Leaf biochemical responses and fruit oil quality parameters in olive plants subjected to airborne metal pollution.

This study was carried out in two olive orchards (Olea europaea L., cv. Chemlali) located in a polluted area near a fertilizers factory and in a control unpolluted site, managed with similar cultivation techniques. The aim was to investigate the physiological and biochemical responses of polluted plants (PP), exposed to atmospheric metal contamination (Cd, Cu, Fe, Mn, Ni and Pb) as compared to control plants (CP). Leaves, roots and fruits of PP showed a depression of their non-enzymatic and enzymatic antioxidant defences and a disruption of their hormonal homeostasis. The anomalous physiological status of PP was also demonstrated by the lower values of pigments in leaves and fruits, as compared to CP. Atmospheric metals negatively affected olive oil chemical and sensory quality. However, despite metal deposition on fruit surfaces, the accumulation of potentially toxic metals in olive oil was negligible. Considering that olive oil is an important food product worldwide and that many productive olive orchards are exposed to several sources of pollution, this work could contribute to clarify the effects of atmospheric metal pollution on olive oil quality and its potential toxicity for humans.

Impact of proline application on cadmium accumulation, mineral nutrition and enzymatic antioxidant defense system of Olea europaea L. cv Chemlali exposed to cadmium stress.

Proline plays an important role in plant response to various environmental stresses. However, its involvement in mitigation of heavy metal stress in plants remains elusive. In this study, we examined the effectiveness of exogenous proline (10 and 20 mM) in alleviating cadmium induced inhibitory effects in young olive plants (Olea europaea L. cv. Chemlali) exposed to two Cd levels (10 and 30 mg CdCl2 kg(-1) soil). The Cd treatment induced substantial accumulation of Cd in both root and leaf tissues and a decrease in gas exchange, photosynthetic pigments contents, uptake of essential elements (Ca, Mg and K) and plant biomass. Furthermore, an elevation of antioxidant enzymes activities (superoxide dismutase, catalase, glutathione peroxydase) and proline content in association with relatively high amounts of hydrogen peroxide, thiobarbituric acid reactive substances and electrolyte leakage were observed. Interestingly, the application of exogenous proline alleviated the oxidative damage induced by Cd accumulation. In fact, Cd-stressed olive plants treated with proline showed an increase of antioxidant enzymes activities, photosynthetic activity, nutritional status, plant growth and oil content of olive fruit. Generally, it seems that proline supplementation alleviated the deleterious effects of young olive plants exposed to Cd stress.

Dose and frequency dependent effects of olive mill wastewater treatment on the chemical and microbial properties of soil.

Olive mill wastewater (OMW) is a problematic by-product of olive oil production. While its high organic load and polyphenol concentrations are associated with troublesome environmental effects, its rich mineral and organic matter contents represent valuable nutrients. This study aimed to investigate the valorization of this waste biomass as a potential soil conditioner and fertilizer in agriculture. OMW was assayed at three doses 50, 100, and 200 m(3) ha(-1) year(-1)) over three successive years in olive fields. The effects of the effluent on the physico-chemical and microbial properties of soil-layers were assessed. The findings revealed that the pH of the soil decreased but electrical conductivity and organic matter, total nitrogen, sodium, and potassium soil contents increased in proportion with OMW concentration and frequency of application. While no variations were observed in phosphorus content, slow increases were recorded in calcium and magnesium soil contents. Compared to their control soil counterparts, aerobic bacteria and fungi increased in proportion with OMW spreading rates. The models expressing the correlation between progress parameters and OMW doses were fitted into a second degree polynomial model. Principal component analysis showed a strong correlation between soil mineral elements and microorganisms. These parameters were not related to phosphorus and pH.

Saline water irrigation effects on soil salinity distribution and some physiological responses of field grown Chemlali olive.

The shortage of water resources of good quality is becoming an issue in arid and semi arid regions. Per consequent, the use of water resources of marginal quality is becoming an important consideration, particularly in arid regions in Tunisia, where large quantities of saline water are used for irrigation. Nevertheless, the use of these waters in irrigated lands requires the control of soil salinity and a comprehensive analysis even beyond the area where water is applied. The aim of this study was to investigate the effects of saline water irrigation on soil salinity distribution and some physiological traits of field-grown adult olive trees (Olea europaea L. cv. Chemlali) under contrasting environmental conditions of the arid region in the south of Tunisia. The plants were subjected, over two growing seasons, to two drip irrigated treatments: fresh water (ECe=1.2 dS m(-1), FW) and saline water (ECe=7.5 dS m(-1), SW). Saline water irrigation (SW) has led to a significant increase in soil salinity. Furthermore, these results showed that soil salinity and soil moisture variations are not only dependent on water salinity level but are also controlled by a multitude of factors particularly the soil texture, the distance from the irrigation source and climatic conditions (rainfall pattern, temperature average, …). On the other hand, salt treatment reduced leaf midday water potential (LMWP), relative water content and photosynthetic activity and increased the leaf proline content, and this increase was season-dependent. Indeed, LMWP in SW plants decreased to -3.71 MPa. Furthermore, the highest level of proline in SW plants was registered during summer period (2.19 µmol/mg Fw). The proline accumulation recorded in stressed plants has allowed them to preserve appropriate leaf water status and photosynthetic activity. More to the point, this olive cultivar seems to be more sensible to soil salinity during the intense growth phase. Such tendencies would help to better manage water resources for irrigation, particularly under actual climatic conditions of water scarcity. For example, in the case of the availability of different water qualities, it would be better to preserve those of high quality for olive irrigation during the intense vegetative growth phase, in coincidence with high salt sensitive period, and those of low quality for irrigation during partial growth and plant rest phases. What's more, the urgent use of saline water for irrigation should not be applied without taking into consideration the different surroundings conditions where it is used, particularly the water salinity level, the soil type, the adopted irrigation system, the degree of the crop salt tolerance, the plant growth phase and the climatic conditions of the experimental site.

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".