Effects of Na+, K+ and Ca2+ Accumulation on the Expression of Ca2+-ATPase Gene in Rice KDML 105

Abstract

Having been exposed to 150 mM NaCl supplemented in the growth medium, the roots of KDML105 started to accumulate Na+ in three hours but the leaves showed the amount of Na⁺ change after one day. Addition of either 0.4 mM or 10 mM of CaCl₂ to the 150 mM NaCl supplemented medium, on the other hand, caused a small drop in Na⁺ accumulation in the leaves and roots on day 8. K⁺, however, significantly decreased in both leaves and roots as the result of NaCl in the medium. As for Ca²⁺ deposition in KDML105, NaCl supplemented alone in the medium had little effect but the combined NaCl and CaCl₂ caused the rise of Ca²⁺ in both leaves and roots. The expression of Ca²⁺-ATPase gene in the leaves of KDML105 seemed to be directly activated by the exposure to Na+. The combined effect of Na⁺ and Ca²⁺ also showed the drastic change in Ca²⁺- ATPase expression, and rice, therefore, try to maintain Ca²⁺ homeostasis by producing more Ca²⁺- ATPase mRNA especially in the leaves. Since the roots are not the main accumulation site of Na⁺, the effect of NaCl alone on the Ca²⁺-ATPase gene in the roots was not as distinctively seen. However, the addition of 10 mM CaCl2 caused a large increase of Ca²⁺-ATPase gene expression in the roots, while both Na+ and Ca²⁺ accumulation seemed to affect more to the gene expression in the leaves.