Comparative Photobiology of Growth Responses to Two UV‐B Wavebands and UV‐C in Dim‐red‐light‐ and White‐light‐grown Cucumber (Cucumis sativus) Seedlings: Physiological Evidence for Photoreactivation^†

Abstract

We examined the influence of short-term exposures of different UV wavebands on the elongation and phototropic curvature of hypocotyls of cucumbers (Cucumis sativus L.) grown in white light (WL) and dim red light (DRL). We evaluated (1) whether different wavebands within the ultraviolet B (UV-B) region elicit different responses; (2) the hypocotyl elongation response elicited by ultraviolet C (UV-C); (3) whether irradiation with blue light-enriched white light (B/WL) given simultaneous with UV-B treatments reversed the effect of UV in a manner indicative of photoreactivation; and (4) whether responses in WL-grown plants were similar to those grown in DRL. Responses to brief (1-100 min) irradiations with three different UV wavebands all induced inhibition of elongation measured after 24 h. When WL-grown seedlings were irradiated with light containing proportionally greater short wavelength UV-B (37% of UV-B between 280 and 300 nm), inhibition of hypocotyl elongation was induced at a threshold of 0.5 kJ m(-2), whereas exposure to UV-B including only wavelengths longer than 290 nm (and only 8% of UV-B between 290 and 300 nm) induced inhibition of hypocotyl elongation at a threshold of 1.6 kJ m(-2). The UV-C treatment induced reduction in elongation at a threshold of <0.01 kJ m(-2) for DRL-grown plants and <0.03 kJ m(-2) for WL-grown plants. B/WL caused 50% reversal of the short-wavelength UV-B-induced inhibition of elongation in DRL-grown seedlings but did not reverse the effect of long-wavelength UV-B. B/WL caused 30% reversal of the UV-C-induced inhibition of elongation in WL-grown seedlings but did not affect the response to short-wavelength UV-B. Short-wavelength UV-B also induced positive phototropic curvature in both types of seedlings, and this was reversed 60% or completely in DRL-grown and WL-grown seedlings, respectively. The similarity of responses between the etiolated (DRL-grown) and de-etiolated (WL-grown) seedlings indicates that the short-wavelength specific response may be relevant to natural light environments, and the apparent photoreactivation implicates DNA damage as the sensory mechanism for the response.

An unidentified ultraviolet-B-specific photoreceptor mediates transcriptional activation of the cyclobutane pyrimidine dimer photolyase gene in plants

“…For example, the action spectrum for the inhibition of root elongation in cress resembled the UV absorption spectrum of DNA (Steinmetz and Wellmann 1986). Furthermore, diminished magnitudes of the UVB eVects under accelerated photoreactivation have suggested that DNA damages might be associated with the inhibition of hypocotyl elongation in cucumber (Shinkle et al 2005). On the other hand, for the enhancement eVects of UVB on phytochrome-mediated cotyledon opening, experiments using DNA-repair mutants have indicated that DNA lesions are not involved and, thus, could not constitute the primary event leading to UVB signaling (Boccalandro et al 2001).…”

UV-B Promotes Rapid Nuclear Translocation of the Arabidopsis UV-B–Specific Signaling Component UVR8 and Activates Its Function in the Nucleus

“…Damage may be caused by exposure to relatively high fluence rates of UV-B (Dai et al, 1997;Kim et al, 1998). The effect on the plant will be determined not only by the amount of UV-B but also by the wavelength (Ulm et al, 2004;Shinkle et al, 2004Shinkle et al, , 2005, the degree of prior acclimation, and to some extent by interaction with other environmental factors (Caldwell et al, 2007). High fluence rates of UV-B are known to generate reactive oxygen species (Dai et al, 1997;Allan and Fluhr, 1997;Barta et al, 2004) and to increase levels of signaling molecules involved in wound and defense responses, such as jasmonic acid and ethylene (A-H-Mackerness et al, 1999).…”

UV-B Signaling Pathways with Different Fluence-Rate Response Profiles Are Distinguished in Mature Arabidopsis Leaf Tissue by Requirement for UVR8, HY5, and HYH

“…For example, in cucumber (Cucumis sativus) hypocotyls, different UV-B wavebands elicit different growth inhibition and phototropic responses, with the short-wavelength responses most likely mediated by DNA damage signaling (Shinkle et al, 2004(Shinkle et al, , 2005. Similarly, Ulm et al (2004) found that different UV-B wavebands induce distinct gene expression responses in Arabidopsis (Arabidopsis thaliana) and that shorter wavelength UV-B antagonizes the response to longer wavelengths.…”