Blue-Light Regulation of Epicotyl Elongation in Pisum sativum

Abstract

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 10⁰ and 10¹ micromoles per square meter, and no suppression at 10⁴ 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 10⁴ micromoles per square meter treated seedlings throughout the 24 hour period. Reciprocity holds for both third and fourth internodes in response to 10¹ and 10⁴ micromoles per square meter of blue light over the range of irradiation times tested (10⁰ to 10⁴ seconds, 10¹ micromoles per square meter; 10⁰ to 10³ seconds, 10⁴ 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.