The physiological changes and the mechanism of stress tolerance in tomato were studied under low temperature and low light conditions. Two growth chamber experiments evaluated three temperatures regimes under standard and relatively low illumination levels with three tomato genotypes. Both experiments used a completely randomized split-plot design (CRD), with temperature regime as the main plot and tomato genotype as the split-plot. The three tomato varieties were “Fenyan No.1”, “SV0313TG”, and “Ousa”. In both experiments, activity of superoxide dismutase (SOD) and peroxidases (POD) in tomato seedlings decreased under low temperature regime and the combination of low temperature and low light. Decreasing temperature had the greatest effect on the increase in enzyme activity. Decrease in POD activity was the greatest under low light and low temperature. The concentration of malondialdehyde (MDA) in plant tissue also decreased under low temperature (20°C/10°C day/night) compared to the standard temperature control (25°C/16°C day/night), but increased at 15°C/5°C day/night temperatures in both experiments and was the greatest under the lowest light and temperature conditions. In both experiments, proline concentrations were the greatest under the standard light intensity (30,000 lux), and proline concentrations increased as temperature decreased. The content of soluble sugar decreased under only low temperature stress but increased under double stresses. The relative value of osmotic potential increased a little under low temperature stress but decreased under double stresses.
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