2013 ASHS Annual Conference

To unravel the inhibition of root restriction on shoot growth, the changes of nitrogen levels and glutamine synthetase (GS) 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. Results showed that root restriction significantly decreased nitrogen levels (the total amount of N, (NO₃⁻ + NO₂⁻)–N and NH₄⁺–N content) in leaves and roots of grapevines. 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. Therefore, less N reserve in root-restricted vines might be responsible for shoot growth inhibition under root restriction. To further evaluate the effect of root restriction on expression of key nitrogen metabolism-involved genes (NR, NiR, pGS1;1, pGS1;2, GS2, Fd-GOGAT and NADH-GOGAT), two-year-old 'Jumeigui' grapevines (Vitis vinifera L. × Vitis labrusca L.) were selected for the experiment. Root restriction resulted in down-regulation of genes involved in nitrate reduction and ammonium assimilation in leaves, especially at midday, regardless of the slightly higher transcript levels of all these genes in white and brown roots under root restriction. In addition, the mRNA levels of genes related to GS1/NADH-GOGAT pathway was lower in root-restricted petioles, while coinciding with the up-regulation of genes involved in GS2/Fd-GOGAT route, suggesting a compensatory strategy helpful to alleviating the reduced ammonium assimilation efficiency under root restriction. The inhibition of vegetative growth in grapevines under root restriction is closely associated with the down-regulation of gene expression in nitrogen metabolism at the whole-plant level.