Water relations, proline accumulation and photosynthetic activity in olive tree (Olea europaea L. cv "chemlali") in response to salt stress

This study was conducted to evaluate the effects of salt stress on photosynthetic capacity and proline accumulation in the Chemlali olive cultivar (Olea europaea L.) grown under field conditions at Sfax, Tunisia. Twelve year-old- olive trees were subjected to two drip irrigated treatments. The first was fresh water (EC = 1.2 dS m-1, control plants CP) and the second was saline water (EC = 7 dS m-1, Stressed plants SP). Each treatment contained twenty uniform plants. Salt stress adversely affect plant water status, net CO2 assimilation rate, stomatal conductance and transpiration rate of stressed plants. However, the most important reduction of these activities was observed in summer season. Maximum photosynthetic activity was recorded during vegetative growth phase as well in CP as in SP. The severe reduction in photosynthetic performances in CP during summer season was clear evidence that photosynthesis of olive tree is not only related to water quality treatment but is also environmental conditions dependent. Salt stress has also led to the increase of proline content in both leaves and roots of salt stressed plants. Salt stressed olive trees tend to activate osmotic adjustment mechanism by the accumulation of proline, in order to activate water uptake to actively growing tissues to accomplish their photosynthetic activity even in low rates. Likewise, a possible protective role of proline in improving photosynthetic capacity is suggested.