Alteration of Soybean Seedling Development in Darkness and Light by the Stay-green Mutation cytG and Gd1d2

The stay-green mutations cytG and Gd1d2 prevent the normal yellowing during senescence of soybean (Glycine max) leaves and cotyledons. Because light plays such an important role in regulating morphogenesis and it promotes the formation of chlorophyll (Chl), we determined the effect of cytG and Gd1d2 (in a cv. Clark background) on the development and some light responses of seedlings. Although cytG and Gd1d2 seeds, particularly the cotyledons, are green when mature, 44 and 71 % respectively of this Chl broke down when the seeds were germinated in darkness. Chlorophyllides and phaeophytins were not present in the seeds in significant amounts. cytG and Gd1d2 as well as wild type (cv. Clark) seedlings developed a full etiolation syndrome (morphology and lack of Chl) in darkness. Light induced rapid Chl accumulation in the dark-grown seedlings with no apparent difference among the three isolines. A short (8 h) exposure to light induced some Chl in the cotyledons of dark-grown plants, and 22 h of light produced four times more. Following return to darkness, the 8-h group showed very little breakdown over the next 12 d. After the 22-h group was returned to darkness, the wild-type lost Chl steadily, but Gd1d2 and eventually also cytG inhibited this breakdown. In the 22-h group, the Chl a/b ratio decreased in wild type and cytG indicating preferential breakdown of Chl a relative to Chl b; however, Gd1d2 prevented this change. cytG and Gd1d2 seem to act preferentially on Chl breakdown rather than synthesis.