Quercitol plays a key role in stress tolerance of Eucalyptus leptophylla (F. Muell) in naturally occurring saline conditions

Understanding trees adaptation to arid, saline conditions is a major challenge for catchment revegetation in Australia. The accumulation of low molecular weight solutes is an established response of trees to the effects of salt and/or drought stress. Recent studies have shown that quercitol – a cyclitol – contributes significantly towards the adjustment of osmotic potential in some species of Eucalyptus. The present study investigated the role of quercitol in leaf tissues of Eucalyptus leptophylla (F. Muell) under fluctuating environmental stresses. Analysis of leaf tissues from trees growing at distances between 0 and 125 m from hyper-saline lakes suggests that quercitol contributes significantly to the adjustment of osmotic potential induced by drought in E. leptophylla. The presence of substantial concentrations of quercitol in xylem sap suggests that quercitol plays additional roles in signalling amelioration of osmotic stress in myrtaceous species. Quercitol concentrations fluctuate in both xylem and leaf tissues on a seasonal basis, suggesting a form of environmental regulation of solutes. The capacity of soil profiles to store rainwater, rather than proximity to hyper-saline groundwater largely determined osmotic stress in studied trees. Understanding such avoidance/tolerance mechanisms will be crucial to advance tree selection and breeding for stress tolerance.