Blue Light Photoreception in Higher Plants Studied with ESR Spectrometry

Abstract

Summary As part of an ongoing study on the effects of blue light on plants, redox changes of neutral and charged nitroxides, viz. Tempone, 15 N-perdeuterated Tempone and Cat 1 , were measured in tissues of etiolated oat seedlings under various light conditions. In both coleoptiles and roots the nitroxides were reduced readily in the dark. High fluence rate blue light (50–200 Wm -2 , band width 400–480 nm) caused rapid reoxidation of the nitroxide in coleoptiles, but not in roots. A new stationary state was reached after 4 to 5 min of constant irradiation. The reaction was reversible but the amplitude of the ESR signal diminished slightly after each light-dark cycle. The effect was not due to changes in the concentration of oxygen. Red light did not induce the reoxidation. The concentrations of nitroxides used in these experiments reversibly inhibited blue light-induced chloroplast translocations in Lemna trisulca . The results suggest that reduced nitroxides can function as competitive electron donors, substituting for the natural donor in the first step of the signal transduction chain, connected with the receptor for blue light.