| The BL regulation of a variety of gene expression and physiological events in pea (Pisum sativum L.) was investigated in order to elucidate BL signal transduction in pea. Based on fluence response characteristics of accumulation of specific nuclear-coded transcripts, epicotyl elongation and accumulation of chlorophyll and carotenoids, pea exhibit two blue-light (BL) regulatory systems: the blue low fluence (BLF) system and the blue high fluence (BHF) system. These two systems are defined by their thresholds to BL ({dollar}<{dollar}10{dollar}sp{lcub}-1{rcub}{dollar} {dollar}mu{dollar}mol m{dollar}sp{lcub}-2{rcub}{dollar} and 10{dollar}sp2{dollar}-10{dollar}sp3{dollar} {dollar}mu{dollar}mol m{dollar}sp{lcub}-2{rcub}{dollar}, respectively). The BLF system regulates the increase of Cab RNA, pEA215 RNA, decrease of pEA25 RNA, suppression of epicotyl elongation, increase of chlorophyll and carotenoid accumulation. The BHF system regulates decrease of Cab RNA, pEA215 RNA and pEA207 RNA, and the alleviation of suppression of epicotyl elongation. Although the specific biochemical mechanisms regulating the various responses are likely to be different, the early cognate signal transduction mechanisms may be shared. In the apical bud there exists a BL-regulated, plasma-membrane-associated G protein which is induced by BL by 15 s post-irradiation. Based on fluence-response data, this G protein is regulated by the BLF and may be a key mechanism in BL signal transduction in the plant. |
