Inter-population variability of leaf morpho-anatomical and terpenoid patterns of Pistacia atlantica Desf. ssp atlantica growing along an aridity gradient in Algeria

Three Algerian populations of female Pistacia atlantica shrubs were investigated in order to check whether their terpenoid contents and morpho-anatomical parameters may characterize the infraspecific variability. The populations were sampled along a gradient of increasing aridity from the Atlas mountains into the northwestern Central Sahara. As evidenced by Scanning Electron Microscopy, tufted hairs could be found only on seedling leaves from the low aridity site as a population-specific trait preserved also in culture. Under common garden cultivation seedlings of the high aridity site showed a three times higher density of glandular trichomes compared to the low aridity site. Increased aridity resulted also in reduction of leaf sizes while their thickness increased. Palisade parenchyma thickness also increases with aridity, being the best variable that discriminates the three populations of P. atlantica. Analysis of terpenoids from the leaves carried out by GC-MS reveals the presence of 65 compounds. The major compounds identified were spathulenol (23 mu g g(-1) dw), alpha-pinene (10 mu g g(-1) dw), verbenone (7 mu g g(-1) dw) and beta-pinene (6 mu g g(-1) dw) in leaves from the low aridity site: spathulenol (73 mu g g(-1) dw), alpha-pinene (25 mu g g(-1) dw), beta-pinene (18 mu g g(-1) dw) and gamma-amorphene (16 mu g g(-1) dw) in those from medium aridity and spathulenol (114 mu g g(-1) dw), alpha-pinene (49 mu g g(-1) dw), germacrene D (29 mu g g(-1) dw) and camphene (23 mu g g(-1) dw) in leaves from the high aridity site. Terpene concentrations increased with the degree of aridity: the highest mean concentration of monoterpenes (136 mu g g(-1) dw), sesquiterpenes (290 mu g g(-1) dw) and total terpenes (427 mu g g(-1) dw) were observed in the highest arid site and are, respectively, 3-, 5- and 4-fold higher compared to the lower arid site. Spathulenol and alpha-pinene can be taken as chemical markers of aridity. Drought discriminating compounds in low, but detectable concentrations are delta-cadinene and beta-copaene. The functional roles of the terpenoids found in P. atlantica leaves and principles of their biosynthesis are discussed with emphasis on the mechanisms of plant resistance to drought conditions. (C) 2010 Elsevier GmbH. All rights reserved.