PLANT PHYSIOLOGY , Vol 102, Issue 2 671-677, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Specificity and Photomorphogenic Nature of Ultraviolet-B-Induced Cotyledon Curling in Brassica napus L
M. I. Wilson and B. M. Greenberg
Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1 Canada
Three general classes of photomorphogenic photoreceptors have been
characterized in higher plants: phytochrome, a blue light/ultraviolet
(UV)-A photoreceptor(s), and a UV-B sensory system(s). Although a great
deal is known about phytochrome and the blue light/UV-A photoreceptor(s),
little is known about UV-B detection processes. One reason for this is the
lack of readily quantifiable morphogenic responses that are specifically
induced by UV-B radiation. We have discovered a response to UV-B, upward
curling of Brassica napus L. cotyledons, that may be useful for probing the
mechanism of UV-B photoreception. The process was initially observed when
B. napus seeds were germinated under visible light plus UV-B radiation, but
did not occur under visible light alone or visible light plus UV-A. When
5-d-old seedlings grown in visible light were given relatively short
exposures of UV-B (100 min of 5.5 [mu]mol m-2 s-1), the curling response
was also observed. Development of curling was separated from the
application of this UV-B pulse by a 14-h latent period. Pulses of red
light, blue light, farred light, and UV-A (100 min of 5.5 [mu]mol m-2 s-1)
did not induce curling, indicating UV-B specificity Additionally, these
other spectral regions did not reverse or enhance the UV-B-triggered
response. The degree of curling showed a log-linear dependence on UV-B
fluence (6-40 mmol m-2) and reciprocity with respect to length of exposure
and fluence rate. The data indicate that curling is photomorphogenic in
nature and may be triggered by a single photoreceptor species.
