Abstract:

【Objective】 The effects of indole-3-acetic acid (IAA) on malic acid secretion in wheat roots were studied under Al stress. The mechanism of malic acid secretion difference of different Al-tolerant wheat varieties was investigated. 【Method】Hydroponic experiments were performed by two wheat (Tritium aestivum L.) cultivars, ET8 (Al-resistant) and ES8 (Al-sensitive). The effects of exogenous IAA, N-1-napthyl-phtalamic acid (NPA), 2, 3, 5-triiodobenzoic (TIBA), anthracene-9-carboxylic acid (A9C)and niflumic acid (NIF) on secretion rate of malic acid were investigated. 【Result】 Effects of different concentrations of IAA (0, 25, 50, and 100 μmol•L-1) treatments on the secretion of malic acid were not observed in both ET8 and ES8. After a pretreatment with 50 μmol•L-1 Al for 3 h, different concentrations of IAA were applied at the Al free condition for 24 h, the secretion of malic acid increased significantly with the increasing concentrations of IAA in the ET8 but not ES8. Compared to Al (50 μmol•L-1) treatments, the secretion of malic acid in ET8 increased significantly under the co-treatment of IAA (50, 100 μmol•L-1) and Al (50 μmol•L-1), but no significant changes were seen in ES8 under the co-treatments of IAA (25, 50 μmol•L-1) and Al (50 μmol•L-1). Compared to Al (50 μmol•L-1) treatments, the secretion rate of malic acid in ET8 and ES8 decreased under the co-treatments of IAA transport inhibitors NAP (TIBA) and Al (50 μmol•L-1). Results above suggested that IAA involved in the Al-induced malic acid secretion. Compared to Al (50 μmol•L-1) treatments, significant decrease of malic acid secretion rate were observed in ET8 and ES8 under the co-treatments of 5 μmol•L-1 A9C (NIF) and Al (50 μmol•L-1). Compared to the co-treatments of A9C (NIF) and Al (50 μmol•L-1),significant increase of malic acid secretion rate were observed in ET8 and ES8 under the co-treatments of different concentrations of IAA, 5 μmol•L-1 A9C (NIF) and Al (50 μmol•L-1). Results above suggested that IAA may regulate Al-induced malic acid secretion of wheat roots via anion channel. 【Conclusion】 On the condition that malic acid secretion pathway was activated by Al, the secretion of malic acid could be increased by IAA. The different regulation effects of IAA on the secretion of malic acid of wheat with different Al-tolerant levels related with the difference of malic acid secretion.

Key words: wheat, Aluminum-toxicity, IAA, malic acid, anion channel