Abstract:

【Objective】 To reveal the mechanism responsible for Al-resistance in stylo (Stylosanthes), Al-induced secretion of citrate from roots was investigated. 【Method】 The Al-resistance and the effect of Al on the secretion of citrate from roots in stylo (cv. Reyan 2) with comparison to alfalfa (Medicago sativa L., cv Sunshine 3) were studied by hydroponics. 【Result】 There was no dramatic inhibition on the root elongation of stylo exposed to a 10 μmol?L-1 AlCl3 solution, while root elongation was inhibited significantly and the root apices were strongly stained by cyanine R in alfalfa after exposure of roots to 3 or 5 μmol?L-1 AlCl3 for 24 h. Under Al stress, citrate was secreted from roots of stylo. The amount of citrate secretion in stylo was increased with the increasing Al concentration (10, 20, 30 μmol?L-1 AlCl3) and the duration of Al treatment (6, 12, 18, 24 h), but citrate was not secreted from roots in alfalfa. On the other hand, 10 μmol?L-1 anion channel inhibitors including phenylglyoxal, niflumic acid, 4,4’-disothiocyanastilbene- 2,2’-disulfonic acid, and 9-anthracenecarboxylic acid blocked the secretion in stylo. However, neither Al treatment nor the treatment with A-9-C failed to affect the citrate synthase activity of the root apices significantly in stylo. 【Conclusion】 These results suggest that Al-induced secretion of citrate from roots may be a mechanism responsible for Al-resistance and the anion channels involve in the secretion in the stylo.

Key words: aluminum, Stylosanthes, secretion, citrate