The Interaction of Ultraviolet-B Radiation and Water Deficit in Two Arabidopsis thaliana Genotypes

It has been demonstrated, in both herbaceous and woody species, that tissue hydration resulting from exposure to drought is less pronounced if plants are concurrently exposed to ultraviolet-B radiation (UV-B). An explanation for the mechanisms underlying this phenomenon has been elusive. Arabidopsis thaliana(L.) Heynh. genotypes, defective in specific defences against UV-B exposure, may permit more insightful study of drought-UV-B interactions than is possible with genetically uniform plants. Arabidopsis has a rosette stature and has predominantly abaxial stomata. Thus, it is difficult to investigate its stomatal behaviour and gas exchange using conventional techniques and instrumentation. In this study, the relative abundance of13C and12C in leaf tissue (δ13C) was used as a means of determining water use efficiency (WUE) and the relative balance, at the site of carbon fixation, between CO2supply and demand. UV-B insensitive (L er) and sensitive (fah1)Arabidopsis genotypes were raised in a growth chamber and exposed to 6kJm−2d−1UV-B irradiation and subjected to drought. In both genotypes, leaf desiccation was less pronounced than that of control plants that were subjected to drought but not exposed to UV-B. The relatively low (more negative) leaf δ13C values (indicating low WUE), but high dry matter production of the UV-B exposed plants suggest that their higher leaf water content was not primarily due to stomatal closure. We propose that the mechanisms underlying the maintenance of higher leaf water content involved UV-B and water stress induced biosynthesis of stress proteins and compatible osmolytes.