (sid) mutant in Festuca pratensis (Thomas and Stoddart, 1975); the cytG and d 1 d 2 mutants in soybean (Guiamé t et al, 1991); the green flesh mutant in tomato (Solanum lycopersicum) (Cheung et al, 1993;Akhtar et al, 1999); the nonyellowing mutants in Phaseolus vulgaris (Fang et al, 1998) and Dendranthema grandiflora (Reyes-Arribas et al, 2001); the oresara10 (ore10) mutant in Arabidopsis thaliana (Oh et al, 2000); and the chlorophyll retainer mutant in pepper (Capsicum annuum) (Efrati et al, 2005).…”

Update on the biochemistry of chlorophyll breakdown

“…Among them are mutants of bell pepper, tomato, rice, meadow fescue, Arabidopsis (termed nye1) as well as Gregor Mendel's famous green cotyledon mutant of pea [for a recent review, see Hörtensteiner (2009)]. It is likely that molecular defects in SGR are present in further stay-green mutants, such as soybean d 1 d 2 (Guiamét et al 1991) and Arabidopsis ore10 (Oh et al 2003).…”