ROLE OF ABSCISIC ACID IN THE ADAPTATION OF GRAFTED TOMATO TO MODERATELY SUBOPTIMAL TEMPERATURE STRESS

Low temperature is one of the most important environmental stress factors that modifies plant growth and development. The root system has a strong impact on the susceptibility of plants to temperature and this has been attributed to several root functions, including production of phytohormones, their upward transport, and root-to-shoot signaling which change shoot physiology and thus growth and productivity. Since low temperature tolerant rootstocks are available grafting might be used as an efficient tool to enhance temperature stress tolerance of fruit vegetables. In order to verify to what extent rootstocks are able to alleviate the negative effects of low temperature by altering the biosynthesis of hormones at the root level, reciprocal grafting of cultivars and mutants expressing or lacking abscisic acid (ABA) has been used. The tested tomato mutants were ‘sitiens’ and ‘notabilis’. After two weeks of regular growth in a greenhouse at a mean air temperature of 22°C, the latter was lowered to a suboptimal level (15°C) for three weeks and then raised again to 22°C to test plant adaptation. Growth and physiological characteristics, such as leaf area and photosynthesis were examined. The concentrations of the stress indicator, chlorophyll, were measured as well. The results confirmed the negative impact of low temperature on growth characteristics. However, net photosynthesis was more severely affected by low temperature in plants grafted onto ABA-deficient mutants than in those grafted onto standard cultivars, irrespective of the scion genotype. Overall, when a standard cultivar producing ABA was used as rootstock, the grafted plant exhibited significantly higher growth rates and lower photoinhibition under cold stress, and could more efficiently readapt after re-exposure to normal temperature levels.