Contribution of arbuscular mycorrhizal symbiosis to plant drought tolerance: state of the art

Water deficit is considered one of the most important abiotic constraints limiting plant growth and yield in many areas on the Earth. Indeed, it accounts for over 70 % of yield losses during crop production. Several eco-physiological studies have demonstrated that the arbuscular mycorrhizal (AM) symbiosis improves plant tissue hydration and physiology under drought stress conditions. It is currently accepted that the contribution of AM symbiosis to plant drought tolerance is the result of accumulative physical, nutritional, physiological, and cellular effects. This chapter summarizes, from physiological and molecular points of view, the current knowledge about the mechanisms by which the AM symbiosis is thought to protect host plants against the detrimental effects of water deficit. Thus, the role of fungal hyphae in water uptake and transfer to plant tissues and in modification of soil water retention properties is updated. At the same time, the implication of plant aquaporins in regulation of root hydraulic properties is discussed. The influence of the AM symbiosis on host plant processes such as osmotic adjustment, gas exchange, hormonal balance, and antioxidant capacity is also reviewed.This work is part of a MICINN-FEDER project (Project AGL2008-00898).Peer reviewe