Arkansas Biosciences Institute, Arkansas State University, PO Box 639, State University, AR 72467, USA.
Department of Chemistry and Physics, Arkansas State University, PO Box 419, State University, AR 72467, USA.
J Exp Bot. 2024 May 3;75(9):2644-2663. doi: 10.1093/jxb/erae120.
l-Ascorbic acid (AsA) is an antioxidant with important roles in plant stress physiology, growth, and development. AsA also plays an essential role in human health, preventing scurvy. Humans do not synthesize AsA, which needs to be supplied via a diet rich in fresh produce. Research efforts have provided progress in the elucidation of a complex metabolic network with at least four routes leading to AsA formation in plants. In this review, three alternative pathways, namely the d-galacturonate, the l-gulose, and the myo-inositol pathways, are presented with the supporting evidence of their operation in multiple plant species. We critically discuss feeding studies using precursors and their conversion to AsA in plant organs, and research where the expression of key genes encoding enzymes involved in the alternative pathways showed >100% AsA content increase in the transgenics and in many cases accompanied by enhanced tolerance to multiple stresses. We propose that the alternative pathways are vital in AsA production in response to stressful conditions and to compensate in cases where the flux through the d-mannose/l-galactose pathway is reduced. The genes and enzymes that have been characterized so far in these alternative pathways represent important tools that are being used to develop more climate-tolerant crops.
抗坏血酸（AsA）是一种抗氧化剂，在植物应激生理学、生长和发育中具有重要作用。AsA 对人类健康也至关重要，可以预防坏血病。人体不能合成 AsA，需要通过富含新鲜农产品的饮食来供应。研究工作在阐明植物中至少有四条通往 AsA 形成的复杂代谢网络方面取得了进展。在这篇综述中，介绍了三种替代途径，即 D-半乳糖酸途径、L-吡喃葡萄糖醛酸途径和肌醇途径，并提供了这些途径在多种植物中起作用的证据。我们批判性地讨论了使用前体进行的喂养研究及其在植物器官中转化为 AsA 的情况，以及在关键基因表达研究中，涉及替代途径的酶编码基因的表达在转基因中增加了超过 100%的 AsA 含量，在许多情况下伴随着对多种胁迫的耐受性增强。我们提出，替代途径在应激条件下产生 AsA 以及补偿 D-甘露糖/L-半乳糖途径通量减少的情况下是至关重要的。迄今为止，在这些替代途径中已鉴定出的基因和酶是开发更能耐受气候变化的作物的重要工具。
