Antisense-mediated depletion of tomato chloroplast glutathione reductase enhances susceptibility to chilling stress

A tomato (Lycopersicon esculentum Mill.) chloroplast glutathione reductase gene (LeGR) was isolated and antisense transgenic tomato lines were obtained. Under chilling stress, transgenic plants accumulated more H2O2, leaked more electrolyte and showed lower net photosynthetic rate (Pn), maximal photochemical efficiency of PSII (Fv/Fm) and oxidizable P700 compared with wild-type (WT) plants. Transgenic seedlings were more suppressed in fresh-weight growth and lost more cotyledon chlorophyll. The decrease in the activity of ascorbate peroxidase (APX) was implied to be potentially relevant to the greater accumulation of H2O2 in transgenic plants. Chilling treatment induced more decrease in the level of reducted glutathione (GSH) and redox ratio of glutathione in transgenic plants than in WT plants, but aroused more increase in GSSG in transgenic plants than in WT plants. Total glutathione displayed no change. Besides, chilling stress resulted in greater decreases in the level of reducted ascorbate (AsA), total ascorbate and redox ratio of ascorbate in transgenic plants than in WT plants, but led to equivalent degree of dehydroascorbate (DHA) increase in WT and transgenic plants. These assessments of glutathione–ascorbate cycle revealed that the decrease of glutathione reductase activity in transgenic plants affected glutathione regeneration, and consequently affected ascorbate regeneration and total ascorbate content. This resulted in a greater accumulation of H2O2 and an enhanced sensitivity to chilling stress in transgenic plants. Moreover, a putative concept model of ecophysiological reaction was discussed.