NADP-dehydrogenases contribute to aluminum tolerance through the maintenance of redox homeostasis in soybean

Soybean is one of the most important crops globally, however its cultivation in acidic soils is limited by aluminum (Al) toxicity, which impairs root growth and triggers oxidative stress. Maintaining cellular redox balance is essential for Al tolerance to this stress, with NADPH acting as the primary reducing agent in antioxidant systems, such as the ascorbate–glutathione (AsA-GSH) cycle. This study evaluated the role of NADP-dehydrogenase enzymes (G6PDH, 6PGDH, ICDH, and NADP-ME) in response to Al in two contrasting soybean genotypes: NEO610 (Al-tolerant) and M5917I (Al-sensitive). Upon Al exposure, NEO610 exhibited a greater increase in the activity of these enzymes, accompanied by gene expression upregulation particularly for 6PGDH and NADP-ME, elevating NADPH levels and the NADPH/NADP⁺ ratio. The elevated NADPH concentration favored increased activity of AsA-GSH cycle enzymes (APX, MDHAR, DHAR, and GR), promoting efficient regeneration of ascorbate and glutathione levels, maintenance of low H 2 O 2 levels, and reduction of lipid peroxidation. In contrast, M5917I showed stronger transcriptional responses, particularly for NADP-ME, but lower increases in enzyme activities, which were associated with greater H 2 O 2 accumulation and oxidative damage under Al exposure. These results suggest that Al tolerance relies on the ability to maintain redox homeostasis through NADP-dehydrogenases, which are essential for sustaining the antioxidant defense system and root growth. Thus, redox metabolism may be associated with aluminum tolerance and could represent a potential target for further investigation in soybean breeding programs aimed at acidic soils.