| Platycodon Grandiflorus(Jacq.)A. DC.,platy codon genus, campanulaceae family, campanulales order, magnoliopsida class. Because of its high medicinal value, the demand of people for it increased dramatically at home and abroad. Therefore, people cultivate it. However, the problem of salinization of soil is common in agricultural cultivation at home and abroad. It has seriously affected the yield and quality of crops.Therefore, we studied the Platycodon grandiflorum under salt stress.In order to get the method of improve the salt resistance of seeds and seedlings for Platycodon grandiflorum under NaCl stress,we determined the different concentration of 5-aminolevulinic acid (ALA),sodium nitroprusside (SNP),spermidine (Spd) effect on P. grandiflorum seed germination indicaters (seed germination rate, seed germination index, and the average length of root) and the indicators of physiological characteristic (the enzemy activity of SOD, CAT, APX, and the content of soluble protein, soluble sugar, MDA,chlorophyll) under different concentrations of NaCl stress.The results of seed germination experimental showed that, under 75 mmol·L-1 concentrations of NaCl stress the seed germination was inhibited. But when with different concentrations of ALA, SNP and Spd on the P. grandiflorum seeds, all germination indexs were significantly higher. Spd (2.5 mmol·L-1),ALA (5mg·L-1) and SNP (0.1 mmol·L-1) could obviously alleviate the damage of salt stress to the seeds of P. grandiflorum.Spd (2.5 mmol·L-1) can significantly increase all indexes. The germination vigor was 40.3%, the germination rate was 49.5%, the germination index was 9.28 and the average length of root was 2.80 cm. So we conclude that, ALA, SNP, and Spd with appropriate concentration could significantly alleviate the damages to the P. grandiflorum seeds under NaCl stress and promote the salt resistance of the seeds, the best of them is Spd, the second is SNP, furthermore is the ALA.The results of seedling growth showed that:under 100 mmol·L-1 concentrations of NaCl stress, the activitiy of protective enzymes (SOD, CAT, and APX) were decreased, and the content of osmoprotectant (malondialdehyde, soluble sugar, soluble protein) were increased.But when with different concentrations of ALA, SNP and Spd on the P. grandiflorum seedlings, the related physiological indicators were showed the oposite trend with salt stress. With the different concentration and processing time of these three substances the physiological indicators are different. At the early stage of processing, ALA (50 mg·L-1) is better on the content of chlorophyll, superoxide anion and the enzemy activity of SOD, APX than the other concentration. However, the later processing, ALA (2.5 mg·L-1) is better.The effect of Spd (5 mmol·L-1) on the content of chlorophyll, superoxide anion and the enzyme activity of CAT, Asp is better at the early stage of processing, and the latter, Spd (0.5 mmol·L-1) and Spd (2.5 mmol·L-1) are better. The effect of SNP (0.05 mmol·L-1) on the content of the superoxide anion, soluble sugar, MDA is better. However, the effect of SNP (0.25 mmol·L-1) is better on the enzyme activity of SOD, CAT, and APX. Overall, the concentrations of ALA and SNP are concentrated at both ends, the concentrations of Spd are concentrated at the larger concentration:0.5 mmol·L-1,2.5 mmol·L-1,5 mmol·L-1. And these three substances showed the trend:the lower concentration ease the injury of salt stress, the higher concentration damage the plants together with the salt stress.Comparison the effect of these three substances on the physiological indicators we conclud that:the best of them is Spd, the second is SNP, furthermore is the ALA.In summary, the P. grandiflorum seeds and seedlings with different concentrations of Spd, ALA, and SNP under NaCl stress (100 mmol·L-1). The enzemies activity of SOD, CAT, and APX were improved, and the concentration of Soluble protein, soluble sugar, and chlorophyll were increased, and the MDA and O2-·were decreased. So this study showed that, ALA, SNP, and Spd with appropriate concentrations could significantly alleviate the process of membrane lipid peroxidation caused by salt stress, and the damages to the P. grandiflorum seeds, and promote the salt resistance of the seeds and seedlings.When encountered the problem of salt stress in cultivating P. grandiflorum, we can deal the seeds with Spd (2.5 mmol·L-1), ALA (5 mg·L-1) or SNP (0.1 mmol·L-1).We can deal the seedlings with appropriate concentration of ALA, SNP, and Spd according to the degree of impairment and the processing time:Spd (0.5,2.5,5 mmol·L-1), ALA (2.5,50 mg·L-1) or SNP (0.05,0.25 mmol·L-1). |
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