A role of G-proteins and calcium in light-regulated primary leaf formation in Sorghum bicolor

Primary leaf development in Sorghum bicolor is a phytochrome-mediated response. Primary leaves are not produced in Sorghum seedlings even after 10 d of germination if grown in darkness. However, 5 min irradiation with white light or red light given to 5 d etiolated seedlings resulted in the formation of etiolated leaves. This effect of red light was reversed by far-red light. When calcium (3–5 mM) was added exogenously, complete leaf formation was obtained in darkness; however, the kinetics of the response was slower than that seen with light irradiation. This effect was also obtained with potassium ions but magnesium ions had no effect. Light- and calcium-mediated leaf development could be arrested at the stage of leaf emergence or leaf expansion by the addition of inhibitors of G-proteins or by calcium channel blockers suggesting a role of G-proteins and calcium in phytochrome signal transduction during primary leaf development.