Stavenga Doekele G, Leertouwer Hein L, Dudek Bettina, van der Kooi Casper J
Zernike Institute for Advanced Materials, University of Groningen, Groningen, Netherlands.
Research Group Biosynthesis/NMR, Max Planck Institute for Chemical Ecology, Jena, Germany.
Front Plant Sci. 2021 Jan 8;11:600124. doi: 10.3389/fpls.2020.600124. eCollection 2020.
Flavonoid pigments are key determinants of flower colors. As absorption spectra of flavonoids are known to be severely pH-dependent, cellular pH will play a crucial role in flower coloration. The flavonoids are concentrated in the vacuoles of the flowers' epidermal cells, and thus the pigments' absorption spectra are modulated by the vacuolar pH. Here we study the pH dependence of flavonoid absorption spectra in extracts from flowers of two poppy species (red) and (orange), and a white and red variety. In the red poppy and flowers, absorption spectra of the cyanidin- and pelargonidin-based anthocyanins peak in the blue-green-wavelength range at low pH, but exhibit a distinct bathochromic shift at higher pH. This shift to longer wavelengths is not found for the blue-absorbing nudicaulin derivatives of , which have a similar absorption spectrum at low and high pH. The pH-dependent absorption changes of the white 's flavonoid remained restricted to the UV. An analysis of the spectra with logistic functions suggests that the pH-dependent characteristics of the basic states of flavonols and anthocyanins are related. The implications of tuning of pH and pigment absorption spectra for studies on flower color evolution are discussed.
类黄酮色素是花朵颜色的关键决定因素。由于已知类黄酮的吸收光谱严重依赖于pH值，因此细胞pH值在花朵着色过程中起着至关重要的作用。类黄酮集中在花朵表皮细胞的液泡中，因此色素的吸收光谱受液泡pH值的调节。在此，我们研究了两种罂粟（红色和橙色）以及一个白色和红色品种花朵提取物中类黄酮吸收光谱对pH值的依赖性。在红色罂粟和花朵中，基于花青素和天竺葵色素的花青素吸收光谱在低pH值下于蓝绿色波长范围内达到峰值，但在较高pH值下呈现出明显的红移。对于蓝色吸收的裸茎甲素衍生物而言，未发现这种向更长波长的转变，其在低pH值和高pH值下具有相似的吸收光谱。白色的类黄酮的pH值依赖性吸收变化仍局限于紫外线区域。用逻辑函数对光谱进行分析表明，黄酮醇和花青素基本状态的pH值依赖性特征是相关的。本文讨论了pH值调节和色素吸收光谱对花朵颜色进化研究的意义。
