Exogenous proline effects on photosynthetic performance and antioxidant defense system of young olive tree.

The ability of exogenous compatible solutes, such as proline, to counteract salt inhibitory effects in olive plants ( Olea europaea L. cv. Chemlali) was investigated. Two-year-old olive trees were subjected to different saline water irrigation levels supplied or not with exogenous proline. Leaf water relations (relative water content, water potential), photosynthetic activity, and leaf chlorophyll content decreased under either saline water level. The proline supplement mitigated the reduction of growth and photosynthetic activity under salt stress, and the mitigating effect of proline was different among treatments. The increment rate of leaf relative water content (RWC) in the presence of 25 and 50 mM proline was 4.45 and 6.67%, respectively, in comparison to values recorded in SS1-treated plants (plants irrigated with water containing 100 mM NaCl). In SS2 (200 mM NaCl) plus proline-treated plants, this increase was 1.14 times for 25 mM proline and 1.19 times for 50 mM proline higher than those recorded in severe salt stress treatment (SS2). In response to salt stress, Chemlali olive plants seem to activate a complex antioxidative defense system that was displayed via the increase of activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) and the decrease of polyphenol oxidase (PPO) under either salt stress treatment. The exogenous application of proline improved the antioxidative enzyme activities of salt-stressed olive plants. Indeed, in young or old leaf tissues, the highest levels of these antioxidant enzymes activities were recorded in (SS2 + P2)-treated plants (plants irrigated with water containing 200 mM NaCl plus 50 mM proline). In young leaves, this increase was 2.11, 2.96, and 2.76 times, respectively, for SOD, APX, and CAT enzyme activities in comparison to their respective activities in control plants (nonstressed plants irrigated with fresh water). In old leaves, this increase was 2, 2.41, and 2.48 times, respectively, for the various enzymes. If compared to high water salinity-treated plants (SS2), this increase was 1.1, 1.3, and 1.4 times in young leaves, respectively, for SOD, APX, and CAT activities. From these results, the proline supplements seem to improve olive salt tolerance by amelioration of some antioxidative enzyme activities, photosynthetic activity, and, so, plant growth and the preservation of a suitable plant water status under salinity conditions. More to the point, the decrease of soluble sugars contents in proline treated-plants revealed the important osmoprotectant effect played by the added proline in such a way that limited the need of salt-stressed plants for soluble sugars synthesis.

Saline water irrigation effects on antioxidant defense system and proline accumulation in leaves and roots of field-grown olive.

Field-grown olive trees (Olea europaea L. cv. Chemlali) were used over two growing seasons to determine the effects of different saline water irrigation levels on levels of proline and chlorophyll contents and activities of superoxide dismutase (SOD), polyphenol oxidase (PPO), ascorbate peroxidase (APX), and catalase (CAT). The plants were irrigated with fresh water (FW; ECe = 1.2 dS m(-1)) and saline water (SW; ECe = 7.5 dS m(-1)). Leaf water relations (relative water content, water potential), photosynthetic activity, and leaf chlorophyll content decreased under irrigation with saline water. In spring 2005, net photosynthesis of young leaves was 24.5 and 14.9 micromol m(-2) s(-1) in FW- and SW-treated plants, respectively. In old leaves, these rates were 20.2 and 12.2 micromol m(-2) s(-1), respectively. The relative reduction of net photosynthesis in SW-treated plants varied from 39 to 46% and from 39 to 61%, compared to FW-treated plants during the first and second crop seasons, respectively. The relative reduction of leaf chlorophyll (a + b) content under high water salinity level exceeds 50%, compared to FW-treated plants. However, proline content and activities of SOD, CAT, and APX increased under saline water irrigation. The increase of proline content was more important in leaves than in roots. In young leaves, the increment of antioxidant activities in SW-treated plants was 2.67, 3.61, and 1.85 times, respectively, for SOD, APX, and CAT, compared to FW-treated plants. From these results, interaction between antioxidant defense system and proline contents seems to be involved in the salt tolerance mechanisms of Chemlali olive tree.

Saline water irrigation effects on fruit development, quality, and phenolic composition of virgin olive oils, cv. Chemlali.

Field-grown olive trees (cv. Chemlali) were used over two growing seasons to determine the effect of different saline water irrigation levels on fruit development characteristics, yield, and virgin olive oil (VOO) quality. The plants were irrigated with fresh water (FW; ECe=1.2 dS m(-1)) and saline water (SS; ECe=7.5 dS m(-1)). Fruit weight, olive, and oil content decreased under irrigation with saline water. Total oil contents were 27.85 and 25.7% fresh weight (fw) during 2005 in FW and SS irrigated plants, respectively. However, major phenolic compounds (tyrosol, hydroxytyrosol, vanillic,...) and total phenol concentrations in VOO increased under saline water irrigation. In 2005, total phenol contents were 198 and 223 mg/kg of oil in FW and SS treatments, respectively. Furthermore, VOO from SS treated plants showed higher contents of oleic, linoleic, linolenic, and heptadecanoic acids than FW ones, and oil samples of both treatments were classified as "extra virgin".