Effect of light on the formation of multiple molecular forms of glutamine synthetase in plants

The presence of multiple molecular forms (MMF) of glutamine synthetase (GS) has been studied in pumpkin plants and in cotyledons of bean plants. Two MMF of GS have been found in pumpkin leaves and in green cotyledons: chloroplast GS and cytosol GS. Cotyledons of etiolated pumpkin seedlings contain only the cytosol GS. Illumination of etiolated pumpkin seedlings with white light results in the appearance, within one minute, of the second molecular form, the chloroplast GS, which appears to be due to activation rather than de novo synthesis of the enzyme. Cotyledons of resting seeds of horse bean, pea, soybean and lupine contain only one form of GS. The second form, chloroplast GS, appears after germination in the light, but only in those cotyledons of soybean and lupine that can become green.