随着香蕉从成熟变为腐烂，亮黄色的果皮出现棕色和黑色的斑点，它们生长迅速，而且最终包裹了整个香蕉。这种斑点——它是表明香蕉将很快不可食用的警告标记——代表了死亡的组织。
Bernhard Kraeutler及其同事报告说，香蕉在紫外线照射下发出蓝光，而在死亡斑点周围显示出亮蓝色的光晕。这组作者指出，这种荧光蓝色是由叶绿素分解造成的。叶绿素是植物叶子的颜料，也是光合作用的关键。这组作者证明了当叶绿素在香蕉中分解的时候，这种化合物产生了荧光分子，让香蕉在紫外线下发出蓝光。这组作者证明了这些残留的荧光分子在变老的组织中积累，而且让它出现了蓝色冷光，他们还提出，这种色彩化可能成为一种发现凋亡和正在死亡的植物细胞的工具。这组作者说，一些吃水果的动物可能适应了这种蓝色荧光光晕，把它作为食物成熟的标记。（生物谷Bioon.com）
生物谷推荐原始出处：
PNAS September 8, 2009, doi: 10.1073/pnas.0908060106
Fluorescent chlorophyll catabolites in bananas light up blue halos of cell death
Simone Mosera,b, Thomas Müllera,b, Andreas Holzingerc, Cornelius Lützc, Steffen Jockuschd, Nicholas J. Turrod,1 and Bernhard Kr?utlera,b,1
aInstitute of Organic Chemistry and
bCentre for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria;
cInstitute of Botany, University of Innsbruck, A-6020 Innsbruck, Austria; and
dDepartment of Chemistry, Columbia University, New York, NY 10027
Breakdown of chlorophyll is a major contributor to the diagnostic color changes in fall leaves, and in ripening apples and pears, where it commonly provides colorless, nonfluorescent tetrapyrroles. In contrast, in ripening bananas (Musa acuminata) chlorophylls fade to give unique fluorescent catabolites (FCCs), causing yellow bananas to glow blue, when observed under UV light. Here, we demonstrate the capacity of the blue fluorescent chlorophyll catabolites to signal symptoms of programmed cell death in a plant. We report on studies of bright blue luminescent rings on the peel of very ripe bananas, which arise as halos around necrotic areas in ‘senescence associated' dark spots. These dark spots appear naturally on the peel of ripe bananas and occur in the vicinity of stomata. Wavelength, space, and time resolved fluorescence measurements allowed the luminescent areas to be monitored on whole bananas. Our studies revealed an accumulation of FCCs in luminescent rings, within senescing cells undergoing the transition to dead tissue, as was observable by morphological textural cellular changes. FCCs typically are short lived intermediates of chlorophyll breakdown. In some plants, FCCs are uniquely persistent, as is seen in bananas, and can thus be used as luminescent in vivo markers in tissue undergoing senescence. While FCCs still remain to be tested for their own hypothetical physiological role in plants, they may help fill the demand for specific endogenous molecular reporters in noninvasive assays of plant senescence. Thus, they allow for in vivo studies, which provide insights into critical stages preceding cell death.
