Specificity and Photomorphogenic Nature of Ultraviolet-B-Induced Cotyledon Curling in Brassica napus L

Abstract

Three general classes of photomorphogenic photoreceptors have been characterized in higher plants: phytochrome, a blue lightl 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 detedion 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 1. cotyledons, that may be useful for probing the mechanism of UV-B photoreception. The process was initially observed when 8. 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 rmol m-' s-'), 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 rcmol m-* s-') did not induce curling, indicating UV-B specificity. Additionally, these other spectral regions did not reverse or enhance the UV-8-triggered response. The degree of curling showed a log-linear dependence on UV-B fluence (6-40 mmol m-') 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.

Low threshold levels of ultraviolet‐B in a background of photosynthetically active radiation trigger rapid degradation of the D2 protein of photosystem‐II

“…Fluence rates were adjusted by changing the distance of the lamps to the plants. To allow comparison with the work of others, we have estimated the biologically effective UV-B radiation as the cross-sectional overlap between the generalized plant action spectrum normalized to 300 nm (Caldwell et aL, 1986) and the spectral output of the Rayonet 300 nm photoreactor tube (Wilson and Greenberg, 1993a). For 0.25, 1 and 6 I~mol m -2 sec -1 of radiation in the UV-B region, the values were 0.11, 0.43 and 2.6 I~mol m -2 sec -1, respectively.…”

A garden study of the effects of ultraviolet-B radiation on pollination success and lifetime female fitness in Brassica

“…A greenhouse study of two species of Brassica (Feldheim and Conner 1996) found increases in female ®tness with increased UV-B in three of four cases, in spite of the fact that the family Brassicaceae is known to be sensitive to UV-B ( Van et al 1976;Hashimoto and Tajima 1980;Tevini et al 1981;Wilson and Greenberg 1993). However, responses of plants in the greenhouse to UV-B may be quite dierent from responses in the ®eld (Teramura 1986b;Teramura and Murali 1986).…”

Efeitos da radiação ultravioleta-B sobre a morfologia foliar de Arabidopsis thaliana (L.) Heynh. (Brassicaceae)

“…Em Brassica napus L., o enrolamento está associado com a degradação da auxina na epiderme da face adaxial ou ainda, devido aos danos que a radiação causa às proteínas, ao DNA ou aos fotossistemas durante o desenvolvimento foliar (Wilson & Greenberg 1993;Krol et al 2000). O enrolamento das margens pode ser considerado como um mecanismo fotoprotetor das folhas para minimizar o efeito da radiação UV-B, uma vez que a área foliar exposta é menor.…”