Submitted to: Environmental and Experimental Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/19/2004
Publication Date: 6/1/2005
Citation: Gitz, D.C., Britz, S.J., Liu Gitz, L., Sullivan, J. 2005. Ultraviolet-B effects on stomatal density, water-use efficiency, and stable carbon isotope discrimination in four glasshouse-grown soybean (Glyicine max) cultivars. Environmental and Experimental Botany. 53(3): 343-355. Interpretive Summary: During growth and development plants respond to specific components in sunlight in order to adapt their environment. UV-B radiation, the ultraviolet radiation in sunlight “that can burn you”, might provide a signal to the developing plant that stressful environmental conditions lie ahead. We grew soybean in the field under plastic shelters that let solar UV-B through or under plastic that screened out UV-B. We found that some soybean varieties used water more efficiently while others used water less efficiently with UV-B from the sun. We found that this occurred because the plants altered the numbers of stoma, small pores in the leaf which allow the plant to lose. water to the atmosphere. This shows that solar UV has the potential to act as a "drought signal" and affect plant development. This work is also significant because it identifies a specific trait which directly increases water use efficiency and traits indirectly associated with increased water use efficiency.
Technical Abstract: Interactions between UV-B radiation and drought stress have been studied but the underlying mechanisms have not been thoroughly investigated. We hypothesized that ambient UV-B radiation would improve water-use efficiency (WUE) by its effects on epidermal development, specifically reduced stomatal density leading to decreased stomatal conductance. Soybean (Glycine max) isolines (OX921, OX922, OX941, OX942) with different stomatal development and flavonol expression patterns were field grown under shelters that transmitted or blocked solar UV-B. All isolines exposed to solar UV-B Soluble accumulated higher concentrations of UV-screening phenols. Leaf area was reduced in all isolines except OX921. Similarly, above ground biomass was unaffected in all isolines except in OX921 which exhibited a 33% increase with ambient UV-B. Increased biomass was associated with increased stomatal density and conductance. Solar UV-B elictited decreased stomatal density and conductance in isolines which expressed a unique branched kaempferol triglycoside (OX922 and OX941). Decreased stomatal density was associated with increased season-long WUE and decreased leaf internal CO2 concentration (estimated by d13C discrimination). Plant photomorphogenic responses to UV-B affects stomatal density and WUE in field grown soybean, but the magnitude and direction of this response is dependent on intervarietal differences. UV-B radiation had no effect on biomass accumulation or yield in OX942, which accumulates only trace flavonol (kaempferol) concentrations suggesting that flavonol expression is not prerequisite to UV-B tolerance.