A Study Of Correspond Regulation On Al-induced Secretion And Metabolism Of Organic Acids And The Physiology Characteristic Of Aluminum Toxicity Of Oilseeds Rape

The efflux of organic acid anions from plant roots under aluminum (Al) were likely related to two aspects, one was metabolism of organic acids, which Al increased the synthesis of organic acid in root-cells to increase accumulation of organic acid in plant, finally induced organic acid excreted; the other was transport of organic acids, which Al induced the opening of organic acid anion channel to induced organic acid excreted, and the carrier on the mitochondrial membrane was also may be the key regulation factor of organic acid excreted. Bases of the previously research, oilseed rape which belonged to patternâ…¡of exudation of organic acid was taken as object for the study, by the way of supplying A9C (a inhibitor of anion channel) and Mersal (a inhibitor of citrate carrier) in the Al³⁺ solution, the purpose of the study was to compare the difference of two inhibitor on the regulation of organic acid excreted, and the response of metabolism of organic acid to Al stress which contained inhibitor, thus explored the relation between metabolism and excretion of organic acid. Besides, the physiological characteristics and mineral nutrient absorb of oilseed rape under Al stress were investigated in the study. The main results were summarized as follows:Under 200μmol/L AlCl₃ stress, the secretion of citric acid and malic acid increased respectively 3.4 times and 4.4 times compared to CK, at the time both of the two organic acids took up more than 70% in total organic acids secretion. A9C and Mersal could inhibit the secretion of organic acid which was induced by Al, compared to single Al-treatment, A9C inhibited significantly the malic acid by 15% and 35% under 5μmol/L and 20μmol/L of concentration, the corresponding inhibition for Mersal to citric acid were 13% and 28%. These results indicated that both of anion channel and citrate carrier could regulated the secretion of organic acid, and it had association between the two.Under 200μmol/L AlCl₃ stress, the synthesis of citric acid and malic acid in roots and leaves increased too compared to CK, which citric acid increased by 111% and 103%, malic acid increased by 223% and 147%, respectively. As same as excretion of organic acid, A9C and Mersal could inhibit the synthesis of organic acid which was induced by Al, but that higher markedly than CK. It was found that the synthesis of organic acid in roots was intensive that of in leaves. The excretion of organic acid and the synthesis of citric acid and malic acid in roots or leaves was a significant positive correlation. These indicated that anion channel and citrate carrier not only regulated excretion of organic acid, but also affected synthesis of organic acid.The activities of CS, MDH, PEPC and ACO of roots and leaves increased significantly in oilseed rape under single Al stress, the increasing ratios of CS, MDH, PEPC were over 100%, whereas ACO increased less than the three. The trend of change made for accumulation of citric acid and malic acid in roots and leaves. With adding inhibitors into AlCl₃ culture solution, the activities of CS, MDH, PEPC decreased with different degree, ACO was reverse, compared to single Al treatment. These indicated that inhibitor-Al treatments depressed the ability of synthesis of organic acid in plant, and may to citric acid transformed into aconitic acid, thus reduced the contents of citric acid in organization of plant, finally decreased the excretion of organic acid.The contents of amino acid and soluble sugar increased under Al stress, but it was not significantly difference compared to CK. Complex treatments more increased the osmosis of amino acid and soluble sugar in the root exudation, especially 20μmol/L of A9C that reached markedly level (P<0.05) compared to single Al treatment and CK. The permeability of plasma membrane was increased under Al stress, especially added the A9C and Mersal in the Al solution. It was considered that the osmosis increasing of amino acid and soluble sugar was result of the damage of plasma membrane damage by Al stress. The increasing of pH in excretion under single Al stress was considered an adaptive response on Al stress, and the pH declining after subjoining A9C and Mersal in Al solutions was result in more toxicity of Al to oilseed rape seedlings.When addition of A9C or Mersal under the Al stress, the dry weights of root and shoot and the ratio of root/shoot decreased rapidly, the growth ratios of main root, plant height and leaf amount inhibited significantly, the root morphology (root length, surface area, average diameter of root, root volume and number of root tips) and moisture contents of root and shoot descended too. In addition, the contents of N, P, K, Ca and Mg in root, stem and leaf of plant declined while Na increased in different extent compared to single Al treatment, which consequently enhanced the ratio of Na⁺/ K⁺ of root, stem and leaf. Moreover, the accumulation of Al in root, stem and leaf increased obviously with adding A9C and Mersal. It was suggested that A9C and Mersal might decrease the synthesis or excretion of organic acid in oilseed rape, therefore reduced the combine to organic acid with Al, finally the Al toxicity was fierce in plant.