Investigation of low temparature stress in tomato in respect to antioxidative mechanisms

Low temperature stress is a major environmental factor limiting plant productivity. Lowtemperature stress causes severe depressions in yield in greenhouse grown tomato. In this thesis study137 different tomato genotypes were screened for their efficiency to grow under low temperatures. Ingenotypes with contrasting efficiency under low temperature stress, the role of antioxidants andantioxidative enzymes in detoxification of toxic O2 radicals were evaluated.In screening experiments, average efficiency of the genotypes tested was 45.1, 9 % and 73.9% in 14 and 9-day-cold treated plants respectively. Under long term low temperature regime,activation of antioxidative enzymes were in the order of superoxide dizmutaze (44 % increase),ascorbate peroxidase (15 % increase), glutathione reduktase (19 % decrease) and catalase (23 %decrease). The levels of antioxidants were also significantly enhanced under low temperature stress.Concentration of buffer soluble SH-groups was induced by a factor of 1.8. Foliar application of stressenhancers H2O2 and paraquat (PQ) prior to low temperature treatment were also effective in inductionof SH-groups.There were significant differences in activation of antioxidative systems depending on theage of leaf tissue in all genotypes. Cold induced chlorophyll degradation was more pronounced in theold leaves of non-efficient plants. Oxidative stress inducers (OSI) were only effective in dry matterproduction of genotypes. Pre-OSI treatment resulted in induction or reduction in dry matterproduction under low temperature stress. It is suggested that OSI treatment before the onset of lowtemperature treatment may have some beneficial effect on the efficiency of some genotypes.Results obtained in this research have shown a significant and exploitable variation in coldtolerance of tomato genotypes. However changes in antioxidative systems under low temperatureregimes was not enough to explain the variations in efficiency.Key words: Tomato, low temperature stress, tolerance, antioxidative enzymes andantioxidants, toxic O2 radicalsII