The impact of dopamine on the photosynthetic performance and quality of Shine Muscat grape in the Hexi Corridor of Gansu province

[Objective] The Hexi Corridor region in Gansu Province experiences high temperatures in summer, cold and cool conditions in autumn and winter, scarce rainfall, barren soils, and varying degrees of salinization, which can lead to early yellowing and senescence of grape leaves. This results in weakened photosynthesis, reduced assimilates and insufficient nutrient storage in the plant, and often leads to insufficient fruit ripening and a decrease in yield, severely restricting the sustainable development of delayed cultivation of grapes in facilities. Dopamine has physiological functions such as enhancing the photosynthetic capacity of crops, promoting plant growth and development, and improving fruit quality. The study aims to explore the mechanism of dopamine's impact on the photosynthetic performance and quality of grapes, and to screen for suitable control concentrations and methods for production. [Methods] The experiment used Shine Muscat grape grown under delayed cultivation in facility as the material with four exogenous dopamine treatments at 50 μmol·L-1 (T1), 100 μmol·L-1 (T2), 150 μmol·L-1 (T3), and 200 μmol·L-1 (T4), with water treatment as the control (CK). The whole plant was sprayed at different stages: the initial flowering stage, young fruit stage (30 days after flowering), fruit expansion stage (60 days after flowering), and color change stage (90 days after flowering). Photosynthetic performance of the leaves at different stages and fruit quality indicators at maturity were measured. [Results] The results showed: (1) Dopamine treatments enhanced the leaf function of Shine Muscat grape cultivated in delayed facilities, with T2 being the most pronounced. Under T2 treatment, the leaf thickness, the thicknesses of palisade tissue, spongy tissue, upper epidermis, and lower epidermis, and palisade to spongy tissue ratio at the above mentioned stages increased by 8.72%, 13.68%, 8.62%, 23.18%, 12.44%, and 3.92% respectively, compared to the control (CK). (2) Dopamine treatments improved the photosynthetic performance of grape leaves. Specifically, the average content of Chl a at different stages increased by 24.42%, 48.37%, 42.56%, and 19.08% in T1, T2, T3 and T4 compared to CK, respectively; the average content of Chl b increased by 30.67%, 61.26%, 48.17%, and 16.34% respectively; the average content of Car increased by 60.76%, 111.72%, 99.30%, and 31.37% respectively; the average content of Chl t increased by 26.88%, 53.44%, 44.77%, and 18.00% respectively; the average net photosynthetic rate (Pn) increased by 7.09%, 16.97%, 12.69%, and 7.86% respectively; the average stomatal conductance (Gs) increased by 5.17%, 18.28%, 14.14%, and 5.17% respectively; the average intercellular CO2 concentration (Ci) decreased by 4.55%, 6.27%, 5.86%, and 2.48% respectively; the average transpiration rate (Tr) increased by 3.98%, 8.17%, 7.45%, and 4.95% respectively; and the average water use efficiency (WUE) increased by 3.01%, 7.83%, 4.87%, and 2.92%, respectively. The effect on all the above indicators was significant (p<0.05) and strongest in T2 treatment. (3) Dopamine treatments improved the appearance quality of grape berries, and increased soluble solids, sugar to acid ratio, soluble sugars, vitamin C (Vc), total phenols, anthocyanins, total flavonoids, and sugar components (fructose, glucose, and sucrose), but reduced the contents of titratable acidity and tannins in the fruit. T2 treatment showed the most significant effect followed by T3 treatment. Compared with the control, single fruit weight increased by 26.32%, 16.56%, 7.54%, and 3.53% in T1, T2, T3 and T4, respectively; fruit firmness increased by 9.27%, 33.66%, 19.51%, and 1.46% respectively; soluble solids increased by 10.64%, 13.83%, 11.57%, and 8.38% respectively; titratable acidity decreased by 6.55%, 10.48%, 11.79%, and 21.83% respectively; soluble sugars increased by 3.32%, 4.92%, 3.36%, and 3.12% respectively; total phenols increased by 40.82%, 20.86%, 12.32%, and 6.56% respectively; tannins decreased by 19.78%, 26.35%, 20.13%, and 18.45% respectively; fructose increased by 1.78%, 7.92%, 6.65%, and 0.06% respectively; and glucose increased by 27.17%, 23.64%, 21.00%, and 20.18% respectively. [Conclusion] Compared to the control (CK), dopamine treatment can improve the leaf development of Shine Muscat grape under delayed cultivation in facilities and enhance their photosynthetic performance, thereby improving the fruit quality. Treatment with 100 μmol·L-1 dopamine is effective to increase leaf thickness, the thicknesses of palisade and spongy tissues, upper and lower epidermis, and the palisade to spongy tissue ratio, and improve the contents of photosynthetic pigments in the leaves, thereby enhancing the utilization of light energy and thus net photosynthetic rate. After dopamine treatment, the appearance quality of the fruit, soluble solids, sugar-acid ratio, soluble sugars, Vc, total phenols, anthocyanins, total flavonoids, fructose, glucose, and sucrose were all increased, while the contents of titratable acidity and tannins reduced. Principal component analysis showed that the treatment with 100 μmol·L-1 dopamine was the most effective.