| Platycodon grandiflorums for Campanulaceae Platycodon is a perennial herbaceous plant, is a kind of medicine, food, enjoy combination of plant, and was deeply loved by the masses of people. With its roots as a medicine, has very high medicinal value. The Campanulaceae food is the specialty of the Northeast of China and Japan, South Korea, North Korea and other East Asian countries, nutrient-rich, containing a variety of amino acids and the human body essential trace elements. Therefore, the increasing demand of P. grandiflorum for artificial cultivation has become one of the effective ways to alleviate the shortage of wild resources. But in the long-term cultivation process, limited by factors such as environment and cultivated land, seriously affect of the P. grandiflorum yield and quality, and soil drought is one of them. In recent years, many scholars have found that exogenous substances can effectively induction of plant resistance to abiotic stresses, and drought resistance of exogenous substances under abiotic stress P. grandiflorum has not yet been reported. Therefore, this experiment by the characteristics of P. grandiflorum seeds and seedlings as the research material, chosen5-aminolevulinic acid (ALA), nitric oxide (NO) donor sodium nitroprusside (SNP) and glycinebetaine (GB) three exogenous substances under simulated drought stress of the seed germination and seedling growth and other related physiological characteristics of PEG-6000was studied, according to the experimental results were improved P. grandiflorum seed and seedling drought resistance good exogenous substances and its concentration, and provide a theoretical basis for the standardized cultivation of P. grandiflorum. The results show that:1、Using12%PEG-6000to simulate drought stress significantly reduced seed germination indices, such as germination potential, germination rate and germination index, inhibited the growth of the radicle of P. grandiflorum, and by the stress seed initial germination time delay. With different concentrations of ALA, SNP and GB treatment of P. grandiflorum seed under drought stress, its seed germination potential, germination rate, germination indices and radicle length have different degree of change.10～50mg·L-1ALA has effect in alleviating the degree of inhibition on Platycodon grandiflorum seed germination, with10mg·L-1of ALA works best.0.05～0.25mmol·L-1SNP treatment could promote the P. grandiflorum seed germination under drought stress,0.1mmol·L-1SNP is better. The germination potential, germination rate, germination index and radicle length were significantly alleviated after1.0mmol·L-1GB treatment under drought stress, comparing with drought control, the difference is extremely significant (P<0.05).2、After exogenous ALA, SNP and GB can effectively mitigate P. grandiflorum seedlings chlorophyll a, chlorophyll b, total chlorophyll and carotenoid content and chlorophyll a/b ratio declined trend, which the concentration of25mg·L-1ALA,0.25mmol·L-1SNP and2.5mmol·L-1GB treatment was the most significantly effect. That is to say, the concentrations of three kinds of exogenous substances could better protect the characteristics of P. grandiflorum seedlings photosynthetic structures from the damage of drought stress.3、A significant increase in O2-·content and MDA content, and the SOD, POD, CAT and APX activity gradually decreased in P. grandiflorum seedlings leaves under drought stress. Respectively with different concentrations at10～100mg·L-1ALA,0.05～1.Ommol·L-1SNP and1.0-20mmol·L-1GB could alleviates Oxidative damage caoused by drought stress of P. grandiflorum seedlings leaves, and reduced the accumulation of O2-·and MDA content, enhanced the enzyme activity of SOD, POD, CAT and APX. With extending the stress time, lower concentrations preferably alleviates the Oxidative damage effect in these three kinds of exogenous substances under drought stress, but a higher concentration effect is not obvious.25mg·L-1ALA,0.25mmol·L-1SNP and2.5mmol·L-1GB seedling made significant effect, significantly slowed down the O2-·and MDA content increased, and promoted antioxidant enzyme activities. This may be appropriate concentration of ALA、SNP and GB stabilized the structure and function of antioxidant enzymes and other biological macromolecules, the stability of the antioxidant enzymes activity conducive to remove excess reactive oxygen species, reduced the oxidative damage under drought stress.4、Drought stress-induced the leaves accumulation of the Proline, soluble sugar and soluble protein content of P.grandiflorum seedlings. The application of10～100mg·L-1ALA,0.05～1.0mmol·L-1SNP and1.0～20mmol·L-1GB to P.grandiflorum seedlings further increased the content of Osmotic adjustment substances, which2.5mmol·L-1GB seedlings treatment is the most obvious difference. Followed by25mg·L-1ALA and0.25mmol-L"1SNP effect. The results indicated that three kinds of exogenous substances could relieve the damage of the P. grandiflorum seedling by regulating Penetration material metabolism under drought stress, and that appropriate concentration of these three exogenous substances could improve infiltration protection capacity of the P. grandiflorum seedling leaves under drought stress conditions.In summary, different concentrations of ALA, SNP and GB treatment could rise to alleviate certainly action of P. grandiflorum seeds and seedlings physiology under drought stress. Among10～100mg·L-1of ALA, the concentration of10mg·L-1could significantly improve seed germination indices of P. grandiflorum under drought stress, and the leaves of Photosynthetic pigment content, Antioxidase activities, osmotic adjustment content was on the rise, reduced the accumulation of O2-·and MDA content in25mg·L-1ALA,0.05～1.0mmol·L-1of SNP, the concentration of0.1mmol·L-1and0.25mmol·L-1treatment on seeds and seedlings effect was better;1.0-20mmol·L-1of GB, the concentration of1.0mmol·L-1and2.5mmol-L"1mitigation better on seeds and seedlings. In this three kinds of exogenous substance,2.5mmol·L-1GB could significantly alleviate the damages and improve the effect of drought resistance is the best to P. grandiflorum seedlings under drought stress,25mg·L-1ALA and0.25mmol·L-1SNP effect quite. |
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