چكيده انگليسي :
High temperature is one of the major abiotic stress influencing growth plant and yield by disruption of mechanisms of plant survival by inducing oxidative stress. In Iran, planting strawberry in spring will expose plants to higher air temperatures (above 30 °C), particularly in the daytime, that can cause damage to vegetative and reproductive growth of the plant. selection and use of the heat-tolerant cultivars and exogenous application of chemical compounds such as melatonin (ME) and nitric oxide (NO) are the most convenient methods to improve heat stress tolerance in strawberry plants.ME and NO as free radical small signaling molecules are involved in many plant physiological and molecular functions and can modulate plant responses to a variety of biotic and abiotic stresses.
This study was designed in four separate experiments in order to screening of different cultivars of strawberry to heat stress and to determine whether ME and NO activates protective responses to heat stress. In the first experiment, seven cultivars of strawberry (Aromas, Camarosa, Gaviota, Kurdistan, Gaviota, Paros, Queen Eliza, and Ventana) were subjected to 5 temperature levels (25, 30, 35, 40, and 45 °C) for 48 hours and their morphological and physiological parameters were evaluated. The aim of the second experiment was to compare the relative expression of the heat shock transcription factor proteins (HSFs), heat shock proteins (HSPs), and NCED genes in two strawberry cultivars including Kurdistan as a heat-tolerant cultivar and Ventana as a heat-sensitive cultivar, at temperatures of 25, 35, and 40 °C and three time-points (after 2, 5, and 10 h of exposure to heat). In the third experiment, we investigated the effect of the application of three concentrations of ME and NO (0, 50, and 100 μM) on the morphological and physiological traits of Ventana and Kurdistan strawberry cultivars when the plants were subjected to various temperatures (25, 35, and 40 °C). In the last experiment, the effects of ME and NO (0 and 100 μM) on the expression of the HSFs, HSPs, and NCED genes after 2, 5, and 10 h exposure to 25 and 40 °C were evaluated. Results showed that the increasing temperature caused an increase in the heat injury symptoms, hydrogen peroxide, and electrolyte leakage in all cultivars. However, under heat stress conditions, plants of Ventana, Aromas, and Camarosa cultivars had higher content hydrogen peroxide, and electrolyte leakage compare with other cultivars. The Kurdistan, Gaviota, and Queen Eliza had the highest leaf relative water content, total chlorophyll, photochemical efficiency of photosystem ІІ (Fv/Fm), osmotic regulators (proline, carbohydrates and soluble proteins) content, antioxidant enzyme activity (superoxide dismutase, catalase, and guaiacol peroxidase) and non-enzymatic antioxidants (reduced glutathione, ascorbic acid, and carotenoids) under high temperatures. Our results demonstrated that among the seven strawberry cultivars, Ventana, Aromas, and Camarosa are heat tolerant cultivars, Kurdistan, Gaviota, and Queen Eliza are heat sensitive, and Paros is relatively heat sensitive cultivar. In both Kurdistan and Ventana cultivars, heat stress increased the expression level of HSFs, HSPs and decreased the expression level of NCED genes. In Kurdistan cultivar, the maximum expression of FaTHSFA2a and HSP90 were observed when plants subjected to heat shock at 40 °C for 2 h, and the highest expression of HSP60 was obtained at 40 °C for 10 h. In Ventana cultivar,
