Bicarbonate blocks the expression of several genes involved in the physiological responses to Fe deficiency of Strategy I plants.

Bicarbonate is considered one of the most important factors causing Fe chlorosis in Strategy I plants, mainly on calcareous soils. Most of its negative effects have been attributed to its capacity to buffer a high pH in soils, which can diminish both Fe solubility and root ferric reductase activity. Besides its pH-mediated effects, previous work has shown that bicarbonate can inhibit the induction of enhanced ferric reductase activity in Fe-deficient Strategy I plants. However, to date it is not known whether bicarbonate affects the upregulation of the ferric reductase gene and other genes involved in Fe acquisition. The objective of this work has been to study the effect of bicarbonate on the expression of several Fe acquisition genes in Arabidopsis (Arabidopsis thaliana L.), pea (Pisum sativum L.), tomato (Lycopersicon esculentum Mill.) and cucumber (Cucumis sativus L.) plants. Genes for ferric reductases AtFRO2, PsFRO1, LeFRO1 and CsFRO1; iron transporters AtITR1, PsRIT1, LeIRT1 and CsIRT1; H-ATPases CsHA1 and CsHA2; and transcription factors AtFIT and LeFER have been examined. The results showed that bicarbonate could induce Fe chlorosis by inhibiting the expression of the ferric reductase, the iron transporter and the H-ATPase genes, probably through alteration of the expression of Fe efficiency reactions (FER) (or FER-like) transcription factors.