The exogenous application of spermidine alleviates photosynthetic inhibition and membrane lipid peroxidation under low-light stress in tomato (Lycopersicon esculentum Mill.) seedlings

The effects of three concentrations (0.001, 0.01, and 0.1 mg/L) of exogenous spermidine (Spd) on the O-2(center dot-) production rate, malondialdehyde (MDA) content, antioxidant enzyme activities, leaf photosynthesis, chlorophyll content, chlorophyll fluorescence, and light response curve parameters were investigated in the seedlings of two tomato cultivars: low-light-stress-tolerant 'Zhongza 9' and sensitive 'Zhongshu 6'. Low-light stress of 150 mu mol m(-2) s(-1) resulted in an increase in the O-2(center dot-) production rate, MDA content, and peroxidase activity, whereas the superoxide dismutase and catalase activities decreased. Exogenous Spd effectively ameliorated these effects. The net photosynthetic rate (P-n), maximal photochemical quantum efficiency of photosystem II (F-v/F-m), light saturation point, net photosynthetic rate at light saturation point (A(max)), and dark respiration rate (R-d) simultaneously decreased under low light, but the chlorophyll content, particularly the chlorophyll b (chl(b)) content, markedly increased when compared to the normal-light (control) plants. Exogenous Spd diminished the decrease in leaf P-n and F-v/F-m and induced a further increase in the chlb content and decrease in R-d and chl(a)/chl(b) under low-light stress. These results suggested that exogenous Spd could improve plant tolerance by alleviating the membrane lipid peroxidation and photosynthetic inhibition resulting from low light. However, the optimal Spd concentration generally differed in the two cultivars.