Flavonoids may mediate UV protection in plants either by screening of harmful radiation or by minimizing the resulting oxidative stress. To help distinguish between these alternatives, more precise knowledge of flavonoid distribution is needed. We used confocal laser scanning microscopy (cLSM) with the “emission fingerprinting” feature to study the cellular and subcellular distribution of flavonoid glucosides in the giant duckweed (Spirodela polyrhiza), and investigated the fitness effects of these compounds under natural UV radiation and copper sulphate addition (oxidative stress) using common garden experiments indoors and outdoors. cLSM “emission fingerprinting” allowed us to individually visualize the major dihydroxylated B‐ring‐substituted flavonoids, luteolin 7‐O‐glucoside and luteolin 8‐C‐glucoside, in cross‐sections of the photosynthetic organs. While luteolin 8‐C‐glucoside accumulated mostly in the vacuoles and chloroplasts of mesophyll cells, luteolin 7‐O‐glucoside was predominantly found in the vacuoles of epidermal cells. In congruence with its cellular distribution, the mesophyll‐associated luteolin 8‐C‐glucoside increased plant fitness under copper sulphate addition but not under natural UV light treatment, whereas the epidermis‐associated luteolin 7‐O‐glucoside tended to increase fitness under both stresses across chemically diverse genotypes. Taken together, we demonstrate that individual flavonoid glucosides have distinct cellular and subcellular locations and promote duckweed fitness under different abiotic stresses.

中文翻译：

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非生物胁迫下水生植物中类黄酮苷的差异化定位涉及不同功能

类黄酮可通过屏蔽有害辐射或将产生的氧化应激降至最低来介导植物的紫外线防护。为了帮助区分这些替代方法，需要更精确的类黄酮分布知识。我们使用具有“发射指纹”功能的共聚焦激光扫描显微镜（cLSM）来研究巨型浮萍（Spirodela polyrhiza）中黄酮苷的细胞和亚细胞分布），并使用室内和室外常见的花园实验研究了这些化合物在自然紫外线辐射和添加硫酸铜（氧化应激）下的健身效果。cLSM“发射指纹图谱”使我们能够在光合器官的横截面上分别观察主要的二羟基化的B环取代的类黄酮，木犀草素7-O-葡萄糖苷和木犀草素8-C-葡萄糖苷。木犀草素8-C-葡萄糖苷主要积累在叶肉细胞的液泡和叶绿体中，而木犀草素7-O-葡萄糖苷主要存在于表皮细胞的液泡中。与叶绿素相关的木犀草素8-C-葡糖苷与其细胞分布一致，在添加硫酸铜的情况下提高了植物的适应性，但在自然紫外线照射下却没有，而表皮相关的木犀草素7-O-葡萄糖苷在两种胁迫下都倾向于增加化学多样性基因型的适应性。综上所述，我们证明了单独的类黄酮苷具有独特的细胞和亚细胞位置，并在不同的非生物胁迫下促进浮萍的适应性。