Effect Of H₂O₂ On The Adventitious Root Growth And Chilling Resistance Of Sweetpotato Seedlings

When we try to extend sweetpotato planting area to the north of china,We often faced two main key problems, these are drought-induced low survival rate and confronted with chilling stress.We take the former studies,which on the H₂O₂ in plant root growth and stress resistance as well as the role of transfer antioxidant enzyme gene in plants to stress resistance, as a guide, Using transgenic sweet potato that expressing both Cu/Zn SOD and APX in chloroplasts and its non-transgenic control plant as materials, to study on whether the adding of exogenous H₂O₂ in seedlings culture solution to promote the adventitious roots growth, and also on whether the use of exogenous H₂O₂ sprayed on the leaves of potted sweet potato seedling as well as the transfer antioxidant enzyme gene strategy could resolve these chilling resistance problem of sweetpotato.And then we got these results as following:1. In the experiment, varies concentrations of exogenous hydrogen peroxide as well as a hydrogen peroxide scavenger ascorbic acid were added into the sweetpotato seedlings'culture solution to study the effect of H₂O₂ on adventitious roots and leaves growth of sweetpotato seedling. Results showed that:(1) When sweetpotato seedling cultured in lower concentrations H₂O₂ solutions (0.5mmol/L and 2.5 mmol/L) had display an inducement on adventitious root formation and growth, the total root weight, root number, total root length and total root surface area per seedling, as well as root activity of were significantly higher than the control which added nothing, especially in 0.5 mmol/L H₂O₂ treatment; As the concentration of H₂O₂ reached to 5 mmol/L, almost the whole growth of adventitious roots were significant inhibited, roots were seriously damaged also; While added with AsA in the culture solution also showed a significant inhibition on adventitious roots growth, neither the concentration was 4.0 mmol/L nor 10.0 mmol/L, the formation of adventitious roots has been completely inhibited, the damage-reparation on the stem cross-section of the cutting seedlings has also been hindered; However, in the treatment with 4 mmol/L AsA added after treated with 2.5 mmol/L H₂O₂ for three days, the elongation of adventitious roots was inhibited to a certain degree.(2) It has been found that there has a consistency between the growth status of adventitious roots and the leaves growth status, leaves MDA content, leaves water content as well as the changes in the photosynthetic pigments by further analyze the leaves physiology metabolism status, but no consistency has been discovered between the concentrations of endogenous H₂O₂ in leaves and the exogenous H₂O₂ concentrations which added in culture solution. In conclusion, the adventitious roots growth could be induced by exogenous H₂O₂ below the injury concentration (5.0 mmol/L) and it could be reversed by AsA treatment, it also showed that a certain concentration of accumulated endogenous H₂O₂ is indispensable for the plants in the course of adventitious roots formation. H₂O₂ effect on leaves'physiological process was result from the effects it did on roots growth status first, and then the growth status of roots affect the leaves growth status. The best inducement on adventitious roots and leaves growth was found in 0.5 mmol/L H₂O₂ treatment during our experiment.2. We take transgenic potted sweetpotato that expressing both Cu/Zn SOD and APX in chloroplasts and its non-transgenic control plant as materials, study on the recoverability of them after one night (12h) chilling stress at 5℃, and also the enhancement of chilling resistance when treated them with 1.0 mmol/L H₂O₂ before chilling stress. The results showed that:(1) Soon after a short time (12h) chilling stress, the activity of anti-oxidative enzymes as SOD, AXP and CAT in non-transgenic sweet potato decreased significantly and so did the content of carotenoid, but the membrane permeability increased significantly, photosynthetic pigment and photosynthetic electron transport chain were damaged, so the photosynthetic rate reduced; while after one day recovery in room temperature, the activities of above mentioned anti-oxidative enzymes and the content of carotenoid all increased significantly, membrane permeability also increased continuously, and photosynthetic electron transport chain was repaired completely while photosynthetic pigment decreased significantly, but the photosynthesis recovered to a large extent.(2) After chilling stress, compared with non-transgenic sweet potato, it could be observed that in transgenic sweet potato, the activities of above mentioned anti-oxidative enzymes and the content of caroternoid were higher, membrane permeability was lower, have a stronger ability to protect photosynthetic pigment and photosynthetic electron transport chain, therefore the photosynthetic rate was relatively higher, so a stronger chilling resistance was showed in transgenic sweet potato.(3) It could also be observed in the recovery process of the plants that had been treated with 1.0 mmol/L H₂O₂ compared with non-treatments before chilling stress, the recovery capabilities of the anti-oxidative enzymes were stronger, the content of MDA and membrane permeability were lower, and the growth status after chilling was better, therefore it could be concluded that the pretreatment with 1.0 mmol/L H₂O₂ could improve the recovery capability of the plant after chilling and enhance the chilling resistance.3. From results of the above two experiment, we can obtained: (1) When treated root with exogenous H₂O₂, it can promote the formation of sweetpotato seedling adventitious roots to a large number and accelerate root elongation growth, the optimal induce concentration is 0.5mmoL / L; Through transfer the Cu/Zn SOD and APX genes in sweetpotato can enhance its chilling resistance, and sprayed with 1.0mmoL /L H₂O₂ on leaves before the arrival of cold weather could also be able to improve plant chilling resistance , further more,combined theses two strategies would be more significant to improve the cold resistance of plants.