Sugares and flavonoids accumulation dynamics in pear leaves under simulated osmotic stress

The purpose of the study is to conduct a comparative assessment of three pear varieties in terms of the content of soluble sugars and flavonoids under simulated osmotic stress. The objects of the study are three varieties of pear Pyrus communis L.: two varieties Williams and Conference of European origin and one domestic variety Flamenco selected by the North Caucasus Federal Scientific Center for Horticulture, Viticulture, and Winemaking. Drought was simulated in two ways. In the first case, the leaves were cut into leaf disks with a diameter of 1 cm, then immersed in a 20 % solution of polyethylene glycol (PEG-6000) for 2 hours at room temperature. Control is buffer solution not containing polyethylene glycol. The second method is to place pear shoots in a solution of 15 % sorbitol for a day at room temperature, where water was the control. Exposure to 15 % sorbitol caused more intense synthesis of primary and secondary metabolites compared to 20 % PEG solution. In July, an increase in the accumulation of sugars compared to the control was noted in the Conference variety (25.6 mg glucose equivalent/g fresh weight), in August this figure sharply increased in the Flamenco and Williams varieties to 24.3 and 25.7 mg equivalent. glucose/g wet weight, respectively. A significant increase in flavonoid content in response to sorbitol stress was detected in August for the Flamenco and Conference varieties, in which the average values changed from 2.1 and 2.5 to 3.6 and 4.2 mg/g fresh weight, respectively. Treatment of leaf disks with PEG did not initiate an increase in the synthesis of primary and secondary metabolites. A more effective way to create osmotic stress in the tissues of pear leaves was treatment with a sorbitol solution.