Perception of shade

Abstract

Plants perceive shade by responding to both the fluence rate and to the spectral quality of the natural radiation environment. Changes in fluence rate are perceived by separate photoreceptors absorbing in both the blue and the red wavebands. The identity of the photoreceptor (or photoreceptors) responding to changes in the fluence rate of blue light is unknown (see Briggs, this volume). Physiological responses to changes in the fluence rate in the red waveband appear to be mediated through phytochrome. The relative roles played by the blue-light-absorbing photoreceptor and phytochrome in determining the response to changes in fluence rate varies between species and organs and is also dependent on the physiological age of the plant. Evidence is also presented that supports the concept that phytochrome functions to perceive the specific form of shade caused by surrounding competitive vegetation.