Effect of root restriction on the quality and endogenic hormone of grape berry (Vitis vinifera L.‘Muscat Hamburg’)

Abstract:【Objective】Abundant precipitation and high water table is the characteristic water conditions in southern China. Low sugar content and poor coloration frequently occurs in grape berry produced in this region, which directly affects economic benefits. Root restriction can be applied to different soil environments and enables plants to be planted in conditions with high water table. It improves the grape quality and thus the economic benefits. To clarify the relationship between berry quality and hormone content under root restriction, a series of experiments were conducted.【Methods】Four-year-old Muscat Hamburg grapevines (Vitis vinifera L.) under root restriction and control were selected as materials in a greenhouse at the School of Agriculture and Biology of Shanghai Jiaotong University. The root restric-tion group was planted in limited volume and root zone was isolated from the surrounding soil. The con-trol group was planted in a ridge bed. The same water and fertilizer management and pruning practice were applied to the vines in both groups. At different development stages, samples were randomly selected from different bunches to measure sugars, organic acids, total and individual anthocyanins, phe- nolics and hormone contents. Glucose, fructose, and sucrose contents were detected by HPLC accord-ing to a previously described method with minor modifications. The juice was centrifuged at 10 000×g for 15 min; the supernatant was diluted with 9 ml water and filtered through a 0.22 syringe filter, and  the filtrate was ready for detection. The separating column was a ZORBAX NH2 (250 mm × 4.6 mm,5 μm, Agilent) column. Acetonitrile-water mixture (75∶25) was used as the mobile phase at a flow rate of 0.6 mL · min^-1 and a column temperature of 25 ℃ and an injection volume of 20 µL were adopted.The analysis was carried out with three technical replicates and the corresponding sugar content was cal-culated using a standard curve. The grape skin was ground into powder in liquid nitrogen and approxi-mately 1 g powder was added to 5 mL methanol-1% formic acid. The solution was sonicated for 10 min and shaken in the dark at 150 r·min^-1 and 25 ℃ for 30 min. The mixture was then centrifuged for 10min at 9000×g and 4 ℃, and the supernatant was collected for further analysis. The extraction proce-dure was repeated three times and the collected supernatants were pooled and evaporated at 37 ℃ in an evaporator. The residual material was resuspended in 5 mL of an ethanol-water mixture containing 2% formic acid and 10% methanol. The relative anthocyanin content was measured at 530 nm and 657 nm with an Ultraviolet spectrophotometer and calculated using the following equation: (A530−A657)/Fw, where Fw represents the fresh weight of the grape berry. Individual anthocyanins were measured with a HPLC-Mass Spectrometry (HPLC-MS). Endogenous hormones were determined by HPLC. Finally, cor-relation analysis was conducted between glucose, fructose, total anthocyanin, individual anthocyanin and six hormones detected.【Results】New shoot lengths were measured from 20 to 105 days after anthe-sis (DAA), and the results indicated that new shoot length under root restriction was significantly lower than that in the control group. A similar trend of the basal diameter of the new shoots was observed in both groups, but root restriction had thinner shoots than the control during the whole period. However, the horizontal diameter, vertical diameter, and single berry weight at maturity stage did not significantly differ between the two groups. Glucose, fructose, and sucrose contents under both cultivation modes were determined by HPLC. The results showed that contents of glucose and fructose progressively in-creased from 55 to 110 DAA in both groups, and at 110 DAA, they were significantly higher in root re-striction group. Total anthocyanin content was almost undetectable at 40 and 50 DAA. Anthocyanin ac-cumulation was initiated at 60 DAA (veraison), and the total anthocyanin content in grape berries in the root restriction group was significantly higher (up to 3.2-folds higher) than that in the control group) from 60 DAA to 110 DAA. 15 anthocyanins were detected in both groups and 12 individual anthocya-nins were significantly increased during maturity stage. Acylation and methylation levels were signifi- cantly increased, which is beneficial to the stability of berry color. The organic acid content increased gradually in both groups and their contents in root restriction groups were lower than those in the con-trol. 11 organic acids were detected from samples in the control and root restriction groups. D-malic, L-malic and tartaric acids were the main organic acids in grape berry. ABA (abscisic acid), GA4, GA3,GA7, BR and IAA were detected in both groups, and ABA content was significantly increased by root restriction in periods around veraison, implying that ABA plays an important role during the growth and development of grape berry. The correlation analysis showed that ABA content was positively correlat-ed with glucose content, fructose content, total anthocyanin content and individual anthocyanin content.【Conclusion】Root restriction could regulate the balance between vegetative growth and reproductive growth. It promotes the accumulation of sugars, anthocyanins and phenolic metabolites, decreases or-ganic acid content, and thus improves the quality of grape berry, and can be applied in different regions.