Nitric oxide protects sour pummelo (Citrus grandis) seedlings against aluminum-induced inhibition of growth and photosynthesis

► Under Al stress, SNP increased root P and Al, but decreased shoot Al. ► SNP alleviated Al-induced impairment of photosynthetic electron transport chain. ► SNP stimulated Al-induced-secretion of malate and citrate from +Al excised roots. ► Root and leaf antioxidant system was up- and down-regulated by Al, respectively. ► SNP prevented Al-induced accumulation of MDA in roots and leaves.