Ethylene is required in tobacco to successfully compete with proximate neighbours

Plants sense neighbours even before these cause a decrease in photosynthetic light availability. Light reflected by proximate neighbours signals a plant to adjust growth and development, in order to avoid suppression by neighbour plants. These phenotypic changes are known as the shadeavoidance syndrome and include enhanced shoot elongation and more upright-positioned leaves. In the present study it was shown that these shade-avoidance traits in tobacco ( Nicotiana tabacum ) are also induced by low concentrations of ethylene. Furthermore, it was shown that transgenic plants, insensitive to ethylene, have a delayed appearance of shade-avoidance traits. The increase in both leaf angles and stem elongation in response to neighbours are delayed in ethylene-insensitive plants. These data show that ethylene is an important component in the regulation of neighbour-induced, shade-avoidance responses. Consequently, ethylene-insensitive plants lose competition with wild-type neighbours, demonstrating that sensing of ethylene is required for a plant to successfully compete for light. Key-words : Nicotiana tabacum ; competition; ethyleneinsensitivity; leaf angle; neighbour signalling; phytochrome; red/ far-red ratio; shade avoidance; stem elongation.