Changes induced by aluminum stress in the organic acid content of maize seedlings: The crucial role of exogenous citrate in enhancing seedling growth

Abstract

We have studied the effect of Al on growth and morphology of maize seedlings (Zea mays L.), the changes in organic acid content as well as the role of application of exogenous citrate in enhancing the Al tolerance. Al treatment induced inhibition of root growth, causing morphological symptoms of Al toxicity. Al decreased significantly the malate content in roots compared to control plants. However, the citrate and total organic acids did not show any change, indicating that one mechanism underlying plant defense may involve the maintenance a normal levels of organic acids in roots. The succinate content increased in roots at 1000 µmol L−1 Al, while that of lactate decreased. However, 500 and 1000 µmol L−1 Al significantly increased the total organic acid in shoots, due to an increase in the succinate and malate contents. By contrast, the citrate and lactate levels decreased at 250 and 500 µmol L−1 Al. To investigate the role of citrate in enhancing the plant growth, citrate was supplied to nutrient medium containing 500 µmol L−1 Al at different Al:Citrate ratios (1:1, 1:2 and 1:3). The addition of citrate in the nutrient solution resulted in an alleviation of Al toxicity, with the maximal effect obtained at Al:Citrate ratio of 1:2. These data provide evidence that in maize, the organic acids, mainly citrate play an important role in enabling the plant to tolerate elevated exposure to Al concentration.