This year marks the 20th anniversary of the discovery and characterization of the two Arabidopsis PHT1 genes encoding the phosphate transporter in Arabidopsis thaliana. So far, multiple inorganic phosphate (Pi) transporters have been described, and the molecular basis of Pi acquisition by plants has been well-characterized. These genes are involved in Pi acquisition, allocation, and/or signal transduction. This review summarizes how Pi is taken up by the roots and further distributed within two plants: A. thaliana and Oryza sativa L. by plasma membrane phosphate transporters PHT1 and PHO1 as well as by intracellular transporters: PHO1, PHT2, PHT3, PHT4, PHT5 (VPT1), SPX-MFS and phosphate translocators family. We also describe the role of the PHT1 transporters in mycorrhizal roots of rice as an adaptive strategy to cope with limited phosphate availability in soil.

Vacuolar H -ATPase (V-ATPase; EC 3.6.3.14) is the main enzyme responsible for generating a proton gradient across the tonoplast. Under cadmium (Cd) stress conditions, V-ATPase activity is inhibited. In the present work, hydrogen sulfide (H S) and hydrogen peroxide (H O ) cross-talk was analyzed in cucumber (Cucumis sativus L.) seedlings exposed to Cd to explain the role of both signaling molecules in the control of V-ATPase. V-ATPase activity and gene expression as well as H S and H O content and endogenous production were determined in roots of plants treated with 100 μM CdCl and different inhibitors or scavengers. It was found that H S donor improved photosynthetic parameters in Cd-stressed cucumber seedlings. Cd-induced stimulation of H S level was correlated with the increased activities of the H S-generating desulfhydrases. Increased H O and lowered H S contents in roots were able to reduce V-ATPase activities similar to Cd. H O and H S-induced modulations in V-ATPase activities were not closely related to the transcript level of encoding genes, suggesting posttranslational modifications of enzyme protein. On the other hand, exogenous H O raised H S content in root tissues independently from the desulfhydrase activity. Although treatment of control plants with H S significantly stimulated NADPH oxidase activity and gene expression, H S did not affect H O accumulation in roots exposed to Cd. The results suggest the existence of two pathways of H S generation in Cd-stressed cucumber roots. One involves desulfhydrase activity, as was previously demonstrated in different plant species. The other, the desulfhydrase-independent pathway induced by H O /NADPH oxidase, may protect V-ATPase from inhibition by Cd.

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