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 t han is possible with genetically uniform plants. Arabidopsis has a rosette stature and has predominantly abaxial stomata. Thus, it is difficult to inv estigate its stomatal behaviour and gas exchange using conventional techniq ues and instrumentation. In this study, the relative abundance of C-13 and C-12 in leaf tissue (delta C-13) was used as a means of determining water u se efficiency (WUE) and the relative balance, at the site of carbon fixatio n, between CO2 supply and demand. UV-B insensitive (Ler) and sensitive (fah 1) Arabidopsis genotypes were raised in a growth chamber and exposed to 6 k J m(-2) d(-1) UV-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 neg ative) leaf delta C-13 values (indicating low WUE), but high dry matter pro duction of the UV-B exposed plants suggest that their higher leaf water con tent was not primarily due to stomatal closure. We propose that the mechani sms underlying the maintenance of higher leaf water content involved UV-B a nd water stress induced biosynthesis of stress proteins and compatible osmo lytes. (C) 2000 Annals of Botany Company.