Fagopyrum Esculentum at Early Stages Copes With Aluminum Toxicity by Increasing ABA Levels and Antioxidant System

Aluminum toxicity (Al) is one of the main constraints for plant growth on acid soils. While most plants are sensitive to Al, some species have developed strategies to cope with this metal. Fagopyrum esculentum, Moench., var Mancan (Polygonaceae), despite being an aluminum-tolerant plant, shows root inhibition as a seedling during the first hours of exposure to Al, whereas at later times, it fully recovers. In this study, we assessed whether abscisic acid (ABA) levels and the antioxidant system might be involved in the early tolerance mechanisms of F. esculentum. The results showed that seedlings exposed to 50 μM Al for 3, 6, 12, 24, and 48 h showed decreases in the relative root growth (RRG), and there was an accumulation of Al in the root apex from 3 to 24 h. In addition, reactive oxygen species (ROS) levels increased, and were detected early after Al exposure; endogenous ABA levels increased and antioxidant enzyme activity increased, including catalase (CAT, EC1.11.1.6), glutathione reductase (GR, EC 1.6.4.2), ascorbate peroxidase (APX, EC 1.11.1.11), and superoxide dismutase (SOD, EC 1.15.1.1) activity. Seedlings treated with exogenous ABA also showed increased ROS levels and CAT and APX activity. The results suggest that after the first 12 h of Al treatment, root growth declines while ROS levels increase due to the entrance of Al into the root. However, the enzyme antioxidant system is promoted, which may impact the recovery of the root growth at later times and increasing levels of ABA might mediate this effect.

Keywords: ABA; Al-tolerance; Antioxidant defense; Buckwheat; Fagopyrum esculentum; ROS levels.