Ion Homeostasis in Chloroplasts under Salinity and Mineral Deficiency

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Abstract
Spinach (Spinacia oleracea var "Yates") plants grown hydroponically were exposed to an excess or deficiency of various mineral ions. Solutes were measured in leaf extracts and in isolated intact chloroplasts. Under phosphate (120 millimoles per liter NaH2 PO4), sulfate (200 millimolar per liter (Na2 SO4)), or magnesium excess (150 millimolar per liter MgCl2), concentrations of these ions in leaf extracts increased, but in chloroplasts, concentrations of all ions remained constant. Concentrations of quarternary ammonium compounds in chloroplasts increased. Under mild phosphate or magnesium deficiency, concentrations of these ions decreased in chlorplasts less than in whole leaf extracts. Under severe sulfate deficiency causing chlorosis in younger leaves, sulfate concentrations in chloroplasts even remained unchanged, despite a drastic decrease of sulfate concentrations both in green and in chlorotic leaves. Together with results from a companion study (G Schroppel-Meier, WM Kaiser 1988 Plant Physiol 87:822-827) our data demonstrates that leaf cells are able to keep the concentrations of several mineral ions rather constant in metabolically active compartments even at extremely large variations of ion concentrations in the culture solution and in the leaves.