Study on the relationship of abscicic acid accumulation and citrate secretion of soybean roots under aluminum stress

Aluminum(Al)-induced organic acid anions secretion is known as one of important Al-resistance mechanisms in plants. Abscisic acid(ABA)plays an important role in mediating some biotic and abiotic stresses. A series of experiments including split-root experiment and time course experiment were carried out to clarify whether ABA is involved in the process of Al-induced secretion of citrate from soybean roots. The results are as follows: 1)ABA accumulation in Al-induced soybean roots is increased under the exogenous ABA application, while ABA accumulation is inhibited under the Fluridone(ABA biosynthesis inhibitor). However, the both applications no effects on either Al induced citrate exudation, or the Al induced increase of citrate content and citrate synthase activity. 2)In the split-root experiment(the whole roots of soybean plant were separated equally to Part A and Part B), endogenous ABA content of root apices is increased in part A, while the content is decreased in part B when roots of part A are exposed to Al(Part A,+Al; Part B,-Al), and Al-induced citrate secretion is only found in part A. 3)The amount of citrate secretion of Al-tolerant cultivar is higher than that of Al-sensitive cultivar, while the ABA contents of roots of both cultivars have no differences under same Al stress. 4)In the time course experiment, both citrate secretion rate and endogenous ABA content are increased with increase of Al treatment time during 0-12 h. During the next 6 h pulse(12-18 h)without Al stress, endogenous ABA is dropped quickly, while citrate secretion rate is increased. The above results suggest that endogenous ABA in soybean roots is not involved in modulating Al-induced citrate exudation.