Ascorbic acid metabolism: New knowledge on mitigation of aluminum stress in plants

Ascorbic acid (ASC) is an important antioxidant in plant cells, being the main biosynthesis pathway is L-galactose or Smirnoff-Wheeler. ASC is involved in plant growth and development processes, being a cofactor and regulator of multiple signaling pathways in response to abiotic stresses. Aluminum toxicity is an important stressor under acidic conditions, affecting plant root elongation, triggering ROS induction and accumulation of hydrogen peroxide (H₂O₂). To mitigate damage from Al-toxicity, plants have evolved mechanisms to resist stress conditions, such as Al-tolerance and Al-exclusion or avoidance, both strategies related to the forming of non-phytotoxic complexes or bind-chelates among Al and organic molecules like oxalate. Dehydroascorbate (DHA) degradation generates oxalate when ASC is recycled, and dehydroascorbate reductase (DHAR) expression is inhibited. An alternative strategy is ASC regeneration, mainly due to a higher level of DHAR gene expression and low monodehydroascorbate reductase (MDHAR) gene expression. Therefore, studies performed on Fagopyrum esculentum, Nicotiana tabacum, Poncirus trifoliate, and V. corymbosum suggest that ASC is associated with the Al-resistant mechanism, given the observed enhancements in defense mechanisms, including elevated antioxidant capacity and oxalate production. This review examines the potential involvement of ASC metabolism in Al-resistant mechanisms.