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Na + /H + antiport activity in tonoplast vesicles isolated from sunflower roots induced by NaCl stress
Author(s) -
Ballesteros Emilia,
Blumwald Eduardo,
Donaire Juan Pedro,
Belver Andrés
Publication year - 1997
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1997.tb05420.x
Subject(s) - antiporter , vacuole , vesicle , chemistry , nigericin , shoot , acridine orange , sodium , valinomycin , proton transport , diaphragm pump , biophysics , biochemistry , botany , membrane , biology , cytoplasm , apoptosis , materials science , organic chemistry , micropump , nanotechnology
Na + transport across the tonoplast and its accumulation in the vacuoles is of crucial importance for plant adaptation to salinity. Mild and severe salt stress increased both ATP‐ and PP i ‐dependent H + transport in tonoplast vesicles from sunflower seedling roots, suggesting the possibility that a Na + /H + antiport system could be operating in such vesicles under salt conditions (E. Ballesteros et al. 1996. Physiol. Plant. 97: 259–268). During a mild salt stress, Na + was mainly accumulated in the roots. Under a more severe salt treatment, Na + was equally distributed in shoots and roots. In contrast to what was observed with Na + , all the salt treatments reduced the shoot K + content. Dissipation by Na + of the H + gradient generated by the tonoplast H + ‐ATPase, monitored as fluorescence quenching of acridine orange, was used to measure Na + /H + exchange across tonoplast‐enriched vesicles isolated by sucrose gradient centrifugation from sunflower ( Helianthus annuus L.) roots treated for 3 days with different NaCl regimes. Salt treatments induced a Na + /H + exchange activity, which displayed saturation kinetics for Na + added to the assay medium. This activity was partially inhibited by 125 μ M amiloride, a competitive inhibitor of Na + /H + antiports. No Na + /H + exchange was detected in vesicles from control roots. The activity was specific for Na + . since K + added to the assay medium slightly dissipated H + gradients and displayed non‐saturating kinetics for all salt treatments. Apparent K m for Na + /H + exchange in tonoplast vesicles from 150 m M NaCl‐treated roots was lower than that of 75 m M NaCl‐treated roots, V max remaining unchanged. The results suggest that the existence of a specific Na + /H + exchange activity in tonoplast‐enriched vesicle fractions, induced by salt stress, could represent an adaptative response in sunflower plants, moderately tolerant to salinity.