Evolutionary response of plants to increased UV-B radiation: Greenhouse and field studies with Arabidopsis thaliana

Two approaches were used to examine the evolution of UV-B tolerance in Arabidopsis thaliana. In the first approach, I studied adaptation to past levels of UV-B radiation by examining the impact of enhanced UV-B radiation on two ecotypes of A. thaliana that originated from very different natural UV-B environments. The Libyan ecotype (from a high UV-B environment) showed no UV-B induced damage to rosette mass or the germination success of seeds harvested from irradiated plants. The Norwegian ecotype (from a low UV-B environment) showed a significant reduction in these variables in response to enhanced UV-B. The concentration of kaempferol, a putative UV-B protective filter, increased in the Libyan ecotype by 81% compared to a 22% increase in the Norwegian ecotype.; In the second approach, both greenhouse and field experiments were done to measure variation for UV-B sensitivity in a natural population of A. thaliana. This population consists of four morphologically and genetically discrete groups. There was no genetic variation for UV-B tolerance in two of the three greenhouse experiments. In the 1993-94 field study, we found genetic variation for UV-B sensitivity in this population. The high UV-B treatment caused a change in fruit number (relative to ambient UV-B) ranging from an increase of 30% (genotype B) to a decrease of 45% (genotype D). The seeds from this experiment were allowed to disperse naturally and a random sample of the F, rosettes were identified using RAPD markers. The relative frequency of genotype D in the F, generation was reduced by 34%. Given that genotype D comprises greater than 90% of this population, projected increases in solar UV-B may have significant consequences for the genetic structure of this population. However, evidence from the 1994-95 experiment indicates that UV-B selection may be variable between years. In this study, there was no genetic variation for UV-B sensitivity but the high UV-B treatment did cause an overall reduction in fruit number ({dollar}-{dollar}19%). This year to year variation in UV-B selection may act to maintain genetic variation for UV-B tolerance within this population.