Which ATPase is crucial for acidifying vacuoles in plant cells?
Plant central vacuole occupies major cellular volume functioning in turgor generation, storage of ions, sugars, pigments, anthocyanins and toxic metabolites, pH regulation and degradation analogous to animal lysosomes. Luminal pH typically 5 to 5.5 maintained acidic relative to cytosol 7.5 to support proton coupled antiport of calcium via CAX, sodium via NHX, sugars and sequestration of xenobiotics. Acidification achieved by two proton pumps coexisting in tonoplast: V-type proton ATPase and proton pyrophosphatase using pyrophosphate. Dominant contributor is V-ATPase, multisubunit rotary machine similar to lysosomal pump, comprising V1 domain A3B3 hexamer hydrolyzing ATP and Vo domain containing c-ring proteolipids and subunit a forming proton path, consuming cytosolic ATP to move protons inward without phosphoenzyme intermediate, sensitive to bafilomycin and concanamycin. Pyrophosphatase provides backup using PPi from metabolism. F-type ATP synthase located exclusively in mitochondria chloroplasts synthesizes ATP driven by proton motive force, does not reside in vacuole. Na+/K+ ATPases absent in higher plants; calcium ATPases distinct. Thus plant vacuolar acidification crucially depends on V-ATPase creating proton motive force.
Ref: Sze et al., Trends Plant Sci, Plant Vacuolar V-ATPase Acidification of Vacuoles and Tonoplast.