Document Type : Research Paper - Biotic and Abiotic Stress
Authors
1 Department of Horticulture and Landscape Engineering, Faculty of Agriculture, Malayer University, Malayer, Iran
2 Horticulture, Department of Landscape, Faculty of Agriculture, Malayer University, Malayer
Abstract
Introduction
Environmental stresses, especially damage caused by frost, often have a significant effect on plant growth and development. In order to adapt to the cold, plants show specific physiological and biochemical responses that lead to an increase in their duirability and survival during exposure to low temperature. The use of ultraviolet (UV) rays to increase cold tolerance and physiological and biochemical changes related to it has been less researched. This is while UV-B is not necessarily a source of stress, but moderate, non-harmful levels of UV-B act as an environmental signal in higher plants and able to induce several key reactions in order to adapt to cold in the plant.
Materials and Methods
This experiment was carried out on rooted seedlings of Vitis vinifera L. cv. Yaghooti in a factorially (3×3) based on a completely randomized design with three replications in the research greenhouse of Malayer University in the spring and summer of 2022. In the 15-leaf stage, the vines (except for the control) were exposed to two doses of UV-B radiation in the following order: first dose (control): natural light, second dose (moderate): 5.98 kJ m-2 d-1 ( equal to 0.55 W/m2 for 3 hours) and the third dose (severe): 9.66 kJ m-2 d-1 (equal to 0.55 W/m2 for 4.5 hours) was applied to the plants under the natural photoperiod in the greenhouse in June. After applying UV-B radiation treatments, one group of pots was kept in the greenhouse (temperature 24±1 ºC) and another group of pots (control vines and treated with UV-B rays to apply cold stress to the cooling chamber) transferred and placed under the temperature of 4ºC and -4ºC (for 6 hours at each temperature).
Results and Discussion
According to the results, the highest and lowest total chlorophyll content was related to the treatment without irradiation and temperature of 24°C and the treatment of severe irradiation and temperature of -4°C, respectively. The highest and lowest carotenoid content was related to the severe UV-B irradiation treatment and 24°C temperature and the treatment without irradiation and 24°C temperature, respectively. The relative water content was the highest in the treatments without radiation and temperature of 24°C, and the lowest in the treatment of moderate irradiation and temperature of -4°C. The highest and lowest percentages of electrolyte leakage were observed in treatments without irradiation and temperature of -4°C and treatment without irradiation and temperature of 24°C, respectively. The content of malondialdehyde and hydrogen peroxide was the highest in the vines under severe UV-B irradiation along with (-4°C) and was the lowest in treatment without irradiation along with 24°C. The highest content of soluble sugar and soluble protein was observed in plants treated with severe irradiation + (-4°C), and the lowest amount of these compounds was observed in the treatment without UV-B irradiation + (24°C). The content of proline was the highest in the treatments with severe irradiation + (4°C), and the lowest in the treatment without radiation and temperature of 24°C. The highest and lowest activity of ascorbate peroxidase (APX) enzyme was observed in the treatments of sever irradiation + (4°C) and moderate irradiation + (-4°C), respectively. The activities of guaiacol peroxidase (GPX) and catalase enzymes (CAT) were the highest in plants under moderate irradiation + (4°C), and the lowest activity of these enzymes observed under non-irradiation condition + (-4°C). The highest and lowest total phenol and flavonoid contents were related to those vines that were treated with sever irradiation + (4°C) and without UV-B irradiation + 24°C, respectively.
Conclusion
Totally, it can be concluded that moderate radiation treatment through the stimulation of antioxidant systems, the accumulation of UV-B absorbing compounds and acclimate osmolytes in the plant led to an increase in their tolerance to chilling temperatures (+4°C), but there was no effect on frost tolerance (-4°C). However, sever UV-B irradiation treatment both at normal and low temperatures caused damage to cell membranes and leaf necrosis. Based on the results of application of moderate dose of UV-B rays, it can be used as an elicitor to improve plant antioxidant system and cell membrane stability under chilling temperature (4°C).
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