Keeping up with the neighbours: phytochrome sensing and other signalling mechanisms.

Plants 'forage' for light in plant canopies using a variety of photosensory systems. Far-red radiation (FR) reflected by neighbours is an early signal of competition that elicits anticipatory shade-avoidance responses. In Arabidopsis and cucumber, perception of reflected FR requires phytochrome B. Horizontal blue (B) light gradients also guide plant shoots to canopy gaps in patchy vegetation, and these B light signals are perceived by specific photoreceptors. When plants are shaded by neighbours they undergo extensive reprogramming of their morphological development. Although phytochromes and B light receptors are certainly involved in these responses to shading, other sensory systems probably play important roles in the field. Recent studies of plant-plant signalling are unveiling a paradigm of sensory diversity and sophistication, which has important implications for understanding the functioning of plant populations and communities.