Drought is the most serious environmental stress affecting agricultural production in the world. Many perennial plant species have developed mechanisms to cope with drought. Plants can avoid drought stress by maximizing water uptake (e.g., tapping ground water by deep roots) or minimizing water loss (e.g., stomatal closure, small leaves). Some species tolerate water stress through osmotic or elastic adjustment or the accumulation of osmoprotective substances. The effects of different water stress treatments applied to pear (Pyrus communis cv. Spadona) saplings planted in 16-L plastic pots were investigated in a greenhouse, in response to imposed water deficit stress and subsequent recovery. Three water stress treatments were used: Control, plants watered at field capacity, -0.5 MРa and -1 MРa, plants watered when soil water potential reached -0.5 and -1 Mрa, respectively. Leaf relative water content (RWC), leaf proline content, total soluble content (TSS) and gas exchange parameters including; net photosynthetic rate, transpiration rate, sub-stomatal CO2 and stomatal conductance were studied before, during and two day after recovery. Water stress had significant effect on all treatments. RWC (75.26 %), net photosynthetic rate (6.32 µmolm-2 s-1 ), transpiration rate (4.12 mmolm-2 s-1 ) and stomatal conductance (0.04 molm-2 s-1 ) had the lowest value in -1 MРa treatment during the water stress. Leaf proline content, TSS and sub- stomatal CO2 were increased under stress condition and they were highest in -1 Mрa treatment. All measured parameter values of stressed plants were equal to control levels after recovery except proline in -1 MPa water stress treatment. This study provided evidence for proline and TSS accumulation under water stress and rapid recovery after mild water stress in pear cv. spadona.
