Different Phototransduction Kinetics of Phytochrome A and
Phytochrome B in Arabidopsis thaliana |
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Authors: | Jorge J Casal Pablo D Cerdán Roberto J Staneloni and Laura Cattaneo |
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Institution: | I.F.E.V.A., Departamento de Ecología, Facultad de Agronomía, Universidad de Buenos Aires, Avenida San Martín 4453, 1417-Buenos Aires, Argentina (J.J.C., L.C.);Instituto de Investigaciones Bioquímicas Fundación Campomar, Avenida Patricias Argentinas 435, 1405-Buenos Aires, Argentina (P.D.C., R.J.S.) |
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Abstract: | The kinetics of phototransduction of phytochrome A (phyA) and phytochrome B (phyB) were compared in etiolated Arabidopsis thaliana seedlings. The responses of hypocotyl growth, cotyledon unfolding, and expression of a light-harvesting chlorophyll a/b-binding protein of the photosystem II gene promoter fused to the coding region of β-glucuronidase (used as a reporter enzyme) were mediated by phyA under continuous far-red light (FR) and by phyB under continuous red light (R). The seedlings were exposed hourly either to n min of FR followed by 60 minus n min in darkness or to n min of R, 3 min of FR (to back-convert phyB to its inactive form), and 57 minus n min of darkness. For the three processes investigated here, the kinetics of phototransduction of phyB were faster than that of phyA. For instance, 15 min R h−1 (terminated with a FR pulse) were almost as effective as continuous R, whereas 15 min of FR h−1 caused less than 30% of the effect of continuous FR. This difference is interpreted in terms of divergence of signal transduction pathways downstream from phyA and phyB. |
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