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Twenty-two cultivars of rice (Oryza sativa L.) from diverse origins were grown under greenhouse conditions and exposed to ultraviolet-B radiation (UV-B; 280-320 nm) simulating a 5% reduction in stratospheric ozone in spring for the Philippines (14 degrees N lat.) to evaluate growth and morphological responses to UV-B. In comparison to controls that received no UV-B, plants exposed to UV-B exhibited significantly reduced dry matter production (total plant and shoot), shoot height, leaf blade length and total leaf area, increased number of tillers, and greater weight fractions in leaf blades and roots. For most cultivars, the relative effects of UV-B on shot morphology were greater than the effects on biomass production. The direction of the UV-B effects were generally similar for all cultivars, however, there were significant differences among cultivars in the magnitude of the UV-B-induced changes. Upland cultivars (IRAT104 and OS4) and two low-land cultivars commonly planted in the USA (Star Bonnet and Lemont) were found to be least affected by the UV-B, whereas modern, high yielding, lowland cultivars developed in the Philippines (IR52, IR35546-17-33, and IR58) were found to be among the most sensitive to UV-B. Our results indicate that in rice, as in other grasses, shoot morphology may be more responsive to solar UV-B change than plant productivity. Intraspecific variation in morphological responses to UV-B could contribute to differences among cultivars in susceptibility to UV-B induced changes in competitive balance between rice and associated weeds of the rice agroecosystem.

Plants perceive ultraviolet-B (UV-B) radiation through the UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8), and initiate regulatory responses via associated signalling networks, gene expression and metabolic pathways. Various regulatory adaptations to UV-B radiation enable plants to harvest information about fluctuations in UV-B irradiance and spectral composition in natural environments, and to defend themselves against UV-B exposure. Given that UVR8 is present across plant organs and tissues, knowledge of the systemic signalling involved in its activation and function throughout the plant is important for understanding the context of specific responses. Fine-scale understanding of both UV-B irradiance and perception within tissues and cells requires improved application of knowledge about UV-attenuation in leaves and canopies, warranting greater consideration when designing experiments. In this context, reciprocal crosstalk among photoreceptor-induced pathways also needs to be considered, as this appears to produce particularly complex patterns of physiological and morphological response. Through crosstalk, plant responses to UV-B radiation go beyond simply UV-protection or amelioration of damage, but may give cross-protection over a suite of environmental stressors. Overall, there is emerging knowledge showing how information captured by UVR8 is used to regulate molecular and physiological processes, although understanding of upscaling to higher levels of organisation, i.e. organisms, canopies and communities remains poor. Achieving this will require further studies using model plant species beyond Arabidopsis, and that represent a broad range of functional types. More attention should also be given to plants in natural environments in all their complexity, as such studies are needed to acquire an improved understanding of the impact of climate change in the context of plant-UV responses. Furthermore, broadening the scope of experiments into the regulation of plant-UV responses will facilitate the application of UV radiation in commercial plant production. By considering the progress made in plant-UV research, this perspective highlights prescient topics in plant-UV photobiology where future research efforts can profitably be focussed. This perspective also emphasises burgeoning interdisciplinary links that will assist in understanding of UV-B effects across organisational scales and gaps in knowledge that need to be filled so as to achieve an integrated vision of plant responses to UV-radiation. [ABSTRACT FROM AUTHOR]

The accumulation of ultraviolet (UV)-absorbing compounds (flavonoids and related phenylpropanoids) and the resultant decrease in epidermal UV transmittance (TUV) are primary protective mechanisms employed by plants against potentially damaging solar UV radiation and are critical components of the overall acclimation response of plants to changing solar UV environments. Whether plants can adjust this UV sunscreen protection in response to rapid changes inUV, as occurs on a diurnal basis, is largely unexplored. Here, we use a combination of approaches to demonstrate that plants can modulate their UV-screening properties within minutes to hours, and these changes are driven, in part, by UVradiation. For the cultivated species Abelmoschus esculentus, large (30-50%) and reversible changes in TUV occurred on a diurnal basis, and these adjustments were associated with changes in the concentrations of whole-leaf UV-absorbing compounds and several quercetin glycosides. Similar results were found for two other species (Vicia faba and Solanum lycopersicum), but no such changes were detected in Zea mays. These findings reveal a much more dynamic UV-protection mechanism than previously recognized, raise important questions concerning the costs and benefits of UV-protection strategies in plants and have practical implications for employing UV to enhance crop vigor and quality in controlled environments. [ABSTRACT FROM AUTHOR]