The blue light effect and its interaction with phytochrome in the control of nitrite reductase activity in Sorghum bicolor Willd.

Abstract

Irradiation with red light for 5 min stimulated nitrite reductase activity in 5-d-old etiolated seedlings of Sorghum bicolor. The stimulation was less when measured after a subsequent dark period of 12 h than after one of 24 h. A short period of irradiation with blue light did not alter the enzyme activity nor did it elicit any effect even if given for 4-6 h prior to the red light irradiation. Exposure to blue light for 12 h prior to the red light treatment increased the enzyme activity, when measured after 12 h of darkness, to the same level as that obtained by red light irradiation alone followed by 24 h of darkness. Blue light given continuously for 24 h increased nitrite reductase activity and this increase was inhibited by 6-methylpurine (5 μg ml⁻¹) or cycloheximide (25 μg ml⁻¹). Transfer of seedlings to continuous white light for 6 h after treatment with a pulse of red light followed by 24 h of darkness, or with continuous blue light for 24 h, revealed an independent action of blue light and light operating via phytochrome, in the control of nitrite reductase activity. The accumulation of nitrate was unaffected either by a red light pulse followed by a subsequent dark period, or by continuous blue light. In contrast, continuous white light led to an increased accumulation of nitrate.