Department of Plant Agriculture, University of Guelph, 50 Stone Rd E., Guelph, ON, N1G 2W1, Canada.
Department of Plant Agriculture, University of Guelph, 50 Stone Rd E., Guelph, ON, N1G 2W1, Canada.
Plant Sci. 2021 Jul;308:110904. doi: 10.1016/j.plantsci.2021.110904. Epub 2021 Apr 5.
Plants are the sole source of flavonoids, a chemical category that includes flavonols. For the most part, flavonols occur as glycosides with numerous postulated biological roles in plants, including photoprotection, modulation of hormone translocation, and sequestration of reactive oxygen species. Flavonol glycosides are often considered as dead-end metabolites because related flavonoids (i.e., anthocyanins) occur in terminal tissues such as flowers and fruit, but recent evidence points to their turnover in planta, including developing photosynthetic tissues. Although microbial degradation pathways for flavonol glycosides of plant origin are well described, plant catabolic pathways are little studied by comparison. This review will address our current understanding of biochemical processes leading to the loss of flavonol glycosides in plants, with a specific emphasis on the evidence for flavonol-specific β-glucosidases. Complete elucidation of these catabolic pathways is dependent on the identification of regiospecific modifying steps, including enzymes associated with the hydrolysis of rhamnosylated flavonols, as well as flavonol peroxidation and their encoding genes. Herein, we highlight challenges for the identification of hypothetical plant α-rhamnosidases and peroxidases involved in flavonol glycoside degradation, and the potential biological role of this catabolism in mitigating oxidative stress in developing and postharvest plant tissues.
植物是类黄酮的唯一来源，类黄酮包括黄酮醇。在大多数情况下，黄酮醇以糖苷的形式存在，在植物中有许多推测的生物学作用，包括光保护、激素转运的调节和活性氧的隔离。黄酮醇糖苷通常被认为是无出路的代谢物，因为相关的类黄酮（如花青素）存在于终端组织如花朵和果实中，但最近的证据表明它们在植物体内发生了转化，包括正在发育的光合组织。虽然微生物降解植物来源的黄酮醇糖苷的途径已经得到很好的描述，但与微生物相比，植物的分解代谢途径研究得很少。这篇综述将讨论我们目前对导致植物中黄酮醇糖苷丢失的生化过程的理解，特别强调黄酮醇特异性β-葡萄糖苷酶的证据。这些分解代谢途径的完全阐明取决于对区域特异性修饰步骤的鉴定，包括与鼠李糖基化黄酮醇水解以及黄酮醇过氧化及其编码基因相关的酶。本文重点介绍了鉴定参与黄酮醇糖苷降解的假设植物α-鼠李糖苷酶和过氧化物酶的挑战，以及这种代谢在减轻发育中和采后植物组织中氧化应激方面的潜在生物学作用。
