干旱胁迫对桔梗种子萌发及幼苗生长的影响

Effects of drought stress on seed germination and seedling growth of Platycodon grandiflorum(Jacq.)A.DC

【目的】阐明桔梗种子萌发及幼苗生长对干旱胁迫的形态与生理响应机制。【方法】以桔梗种子为材料,采用质量分数5%,10%,15%,20%,25%的聚乙二醇(PEG-6000)模拟不同程度的干旱胁迫,以蒸馏水处理为对照,测定干旱胁迫下桔梗种子的发芽特征及幼苗叶片的抗氧化酶活性、渗透调节物质和丙二醛含量等指标,探讨干旱胁迫对桔梗种子萌发和幼苗生长的影响。【结果】(1)干旱胁迫下桔梗种子初始萌发时间延后,发芽率、发芽势、发芽指数、活力指数、胚芽长、胚根长、胚根长/胚芽长和苗鲜质量等指标均较对照明显降低,且随干旱胁迫程度的加剧,以上指标均呈显著下降趋势;干旱胁迫对桔梗幼苗胚根生长的抑制作用较其对胚芽的影响更为明显。(2)随着干旱胁迫程度的增大,桔梗幼苗叶色逐渐变为暗绿色,叶片卷曲,气孔关闭。(3)质量分数10%PEG-6000处理桔梗幼苗的脯氨酸含量略高于对照,其余各处理的游离脯氨酸含量均低于对照;低质量分数(≤5%)PEG-6000处理桔梗幼苗的可溶性糖含量略低于对照,但高质量分数(≥10%)PEG-6000处理的可溶性糖含量均显著高于对照。(4)与对照相比,不同质量分数PEG-6000处理后桔梗幼苗叶片的SOD活性均显著升高,而POD活性均显著下降;质量分数5%PEG-6000处理桔梗幼苗叶片的CAT活性较对照略有升高,但差异并不显著,而高质量分数(≥10%)PEG-6000处理叶片的CAT活性较对照显著降低;PEG-6000处理幼苗叶片的MDA含量均显著高于对照。【结论】干旱胁迫对桔梗种子萌发和幼根、幼芽生长均有明显的抑制作用,但对幼根生长的抑制作用更加明显,轻度干旱胁迫即能显著抑制幼根生长可能是造成桔梗种子田间出苗率低的主要原因之一。

【Objective】The research investigated the effects of drought stress on seed germination and seedling growth of Platycodon grandiflorum（Jacq.）A.DC.【Method】Indexes such as germination ratio,germination vigor,germination index,and vigor index of Platycodon grandiflorum seed and free proline content,soluble sugar content,activities of antioxidant enzymes,and mass fraction of MDA in Platycodon leaves were determined and compared by treating the seeds with PEG-6000 at different concentrations of5%,10%,15%,20%,and 25%.The effects of drought stress on seed germination and seedling growthwere also studied.【Result】With drought stress,initial germination time of seeds was delayed.Germination ratio,germination vigor,germination index and vigor index of seed as well as radicle length,embryonic bud length,root/shoot ratio,and fresh weight of seedling were significantly lower than the control.With the increase of drought stress,these index reduced fatherly.Drought stress could more clearly inhibit the growth of radicle than the growth of embryonic bud.With the increase of drought stress level,the Platycodon grandiflorum seedling leaves gradually turned into dark green,leaf curled,and stomatal closed.The mass fraction of free proline with 10% PEG-6000 stress was slightly higher than the control while the fractions of other PEG-6000 stress levels were lower than the control.The content of soluble sugar was decreased by low mass fraction PEG-6000（≤5%）stress while it was improved by high mass fraction PEG-6000（〉5%）stress.Compared with the control,activity of SOD in seedling leaves was significantly increased with different drought stress degrees,while activity of POD was significantly decreased.Activity of CAT was slightly enhanced by low mass fractions,but it was reduced by high mass fractions（≥10%）.Content of MDA was higher than that of the control.【Conclusion】Drought stress significantly inhibited seed germination and growth of radicle and bud.The inhibition of radical growth by drought stress could be one of the reasons why the germination ratio of Platycodon grandiflorum seeds in field was low.