Mechanisms of organic acids and boron induced tolerance of aluminum toxicity: A review

the mechanism of aluminum toxicity could be comprised of exclusion mechanism and internal detoxification. Exclusion mechanism carried out by the organic acids with the help of anion transporters. OAs shield the root apex by forming defensive scabbard. There are two pattern of organic acid secretions in plants. In pattern-Ⅰ, there is no apparent delay between the aluminum exposure and release of organic acids. Pattern-Ⅱ involves the exudation of OAs in a delay process. While internal detoxification is carried out by the chelation of Al with oxalate and subsequently sequestration into vacuoles of leaves. Plants can take up Al3+ and then transform into another form (non-phytotoxic) by complexing with oxalate secretions. Al-tolerant plants are known to accumulate a large quantity of aluminum in the upper parts of plants. In xylem tissue, aluminum is translocated by Al-citrate complex through a ligand exchange reaction. Boron induced alleviation of Aluminum toxicity might involve the reduced cellular injury through the reduced uptake of Al and reduced oxidative stress.188