Natural variation in UV-B protection amongst Arabidopsis thaliana accessions

Pronounced altitudinal and latitudinal UV-B gradients exist across the earth. Therefore, we hypothesised that plants from different geographic origins differ in the regulation and/or magnitude of UV-protection. Eight Arabidopsis accessions with different geographic origins (altitude between 32 and 3016 m) were raised under Photosynthetic Active Radiation (PAR), PAR + UV-A or PAR + UV-A + UV-B radiation for 10 days, after which UV-B protection of photosynthesis was assessed by measuring the consequences of exposure to a pulse of acute UV-B. We found significant variation in UV-B protection among accessions exposed to PAR or PAR + UV-A. Yet, all accessions raised under PAR + UV-A + UV-B were well protected. Thus, differences between accessions are not about UV-B protection per sé, but rather about regulation of UV-B protection which varies from constitutive to inducible by UV-A and/or UV-B. Particularly striking are differential UV-A responses, whereby some high altitude accessions lack UV-A regulated accumulation of UV-absorbing pigments, but show a strong UV-A induced morphogenic response. The adaptive relevance of the differential regulation of UVprotection is discussed.