Essential component of the vacuolar proton pump (V-ATPase), a multimeric enzyme that catalyzes the translocation of protons across the membranes. Required for assembly and activity of the V-ATPase. Involved in vacuolar nutrient storage (e.g. accumulation and storage of nitrate) and in tolerance to some toxic ions (e.g. zinc ions sequestration in vacuoles). V-ATPase is a heteromultimeric enzyme composed of a peripheral catalytic V1 complex (components A to H) attached to an integral membrane V0 proton pore complex (components: a, c, c'', d and e). Expressed in etiolated seedlings hypocotyls. When associated with VHA-a2 disruption, day-length-dependent growth retardation associated with a reduced accumulation and storage of nitrate ions in vacuoles. Increased sensitivity to zinc ions due to a lower zinc ions sequestration in vacuoles. Reduced calcium content. No effect on sensitivity to sodium ions. Belongs to the V-ATPase 116 kDa subunit family.