Organic acid accumulation in roots of two sunflower lines with a different response to iron deficiency

Organic acid accumulation in roots is a general response to Fe deficiency which has been related to other responses like acidification of the extracellular medium or an increase in the ferric reducing capacity. In this work we have compared the content of citric and malic acids in the roots of two sunflower (Helianthus annuus L.) lines. Line RHA 271 is Fe‐efficient with a capacity to acidify the medium and line HA 89 is less Fe‐efficient with no acidification capacity. After 6 or 7 days of growth in a nutrient solution with 10 pM Fe‐EDDHA, the plants were subjected to the respective treatments with 0, 1 or 20 μM Fe‐EDDHA. After 3 to 7 days of growth, plants were collected and the concentration of citric and malic acids in the roots was determined by a kit enzymatic method. In line RHA 271, the citric acid concentration increased with Fe deficiency, while the malic acid concentration was not affected. In contrast, in line HA 89 both citric and malic acid concentrations were reduced by Fe deficiency. These relative differences were maintained in spite of the different number of days that plants were grown with normal and low Fe. Our results suggest a relationship between the acidification capacity of the root medium and the accumulation of citric acid in the roots.