| Alfalfa (Medicago sativa) is a kind of perennial forage grass of leguminosae, has a good fame of "king of the pasturage". It's widely cultivated in the world. But the acid soil in southern area of our country restricts the extension of alfalfa. In acid soil, low pH is one of the main obstructive factors of restricting the growth of plants. More importantly, low pH soil engenders indirect effect which resulting in much higher Fe2+ concentration which can be called"Fe toxicity". It's common to happen that stress togetherly resulted by the factors of H+ and Fe2+ etc. influenced the growth of plants in acid soil. Studies of the growth performance of alfalfa in acid soil were not many and most of which primarily focus on breeding selection of alfalfa which beared acid soil and normal physiological indicators, and no reports about organic acid of alfalfa under acid and Fe stress were found. This experiment could provide some reference for knowing the mechanism of oxalic acid in alfalfa under acid and Fe stress and the breeding selection and introduction of alfalfa which adapted to acid soil of southern area.In this experiment, Medicago sativa cv. WL No.52 and Medicago sativa cv. Suntory were used to investigate the change rules of oxalic acid in Alfalfa under the environment of acid and Fe stress through conducting pH and Fe2+ stress treatments, and to investigate the role of Low Molecular Organic Acids(LMOAs) in resistance of alfalfa to acid and Fe stress. The main conclusion was as follows:1) The amount of root oxalate excretion, root oxalate and leef oxalate of alfalfa all increased under acid stress. Besides, leef oxalate might be transported to the root through stem and oxalate accumulated in root, some of which was transported outside root. Increase of the amount of root oxalate excretion induced by acid stress might be related to the increase of membrane permeability resulted by acid stress on on hand. On the other hand, acid stress increased root oxalate amount which continued to rise and was higher than leef oxalate amount, that was to say, oxalate accumulated in root. Oxalate might play an important role in maintaining pH balance in cells. It might be as a buffer material and it's accumulation in root helped adjusting pH and maintained pH balance in cells. At the same time, oxalate was excreted outside environment to combine H+ so as to reduce low pH stress.2) Under Fe-deficiency stress, the amount of root oxalate excretion show a continuingly rising trend, which show that Fe-deficiency stress induced the formation and excretion of oxalate. Long duration Fe-deficiency stress increased the amount of root which showed that oxlate might play an important role in resisting Fe-deficiency stress in alfalfa. Root oxalate excretion continuingly increased under Fe-deficiency stress helped absorbing Fe in the environment, and leef oxalate increase and root oxalate accumulation helped excreted more oxalate to the environment. But they were influenced by many factors.3) Compared to the CK, excessive Fe stress markedly increased root oxalate excretion which was high in 1d treatment in both of the cultivars. Excessive Fe stress markedly increased the amount of leef oxalate. Oxalate accumulated in root largely under excessive Fe stress and some excreted to the environment so as to reduce Fe2+ toxicity. At the same time, the accumulation of oxalate in root helped accumulating more Fe in root to prevent more Fe entering root so that stress could be lightened. More oxalate produced in leef helped oxalate transport to root, which helped chelating Fe2+, oxidation of Fe2+-chelate and Fe transport. All of this showed that oxalate played an important role in resisting excessive Fe stress in alfalfa. It could ease the stress.4) Under acid and Fe-deficiency stress, the amount of root oxalate excretion of both afalfas continuingly increased. The stress markedly increased root oxalate excretion. Also it increased the amount of leef oxalate but not markedly. The longer the treatment time increased, the stronger impact the stress showed. This showed that oxalate had a certain role in resisting acid and Fe-deficiency stress in alfalfa.5) Acid and excessive Fe stress markedly increased the amount of root oxalate which increased at a short time. Compared to CK, the amount of root oxalate increased distinctly under the stress which help excretion of oxalate and dulling Fe2+ toxicity and transport of Fe. Besides, the change of the amount of leef oxalate showed no apparent rules.6) Under all sorts of acid or/and Fe stress, the amount of oxalate in alfalfa showed that: root oxalate>leef oxalate>root oxalate excretion. They interrelated and interacted and worked together to resist the stress.7) Oxalate had a certain role in resisting different kinds of acid and/or Fe stress in alfalfa. |
PDF Full Text Request