Physiological and carbohydrate metabolism traits for discrimination of drought-tolerant elite ecotypes of Argania spinosa

Abstract

Argan (Argania spinosa) tree is a horticultural-forestry species characterized by its endemicity and its adaptive behavior to arid and semi-arid environments in the southwest of Morocco. It plays meaningful ecological, economic and social roles. Argan oil has high nutritional and dietetic values; it is thought to be one of the vegetable oils with the highest quality in the world. To characterize and to identify the most drought-tolerant ecotypes of the Argan tree, we focused our work on certain drought tolerance traits by studying the change in stomatal conductance (gs), Rubisco activity, carbohydrate compounds and enzymes in four different Argan ecotypes. These Argan ecotypes were grown under drought stress for 2 months. Under severe drought conditions, we recorded significant reduction in gs and Rubisco activity, the largest decrease was noted in the both contrasting coastal ecotypes. However, drought stress significantly increased the hexoses concentration in stressed plant leaves indicating stimulation of activity of carbohydrate metabolizing enzymes. The correlations obtained suggest that related enzymes of primary carbohydrate metabolism have highly important effects on foliar hexoses concentration in Argania spinosa during drought stress. Based on canonical discriminant analysis, both contrasting coastal ecotypes were distinctly separated from both contrasting inland ecotypes by the traits showing the high discriminatory potential: Rubisco, aldose 6-phosphate reductase, glucose-6-phosphate dehydrogenase and gs. These traits can be efficiently exploited to identify superior ecotypes suitable for drought conditions. Inland ecotypes appear to be more drought tolerants and interesting for regeneration of Argan tree in dryland areas.