Plant Aquaporins and Mycorrhizae: Their Regulation and Involvement in Plant Physiology and Performance

Abstract

The establishment of a mycorrhizal symbiosis can change plant aquaporin gene expression and protein accumulation. However, the regulation of plant aquaporins seems to be dependent on the plant and fungal species involved in the symbiosis. The implications of such regulation on plant water relations, plant physiology and plant performance under optimal or stressful conditions have been the subject of intensive investigation in the last years. Results from different studies suggest that mycorrhizal symbioses act on host plant aquaporins and alter both plant water relations and plant physiology in order to cope better with stressful environmental conditions such as drought. The fungal aquaporins have been related to water transport in the fungal mycelium and in the internal exchange membranes at the symbiotic interface. Indeed, it is generally observed that mycorrhizal plants exhibit higher osmotic and hydrostatic root hydraulic conductance under drought stress conditions. Moreover, mycorrhizal plants also grow to a greater extent than non-mycorrhizal plants under drought conditions, indicating that the changes induced by the symbiosis on plant aquaporins contribute to enhance the plant tolerance to drought. These effects are likely to be the result of the combined action of different aquaporins regulated by the mycorrhizal symbiosis (including PIPs, TIPs, NIPs and SIPs), influencing the transport of water and, most probably, also of other solutes of physiological importance for the plant under drought stress conditions.