Localization of proton-ATPase genes expressed in arbuscular mycorrhizal tomato plants

The original publication is available at www.springerlink.comIn arbuscular mycorrhizal symbioses, solutes such as phosphate are transferred to the plant in return for photoassimilates. The uptake mechanism is probably facilitated by a proton gradient generated by proton H+-ATPases. We investigated expression of Lycopersicon esculentum Mill. H+-ATPases in mycorrhizal and non-mycorrhizal plants to determine if any are specifically regulated in response to colonization. Tissue expression and cellular localization of H+-ATPases were determined by RNA gel blot analysis and in situ hybridization of mycorrhizal and non-mycorrhizal roots. LHA1, LHA2, and LHA4 had high levels of expression in roots and were expressed predominantly in epidermal cells. LHA1 and LHA4 were also expressed in cortical cells containing arbuscules. The presence of arbuscules in root sections was correlated with lower levels of expression of these two isoforms in the epidermis. These results suggest that LHA1 and LHA4 expression is decreased in epidermal cells located in regions of the root that contain arbuscules. This provides evidence of differential regulation between molecular mechanisms involved in proton-coupled nutrient transfer either from the soil or fungus to the plant.Garry M. Rosewarne, F. Andrew Smith, Daniel P. Schachtman, Sally E. Smit

Arbuscular mycorrhiza effects on plant performance under osmotic stress

At present, drought and soil salinity are among the most severe environmental stresses that affect the growth of plants through marked reduction of water uptake which lowers water potential, leading to osmotic stress. In general, osmotic stress causes a series of morphological, physiological, biochemical, and molecular changes that affect plant performance. Several studies have found that diverse types of soil microorganisms improve plant growth, especially when plants are under stressful conditions. Most important are the arbuscular mycorrhizal fungi (AMF) which form arbuscular mycorrhizas (AM) with approximately 80% of plant species and are present in almost all terrestrial ecosystems. Beyond the well-known role of AM in improving plant nutrient uptake, the contributions of AM to plants coping with osmotic stress merit analysis. With this review, we describe the principal direct and indirect mechanisms by which AM modify plant responses to osmotic stress, highlighting the role of AM in photosynthetic activity, water use efficiency, osmoprotectant production, antioxidant activities, and gene expression. We also discuss the potential for using AMF to improve plant performance under osmotic stress conditions and the lines of research needed to optimize AM use in plant production.The authors thank CONICYT, Chile, for the financial support through FONDECYT 1170264 (P. Cornejo), FONDECYT 1161326 (P. Cartes) and scholarship for Doctoral Thesis, Grant No. 21161211 (C. Santander).Peer Reviewe