Organic acids counteract the determinate root development induced by phosphate deprivation in Arabidopsis thaliana

Phosphate (Pi) deficiency impairs plant development and decreases productivity owing to its critical functions in terms of cell structure, metabolism, and photosynthesis. Here, we assessed the determinate growth program of Arabidopsis primary roots exposed to Pi scarcity to clarify the role of citrate and malate in the expression of the mitotic cyclin CycB1 and changes in the meristem, transition zone, and elongation zone. The transfer of seedlings from high-Pi medium to low-Pi medium, but not to high-Pi medium, inhibits root growth, cell division, and elongation, aspects that are restored upon the application of each organic acid. On the other hand, the exhaustion of the meristem under low Pi related to the loss of auxin and the cytokinin response in columella cells is reversed by organic acids, according to the expression of the DR5:GUS and ARR5:GUS gene constructs, respectively. Histological detection of iron levels at the tip of the primary root and the formation of abundant root hairs, which indicate the repression of mitosis and the advancement of differentiation, decreases with malate and citrate and with the application of ferrozine, an iron chelator, suggesting a relevant role of chelators at the rhizosphere to reduce the adaptive pressure of phosphate scarcity on root growth.