不同耐盐性药用甘草幼苗根对Na~+的响应及其维管组织变化

以甘草属2种耐盐植物胀果甘草、乌拉尔甘草为材料,用不同浓度(50、100、150、200、250mmol·L-1)NaCl处理幼苗21d后,分析其生物量和根、茎、叶中的Na+、K+含量以及K+/Na+,计算根的离子选择吸收和运输系数,并应用光学显微镜观察比较二者的维管组织结构变化,以揭示2种药用甘草幼苗根对Na+的响应及其维管组织结构的变化特征,探讨甘草的耐盐机理。结果表明:(1)NaCl胁迫使2种甘草幼苗生物量均下降,在NaCl浓度为250mmol·L-1时,胀果甘草、乌拉尔甘草幼苗生物量分别是对照的53.34%、46.21%,胀果甘草耐盐性强于乌拉尔甘草。(2)随着NaCl浓度上升,2种甘草根积累的Na+显著增多,其中胀果甘草在所有盐处理下,根Na+含量均高于其它器官,说明其根对吸收的Na+具有显著截留效应;而乌拉尔甘草只在0~150mmol·L-1 NaCl范围内,根Na+含量显著高于叶片,当NaCl为200、250mmol·L-1时,叶片Na+含量显著高于根,说明乌拉尔甘草根对Na+的截留能力有限。(3)在相同盐处理下,胀果甘草离子选择吸收系数SAK,Na、离子运输系数STK,Na均大于乌拉尔甘草,胀果甘草根抑制Na+、促进K+向地上部运输的能力强于乌拉尔甘草。(4)乌拉尔甘草在NaCl为150、200mmol·L-1、胀果甘草在250mmol·L-1时,根结构对盐胁迫产生应激性响应,维管组织比例显著上升,有助于提高根向上的运输能力,减少盐害。研究表明,2种药用甘草根对Na+截留作用和向上运输时促K+抑Na+能力的差异,是导致其耐盐能力不同的主要原因,根对Na+的积累和截留作用的差异与根的结构响应相吻合,能较好地解释二者的耐盐性差异。

Response of Root to Na+ and Changes of Vascular Tissue of Two Glycyrrhiza Species under NaCl Stress

To understand the salt tolerance mechanisms of two Glycyrrhiza species,we examined the response of root to Na⁺ and changes of vascular tissues under NaCl stress.Glycyrrhiza inflata and Glycyrrhiza uralensis seedlings were cultured with a complete Hoagland nutrient solution containing 0,50,100,150,200 and 250 mmol·L^-1 NaCl for 21 days.Then,the dry weight,root diameter,K⁺ and Na⁺ content in different parts of plants,K⁺/Na⁺ and selective absorption and transportation coefficients(SA_K,Na,ST_K,Na) were measured.The vascular tissue of root was also observed.(1)There were different effects of NaCl on seedlings of two Glycyrrhiza species.The dry weights of G.inflata and G.uralensis at 250 mmol·L^-1 NaCl were 53.34% and 46.21% that of no NaCl stress,respectively.It indicated that G.uralensis had relatively lower salt tolerance.(2)Compared with other part of plant,more Na⁺ accumulated in root of G.inflata with increased NaCl concentration,suggesting that root has good interception effect on Na⁺ that from outside salt environment.This interception effect was limited for G.uralensis because it can be only observed at 0-150 mmol·L^-1 NaCl.(3)G.inflata had more greater SA_K,Na and ST_K,Na values of root than those of G.uralensis at same NaCl concentration,implying a stronger selective transport capability for K⁺ of root while Na⁺ was inhibited from being transported to stem.For these reasons,the significant difference of salt tolerance occurred in two Glycyrrhiza species.(4)The ratio of vascular tissue area to total root area of G.inflata and G.uralensis were increased at 250 mmol·L^-1 and 150-200 mmol·L^-1 NaCl,respectively.It displayed the root anatomical adaptation,which contributes to enhancement of transportation capability of root and alleviation of salt injury.