عنوان مقاله [English]
Introduction: Cold stress is one of the limiting factors for plant growth and yield production in most parts of the world. Cold stress damages cells through changes in the activity of macromolecules, decreasing osmotic potential, and significant changes in other parts of the cell. Cold stress in young seedlings generally reduces leaf development, induces wilting and chlorosis and in more severe cases, browning and necrosis become visible. Cucumber is a sensitive plant to low temperature and its cultivation, except the southern and central parts of Iran, occurs in areas where there is a possibility of cold stress in the early part of the growing season due to the low temperature. The different ways for controlling cold stress had been used; one of them is using plant growth regulators such as spermidine. Spermidine is one of the polyamines that has been used in recent years to control cold stress. The effect of cold treatment on the amount of indigenous leaf polyamines has been reported differently between cold-resistant and sensitive cucumber cultivars. During the cold stress, the amount of indigenous spermidine in leaves of cold-resistant cucumber cultivars and sensitive cultivars increased significantly and remained unchanged, respectively. The increase in the content of putrescent, spermidine and spermine in cold resistant cultivars during cold stress was probably due to the increased activity of ornithine decarboxylase (ODC). The amount of polyamines in chickpea plants that were exposured to low temperatures (12-15°C and 4-6°C are related to mean maximum and minimum temperature of the farm, respectively) increased six to nine times. Adding spermidine to the cucumber growing medium before applying cold treatment increased spermidine amount in all organs and increased cold tolerance.
Materials and Methods: To study the effect of spermidine on cold tolerance of cucumber, seedling of ‘Rashid’ cultivar, an experiment was conducted based on completely randomized design with four replications and four treatments consist of different concentrations of spermidine (0, 0.1, 0.5 and 1 mM) in incubator of College of Agriculture, Isfahan University of Technology. So seeds were exposed to 20°C for 7 days in a humid condition and then were treated with 0, 0.1, 0.5 or 1 mM spermidine, the remaining 8 days they were kept at 6 or 9°C. The treatments performed in dark conditions until the second day of germination and received 8 hours of light daily from the third day until the end of the experiment. At the end of each experiment, shoot and root length were measured by use of the ruler, shoot and root fresh and dry weight were measured by use of digital scale, shoot and root ion leakage were measured based on Lates method (3) and shoot and root proline concentration were measured based on Bites et al., (2) method. To compare the effects of temperature and its interactions with spermidine, data of two experiments analyzed as split plot experiment (Different temperatures and spermidine concentrations were as main and subplots, respectively).
Results and Discussion: The findings of this study showed that application of the highest concentration of spermidine (1 mM) in 9°C had the inverse effect on cold tolerance, so it decreased the fresh and dry weight of root. In 6°C, 0.5 mM spermidine was more effective than other concentrations, and it increased root fresh weight, shoot proline concentration and decreased root ion leakage. It has been shown that the non-saturated lipid profile of membranes of cold-resistant plants in comparison of non-resistant plants is significantly increased, and this increase is associated with a decrease in cell ion leakage. Proline works as a nitrogen source and soluble substance that helps the plant to combat again stress conditions. The split-plot analysis of data showed that 0.5 and 0.1 mM spermidine treatments increased root length, root fresh and dry weight significantly. The study of spermidine concentrations ×temperatures showed that the increasing effect of 0.5 mM spermidine on root length, root fresh and dry weight was only visible in 6°C.