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Phytochrome-like responses in Euglena: A low fluence response that reorganizes the spectral dependence of the high irradiance response in long-day photoperiodic induction of cell division

Paper ID Volume ID Publish Year Pages File Format Full-Text
31160 44560 2007 12 PDF Available
Title
Phytochrome-like responses in Euglena: A low fluence response that reorganizes the spectral dependence of the high irradiance response in long-day photoperiodic induction of cell division
Abstract

Irradiance spectra change spatiotemporally, and angiosperms adapt accordingly, mainly through phytochromes. This study challenges the long-held belief that the flagellated alga Euglena gracilis lacks phytochromes and is therefore unaffected by spectral changes. We photoautotrophically cultured the alga under continuous light (LL), then transferred it to darkness. After about 26 h in darkness, different irradiations for 3 h enabled cell division in dark-arrested G2 cells evoking a high-irradiance response (HIR). The spectral characteristics of the irradiation during the LL period (pre-irradiation) defined the spectral sensitivity in the subsequent dark period. LL with light rich in the red spectrum led to a HIR to the red spectrum (R-HIR), whereas light rich in the far-red spectrum (FR) led to a FR-HIR. Finishing the period of pre-irradiation consisting of continuous cool-white fluorescent light (rich in R) by a FR pulse enhanced the characteristics of the FR-HIR 26 h later. By contrast, a R pulse given at the end of the pre-irradiation rich in FR potentiated the R-HIR. The effects were completely photoreversible between R and FR with critical fluences of about 2 mmol m−2, satisfying the classic diagnostic feature of phytochromes. The action spectrum of the FR effect at the end of pre-irradiation consisting of continuous cool-white fluorescent light (rich in R) had a main peak at 740 nm and a minor peak at 380 nm, whereas antagonization of the FR effect had a main peak at 640 nm and a minor peak at 480 nm. Wavelengths of 610 and 670 nm appeared in both spectra. We also demonstrated the photoreversibility of 380/640, 480/740, and (610 and 670)/(640 and 740) nm. We conclude that Euglena displays phytochrome-like responses similar to the ‘shade avoidance’ and ‘end-of-day FR’ effects reported in angiosperms.

Keywords
Cell division; Circadian rhythms; End-of-day; Euglena; Photoperiodism; Phytochrome; Shade avoidance
First Page Preview
Phytochrome-like responses in Euglena: A low fluence response that reorganizes the spectral dependence of the high irradiance response in long-day photoperiodic induction of cell division
Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 86, Issue 2, 1 February 2007, Pages 97–108
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering