Sugar-induced tolerance to atrazine in Arabidopsis seedlings:: interacting effects of atrazine and soluble sugars on psbA mRNA and D1 protein levels

In order to assess the potential environmental impact of atrazine on wild terrestrial plants, the physiological determinants for atrazine sensitivity were investigated in the model plant Arabidopsis thaliana. Atrazine treatment arrested development of Arabidopsis at the stage of heterotrophy-phototrophy transition, with cotyledon bleaching and seedling death. However, sucrose and, to a markedly lesser extent, glucose were found to confer to Arabidopsis seedlings a high level of tolerance to atrazine, with maintenance of chlorophylls, carotenoids, and D I protein, and protection of photosystem II. Moreover, atrazine in the presence of sucrose was found to have a paradoxically positive effect on seedling development. The effects of different carbon substrates and the analysis of Arabidopsis sugar-response mutants showed that sucrose-induced atrazine tolerance was not due to carbon compensation of photosynthesis and probably relied on hexokinase-independent signalling pathways. Enhancement of seedling growth, and of chlorophyll and carotenoid accumulation, by sucrose occurred both in the absence and presence of atrazine. In contrast, whereas sucrose treatment in the absence of atrazine decreased psbA mRNA and D1 protein levels, the combined effects of sucrose and atrazine resulted in increased levels of psbA mRNA and of D1 protein levels, which may thus significantly contribute to the induction of atrazine tolerance. (C) 2004 Elsevier Ireland Ltd. All rights reserved.