Blue-Light Regulation of Specific Transcript Levels in Pisum Sativum: 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.