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干旱是一种复杂的水文和气候灾害,具有持续时间长和破坏力强等特点,全球性干旱问题日趋严重,这致使森林的分布、结构、群落组成及生态多样性不断改变,也对各国林业发展造成严重影响[1-3]。我国干旱、半干旱地区面积不断增加,人工造林成活率仅为4%~30%[4-5]。杨树(Populus L.)作为我国北方地区传统的防风造林速生树种,又是可再生生物能源植物[6],在防风固沙、涵养水源、木材供应等方面起着重要作用。因此,探究杨树响应干旱胁迫的生理和分子机制,对林木的抗逆遗传改良具有重要的意义。
胁迫条件下,植物能够做出形态调节以及生理生化等方面相应的防御机制[7]。有研究表明,逆境胁迫下,谷氨酸(Glutamate)可通过参与改变植物体内某些生理代谢(如:碳、氮代谢),或调节相关基因表达和关键酶活性等方式来增强植物对各种逆境的适应性,从而有利于植物在逆境中的生长[8-10]。谷氨酸(也称α-氨基戊二酸)是一种普遍存在的氨基酸,在氨基酸代谢过程中发挥着重要的作用,尤其是参与合成多种前体物质和植物抗逆相关的蛋白或非蛋白氨基酸,如鸟氨酸(Ornithine)、脯氨酸(Proline)、精氨酸(Arginine)、谷胱甘肽(Glutathione,GSH)、γ-氨基丁酸(γ-aminobutyric acid,GABA)等[11]。谷氨酸还可以作为代谢产物、产生能量的底物、营养物质以及蛋白质结构的决定因素,甚至作为信号分子参与各种生物学反应[12]。Chang等对黄瓜(Cucumis sativus L.)研究发现,外源L-谷氨酸可能通过调节乙烯合成机制来缓解盐胁迫对黄瓜种子发芽率的抑制作用[13]。研究表明,紫花苜蓿短时间低浓度盐胁迫下谷氨酸含量会增加,长时间高浓度盐胁迫下含量则会降低;而铝胁迫下的植物可以分泌谷氨酸到根际,并与游离状态的铝形成稳定的化合物从而缓解铝毒害[14-15]。施燕华等发现,外源谷氨酸对铝胁迫下多花黑麦草(Lolium multiforum Lam.)幼苗叶片叶绿素含量、株高和根系的伸长均有一定的缓解作用[16]。Toyota等人发现,谷氨酸可作为一种信号分子诱导植物产生防御反应。对受伤的拟南芥外源施用谷氨酸,在伤口处发现了谷氨酸的显著积累,并伴随着钙离子信号的显著增加,这表明谷氨酸可以通过影响细胞质游离钙离子浓度([Ca2 + ]cyt)在细胞、组织、器官甚至整个植物之间进行信号传递[17-18]。也有研究表明,谷氨酸处理增加玉米种子发芽率,介导Ca2 + 信号的增加提高耐热性[19]。这为研究外源施加谷氨酸增强植物抗逆性提供了基础。
杨树作为我国速生人工树种,其生长发育长期受到各种胁迫的制约,因此,了解谷氨酸在杨树干旱胁迫下的作用以及对如何提高杨树抗逆性具有重要意义。本研究以银腺杨84K(Populus alba × P. glandulosa ‘84K’)为研究材料,研究添加外源谷氨酸对干旱胁迫下杨树的生长性能和生理指标的变化,测量脯氨酸含量、活性氧积累、抗氧化酶活性等,为揭示谷氨酸在干旱胁迫中对木本植物的缓解作用提供理论依据。
外源谷氨酸对杨树耐旱性的影响
Effect of Exogenous Application Glutamate on Drought Tolerance of Populus alba × P. glandulosa ‘84K’
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摘要:
目的 谷氨酸(Glu)是植物体内普遍存在的氨基酸,在氨基酸代谢过程中发挥着重要的作用。本研究以银腺杨84K(Populus alba × P. glandulosa ‘84K’)为材料,分析外源施加谷氨酸对杨树干旱胁迫下的影响,探讨其在林木响应干旱中的作用,为揭示谷氨酸在林木抗逆性中的作用机制提供参考。 方法 以生长2个月的84K杨为供试材料,分别进行谷氨酸处理后干旱试验和干旱复水试验,观察植株表型,并对叶片含水量、电解质渗透率、谷氨酸含量、渗透调节物质、活性氧含量及活性氧清除酶(CAT、POD和SOD)活性等指标进行分析。 结果 干旱试验表明:谷氨酸处理植株与正常植株相比,显著提高了植物的耐旱能力。经谷氨酸处理的叶片相对含水量增加30.3%、电解质渗透率降低54.0%、谷氨酸含量增加了1.85倍;脯氨酸含量增加33.1%、脯氨酸合成相关基因P5CS、P5CR和P5CDH表达显著升高,分别是对照的2.47倍、2.57倍和8.89倍,而脯氨酸降解基因PDH表达量降低了48.8%。另外,处理后的植株能维持较高的CAT、POD和SOD酶活水平,分别是正常植株的1.67倍、1.35倍、1.17倍,导致过氧化氢含量减少了19.3%。干旱复水试验表明,谷氨酸显著增强了干旱植株的恢复能力。谷氨酸溶液处理植株的叶片相对含水量比未处理植株提高1.08倍,电解质渗透率减少12.1%,脯氨酸含量提高1.09倍,CAT活性和POD活性分别增加了19.0%和62.9%,过氧化氢含量降低31.2%。 结论 外源施加谷氨酸可以提高84K杨叶片谷氨酸含量、诱导脯氨酸合成积累、降低电解质渗透率,减轻干旱胁迫引起的氧化损伤,进而有效缓解植株叶片所受水分胁迫,降低植株对干旱的敏感性。因此,通过外源施加谷氨酸可提高抗氧化能力和渗透调节能力,以提高84K杨在干旱环境下的适应能力,这对揭示谷氨酸在非生物胁迫中的作用起到参考价值。 Abstract:Objective Glutamate is a ubiquitous amino acid in plants, which plays an important role in amino acid metabolism. In this study, poplar 84K (Populus alba × P. glandulosa '84K') was used to analyze the effect of glutamate on the growth of 84K poplar under drought stress, and to explore the role of glutamate in the drought tolerance of 84K poplar. This study provides insights into the amino acid metabolism relating to forest stress resistance. Method 84K grown for 2 months were subjected to drought after glutamate treatment and re-water to analyze phenotypic and physiological changes, including the leaf water content, electrolyte permeability, glutamic acid content, osmotic adjustment substance content, active oxygen content, active oxygen scavenging enzyme (CAT, POD, and SOD) activity and so on. Result The drought test after glutamate treatment showed that glutamate could improve the drought tolerance of plants. Compared with normal drought plants, the relative water content of the leaves increased by 30.3%, the proline content increased by 33.1%, the electrolyte permeability decreased by 54.0%, and the expression of proline synthesis-related genes P5CS, P5CR, and P5CDH significantly increased, 2.47 times, 2.57 times and 8.89 times higher than that of the control, respectively. The expression of proline degradation gene PDH decreased by 48.8%. In addition, glutamate treatment plants could maintain higher CAT, POD, and SOD enzyme activity levels, which were 1.67 times, 1.35 times, and 1.17 times higher than those of normal drought plants, respectively, and the hydrogen peroxide content decreased by 19.3%. The application of glutamic acid after drought significantly enhanced the recovery ability of drought plants. Compared with the re-water plants, the relative water content of the plant leaves increased by 1.08 times, the proline content increased by 1.09 times, the electrolyte permeability decreased by 12.1%, the CAT activity and POD activity increased by 19.0% and 62.9%, respectively, and the hydrogen peroxide content also decreased by 31.2%. Conclusion Exogenous application of glutamic acid can increase the endogenous glutamate content of 84K poplar, induce proline synthesis and accumulation, reduce the electrolyte permeability and oxidative damage caused by drought stress, and effectively alleviate the water stress of plant leaves, thus reducing the sensitivity of plants to drought. Therefore, the exogenous application of glutamic acid can strengthen amino acid metabolism, improve antioxidant capacity and osmotic adjustment ability, and improve the adaptability of 84K poplar in a drought environment, which plays a reference value in revealing the role of glutamic acid in abiotic stress. -
Key words:
- Populus alba × P. glandulosa ‘84K’
- / drought stress
- / glutamate
- / re-water
- / drought tolerance
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