Light dependent proton excretion by roots of entire vine plants (Vitis vinifera L.)

Protons released into distilled water by roots of entire vine plants (Vitis vinifera) were measured by an automatic titration device. Excretion rates were about 500 to 1000 μmol H+/12h/plant showing that H+ excretion was independent of ion uptake. Proton excretion in the light was significantly higher (p < 5 %) than H+ excretion in the dark. The Fe‐chlorosis resistant cultivar “Faber” excreted more than twice as much H+ per plant as compared with the Fe‐chlorosis sensitive cultivar “Huxel” (p < 5 %). There was no great difference in H+ excretion per unit root weight, between the two cultivars. It is suggested that the ability of vine plants to excrete H+ is related to their susceptibility to Fe‐chlorosis. Protons excreted by roots may neutralize the HCO3− in the rhizosphere. Bicarbonate is assumed to induce Fe‐chlorosis.