Plasticity of petioles of white clover (Trifolium repens) to blue light

Petiole response of white clover to variations in blue light (BL) was studi ed on the main axis and on primary and secondary branches. The objectives o f the present work were to determine (1) the time course of petiole respons e to BL and (2) whether these responses were dependent on petiole location. Under BL, clover had shorter petioles, and the switch to conditions withou t; BL increased the length of forthcoming petioles. The fitting of a logist ic function was used to compare the effect of BL on final petiole length, m aximum elongation rate and the duration of petiole elongation between axes and phytomers. Petiole response to BL was not dependent on its location wit hin the plant (axis type or phytomer position along the axis), A reduction in BL induced a rapid increase in leaf elongation rate, despite a small dec rease in the duration of petiole elongation. Moreover, petiole response was dependent on petiole stage of development: the increase in the maximum rat e of petiole elongation was inversely proportional to the petiole stage of development at the time of the switch, We conclude that the effects of BL o n petiole elongation were not dependent on its position within the plant, w hereas internode elongation resulted from the integration of light environm ent at the plant level. The difference between the responses of orthotropic and plagiotropic organs of clover to BL is discussed in relation to their structural function and localisation in the canopy.