Optimization of red light‐induced elongation in Avena coleoptile sections and properties of the phytochrome‐mediated growth response*

Abstract

Abstract Optimal conditions for studying the elongation response to a 1 mmol m−2, 2‐min pulse of red light in subapical coleoptile sections from dark‐grown oat (Avena sativa L. ev. Lodi) seedlings have been determined. A technique for obtaining standard‐length coleoptile sections without exposing either seedlings or sections to any light has been developed, and is described. The optimal conditions found were: sampling time, 12 h after irradiation; buffer conditions, 5 mol m−3 potassium phosphate with 5% (w/v) sucrose (pH 5.9). The optima were determined by obtaining the time course for light‐induced growth under various conditions. The red light‐induced growth response is linear until 12 h after irradiation, when it undergoes an interruption. Optimal incubation conditions were determined by varying the buffer contents systematically and measuring the responses at the optimal lime determined. The results indicate a distinct difference between auxin‐induced and light‐induced growth responses. Even with variations of basal growth rate and several incubation conditions, the red light‐induced elongation appears to be of a constant magnitude, to persist for a constant time period. and to exhibit a constant lag period between irradiation and the onset of response.The use of sections that were produced and handled in complete darkness yielded an unusual response to fusicoccin. A linear, high growth rate in response to I mmol m−3 FC was observed for more than 12 h, both in the irradiated sections and in the dark controls.