Functional differentiation in UV-B-induced DNA damage and growth inhibition between highland and lowland ecotypes of two Arabidopsis species

Ultraviolet-B (UV-B; 280–315 nm) radiation has been shown to be more stressful for plants at higher elevations. Species inhabiting different origins may have evolutionarily altered UV tolerance to match their phenotypes to local conditions. However, little is known about UV adaptation patterns between high- and lowland. Here, we evaluated UV damage to DNA and growth in ecotypes of two species of Arabidopsis from different elevations, four ecotypes of A. thaliana and three ecotypes of A. halleri subsp. gemmifera under supplemental UV-B. Harvests were done before UV-B treatment and at early and late stages after the exposure to enhanced UV-B irradiation. The accumulation level of cyclobutane pyrimidine dimer (CPD) was determined as a measure of UV damage to DNA. At the early stage, lowland ecotypes of two species exhibited a higher CPD level and greater inhibition in biomass production, indicating that lowland ecotypes were more sensitive to increased UV-B than highland ecotypes. In contrast, at the later stage, CPD level and growth inhibition became similar or even lower in lowland ecotypes. These results suggest that the response to UV stress was constitutive in highland ecotypes but more inducible in lowland ecotypes. The relative growth rate was negatively related to CPD level. These ecotypic differentiations were common to two Arabidopsis species, suggesting that local adaptation occurred in parallel under a constraint of tradeoff between growth and UV tolerance.