Blue-Light Regulation of Specific Transcript Levels in Pisum sativum1: Fluence-Response, Time-Course, and Reciprocity Characteristics

The expression of many nuclear genes in plants is light regulated. We have examined the fluence-response, time-course, and reciprocity characteristics of four nuclear, blue-light-regulated transcripts in Pisum sativum L. var Alaska: Cab RNA, pEA207 RNA, pEA215 RNA, and pEA25 RNA. To avoid complications due to blue-light-induced transformation of phytochrome, we have adapted the procedure of measuring blue-light-induced changes in steady-state-RNA levels in seedlings grown in continuous red light. The fluence-response curves for Cab and pEA215 RNA are bell-shaped, with peak accumulations at 10 2 and 10 1 micromoles per square meter, respectively. No response is observed at 10 4 micromoles per square meter. pEA25 RNA has threshold and saturation fluences below 10 −1 micromoles per square meter. pEA207 RNA has a threshold at 10 2 micromoles per square meter and saturates above 10 4 micromoles per square meter. pEA215 and Cab RNA start to increase within 1 hour after the 10 1 micromoles per square meter pulse, and finish accumulation by 5 hours. The decrease in pEA207 RNA in response to 10 4 micromoles per square meter and pEA25 RNA in response to 10 1 or 10 4 micromoles per square meter starts between 3 and 5 hours after the blue-light pulse. The Bunsen-Roscoe Law of Reciprocity is followed in the Cab , pEE215, pEA25, and pEA207 RNA responses to 10 1 and 10 4 micromoles per square meter.