Activation of Ferredoxin-NADP+Oxidoreductase in Vicia fabaLeaves Induced by a Short-Term Increase in Irradiance

Abstract

The effect of a short-term increase in growth irradiance (I) by 1.5–5 times on the rate of the photosynthetic electron transport and the activity of ferredoxin-NADP+oxidoreductase (FNR) in the leaves of broadbean (Vicia fabaL.) plants grown under an irradiance of 8 W/m2was studied. NADPH-diaphorase and cytochrome creductase activities of FNR were determined in isolated chloroplasts and leaf homogenates. The duration of the plant exposure to a higher I varied from 1–30 min to 2 or 24 h. The rate of noncyclic electron transport from water to NADP+and the NADPH-diaphorase activity of FNR increased significantly 15 min after a twofold increase in the I. FNR activation was also found after a short-term (1 min) increase in growth I by 1.5 times. The degree of light-induced activation of FNR was dependent on the light intensity, the duration of plant exposure, and the leaf age. The activation of FNR induced by a short-term increase in the I was reversible. However, inactivation of FNR proceeded more slowly than its light-induced activation. Thus, a relatively small change in the I was sufficient to induce the adaptive response of the photosynthetic apparatus at the level of the electron-transport chain. The results obtained confirm a conclusion made previously that a rapid activation of FNR induced by an increase in the I occurs in the absence of de novoprotein synthesis.