The Study On Regulation Mechanism Of Helianthus Tuberosus Under Al Stress By Exogenous Salicylic Acid

Aluminum toxicity is considered to be one of the main environmental factor which limited crop growth in acidic red soil. Helianthus tuberosus is known as common food of people and livestock in Twenty-first Century by FAO officials. The main ingredient of Helianthus tuberosus tuber is inulin which can be used as a good sugar source to produce ethanol and oil by fermentation. So the impact of aluminum toxicity on the growth of Helianthus tuberosus can not be ignored in promoting the wide cultivation of Helianthus tuberosus in acidic soils. The aluminum tolerance mechanisms of Helianthus tuberosus and regulation mechanism of Helianthus tuberosus under Al stress by exogenous salicylic acid was studied by sand and soil culture methods. Ten different areas of Helianthus tuberosus, which are different in Al resistance, were selected to study the effects of different SA concentrations on oxidation resistance and root exudates was studied under Al stress. The discussion of action mechanism of exogenous salicylic acid on relieving Al stress of Helianthus tuberosus. provided a theoretical basis of aluminum tolerance mechanism of Helianthus tuberosus to delve deeper and a theoretical basis of cultivation and planting promotion of Helianthus tuberosus of high quality, yield and aluminum tolerance in acidic soils. The results were summarized as followings:l.The selection of Al-resistant and Al-sensitive varieties of Helianthus tuberosus:after the Helianthus tuberosus was treated for 7 d with 500μmol/L Al concentration, Helianthus tuberosus produced in ten different regions seedling root relative elongation are all restrained in varying degrees. The Helianthus tuberosus root relative elongation from Nanjing, Shuyang and Jinhua were 98.81%,96.24% and 94.62%, which suggusted that their root relative elongation were significantly higher than Helianthus tuberosus from other places. The root relative elongation of Binzhou and Ziyang Helianthus tuberosus were 83.54% and 75.21%, which suggusted that their root relative elongation were significantly inhibited. And the degree of inhibition on Ziyang Helianthus tuberosus variety was the most prominent in ten different varieties. The result showed that Nanjing Helianthus tuberosus had a higher tolerance to Al toxicity, and Ziyang Helianthus tuberosus were sensitive to Al toxicity. So we chose the most Al-resistant variety of Nanjing Helianthus tuberosus and the most Al-sensitive variety of Ziyang Helianthus tuberosus as the materials of our experiment.2.The effects of different SA concentration onoxidation resistance of Helianthus tuberosus 500μmol/L Al concentration treated for 7 days, SOD, CAT activity of Nanjing Helianthus tuberosus were both higher than the control group while which of Ziyang Helianthus tuberosus were lower that. SOD, CAT activity changed in the opposite trend, which indicated the differences in aluminum tolerance between these two cultivars of Helianthus tuberosus, and obviously, exogenous SA increased SOD, CAT activity. Under single aluminum stress, POD activity of these two Helianthus tuberosus cultivars was reduced. Though exogenous SA could increas POD activity, they were still lower than the level of the control group. Ziyang Helianthus tuberosus root APX activity was decreased after being dealt with single aluminum and was increased after being dealt with exogenous SA. But the root APX activity of Nanjing Helianthus tuberosus were both increased after that two types of treatment. Single aluminum stress increased MDA content of two Helianthus tuberosus cultivars and it was decreased as the treatment of exogenous SA, and with the addition of different SA concentrations, MDA content decreased. So as to the soluble sugar content of root. By increasing onoxidation resistance activities and decreasing MDA content and the soluble sugar content of root, SA enhanced the ability of Helianthus tuberosus to resistance to aluminum toxicity.3.The result of exogenous SA on the root exudates of Helianthus tuberosus under aluminum stress showed that exogenous SA could abate the increasing of root proline content being caused by single aluminum stress. Aluminum stress made the organic acid content of root exudates increased, including citrate, oxalic acid, and malate. Citrate content was much higher compared with oxalic acid and malate; However, the total amino acid content was decreased. The SA content of Nanjing Helianthus tuberosus was decreased, whereas that of Ziyang Helianthus tuberosus was increased, showing opposite change. Comparing with the To group, the addition of exogenous SA significantly increased the organic acids of root exudates as citrate is the main organic acid that alleviates aluminum toxicity. With the increase of SA concentration, the CS activity of Nanjing Helianthus tuberosus and the malate dehydrogenase activity of Ziyang Helianthus tuberosus were decreased; however, the CS activity of Ziyang Helianthus tuberosus and the malate dehydrogenase activity of Nanjing Helianthus tuberosus were increased. This result indicates that the application of exogenous SA affects organic acid metabolism and increases organic acid efflux, and the Al signal may be mediated by the SA signal transduction pathway. The growth condition of Helianthus tuberosus was recovered with the addition of SA. Therefore, this study proved that SA can alleviate aluminum toxicity to some extent.