Argan tree plays a great socio-economical and ecological role in the arid and semi-arid zones of Southwest Morocco. The objective of this study was to characterize biochemical tolerance mechanisms of Argania spinosa under drought stress. Changes of ascorbate-glutathione cycle enzymes and nonenzymatic antioxidants were investigated for the first time in four contrasting ecotypes (Lks, Alz, Rab and Adm). Eighteen-month-old A. spinosa plants were subjected to drought stress (50% and 25% field capacity) during two months. Intra-specific differences were observed in all parameters studied. Under drought stress, inland ecotypes showed a significant increase in activity of ascorbate-glutathione cycle enzymes: ascorbate peroxidase (APX), monodehydro-ascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) compared to coastal ecotypes. Non-enzymatic antioxidants, namely ascorbic acid (AA), α-tocopherol (α-toc) and reduced gluthatione (GSH) were increased significantly in drought-stressed plants. Under severe drought stress, we recorded a strong induction of enzymatic and non-enzymatic defense systems. The four study ecotypes were separated by canonical discriminant based mainly on the following biochemical parameters: DHAR, GSH and α-toc. Lks ecotype was distinguished from the other ecotypes by a significant increase of antioxidant enzymes and metabolites, suggesting a better ability of drought tolerance.
