Institute of Organic Chemistry & Center for Molecular Biosciences, University of Innsbruck, 6020 Innsbruck (Austria).
Chemistry. 2013 Sep 9;19(37):12294-305. doi: 10.1002/chem.201301907. Epub 2013 Aug 14.
Chlorophyll breakdown is a visual phenomenon of leaf senescence and fruit ripening. It leads to the formation of colorless chlorophyll catabolites, a group of (chlorophyll-derived bilin-type) linear tetrapyrroles. Here, analysis and structure elucidation of the chlorophyll breakdown products in leaves of banana (Musa acuminata) is reported. In senescent leaves of this monocot all chlorophyll catabolites identified were hypermodified fluorescent chlorophyll catabolites (hmFCCs). Surprisingly, nonfluorescent chlorophyll catabolites (NCCs) were not found, the often abundant and apparently typical final chlorophyll breakdown products in senescent leaves. As a rule, FCCs exist only fleetingly, and they isomerize rapidly to NCCs in the senescent plant cell. Amazingly, in the leaves of banana plants, persistent hmFCCs were identified that accounted for about 80 % of the chlorophyll broken down, and yellow leaves of M. acuminata display a strong blue luminescence. The structures of eight hmFCCs from banana leaves were analyzed by spectroscopic means. The massive accumulation of the hmFCCs in banana leaves, and their functional group characteristics, indicate a chlorophyll breakdown path, the downstream transformations of which are entirely reprogrammed towards the generation of persistent and blue fluorescent FCCs. As expressed earlier in related studies, the present findings call for attention, as to still elusive biological roles of these linear tetrapyrroles.
叶绿素降解是叶片衰老和果实成熟的一个可见现象。它导致无色的叶绿素降解产物的形成，这些产物是一组（叶绿素衍生的双吡咯型）线性四吡咯。本文报道了对香蕉（Musa acuminata）叶片中叶绿素降解产物的分析和结构阐明。在单子叶植物衰老的叶片中，鉴定出的所有叶绿素降解产物均为高度修饰的荧光叶绿素降解产物（hmFCCs）。令人惊讶的是，没有发现非荧光叶绿素降解产物（NCCs），它们通常是衰老叶片中丰富且典型的最终叶绿素降解产物。通常情况下，FCCs 仅短暂存在，并且它们在衰老的植物细胞中迅速异构化为 NCCs。令人惊讶的是，在香蕉植物的叶片中，鉴定出了持久的 hmFCCs，它们占分解的叶绿素的约 80%，而 M. acuminata 的黄叶显示出强烈的蓝色发光。通过光谱手段分析了来自香蕉叶的八种 hmFCCs 的结构。hmFCCs 在香蕉叶中的大量积累及其官能团特征表明了一条叶绿素降解途径，其下游转化完全重新编程为持久的蓝色荧光 FCCs 的生成。正如之前在相关研究中所表达的那样，这些发现引人注目，因为这些线性四吡咯的生物学作用仍然难以捉摸。
