Enhanced tolerance of photosynthesis to high-light and drought stress in Pseudotsuga menziesii seedlings grown in ultraviolet-B radiation.
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.
Department of Biological Sciences, Idaho State University, Campus Box 8007, Pocatello, ID 83209-8007, USA. poulmary@isu.edu
Mary E
ME
Poulson
Raymon A
RA
Donahue
Julie
J
Konvalinka
M Regina Torres
MR
Boeger
D003681:Dehydration; D008027:Light; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D018515:Plant Leaves / Q000033:anatomy & histology / Q000502:physiology / Q000528:radiation effects; D018526:Plant Transpiration / Q000502:physiology / Q000528:radiation effects; D028224:Pseudotsuga / Q000502:physiology* / Q000528:radiation effects; D036226:Seedlings / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D014197:Trees / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D014466:Ultraviolet Rays
D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex