Effects of Nuclear and Cytoplasmic Genes Altering Chlorophyll Loss on Gas Exchange during Monocarpic Senescence in Soybean

摘要

Several genes can alter the yellowing processes that normally occur during pod development and monocarpic senescence in soybean. CytG and d1+d2cause the leaves and seeds to stay green at maturity. G blocks yellowing of the seed coat but not the leaves or embryos. By contrast, another gene, y3, causes earlier yellowing of the leaves. This paper examines the effects of these genes on photosynthesis and some related parameters of the senescence syndrome in near-isogenic backgrounds (cv. Clark). Neither cytG nor d1d2delays the decline in photosynthetic rate during monocarpic senescence relative to Clark; while Gd1d2does. Again, y3causes an earlier decrease. Similarly, neither cytG nor d1d2alters the decline in stomatal conductance and transpiration, which occurs at the end of podfill; however, Gd1d2delays it and y3advances it. Neither cytG nor d1d2prevents the rise in intercellular CO2during podfill, while Gd1d2does, and y3promotes it. These changes in intercellular CO2may reciprocally reflect the status (maintenance for Gd1d2and early loss for y3) of the photosynthetic enzymes. Gd1d2, d1d2and cytG do not appreciably affect leaf blade abscission; however, y3prevents it. Gd1d2increases the dry weight seed yield, and y3decreases it. Gd1d2inhibits several components in the senescence process, while cytG seems to affect mainly chlorophyll loss and y3may act more broadly than just accelerating senescence. Clearly, the stay-green trait can be caused by more than one genetic locus, and it may or may not maintain photosynthesis.