Effect of UV-B radiation on the shoot dry matter production and stable carbon isotope composition of two Arabidopsis thaliana genotypes.

An application of stable carbon isotope analysis to the mechanistic interpretation of ultraviolet-B (UV-B) effects on growth inhibition is described that is particularly useful for small plants such as Arabidopsis thaliana that are not well suited for gas exchange studies. Many investigators use tissue δ13C, relative abundance of 13C and 12C, as a proxy for water use efficiency and as an indicator of environmental effects on stomatal behaviour and on photosynthesis during growth. Discrimination against 13C is enhanced by both high stomatal conductance and damage to photosynthetic machinery. Because the thinning of the stratospheric ozone layer is permitting more UV-B to enter the biosphere, the mechanisms of action of UV-B radiation on plants are of particular current interest. Arabidopsis thaliana wild-type Landsberg erecta (Ler) and the UV-B-sensitive mutant fah1 , deficient in UV-absorbing sinapate esters, were grown in a controlled environment and exposed to UV-BBE doses of 0 or 6-7 kJ m-2 day-1. UV-B exposure decreased dry matter production and δ 13C in both genotypes, but growth inhibition was generally greater in fah1 than in Ler. The fah1 mutant also had less leaf greenness than Ler. Changes in leaf tissue δ 13C were detected before growth inhibition and were evident in treatments of both genotypes that did not cause marked growth effects. This suggests that the effects of UV-B contributing to increased carbon isotope discrimination in Ler may have been primarily associated with high stomatal conductance, and in fah1 with both high stomatal conductance and damage to photosynthetic machinery. [ABSTRACT FROM AUTHOR]