Effects of Ca2+ on the salt-stress response of barley roots as observed by in-vivo 31P-nuclear magnetic resonance and in-vitro analysis

Calcium has been demonstrated to ameliorate the inhibitory effects of high salinity on nutrient transport in plants. Time-course experiments were carried out to study the effect of high Ca²⁺ (6 mM) supply under saline conditions (100 mM NaCl) on the regulation of intracellular pH in excised barley (Hordeum vulgare L. cv Arivat) roots. In-vivo ³¹P-nuclear magnetic resonance measurements showed an alkalinization of the vacuolar pH after salt treatment. In the presence of high Ca²⁺ the extent of salt-induced vacuolar alkalinization was lower. High Ca²⁺ partially mitigated the salt-induced increase in Na⁺ content and decrease in K⁺ content of the root. The pattern of change in the vacuolar pH paralleled that of Na⁺ accumulation in the root. This correlation is consistent with the involvement of a tonoplast Na⁺/H⁺ antiporter in Na⁺ transport and the role of Ca²⁺ in Na⁺ uptake. High salt appeared to decrease the Pi content of the vacuole while high Ca²⁺ increased this content irrespective of the salt treatment.Abbreviation NMR nuclear magnetic resonance We are grateful to Dr. T.W.M. Fan and R.M. Highasi (University of California, Davis, USA) for their valuable help with the NMR experiments. We also thank Dr. J. Norlyn for his technical assistance. V. Martinez was supported by a Fulbright fellowship.