RESUMEN
Arabidopsis thaliana grown in a light regime that included ultraviolet-B (UV-B) radiation (6 kJ m(-2) d(-1)) had similar light-saturated photosynthetic rates but up to 50% lower stomatal conductance rates, as compared to plants grown without UV-B radiation. Growth responses of Arabidopsis to UV-B radiation included lower leaf area (25%) and biomass (10%) and higher UV-B absorbing compounds (30%) and chlorophyll content (52%). Lower stomatal conductance rates for plants grown with UV-B radiation were, in part, due to lower stomatal density on the adaxial surface. Plants grown with UV-B radiation had more capacity to down regulate photochemical efficiency of photosystem II (PSII) as shown by up to 25% lower phi(PSII) and 30% higher non-photochemical quenching of chlorophyll fluorescence under saturating light. These contributed to a smaller reduction in the maximum photochemical efficiency of PSII (F (v)/F (m)), greater dark-recovery of F (v)/F (m), and higher light-saturated carbon assimilation and stomatal conductance and transpiration rates after a four-hour high light treatment for plants grown with UV-B radiation. Plants grown with UV-B were more tolerant to a 12 day drought treatment than plants grown without UV-B as indicated by two times higher photosynthetic rates and 12% higher relative water content. UV-B-grown plants also had three times higher proline content. Higher tolerance to drought stress for Arabidopsis plants grown under UV-B radiation may be attributed to both increased proline content and decreased stomatal conductance. Growth of Arabidopsis in a UV-B-enhanced light regime increased tolerance to high light exposure and drought stress.
Asunto(s)
Arabidopsis/fisiología , Arabidopsis/efectos de la radiación , Clima , Desastres , Luz , Fotosíntesis , Rayos Ultravioleta , Arabidopsis/crecimiento & desarrollo , Clorofila/metabolismo , Cinética , Hojas de la Planta/fisiología , Hojas de la Planta/efectos de la radiaciónRESUMEN
We investigated the effects of an ambient dose of ultraviolet-B (UV-B) radiation on chamber-grown Pseudotsuga menziesii var. glauca (Beissn.) Franco (Douglas-fir) seedlings, to determine if the presence of UV-B radiation in the growth light regime induces tolerance to environmental stresses such as high light and drought. Douglas-fir seedlings were grown without UV-B radiation or with 6 kJ m-2 day-1 of biologically effective UV-B, which is ambient for the intermountain regions of Idaho. Non-stressed seedlings grown with UV-B radiation had 35% lower seedling dry mass, 36% higher concentrations of UV-B absorbing compounds per unit leaf area, 30% lower stomatal frequencies, 25% lower light-saturated photochemical efficiencies of Photosystem II and 45% lower light-saturated stomatal conductance than non-stressed seedlings grown without UV-B radiation. After 4 days of high-light stress, seedlings grown with UV-B radiation had 32% higher light-saturated carbon assimilation rates (A(CO2)) than seedlings grown without UV-B radiation. After water was withheld from the seedlings for up to 15 days, seedlings grown with UV-B radiation had 50% higher A(CO2) and 40% higher seedling water potentials than seedlings grown without UV-B radiation. The results support the hypothesis that UV-B radiation can act as an environmental signal to induce tolerance to high-light and drought stress in Douglas-fir seedlings. Possible mechanisms for the enhanced stress tolerance are discussed.