Chemische Eigenschaften von Chlorophyllkataboliten

Intellectual Merit: Chlorophyll, because of its role in photosynthesis in plants, is one of the most important and best studied molecules in all of the natural sciences. A signature of chlorophyll in plants is its characteristic brilliant green color. This color, along with the chlorophyll molecule, is transformed in leaves in the Fall season, as evidenced by their spectacular color changes. These color changes are triggered by metabolic processes that produce chlorophyll breakdown products, termed catabolites. The chlorophyll catabolism process also occurs in common fruit, such as bananas. The conversion of the peel of a banana from green (unripe) to yellow (ripe) is a common visual observation of the transformation of chlorophyll molecules through their light absorption properties. Several years ago Professor B. Kraeutler`s group at Innsbruck discovered a new phenomenon that was found to parallel the characteristic change in the absorption spectrum of banana peels: yellow bananas were found to glow blue when excited with UV light and intensity of the photoluminescence was at a maximum when the ripening was at its peak. The catablolites responsible for this striking photoluminescence were isolated and their structures characterized. The photophysics behind the photoluminescence of the catabolites was examined in preliminary exploratory and discovery oriented experiments by the research group at Columbia, lead by Professor Nicholas J. Turro. This proposal describes a continuation of this collaboration, in which the project now builds a transition from mainly discovery driven to mainly hypothesis driven chemical research, that will make important contributions to a fascinating biological phenomenon. Research at Innsbruck be directed towards the synthesis of selected samples of pure and well defined chlorophyll catabolites and include studies of their redox chemistry and antioxidant activities. The photophysical properties of these catabolites will be examined in detail at Columbia. When sufficient information on the structures of the catabolites is established by research at Innsbruck and Columbia, the current speculations concerning "the why" of chlorophyll catabolism will be translated into testable hypothesis concerning the possible role of these catabolites as antioxidants, as the source of "cell poisons" through photosensitized oxidations and as "sun screens" through the absorption of light. The role of catabolites in the presumed photosensitized production of singlet oxygen (1O2) will be directly tested by spectroscopic means at Columbia. The products of photooxidation and autooxidation will be characterized at Innsbruck. Broader Impact: The proposed chemical research and collateral activities will directly advance our knowledge on the impact of chlorophyll catabolites in nature, and will promote and assist the exploration of new paths for the discovery of their relevance in plant physiology. All of this research is driven by a change of paradigm concerning the role of chlorophyll breakdown in higher plants. It will also engage graduate students and postdoctoral associates at a new forefront of research, and promote their intellectual and professional development. Likewise, the proposed activities will enhance the infrastructure for research and education, e.g., by developing internet based cyber infrastructure to boost the effectiveness of the Innsbruck-Columbia collaboration. The PI at Columbia has initiated design of an iCollaboratory (internet collaboration laboratory) that employs commonly available laptop computers and free software to integrate the scientific knowledge exchange between the collaborators. For example, the Innsbruck-Columbia team uses available audio-video tools coupled with free internet connections to discuss on- going research in a face-to-face manner. These cyber tools will be extended to the laboratory where researchers can see experiments being executed in real time. These tools will be especially powerful in preparing for visits of researchers between the laboratories. Both PIs will explore the "glowing banana" photoluminescence phenomena to develop experiments that allow high school students and college undergraduate to experience this stunning visual discovery. The chemistry and biochemistry of pigments related to chlorophyll and their chemical changes, that underlie cell death, provide a stimulating context for inspiring the study of the ripening of bananas and other fruit. Professor Pat O`Hara of Amherst College has used our publications on the phenomenon to develop experiments for high school teachers to design experiments employing fluorescence to monitor the ripening of bananas.

Chlorophyll (Chl) ist das charakteristische grüne Pigment der Pflanzen. Dieses wird im Zuge der faszinierenden Herbstverfärbung von laubwerfenden Pflanzen unter Farbveränderungen abgebaut. Erst vor etwa 25 Jahren wurde die überraschende Bildung von farblosen Chl-Kataboliten in gelben, seneszenten Blättern klar dokumentiert. Vorher war noch unbekannt was beim Chl-Abbau passiert. Inzwischen liegen, auch dank grundlegender Beiträge unserer Gruppe, wichtige Erkenntnisse auf dem Gebiet des Chl-Abbaus vor, die ihren Niederschlag schon in pflanzenbiologischen Lehrbüchern gefunden haben. Die Entdeckung des gehäuften Auftretens von ungewöhnlichen fluoreszierenden Chl-Kataboliten (FCCs) in reifen Bananen, sowie die Beobachtung der von diesen FCCs hervorgerufenen blauen Lumineszenz dieser Früchte, veranlasste uns vorzuschlagen, dass Chl-Kataboliten (heute als Phyllobiline bezeichnet) wichtige physiologische Rollen in der Pflanze zukommen sollten. Das vorliegende Projekt beschäftigte sich mit den chemischen Eigenschaften von farbigen Phyllobilinen und von FCCs, die zumeist nur als transiente Produkte des Chl- Abbaus und in kleinen Mengen in seneszenten Blättern und reifenden Früchten gefunden werden. Untersuchungen an partialsynthetisch hergestellten roten Chl-Kataboliten (RCCs), an FCCs und an gelben Chl-Kataboliten (YCCs) wurden mittels photo-physikalischer, struktur- und redox-chemischer Methoden durchgeführt. Diese Studien weisen auf außergewöhnliche Eigenschaften von RCCs (leicht reduzierbare Phyllobiline), von FCCs (Sensibilisatoren für die Erzeugung des toxischen Singulett Sauerstoffs) und von YCCs (Antioxidantien und ausgezeichnete bidentate Liganden für Übergangsmetall-Ionen) hin, die auch in den Pflanzen von physiologischer Bedeutung sein können. Unsere Arbeiten haben damit die Ansicht bestärkt, dass Phyllobiline (die offenkettigen, tetrapyrrolischen Kataboliten des Chl) nicht mehr (nur) als Abfallprodukte eines biologischen Entgiftungsprozesses zu verstehen sind, wie früher angenommen. Ihre hypothetischen Wirkungen in den Pflanzen dürften dabei zunächst mit den anti-oxidativen Eigenschaften in Verbindung gebracht werden, sowie mit ihrer Absorption von Sonnenlicht und (für FCCs) der Lichtemission (Fluoreszenz), sowie der Erzeugung von Singulett Sauerstoff. Manche dieser photochemischen Eigenschaften der Chl-Kataboliten erlauben Untersuchungen im intakten Pflanzengewebe. Damit ist eine Grundlage für weitere Studien an Pflanzen über die physiologische Wirkung von Chl-Kataboliten gelegt, von welchen einige auch in pflanzenfressenden Säugern und Menschen von Bedeutung sein könnten.