Flavonoids are the most important secondary metabolites in ginkgo (Ginkgo biloba L.) leaves that determine its medicinal quality. Studies have suggested that secondary metabolism is strongly affected by temperature in other plant species, but little is known about ginkgo. In this study, we investigated the effects of different day-night temperature combinations (15/10, 25/20, and 35/30 °C (day/night)) on key enzyme activity, growth regulator concentrations, and flavonoid accumulation in ginkgo leaves. We found that phenylalanine ammonia-lyase (PAL) activity was enhanced and inhibited at 15/10 and 35/30 °C, respectively. Cinnamate-4-hydroxylase (C4H) activity was relatively stable under the three temperature conditions, and the p-coumarate CoA ligase (4CL) activity showed different trends under the three temperature conditions. The concentrations of flavonoid constituents (quercetin, kaempferol, and isorhamnetin) were decreased and increased under the 35/30 and 15/10 °C conditions, respectively. Low temperature promoted soluble sugar accumulation, while temperature had a limited impact on the accumulation of soluble protein. The pattern of change in the total flavonoid concentration was not always in agreement with PAL activity due to its complex pathway. Indoleacetic acid (IAA) and gibberellin (GA) changes shared similar patterns and had limited effects on flavonoid accumulation, while abscisic acid (ABA) acted as a promotor of flavonoid accumulation under high-temperature conditions. The total flavonoids achieved the highest content under the 15/10 °C treatment on the 40th day. Therefore, the lower temperature (15/10 °C) is more favorable for flavonoid accumulation and will provide a theoretical basis for further study.

中文翻译：

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响应不同的昼夜温度组合，银杏叶中的类黄酮代谢调控。

类黄酮是银杏叶中最重要的次要代谢产物，它决定了其药用质量。研究表明，次生代谢受其他植物物种温度的强烈影响，但对银杏知之甚少。在这项研究中，我们研究了不同昼夜温度组合（15 / 10、25 / 20和35/30°C（白天/晚上））对银杏关键酶活性，生长调节剂浓度和类黄酮积累的影响树叶。我们发现苯丙氨酸解氨酶（PAL）活性分别在15/10和35/30°C下得到增强和抑制。在三个温度条件下，肉桂酸-4-羟化酶（C4H）活性相对稳定，而在三个温度条件下，对香豆酸CoA连接酶（4CL）活性显示出不同的趋势。在35/30和15/10°C条件下，黄酮类成分（槲皮素，山奈酚和异鼠李素）的浓度分别降低和升高。低温促进可溶性糖的积累，而温度对可溶性蛋白质的积累影响有限。由于其复杂的途径，总类黄酮浓度的变化模式并不总是与PAL活性相符。吲哚乙酸（IAA）和赤霉素（GA）的变化具有相似的模式，并且对类黄酮积累的影响有限，而脱落酸（ABA）在高温条件下可促进类黄酮的积累。在第40天，在15/10°C处理下，总黄酮含量最高。所以，