title: Mechanisms of aluminum-tolerance in two species of citrus: secretion of organic acid anions and immobilization of aluminum by phosphorus in roots.
abstract: 'Sour pummelo' (Citrus grandis) and 'Xuegan' (C. sinensis) seedlings were irrigated for 18 weeks with nutrient solution containing 0 (-Al) and 1.2 mM AlCl₃ · 6H₂O (+Al) x 0, 50 and 200 μM KH₂PO₄. C. sinensis was more tolerant to aluminum (Al) than C. grandis. Phosphorus (P) alleviated the toxic effects of Al on seedlings. Under Al stress, P increased root Al, but decreased shoot Al; C. sinensis accumulated more Al in roots and less Al in shoots than C. grandis. Al decreased root and shoot P. P content was higher in C. sinensis than in C. grandis seedlings. C. sinensis roots secreted more malate and citrate than C. grandis ones in response to Al. Al-induced-secretion of malate and citrate from +Al excised roots was higher than from -Al ones, while Al-preculture did not increase root malate and citrate. Al-induced-secretion of malate and citrate from +Al excised roots decreased with increasing P supply. To conclude, P can alleviate Al-toxicity through increasing immobilization of Al in roots and P level in seedlings rather than through increasing organic acid (OA) anion secretion. The higher Al-tolerance of C. sinensis may involve secretion of OA anions and precipitation of Al by P in roots.
authors.affiliation: Institute of Horticultural Plant Physiology, Biochemistry and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou 350002, PR China.
authors.forename: Lin-Tong
authors.initials: LT
authors.lastname: Yang
authors.forename: Huan-Xin
authors.initials: HX
authors.lastname: Jiang
authors.forename: Ning
authors.initials: N
authors.lastname: Tang
authors.forename: Li-Song
authors.initials: LS
authors.lastname: Chen
mesh_terms: D000222:Adaptation, Physiological; D000535:Aluminum / Q000378:metabolism* / Q000633:toxicity; D000838:Anions / Q000378:metabolism; D019343:Citric Acid / Q000378:metabolism*; D002957:Citrus / Q000145:classification / Q000187:drug effects / Q000378:metabolism*; D008293:Malates / Q000378:metabolism*; D010758:Phosphorus / Q000172:deficiency / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D036226:Seedlings; D013045:Species Specificity; D013312:Stress, Physiological
chemical_list: D000838:Anions; D008293:Malates; D010758:Phosphorus; D019343:Citric Acid; C030298:malic acid; D000535:Aluminum