Effect of high light conditions on the response of Arabidopsis thaliana plants with suppressed mitochondrial alternative oxidase

BACKGROUND: Plants as sessile organisms have developed biochemical pathways to protect themselves from the excess light energy. Mitochondrial alternative oxidase (AOX) participates in the oxidation of reductants exported from chloroplasts, thereby optimizing photosynthesis and protecting cells from photodamage. AIM: The effect of high light on respiration and the relative transcripts content of a number of genes in Arabidopsis thaliana plants of the T-DNA insertional line for AOX1a (aox1a) was studied and compared with the response of the antisense silencing of AOX1a line (AS-12) and wild type line Col-0. MATERIALS AND METHODS: Four-week-old A. thaliana plants of three lines grown at 90 µmol/m2 · s and then exposed to moderately high light conditions, 400 µmol/m2 · s, in a short-term experiment (8 h). Respiratory pathways activity, gene expression, and superoxide anion content were determined during experiment. RESULTS: Plants of the aox1a line in response to high light were characterized by the absence of the total and alternative respiration reaction and the absence of the AOX1 protein in spite of the increased mRNA level of AOX1c, in contrast to the Col-0 and AS-12 lines. Also, an increased content of transcripts of only SAPX and CHS were found, while in the other lines a compensatory increase in the expression of many “defense” genes was revealed. CONCLUSIONS: Thus, the aox1a line was characterized by a low compensatory effect at the level of defense systems activation. This is apparently caused by the absence of the AOX1 protein and, as a result, the weakening of the stress signal and stress response. The results obtained indicate the important role of AOX in the response of respiration to light stress; can be used to study the signaling pathways of regulation of AOX1a expression.