Blue Light-Induced In Vivo Absorbance Changes and In Vitro Activation of Nitrate Reductase in a Nitrate-Starved Chlorella Mutant

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Illuminating a colorless mutant of Chlorella vulgaris 11h (M125) with blue light caused a reversible photoreduction of b-type cytochrome, i.e., absorbance increases at 423, 525 and 557 nm. This light-induced reduction of cytochrome b was most pronounced in nitrate-starved cells, which showed some blue light responses in carbon metabolism, including enhancement of respiration by blue light as reported previously. Prolonged illumination with blue light caused a decrease in the rate of the reduction. The photoactivation of nitrate reductase in the mutant cells was studied in both cell-free crude extract and purified enzyme. The absorption spectrum of purified enzyme showed three peaks at 423, 525 and 557 nm after the addition of a reductant, indicating that the spectrum is that of cytochrome b associated with nitrate reductase. Nitrate reductase activity was easily enhanced by blue light illumination after 1 min; red light had no effect on it. The blue light activation of nitrate reductase was not significant in growing cells, which showed its high activity. The relationship between the blue light-induced reduction of cytochrome b and carbon metabolism is discussed.
日本植物生理学会の論文
1988-04-00