Sequential and coordinated action of phytochromes A and B during Arabidopsis stem growth revealed by kinetic analysis

Abstract

in this developmental process, but kinetic information that would augment emerging molecular models of phytochrome signal transduction is absent. We have addressed this deficiency by genetically dissecting phytochromeresponse kinetics, after having solved the technical issues that previously limited growth studies of small Arabidopsis seedlings. We show here, with resolution on the order of minutes, that phyA initiated hypocotyl growth inhibition upon the onset of continuous red light. This primary contribution of phyA began to decrease after 3 hr of irradiation, the same time at which immunochemically detectable phyA disappeared and an exclusively phyB-dependent phase of inhibition began. The sequential and coordinated actions of phyA and phyB in red light were not observed in far-red light, which inhibited growth persistently through an exclusively phyAmediated pathway.

Light Induces Peroxisome Proliferation in Arabidopsis Seedlings through the Photoreceptor Phytochrome A, the Transcription Factor HY5 HOMOLOG, and the Peroxisomal Protein PEROXIN11b

“…This role of phyA started to decrease after 3 h of irradiation, at which point the phyA protein began to be degraded and the contribution of phyB to hypocotyl inhibition became predominant (Parks and Spalding, 1999). This finding also correlates with our results, which showed that the expression of PEX11b reached its maximum at 4 h of white-light exposure and declined afterward (Fig.…”

Apyrases (Nucleoside Triphosphate-Diphosphohydrolases) Play a Key Role in Growth Control in Arabidopsis

“…The promoter:GUS results are consistent with PCR assays in hypocotyls, which showed that red light induces a rapid decrease in the level of apyrase transcripts. Even more pertinent to the argument that apyrase expression is correlated with growth is the observation that the red-light signal that activates phytochromes induces the disappearance of the apyrase protein from etiolated hypocotyls within 3 min after the end of 4-min irradiation, or less than one-half the time it reportedly takes for red light to noticeably reduce the growth of hypocotyls, which is about 8 min (Parks and Spalding, 1999). Primary roots grow faster in light than in darkness and promoter:GUS signals appear generally more intense in light-grown roots than in dark-grown roots (Sun, 2003).…”

“…Light rapidly inhibits elongation of hypocotyls in Arabidopsis, where growth changes become apparent in about 8 min (Parks and Spalding, 1999). We tested whether expression of Arabidopsis apyrases in hypocotyls is also light regulated.…”

Green Light Adjusts the Plastid Transcriptome during Early Photomorphogenic Development

“…The work described in this report initiated with a study that characterized the antagonistic effects of GL on stem growth inhibition (Folta, 2004). The study charted the minute-to-minute growth kinetics of developing seedlings using computer-assisted, infrared image capture (Parks and Spalding, 1999;Folta and Spalding, 2001). The highresolution growth study defined a specific and robust effect GL on seedling elongation that peaked 30 to 45 min after the pulse.…”