Nitrogen nutrition influences some biochemical responses to iron deficiency in tolerant and sensitive genotypes of Vitis

The effects of nitrogen source on iron deficiency responses were investigated in two Vitis genotypes, one tolerant to limestone chlorosis Cabernet Sauvignon (Vitis vinifera cv.) and the other susceptible Gloire de Montpellier (Vitis riparia cv.). Plants were grown with or without Fe(III)-EDTA, and with NO3 – alone or a mixture of NO3– and NH4+. Changes in pH of the nutrient solution and root ferric chelate reductase (FC-R) activity were monitored over one week. We carried out quantitative metabolic profiling (1HNMR) and determined the activity of enzymes involved in organic acid metabolism in root tips. In iron free-solutions, with NO3 – as the sole nitrogen source, the typical Fe-deficiency response reactions as acidification of the growth medium and enhanced FC-R activity in the roots were observed only in the tolerant genotype. Under the same nutritional conditions, organic acid accumulation (mainly citrate and malate) was found for both genotypes. In the presence of NH4+, the sensitive genotype displayed some decrease in pH of the growth medium and an increase in FC-R activity. For both genotypes, the presence of NH4 + ions decreased significantly the organic acid content of roots. Both Vitis genotypes were able to take up NH4+ from the nutrient solution, regardless of their sensitivity to iron deficiency. The presence of N-NH4+ modified typical Fe stress responses in tolerant and sensitive Vitis genotypes.