Light-stimulated leaf growth on intact and excised bean plants (Phaseolus vulgaris L.). I. Characterization of basic responses

The effect of root excision on the growth of primary leaves, petioles, and epicotyls of bean plants (Phaseolus vulgaris L.) has been investigated for plants growing in various light conditions. Plants were initially grown in either continuous dim red light (RL; 4 mu Lmol m(-2)s(-1)) or bright white Light (WL; 100 mu molm(-2)s(-1), 16 h light: 8 h dark photoperiod) for 10 d ays. On day 10, some plants were excised. Then, both intact and excised pla nts were returned to RL or WL, or switched to the other light treatment (RL to WL, WL to RL). Exposure to WL on day 10 promoted leaf expansion and inh ibited petiole and epicotyl growth, regardless of light pretreatments befor e day 10. Root excision reduced leaf expansion by 40-50% both in WL and RL. Petiole and epicotyl growth were less affected. Removal of the cotyledons or the stem apex caused a slight but significant reduction of leaf elongati on in both intact and excised plants. Apex removal reduced epicotyl elongat ion but did not stop it. Although excision of roots partially inhibited lea f and epicotyl development, the relative response of excised plants to the Light treatments was similar to that of intact plants. These results justif y the use of derooted plants to study leaf growth in a "whole plant" excise d system.