Analysis of expression of aquaporins and Na+/H+ transporters in tomato colonized by arbuscular mycorrhizal fungi and affected by salt stress

Among the proteins functioning in salt tolerance of plants, Na+/H+ transporters and aquaporins appear to be of paramount importance. The present study compares expression of Na+/H+ transporter and aquaporin genes in tomato colonized by arbuscular mycorrhizal fungi (AMF) and in non-colonized controls under NaCl stress. As revealed by Northern analyses and in situ hybridizations, expression of two Na+/H+ transporter genes is not significantly affected by salt stress or by colonization of the plants with AMF. In contrast, transcript levels of both a tonoplast and a plasmalemma aquaporin gene are reduced by salt stress, and this effect is distinctly enhanced by colonization of the tomato roots with AMF. In leaves, colonization of tomato by AMF results in a drastic increase of the mRNA of all three aquaporin genes assayed under salt stress. Aquaporins are known to significantly contribute to water movement in plants. The results presented here indicate that AMF controls aquaporin expression and thereby presumably regulates water flow in tomato under salt stress.