Phytochrome mediated induction of nitrate reductase activity in etiolated maize leaves

Abstract

AbstractThe effects of red and far‐red light on the enhancement of in vitro nitrate reductase activity and on nitrate accumulation in etiolated excised maize leaves were examined. Illumination for 5 min with red light followed by a 4‐h dark period caused a marked increase in nitrate reductase activity, whereas a 5‐min illumination with far‐red light had no effect on the enzyme activity. The effect of red light was completely reversed by a subsequent illumination with the same period of far‐red light. Continuous far‐red light also enhanced nitrate reductase activity. Both photoreversibility by red and far‐red light and the operation of high intensity reaction under continuous far‐red light indicated that the induction of nitrate reductase was mediated by phytochrome. Though nitrate accumulation was slightly enhanced by red and continuous far‐red light treatments by 17% and 26% respectively, this is unlikely to account for the entire increase of nitrate reductase activity. The far‐red light treatments given in water, to leaves preincubated in nitrate, enhanced nitrate reductase activity considerably over the dark control.The presence of a lag phase and inhibition of increase in enzyme activity under continuous far‐red light‐by tungstate and inhibitors of RNA synthesis and protein synthesis‐rules out the possibility of activation of nitrate reductase and suggests de novo synthesis of the enzyme affected by phytochrome.