Department of Biochemistry and Molecular Biology, University of Nevada, Reno, NV 89557, USA; and Present address: Thermo Fisher Scientific, Carlsbad, CA 92008, USA.
Department of Biology, University of South Dakota, SD 57069, USA.
Funct Plant Biol. 2021 Jun;48(7):717-731. doi: 10.1071/FP20332.
Cactus pear (Opuntia ficus-indica) is a high productivity species within the Cactaceae grown in many semiarid parts of the world for food, fodder, forage, and biofuels. O. ficus-indica utilises obligate crassulacean acid metabolism (CAM), an adaptation that greatly improves water-use efficiency (WUE) and reduces crop water usage. To better understand CAM-related metabolites and water-deficit stress responses of O. ficus-indica, comparative metabolic profiling was performed on mesophyll and epidermal tissues collected from well-watered and water-deficit stressed cladodes at 50% relative water content (RWC). Tissues were collected over a 24-h period to identify metabolite levels throughout the diel cycle and analysed using a combination of acidic/basic ultra-high-performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) and gas chromatography/mass spectrometry (GC/MS) platforms. A total of 382 metabolites, including 210 (55%) named and 172 (45%) unnamed compounds, were characterised across both tissues. Most tricarboxylic acid (TCA) cycle and glycolysis intermediates were depleted in plants undergoing water-deficit stress indicative of CAM idling or post-idling, while the raffinose family oligosaccharides (RFO) accumulated in both mesophyll and epidermal tissues as osmoprotectants. Levels of reduced glutathione and other metabolites of the ascorbate cycle as well as oxylipins, stress hormones such as traumatic acid, and nucleotide degradation products were increased under water-deficit stress conditions. Notably, tryptophan accumulation, an atypical response, was significantly (24-fold) higher during all time points in water-deficit stressed mesophyll tissue compared with well-watered controls. Many of the metabolite increases were indicative of a highly oxidising environment under water-deficit stress. A total of 34 unnamed metabolites also accumulated in response to water-deficit stress indicating that such compounds might play important roles in water-deficit stress tolerance.
仙人掌果（Opuntia ficus-indica）是仙人掌科中一种高生产力的物种，在世界上许多半干旱地区被种植用于食品、饲料、草料和生物燃料。O. ficus-indica 利用专性的景天酸代谢（CAM），这种适应极大地提高了水分利用效率（WUE）并减少了作物的用水量。为了更好地了解 O. ficus-indica 与 CAM 相关的代谢物和水分亏缺胁迫反应，对在相对水含量（RWC）为 50%的充分供水和水分亏缺胁迫下的节间的叶肉和表皮组织进行了比较代谢谱分析。在 24 小时内收集组织，以确定整个昼夜周期中的代谢物水平，并使用酸性/碱性超高效液相色谱/串联质谱（UHPLC/MS/MS）和气相色谱/质谱（GC/MS）联用平台进行分析。共鉴定出 382 种代谢物，包括 210 种（55%）命名和 172 种（45%）未命名化合物，这些化合物在两种组织中均有特征。大多数三羧酸（TCA）循环和糖酵解中间产物在经历水分亏缺胁迫的植物中耗尽，表明 CAM 闲置或闲置后，而作为渗透调节剂的棉子糖家族低聚糖（RFO）在叶肉和表皮组织中积累。在水分亏缺胁迫条件下，还原型谷胱甘肽和抗坏血酸循环的其他代谢物以及氧自由基、应激激素如创伤酸和核苷酸降解产物的水平增加。值得注意的是，与充分供水对照相比，水分亏缺胁迫下叶肉组织中的色氨酸积累（增加了 24 倍）是一种非典型的响应。许多代谢物的增加表明水分亏缺胁迫下存在高度氧化的环境。总共 34 种未命名代谢物也响应水分亏缺胁迫而积累，表明这些化合物可能在水分亏缺胁迫耐受中发挥重要作用。
