Interactive effects of potassium and sodium on root growth and expression of K/Na transporter genes in rice

Sufficient supply of potassium (K) can alleviate the adverse effects of excess sodium (Na) on plant growth. However, it remains unclear if such a beneficial function is related to regulation of root growth and/or expression of K/Na transporters. Herein we report the responses of a rice cultivar, which was pretreated with normal nutrient solution for 1 month, to three levels of Na (0, 25, and 100 mM) without or with supply of K for 9 days. High Na (100 mM) significantly decreased plant growth, root activity, and total K uptake, and increased biomass ratio of roots to shoots. Short-term removal of K supply (9 days) did not affect root morphology and biomass ratio of roots to shoots, but decreased root activity of seedlings grown in high Na solution. K deficiency increased uptake of Na and transport of K from roots to shoots. Moreover, expression of OsHAK1, a putative K transporter gene, was upregulated by low Na (25 mM) and downregulated by high Na (100 mM) in roots. In leaves, its expression was suppressed by the Na treatments when K supply was maintained. Expression of OsHKT2;1, which encodes a protein that acts mainly as a Na transporter, was downregulated by high Na, but was enhanced by K deficiency both in roots and leaves. Expression of five other putative K/Na transporter or Na⁺/H⁺ genes, OsHKT1;1, OsHKT1;2, OsHKT2;3, OsNHX1, and OsSOS1, was not affected by the treatments. The results suggest that OsHAK1 and OsHKT2;1 were involved in the interactive effects of K and Na on their uptake and distribution in rice.