To tolerate water shortage and high temperature, olive cv. ‘Meski’, the main variety of table olives in Tunisia, developed several biochemical changes. The hereby study focused on the adaptation of the olive tree to the climatic conditions, considering the evaluation of phenolic compounds, chlorophylls, carotenoids, saponin and steroid synthesis, as well as the evaluation of the antioxidant activity. The analyses were made upon fresh leaves collected from three coastal areas of Tunisia (North (sub-humid), center (higher semi-arid) and South (lower arid)) and using different leaves’ extracts. The results emphasized that Southern ‘Meski’ trees had leaves with more polyphenols, flavonoids, o-diphenols and tannins compared with the Northern ones. From the North to the South, ‘Meski’ leaves showed an increase of carotenoids and a decrease of chlorophyll a and b contents. The highest level of antioxidant compounds of Southern leaves could be contributed to reduce the oxidative stress of the olive tree. The spectrophotometric analysis of the antioxidant capacity of leaves collected from central and Southern areas, based on DPPH and ABTS radical-scavenging activity, showed a higher value of antioxidant activity than the Northern ones, at different extract concentrations. Therefore, the increase of the analyzed bioactive compounds can be considered as a response of the tree to surround aggressions and to oppose the oxidative stress that results from the severity of climatic conditions, characteristic of the Southern area.

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Introduction Tunisia is the main olive producing country in the southern Mediterranean. 34% of its cultivated land is devoted to olive growing, which extends from the north to the south of the country. This sector plays, economic, social and environmental roles, contributing to food security, job creation, equilibrium of the commercial balance, preservation of natural resources and limitation of the rural exodus. The olive forest is dominated by the oil cultivars, Chemlali in the center and south of the country, and Chetoui in the north. Chemlali alone occupies 56% of the olive-growing area and represents 69% of the total number of olive trees

Oxidation has been related to several diseases in humans. Indeed, to protect the body from high free radical damages, organism requires natural resources of antioxidant compounds, such as phenols, tocopherols (α, β, γ, and σ) which have important roles in the cell antioxidant defense system. In Mediterranean areas, olive oils and pepper fruits are considered among the best foods in a diet, which keeps on attracting the interest of scientists due to the health benefits linked with its consumption. The Olive oil and pepper fruits are among the most consumed nutrients in the Mediterranean diet; their richness in naturally powerful antioxidants, such as alpha-tocopherols, polyphenols, carotenoïds, and capsaicinoïds (specific of capsicum species), and monounsaturated fatty acids in olive and seed pepper oils, constitutes good health protection against oxidative damages and inflammation. Also, these phytochemicals shield and prevent the human body from many diseases such as cardiovascular, coronary, Alzheimer’s diseases, and cancers.

The table olive cultivar ‘Meski’ was subjected to two stresses related to water, scarcity, and salinity. Anatomical adaptations of leaves, stems and roots were studied and compared, to value the water use efficiency of the tree. Two stress levels were adopted corresponding to moderate and severe levels. Thus, the trees behaviour was influenced by the stress type and intensity. The aerial part of the trees showed more adaptation modes than the underground part. Under both stresses, plants have fortified the protection of the leaf tissues by developing upper envelope and multiplying the trichomes. Plants reinforced the support tissues by multiplying the collenchyma and sclereids, and have amplified the transport tissues by enhancing vascularity through multiplying the number of conductive vessels. However, different behaviours seemed to be specific to each stress such an enlargement of liber and reduction of wood in the drought stress and a restriction of liber and wood tissues in salt stress. Additionally, a retraction of the palisade parenchyma and an extension of the spongy parenchyma in drought stress inversely to salt stress were noted. In the treated stems and roots, development of stomata, suber, pericyclic fiber and liber, and a restriction of wood especially in severe stress were observed. The plants developed important changes in moderate stresses; however, in the severe, the plants seemed to be stressed, by presenting no significant changes relatively to the control.