Spatial responses of antioxidative system to aluminum stress in roots of wheat (Triticum aestivum L.) plants

Highlights: • Spatial antioxidative response to Al along root tip is characterized. • Al-sensitive and Al-tolerant wheat were used for 24 h Al stress. • The apical 0–5, 5–10, 10–15, 15–20 and 20–25 mm root segments were excised. • Biochemistry test showed distribution of Al, ROS, antioxidant and enzyme activity. • Antioxidative system is adapted to Al stress in a spatially-specific manner. Aluminum (Al) toxicity associated with acid soils represents one of the biggest limitations to crop production worldwide. The root apex of plants is the major perception site of Al toxicity. In Al stressed wheat primary roots, Al accumulation and loss of plasma membrane integrity were highest in the root apex (0–5 mm), and decreased along the root axis (5–25 mm). To further understand these responses in wheat, spatial profiles of antioxidant responses to Al along the 0–25 mm root tip of two wheat genotypes differing in Al tolerance were analyzed. Under Al stress, the lowest root elongation was in the 0–5 mm root tip, and more severe inhibition was observed in Al-sensitive genotype than Al-tolerant genotype. The highest increase of Al and hydrogen peroxide (H₂O₂) was in the 0–5 mm zone, with the most pronounced increase of malondialdehyde content and Evans blue uptake after Al exposure, especially in Al-sensitive genotype. The activities of superoxides dismutase (SOD), ascrobate peroxidase (APX), catalase (CAT) and peroxidase (POD) and levels of antioxidants (ascorbic acid, reduced glutathione, dehydroascorbate, glutathione disulfide) were significantly increased along the root tip under Al stress, with the 0–5 mm region again being the most active zone. In the same zone, the activities of CAT, APX and contents of antioxidants were higher in Al-tolerant genotype while SOD and POD activities were lower. Our results indicate that Al-induced changes in H₂O₂ production and antioxidative system in root tip are regulated in a spatially-specific manner, suggesting that this response may play an important role in wheat adaptation to Al toxicity.