عنوان مقاله [English]
Cucumber is an important plant that grows all over the world and is very sensitive to prevailing temperature conditions. The optimum temperature for its growth is 20 to 30 °C, and abnormal growth is very common at temperatures above 35 °C. Temperatures above 40°C in the long term often lead to impaired metabolic function, water loss and wilting of cucumbers, and temperatures above 50°C in the short term lead to the destruction of macromolecules, cell structure damage, dehydration and death. will be it has a great effect on the performance and quality of cucumbers. On the other hand, Salicylic acid is known as one of the multifunctional phytohormones widely found in plants. It is also an important biological stimulus that plays a role in regulating the growth and growth stages of horticultural crops. Productivity of horticultural crops has been improved by supplemental use of even small amounts of salicylic acid. It has a good ability to reduce oxidative damage caused by excessive production of reactive oxygen species, potential increase in photosynthesis, chlorophyll pigments and stomatal regulation. Physiological and biochemical processes have shown that SA increases signaling molecules, enzymatic and non-enzymatic antioxidants, osmolytes and secondary metabolites in plant cell compartments. Other studies show that exogenous SA increases plant tolerance to high abiotic stress by improving the activity of antibiotic enzymes.
Materials and Methods
This research was done in factorial form in completely randomized design with 3 replications on Rashid variety cucumber. The factors included 4 levels of temperature (25, 30, 35 and 40 degrees Celsius) and 3 levels of salicylic acid (0, 0.5 and 1 mM). When the seedlings reached the two-leaf stage, they were sprayed with different concentrations of salicylic acid two times with an interval of five days. One week after the application of salicylic acid, temperature treatment was gradually applied. After applying each heat treatment, the corresponding pots were transferred to the greenhouse with a temperature of 25 degrees Celsius.Then, fresh and dry weight of root and shoot, leaf surface, chlorophyll index, electrolyte leakage, proline, polyphenol oxidase enzyme activity and superoxide dismutase enzyme activity were measured.
Results and Discussion
High temperature in summer is an important factor for reducing the growth and yield of cucumber in many parts of the country. Regarding the positive effect of plant growth regulator (salicylic acid) on reducing the adverse effects of heat stress, an experiment was conducted to investigate the effect of salicylic acid on reducing the adverse effects of heat stress on cucumber seedlings on Rashid cultivar in a factorial based on completely randomized design with four temperature treatments (25, 30, 35 and 40 °C) and three salicylic acid concentrations (0, 0.5 and 1 mM) were designed. The results showed that heat stress decreased fresh and dry weight of shoots and roots, leaf surface, relative chlorophyll and polyphenol oxidase and increased the amount of electrolyte leakage, proline and superoxide dismutase. The application of 1 mM salicylic acid reduced the negative effects of temperature stress in such a way that it increased the dry weight of roots, fresh and dry weight of shoots by 36, 16.4 and 23.7% respectively compared to the control and also reduced electrolyte leakage By 13% and the relative chlorophyll, leaf surface, proline, polyphenol oxidase and superoxide dismutase levels increased by 9.7, 2, 37.7, 35.6 and 31.51%, respectively, compared to the control. The mutual effects of salicylic acid and heat stress on stem fresh weight, chlorophyll index, leaf surface, electrolyte leakage, proline polyphenol oxidase and superoxide dismutase were significant. In general, the application of 1 mM salicylic acid reduced the negative effects of heat stress on cucumber Rashid cultivar.
High temperatures caused disturbances in the growth and performance of cucumbers, as the results of this experiment showed, high temperatures caused a decrease in fresh and dry weight of roots and shoots, a decrease in chlorophyll, leaf surface and polyphenol oxidase enzyme activity, while the use of salicylic acid decreased electrolyte leakage, proline, polyphenol oxidase and superoxide dismutase increased. In general, the best progeny was related to the application of 1 mM salicylic acid, which reduced the negative effects of heat stress on Rashid variety cucumber and improved its growth.
Keywords: Cucumber, Electrolyte leakage, Heat Stress, Proline, superoxide dismutase.