根区亚低温下外源GABA对山定子幼苗根系线粒体功能的影响

Effects of exogenous GABA on mitochondrial function of Malus baccata seedling roots under root-zone sublow-temperature

关键词:  根区亚低温, 山定子幼苗, γ-氨基丁酸(GABA), 线粒体功能, 呼吸代谢, 能量代谢, 抗氧化酶

Key words:  root-zone sublow-temperature, Malus baccata seedling, γ-aminobutyric acid(GABA), mitochondrial function, respiratory metabolism, energy metabolism, antioxidant enzyme

摘要:

我国北方冷凉果产区生长季初期根区低温会限制根系功能恢复和地上部的生长发育。为探究外源γ-氨基丁酸(GABA)对根区亚低温下山定子(Malus baccata)幼苗根系线粒体功能的生理效应,该文以一年生山定子实生苗为研究对象,设置根区亚低温(5 ℃)处理,分别施加外源GABA(10 mmol·L^-1)及其代谢抑制剂氨己烯酸(VGB,0.1 mmol·L^-1),于处理后0、2、4、6、12、24 h测定根系线粒体膜透性、细胞色素c/a值、呼吸代谢途径、能量物质含量及抗氧化酶活性等指标。结果表明:(1)与对照相比,5 ℃亚低温下,山定子幼苗根系线粒体的结构与功能发生变化,具体表现为膜透性增强,细胞色素c/a值下降,总呼吸速率加快,细胞色素途径(CP)和交替途径(AP)的活性提高,同时交替氧化酶基因(AOX)的转录水平也明显上调。(2)与单纯亚低温处理相比,外源GABA处理能显著提高线粒体膜稳定性和c/a值,促进CP呼吸及其贡献率,抑制AP呼吸与AOX基因表达,同时维持较高的三磷酸腺苷(ATP)含量与能荷水平,并降低一磷酸腺苷(AMP)积累。(3)外源GABA处理能有效提升植株的抗氧化防御体系,包括超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、抗坏血酸过氧化物(APX),减少丙二醛(MDA)生成,并促进根系活力的提高。(4)VGB处理能加剧线粒体膜损伤和能量代谢紊乱,抑制抗氧化酶活性。综上认为,外源GABA通过保护线粒体膜结构完整性、优化呼吸途径分配、维持细胞能量稳态且增强抗氧化能力,缓解根区亚低温对山定子根系的胁迫损伤,该作用依赖于完整的GABA代谢途径。该研究结果为提高山定子根系耐寒性提供了理论依据,对苹果抗寒砧木的培育具有重要意义。

Abstract:

Dueing the early growth season in cold fruit-producing regions of northern China, Low temperatures in the root-zone restrict the recovery of root function and the growth and development of above-ground tissues. In response to the climatic characteristics of early spring in Northeast China's cold-temperate fruit production areas — namely, rapid temperature recovery with large fluctuations and relatively delayed soil warming — this study aimed to explore the regulatory mechanism of exogenous γ-aminobutyric acid(GABA)on mitochondrial function in root-zone of one-year M. baccata under sublow-temperature. Using M. baccata seedlings as experimental material, we subjected them to a root-zone sublow-temperature treatment at 5 ℃ and applied exogenous GABA(10 mmol·L^-1)or its metabolic inhibitor, vigabatrin(VGB, 0.1 mmol·L^-1), respectively. Mitochondrial membrane permeability, cytochrome c/a value, respiratory metabolic pathways, energy substance contents, and antioxidant enzyme activities in roots were measured at 0, 2, 4, 6, 12 and 24 h after treatment. The results were as follows:(1)Compared with the control, 5 ℃ sublow-temperature significantly increased mitochondrial membrane permeability, decreased the cytochrome c/a value, and enhanced total respiration rate, activities of the cytochrome pathway(CP)and alternative pathway(AP), along with induced upregulation of the alternative oxidase gene(AOX)expression.(2)Compared with sublow-temperature treatment alone, exogenous GABA treatment significantly improved mitochondrial membrane stability and c/a value, promoted CP respiration and its contribution rate, inhibited AP respiration and AOX gene expression, while maintaining higher adenosine triphosphate(ATP)content and energy charge level and reducing adenosine monophosphate(AMP)accumulation.(3)Exogenous GABA treatment also increased the activities of superoxide dismutase(SOD), peroxidase(POD), catalase(CAT)and ascorbic acid peroxidase(APX), decreased malondialdehyde(MDA)content, and enhanced root vigor.(4)VGB treatment aggravated mitochondrial membrane damage and energy metabolic disorder, and inhibited antioxidant enzyme activities. In summary, exogenous GABA effectively alleviates root-zone sublow-temperature stress injury in M. baccata roots by protecting mitochondrial membrane integrity, optimizing respiratory pathway allocation, maintaining cellular energy homeostasis and enhancing antioxidant capacity, and this effect depends on an intact GABA metabolic pathway. These findings provide a theoretical basis for improving cold tolerance of M. baccata roots and are of great significance for breeding cold-resistant apple rootstocks.