Research PaperEffects of alkaline stress on organic acid metabolism in roots of grape hybrid rootstocks

- Under NaHCO3 stress, the organic acids secreted by root system of the rootstocks were mainly oxalic acid.
- The vitis rootstocks which had strong alkaline resistance secreted more oxalic acid.
- H + −ATPase plays an important role in grape root secretion of oxalic acid.

To elucidate the mechanism of organic acid metabolism in rootstocks under alkali stress, rootstocks A15 and A17 (V. amurensis cv. Zuoshan1 × SO4), both with strong alkaline resistance, and a control rootstock 1103P (V. berlandieri × V. rupestris) were used as materials. Tissue culture plants were treated with NaHCO3 or Na3VO4 (H + − ATPase inhibitors). The pH value of the three rootstock rhizospheres decreased following NaHCO3 stress. Oxalic acid was the main organic acid, and its secretion significantly increased after NaHCO3 treatment. Oxalic acid secretion of A15 and A17 was significantly higher than that of 1103P before and after NaHCO3 treatment. Oxalic acid content and secretion decreased in rootstock A15 under Na3VO4 + NaHCO3 treatment. The changes in PEPC (phosphoenolpyruvate carboxylase) activity in A15 and the ICL (isocitrate lyase) activity in A17 were significantly increased. The relative expression of VvICL (isocitrate lyase gene) in A15 and VvPEP (phosphoenolpyruvate carboxylase gene) in A17 was significantly upregulated compared with the control. The relative expression of VvPMA3 (H + −ATPase family gene) was higher in rootstock A15 and peaked after 24 h treatment. This suggests that the proton pump (VvPMA3) may play an important role in NaHCO3 stress, through promotion of organic acid secretion in the roots to reduce NaHCO3 stress.

Total organic acid secretion of vitis rootstocks all increased under alkali stress, and the increment of organic acid secretion was A17 >A15 > 1103P, and whether under normal growth conditions or NaHCO3 treatment, oxalic acid was the main organic acid in root. The H + −ATPase inhibitor Na3VO4 significantly reduced oxalic acid secretion suggesting oxalic acid secretion might be relevant to the proton pump H + −ATPase activity.245