Good Senses Make Good Neighbors

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Science  30 Apr 2004:
Vol. 304, Issue 5671, pp. 653
DOI: 10.1126/science.304.5671.653b

Shade avoidance by stem elongation is a key growth response of plants competing for light within a canopy. The initiation of this response has been attributed to the detection of near neighbors by phytochrome photoreceptors sensitive to the ratio of red light to far-red light; more recently, the plant hormone ethylene has been implicated in shade avoidance. Pierik et al. compared the growth of transgenic ethylene-insensitive and wild-type tobacco plants in high-density monocultures, and also monitored light patterns and ethylene concentrations in the plant canopies. Higher plant densities resulted in more vertically oriented (hyponastic) leaves and more elongated stems, and both responses were more pronounced in the wild-type plants. Within the canopies, ethylene concentrations increased, and all light parameters decreased as the plants grew. Further experiments with individual plants grown under different light regimes showed that low levels of blue light—rather than the red to far-red ratio—induced enhanced stem elongation and leaf hyponasty in the wild-type plants and that this response was mediated by higher ethylene concentration. This work sheds light on how plants sense their neighbors and relates to ecological and agronomic studies on the mechanisms of plant competition. — AMS

Plant J. 38, 310 (2004).

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