The relationship between malic acid secretion differences and organic acid metabolism of wheat with different Al-tolerant levels

There are significant differences of organic acid secretion among species that with different Al-tolerant levels under Al stress.Organic acid is produced during the tricarboxylic acid cycle pathway.However,the relationship between organic acid secretion differences and organic acid metabolism are still needed to be identified.This experiment was performed by two wheat(Tritium aestivum L.) cultivars,ET8(Al-resistant) and ES8(Al-sensitive).Effects of Al on endogenous malic acid content,activities of phosphoenolpyruvate carboxylase(PEPC),citrate synthase(CS) and malate dehydrogenase(MDH) were studied.Results were as fellows: the contents of endogenous malic acid were not affected by Al(0,25,50,and 100(mol-L-1),and there were no differences between ET8 and ES8 when they received same treatment.The endogenous malic acid contents were(0.48±0.01),(0.46±0.03),(0.57±0.02),(0.52±0.02) nmol-root apex-1 and(0.45±0.02),(0.51±0.09),(0.51±0.1),(0.54±0.04) nmol-root apex-1,respectively of ET8 and ES8.Compared with Al free treatment,activities of PEPC were increased significantly under Al(50 or 100(mol-L-1) treatment,but not CS or MDH.The activities of PEPC(or CS,MDH) of ET8 and ES8 were close to each other under the same treatment.In conclusion,the malic acid secretion differences of different Al-tolerant wheat were independent on the endogenous malic acid content and the organic acid metabolism.