To understand the regulation of roots plasma membrane H+-ATPase in Masson pine responding to acid deposition, the changes in biomass, plant morphology, intracellular H+, enzyme activity and H+-ATPase genes expression in Masson pine seedlings exposed to simulated acid rain (SAR, pH 5.6 and 4.6) with and without vanadate were studied. SAR exposure for 60 days increased the intracellular H+ in pine roots whether added with 0.1 mM Na3VO4 or not. The growth of seedlings treated with SAR maintained well, even the primary lateral root length, root dry weight, and number of root tips in seedlings exposed to SAR at pH 4.6 were higher than that of the control (pH 6.6). However, the addition of vanadate resulted in the severe growth inhibition and obvious decline in morphological parameters. Similarly, ATP hydrolytic activity and H+ transport activity of roots plasma membrane H+-ATPase both were stimulated by SAR whereas inhibited by vanadate, and the highest activity stimulation was observed in pine roots subjected to SAR at pH 4.6. In addition, SAR also induced the expression of the investigated H+-ATPase subunits (atpB, atpE, atpF, atpH, and atpI). Therefore, the roots plasma membrane H+-ATPase is instrumental in the growth of Masson pine seedlings adapting to acid rain by a manner of pumping more protons across the membrane through enhancing its activity, and which involves the up-regulated gene expression of roots H+-ATPase subunits at transcriptional level.

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