Blue-Light Regulation of Epicotyl Elongation in Pisum sativum

Blue light is known to induce suppression of stem elongation. To avoid the complication of blue-light-induced transformation of phytochrome we have adapted the procedure of measuring blue-light-induced suppression of stem elongation in Pisum sativum L. var Alaska grown under continuous red light. The resulting fluence-response curve for suppression of epicotyl elongation measured twenty-four hours after a blue-light treatment is bell-shaped, with the peak of suppression between 10(0) and 10(1) micromoles per square meter, and no suppression at 10(4) micromoles per square meter. Suppression is first observed 5 and 11 hours after the blue-light treatment for the fourth and third internodes, respectively. No significant differences in elongation rates were noted for the 10(4) micromoles per square meter treated seedlings throughout the 24 hour period. Reciprocity holds for both third and fourth internodes in response to 10(1) and 10(4) micromoles per square meter of blue light over the range of irradiation times tested (10(0) to 10(4) seconds, 10(1) micromoles per square meter; 10(0) to 10(3) seconds, 10(4) micromoles per square meter). In contrast to the bell-shaped fluence-response obtained for epicotyl elongation, measurements of chlorophyll and carotenoid accumulation indicate increasing accumulation with increasing fluence.