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Title: How do UV photomorphogenic responses confer water stress tolerance?

item Gitz, Dennis
item Liu Gitz, Lan

Submitted to: Photochemistry and Photobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2003
Publication Date: 12/1/2003
Citation: Gitz, D.C., Liu Gitz, L. 2003. How do UV photomorphogenic responses confer water stress tolerance? Photochemistry and Photobiology. 78(6):529-534.

Interpretive Summary: Interactions between UV-B radiation and drought stress have been observed but the underlying mechanisms have not been thoroughly investigated. We present an overview of specific mechanisms by which UV responses may enhance crop plant water use efficiency. We show that UV-B can reduce the numbers of stomata, pores which regulate water loss by plants, on the leaves. As a result, water use was reduced by UV radiation. The role of "flavonoids" which are thought to act as UV screening compounds is discussed. UV-B exerts an influence on plant development that may result in improved water use efficiency and could improve drought tolerance.

Technical Abstract: Though UV-B is potentially harmful radiation, it is an important common component of terrestrial radiation. Plants have long been evolving mechanisms to avoid and repair UV damage. So, it is not surprising that photomorphogenic UV-B responses are often assumed to be adaptations to harmful radiation. This assumes that the function of such responses is to prevent UV damage. It has been hypothesized that UV-B provides a signal important for normal plant development and is perceived by plants through specific signal perception mechanisms rather than as a response to damage. UV perception can lead to developmental responses which may confer adaptive advantages under conditions associated with high light environments, such as water stress. Plant responses to UV radiation include changes in leaf area, leaf thickness, stomatal density, photosynthetic pigment production, and altered stem elongation and branching patterns. Such responses lead to altered transpiration rates and water use efficiencies. We found that the cumulative effect of ambient UV-B radiation upon stomatal density and conductance can lead to altered water use efficiencies. In field settings, UV typically acts as a photomorphogenic signal rather than as a stressor. Hence, it may be insufficient to fully evaluate the adaptive roles of plant responses to UV-B on stress tolerance by the simultaneous application of UV and drought during development. We propose one should also examine how a plant's response to UV induces tolerance to subsequently applied stresses rather than simultaneously applied stresses.