Division Quality and Sensory of Plant Products, Georg-August-Universität Göttingen, Goettingen, Germany.
Department of Biological Sciences and Environment Program, Loyola University New Orleans, New Orleans, Louisiana.
Physiol Plant. 2021 Nov;173(3):725-735. doi: 10.1111/ppl.13517. Epub 2021 Aug 19.
The accumulation of soluble and cell-wall bound UV-absorbing compounds (i.e., flavonoids) in the epidermis and the mesophyll of leaves is a response of plants to UV exposure. These compounds are known to function in UV screening, but they are also of potential value for food quality. One way to non-destructively monitor UV screening in leaves is by optical methods, from which UVA-PAM and Dualex instruments stand out. The degree and rapidity to which plants can modulate UV screening in response to fluctuating solar UV conditions is poorly understood. In this study, okra plants were exposed to two solar radiation treatments (near-ambient UV [+UV] and attenuated UV [-UV]) and the epidermal UV transmittance (T ; UVA-PAM) and flavonoid index (Dualex) were measured in the youngest and second youngest mature leaves over three consecutive days and within an individual day. The day-to-day (measured near solar noon) and diurnal (over the course of a day) measurements of leaf optical properties indicated that T decreased and flavonoid index increased in the adaxial epidermis ~50% until 15:00 CDT then returned close to morning values later in the day. Correlations between UV-B radiation and T and flavonoid index revealed highest values 30 min to 1 h prior to the measurements. These findings indicate that plants can respond quickly to fluctuating solar UV conditions and underlines the importance of the harvest-time point for health-promoting compounds in fruit and vegetables. Our findings also indicate that the UVA-PAM and the Dualex instruments are both suitable instruments to monitor rapid changes in UV screening in plants.
表皮和叶片中叶肉中可溶和细胞壁结合的紫外线吸收化合物（即类黄酮）的积累是植物对紫外线暴露的一种反应。这些化合物已知具有紫外线屏蔽功能，但它们对于食品质量也具有潜在价值。一种非破坏性监测叶片紫外线屏蔽的方法是使用光学方法，其中 UVA-PAM 和 Dualex 仪器尤为突出。植物对波动的太阳紫外线条件迅速调节紫外线屏蔽的程度和速度还知之甚少。在这项研究中，将秋葵植物暴露在两种太阳辐射处理（近环境紫外线 [+UV] 和衰减紫外线 [-UV]）下，并在连续三天内和一天内测量最年轻和第二年轻的成熟叶片的表皮紫外线透过率（T；UVA-PAM）和类黄酮指数（Dualex）。叶片光学特性的日变化（在接近正午时测量）和日变化（在一天的过程中）表明，T 在 adaxial 表皮中降低，类黄酮指数增加了约 50%，直到 CDT 15:00 左右，然后在当天晚些时候接近早晨的值。UV-B 辐射与 T 和类黄酮指数之间的相关性表明，在测量前 30 分钟到 1 小时之间达到最高值。这些发现表明，植物可以迅速对波动的太阳紫外线条件做出反应，并强调了在水果和蔬菜中收获健康促进化合物的时间点的重要性。我们的研究结果还表明，UVA-PAM 和 Dualex 仪器都是监测植物中紫外线屏蔽快速变化的合适仪器。
