Aluminum-mediated alleviation of manganese toxicity in Malus robusta Rehd.: insights into mechanisms and implications.

key messageThis study elucidates the Al-mediated Mn detoxification mechanism in M. robusta, incorporating organ-specific localization, subcellular distribution, transporter regulation, and ion competition. Manganese (Mn) and Aluminum (Al) toxicity are major stressors that limit crop productivity in acidic soils. While studies mainly focus on the individual effects of Al or Mn, the interaction between them, especially how Al modulates Mn uptake, distribution, and homeostasis, remains understudied. This research investigates the synergistic effects of Al and Mn on Malus robusta Rehd., analyzing Mn content, subcellular distribution, Mn transporter expression, reactive oxygen species (ROS) homeostasis, and nutrient variations. We find that Al reduces Mn uptake, alleviating Mn-induced growth inhibition, evidenced by increased plant height, root elongation, and chlorophyll retention. Al also promotes antioxidant enzyme activity, including superoxide dismutase, glutathione, non-protein thiols, and proline, which are suppressed under Mn stress. Organ-specific analysis shows reduced Mn accumulation in roots, stems, and leaves, with slight increases in Mn in the cytoplasm and organelles of leaves. Gene expression analysis reveals changes in key Mn transporters (MTP, VIT, ZIP, NRAMP, YSL, CAX) under Al treatment, suggesting a coordinated regulatory mechanism. Phosphorus (P) and molybdenum (Mo) contents increase under Mn stress and are further enhanced by Al, while calcium (Ca), magnesium (Mg), and potassium (K) levels decrease, but Al alleviates this effect. This study provides insights into plant stress physiology, supporting future resistance breeding in fruit trees.