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

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Abstract
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.