PH REGULATION IN ACID-STRESSED LEAVES OF PEA-PLANTS GROWN IN THE PRESENCE OF NITRATE OR AMMONIUM-SALTS - STUDIES INVOLVING P-31-NMR SPECTROSCOPY AND CHLOROPHYLL FLUORESCENCE
R. Bligny et al., PH REGULATION IN ACID-STRESSED LEAVES OF PEA-PLANTS GROWN IN THE PRESENCE OF NITRATE OR AMMONIUM-SALTS - STUDIES INVOLVING P-31-NMR SPECTROSCOPY AND CHLOROPHYLL FLUORESCENCE, Biochimica et biophysica acta. Bioenergetics, 1320(2), 1997, pp. 142-152
P-31 nuclear magnetic resonance spectroscopy was used to monitor chang
es of cytoplasmic and vacuolar pH values in leaf tissues from young pe
a plants which had been grown in hydroponic culture with either nitrat
e or ammonium salts as sources of nitrogen. When acid stress was appli
ed by the addition of 15% CO2 to air (5.1 mM CO2 in solution), cytopla
smic pH values decreased fast by 0.5 pH units and then increased slowl
y without reaching the initial pH, while vacuolar pH values decreased
by 0.1 pH units. Under anaerobic conditions, the cytoplasmic pH decrea
sed by one pH unit and the vacuolar pH increased by almost 0.4 pH unit
s. These changes were rapidly reversed when CO2 was removed from air o
r, after anaerobiosis, by aeration. However, with mannose present duri
ng and after anaerobiosis, aeration failed to bring pH values back to
the levels observed before anaerobiosis, Simultaneously, mannose phosp
hates accumulated and cytoplasmic phosphate disappeared. Since loss of
phosphate decreases ATP levels, the observations suggest that ATP-dep
endent pumping of protons into the vacuole restored the cytoplasmic pH
partially during acidification by CO2 and fully after anaerobiosis. P
hotosynthesis was initially inhibited by high CO2 and then restored in
dicating that protons are exported not only across the tonoplast into
the vacuole but also across the chloroplast envelope into the cytosol.
No large differences in pH regulation were observed in leaves of pea
plants which were grown with either nitrate or ammonium salts, Apparen
tly, retarded growth of ammonium-fertilized plants cannot be attribute
d to ineffective pH regulation.