Effect of root restriction on nitrogen levels and glutamine synthetase activity in ‘Kyoho’ grapevines

To unravel the inhibition of root restriction on shoot growth, the changes of nitrogen levels and glutamine synthetase (GS, EC 6.3.1.2) activity were investigated in four-year-old root-restricted ‘Kyoho’ grapevines (Vitis vinifera × Vitis labrusca) in greenhouse from veraison up until 62 days after harvest. ‘Kyoho’ grapevines were planted in buried bed as root restriction and in raised bed (unrestricted rooting zone) as the control. Results showed that root restriction significantly decreased the total amount of N in leaves, berry flesh, white and brown roots, (NO3− + NO2−)–N content in leaves, white and brown roots, and NH4+–N content in brown roots. In addition, root restriction reduced not only N remobilization and recycling from leaves to roots after harvest, but also the total GS activity in both leaves and roots, suggesting that root restriction has a negative influence on glutamine synthesis in grapevines. However, soluble protein content in both leaves and white roots significantly increased under root restriction from 118 to 180 days after anthesis (DAA). It can be attributed to the increased synthesis of polypeptides and/or the enhanced de novo synthesis of proteins in root-restricted vines. In summary, the results illustrated less N reserve in root-restricted vines, which might be responsible for shoot growth inhibition under root restriction.

► Root restriction resulted in a significant decrease in total N content in leaves, berry flesh, white and brown roots, in (NO3− + NO2−)–N content in leaves, white and brown roots, and in NH4+–N content in brown roots.
► Root restriction significantly reduced soluble protein content in leaves and white roots.
► Glutamine synthetase (GS) activity in both leaves and roots decreased under root restriction.
► For diurnal variation of total GS activity, root restriction also significantly reduced total GS activity in roots at berry maturation.