Growth, photosynthesis, water use efficiency, and osmoregulation of the wild species Astragalus gombiformis Pomel. Under water deficit

Abstract

The present study was designed to study the effect of drought on several physiological and biochemical parameters three-month-old Astragalus gombiformis Pomel. plants, submitted to water deficit (5, 10, 15, and 20 days of withheld irrigation). The results show that water deficit treatments reduced the biomass accumulation (DM) in both organs parts especially in the shoots. In addition, leaf water potential (ΨW) and leaf relative water content (RWC) decreased significantly with drought stress. Net photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (E), and internal CO2 concentration (Ci) decreased only after 10 days of water deficit. However, chlorophyll a and b remained unchanged in all treatments, suggesting that photosynthetic rate was reduced mainly due to stomatal closure. After prolonged drought stress (20 days), A. gombiformis exhibited increased accumulations of total soluble sugars and proline. Indeed, the lower but significant increases of malondialdehyde occurred only after 20 days of water deficit, explaining the higher aptitude of this species to adjust osmotically. Under prolonged stress (20 days), α-tocopherol concentrations increased by 30 % and ascorbic acid increased by 61 %. In contrast, the accumulation of total polyphenol was unchanged under water deficit, suggesting their minor role as antioxidants in A. gombiformis plants. The lower increase in malondialdehyde content suggest that A. gombiformis was able to maintain leaf cell integrity because of the efficient osmoprotection and antioxidant defense systems. Indeed, the accumulation of α-tocopherol and ascorbic acid showed that these compounds might to participate efficiently in restriction of oxidative damages caused by the H2O2 generation.