Pharmacological Study On The Mechanism For Al-Induced Secretion Of Organic Acids From Root Apices In Rye

Excessive aluminum (Al) ion in acid soils is a major factor limiting plant growth. The secretion of organic acids from roots is a major mechanism for Al-resistant plants to resist Al toxicity, whereas the mechanisms of Al-induced secretion of organic acids in Pattern II has poor document. Five to six-day-old excised root apices of rye was objected to study pharmacological effect of anion channel inhibitor, K⁺ channel inhibitor, K⁺-ATPase inhibitor or abscisic acid (ABA) on Al-induced secretions of both organic acids and K⁺ from root apices of rye to illustrate these mechanisms in present study. The results indicated that Al induced the secretion of citrate (Cit), malate (Mal) and K⁺ from root apices, and the secretion of Cit and K⁺ increased significantly with the increase of the Al concentration (50, 100, 300 μmol·L^-1). Although the secretion of organic acids and K⁺ after the exposure of the apices to 200 μmol·L^-1) Al solution for 3 h was depressed by the pretreatment for 30 min with anion channel inhibitor, phenylglyoxal (PG, 0.1, 0.2 μmol·L^-1)), the secretion of K⁺ waspromoted remarkably by the pretreatment with another anion channel inhibitor, niflumic acid (NA, 0.4 and 0.8 m mol-L'1). More organic acids and K+ were exudated from the apices after the treatment with 25 or 50 umol-L"1 ABA for 30 min followed by 200 umol-L'1 Al for 3 h than that without the pretreatment with ABA. When the secretion of K+ was blocked by K+ channel inhibitors, Cesium chloride (Cs, 20 mmol-L'1) and tetraethylammonium (TEA, 40 m mol-L"1), Al-induced secretion of organic acids decreased. Although Al-induced secretion of K+ was suppressed by the pretreatment for 30 min with 0.50 or 2.0 m mol-L"1 Na3VO4, which is a K+-ATPase inhibitor, Al-induced secretion of organic acids increased significantly. The primary result in present study not only indicated that Al induced secretions of both organic acids and K+ from root apices of rye, but also implied that K+ involved in the secretion of organic acids and might function as a accompanying ions of organic acids secreted or a factors to regulate the secretion of organic acids.