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Different Phototransduction Kinetics of Phytochrome A and
Phytochrome B in Arabidopsis thaliana1
Jorge J. Casal*,
Pablo D. Cerdán,
Roberto J. Staneloni, and
Laura Cattaneo
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.); and Instituto de Investigaciones Bioquímicas Fundación
Campomar, Avenida Patricias Argentinas 435, 1405-Buenos Aires,
Argentina (P.D.C., R.J.S.)
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
-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.
1
This work was supported by grants from the
University of Buenos Aires (no. AG041 to J.J.C. and no. 01/X304 to
R.J.S.), Fundación Antorchas (no. A-13434/1 to J.J.C.), and
Consejo Nacional de Investigaciones Cientificas y Tecnicas (no. PIA
6524 to J.J.C. and no. PICT 0295 to R.J.S.).
*
Corresponding author; e-mail jjcasal{at}ifeva.edu.ar; fax
541-521-1384.
Plant Physiol. (1998) 116: 1533-1538
Copyright Clearance Center: 0032-0889/98/116/1533/06
© 1998 American Society of Plant Physiologists
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