Far-red radiation (FR) reflected by green tissues is a key signal that plants use to detect the proximity of future competitors. Perception of increased levels of FR elicits a suite of responses collectively known as the shade-avoidance syndrome, whic

The effects of solar ultraviolet (UV)-B (280-315 nm) on plants have been studied intensively over the last 2 decades in connection with research on the biological impacts of stratospheric ozone depletion. However, the molecular mechanisms that mediate plant responses to solar (ambient) UV-B and their interactions with response mechanisms activated by other stressors remain for the most part unclear. Using a microarray enriched in wound-and insect-responsive sequences, we examined expression responses of 241 genes to ambient UV-B in field-grown plants of Nicotiana longiflora Cav. Approximately 20% of the sequences represented on the array showed differential expression in response to solar UV-B. The expression responses to UV-B had parallels with those elicited by simulated Manduca sexta herbivory. The most obvious similarities were: (a) down-regulation of several photosynthesis-related genes, and (b) up-regulation of genes involved in fatty acid metabolism and oxylipin biosynthesis such as HPL (hydroperoxide lyase), ␣-DIOX (alpha-dioxygenase), LOX (13-lipoxygenase), and AOS (allene oxide synthase). Genes encoding a WRKY transcription factor, a ferredoxin-dependent glutamate-synthase, and several other insect-responsive genes of unknown function were also similarly regulated by UV-B and insect herbivory treatments. Our results suggest that UV-B and caterpillar herbivory activate common regulatory elements and provide a platform for understanding the mechanisms of UV-B impacts on insect herbivory that have been documented in recent field studies.UV-B induces multiple responses in terrestrial plants. These responses have been studied using a variety of experimental approaches, from controlledenvironment experiments to large-scale field trials, and covering a broad spectrum of scales, from molecular to ecosystem level processes. Controlledenvironment experiments have contributed most of the information presently available on responses at the molecular level. However, this type of experiment, particularly those that are based on the use of heavily unbalanced light sources (i.e. with unnaturally high ratios of UV-B to photosynthetically active radiation [PAR] or UV-B to UV-A [315-400 nm]), are frequently criticized on the grounds that they lack functional and ecological realism (Fiscus and Booker, 1995;Caldwell and Flint, 1997). It has been shown clearly that treatments with high UV-B to PAR ratios, which are the norm in controlled-environment exposures, tend to result in greatly exaggerated effects of UV-B on photosynthesis and growth inhibition. Because these effects have been hard to duplicate under field conditions, it is unclear to what extent the molecular and mechanistic data that have been produced under spectrally unbalanced conditions (which commonly involve PAR levels lower than 1:10 of full sunlight) contribute to our understanding of the normal physiological responses of plants to ambient UV-B stress. In fact, it has been clearly demonstrated that the level of PAR strongly modulates the effect of UV-B on...

The results suggest that the anti-herbivory effect induced by UV-B may be mediated at least in part by the accumulation of phenylpropanoid derivatives that are similar to those induced by the plant in response to insect herbivory.