The Response Mechanism Of Chloroplasts And Mitochondria In Tetraploid Black Locust Under High CO₂ （0.5%） Stress

In order to probe the chloroplast and mitochondria responses to high CO₂ （0.5%） stress and the resistance of tetraploid R. pseudoacacia. In our study, diploid and tetraploid R. pseudoacacia were used as materials, which subjected to high CO₂ treatment for 0,3 and 6 days. The changes in ultramicrostructure, membrane lipid peroxidatio, photosynthesis, respiration and the anti-oxidative metabolism of chloroplast and mitochondria were investigated. Conclusions are listed as follows:The results showed that high CO₂ stress significantly inhibited plant growth, chloroplast and mitochondria ultrastructure of diploid black locust damaged more significantly than that of tetraploid black locust. High CO₂ concentration decreased the chloroplast relevant parameters （photosynthesis rate, transpiration rate, stomatal conductance, intercellular CO₂ concentration, non-photochemical quenching coefficient and maximal photochemistry efficiency）. Both respiration pathway in mitochondria and photosynthetic pigments in chloroplast had a significant decrease.CO₂ injury symptoms of tetraploid black locust were lighter than that in diploid. Compared with diploids, MDA and H₂O₂ contents of tetraploids were lower. Meanwhile, tetraploid black locust maintained a higher proline degree and a better osmotic balance. It is noteworthy that tetraploids possessed higher CO₂ tolerance than diploids.In addition, high CO₂ concentration caused an immediate response of the antioxidant defense system with enzymatic and non-enzymatic compounds in both diploid and tetraploid black locust. But tetraploid black locust obtained greater positive response of antioxidant system from CO₂ stress than diploids in the later treatment.The levels of the SOD, APX, GR, DHAR, MDHAR, GST, COX activities, ascorbate and glutathione （AsA, DHA, GSH and GSSG） in the chloroplast and mitochondria of tetraploid black locust were higher than diploids. It indicated that the better resistance and more active involvement of the antioxidant system in tetraploid black locust can prevent oxidative stress caused by high CO₂ concentration.