Chlorophyll Breakdown in Leaves and Fruit

The emergence of the fall colours in the foliage of deciduous trees and the change of colour observable during ripening of fruit are particularly highly visible manifestations associated with the breakdown of the chlorophylls, the "green" pigments of plants. Indeed the seasonal metabolism of chlorophyll is probably the most visible sign of life on earth. Over the last fifteen years only, has biological and chemical information on chlorophyll breakdown become available. Major chemical contributions to this subject were provided by our group. So far, chlorophyll has been found to be rapidly "detoxified" in senescent leaves of higher plants to colourless and non-luminescent tetrapyrroles, the so called "nonfluorescent" chlorophyll catabolites (NCCs). Rather than providing coloured products, as expected earlier, chlorophyll breakdown is thus suggested to play a passive part only, when the fall colours appear. The present project concerns the natural occurrence of tetrapyrrolic chlorophyll breakdown products, not only in senescent leaves, but in ripening fruit, as well, and also addresses the specific question of whether luminescent and coloured chlorophyll breakdown products would not directly contribute to the colour in fall leaves and of ripe fruit, after all. Coloured tetrapyrroles are suggested to be of interest as natural oxidation products of the NCCs, which were, indeed, found to be effective antioxidants. "Fluorescent" chlorophyll catabolites are the generally short lived, direct precursors of the NCCs, but appear to accumulate in some senescent plants, for still unknown reasons. The identification of luminescent and coloured tetrapyrrolic chlorophyll degradation products will help to better understand the path and the role of natural chlorophyll breakdown during senescence and ripening in higher plants. To achieve these specific contributions, it is proposed (i) to explore systematic pathways for the preparation of coloured, tetrapyrrolic chlorophyll catabolites as synthetic reference materials; (ii) to search for (luminescent and coloured) chlorophyll catabolites in senescent leaves of higher plants and in ripening fruit and (iii) to investigate the influence of environmental factors on the identity and occurrence of tetrapyrrolic chlorophyll catabolites in higher plants. Chlorophyll breakdown in higher plants is a fascinating natural phenomenon and a subject of ecological and economical importance, as well. It has been suggested to be relevant as a detoxification process. The planned work is intended to investigate further the fate of chlorophyll in higher plants and to provide chemical evidence for possible physiological activity of some of its tetrapyrrolic breakdown products.

The emergence of the fall colours in the foliage of deciduous trees and the change of colour observable during ripening of fruit are particularly highly visible manifestations associated with the breakdown of the chlorophylls, the "green" pigments of plants. Indeed the seasonal metabolism of chlorophyll is probably the most visible sign of life on earth. Over the last fifteen years only, has biological and chemical information on chlorophyll breakdown become available. Major chemical contributions to this subject were provided by our group. So far, chlorophyll has been found to be rapidly "detoxified" in senescent leaves of higher plants to colourless and non-luminescent tetrapyrroles, the so called "nonfluorescent" chlorophyll catabolites (NCCs). Rather than providing coloured products, as expected earlier, chlorophyll breakdown is thus suggested to play a passive part only, when the fall colours appear. The present project concerns the natural occurrence of tetrapyrrolic chlorophyll breakdown products, not only in senescent leaves, but in ripening fruit, as well, and also addresses the specific question of whether luminescent and coloured chlorophyll breakdown products would not directly contribute to the colour in fall leaves and of ripe fruit, after all. Coloured tetrapyrroles are suggested to be of interest as natural oxidation products of the NCCs, which were, indeed, found to be effective antioxidants. "Fluorescent" chlorophyll catabolites are the generally short lived, direct precursors of the NCCs, but appear to accumulate in some senescent plants, for still unknown reasons. The identification of luminescent and coloured tetrapyrrolic chlorophyll degradation products will help to better understand the path and the role of natural chlorophyll breakdown during senescence and ripening in higher plants. To achieve these specific contributions, it is proposed 1. to explore systematic pathways for the preparation of coloured, tetrapyrrolic chlorophyll catabolites as synthetic reference materials; 2. to search for (luminescent and coloured) chlorophyll catabolites in senescent leaves of higher plants and in ripening fruit and 3. to investigate the influence of environmental factors on the identity and occurrence of tetrapyrrolic chlorophyll catabolites in higher plants. Chlorophyll breakdown in higher plants is a fascinating natural phenomenon and a subject of ecological and economical importance, as well. It has been suggested to be relevant as a detoxification process. The planned work is intended to investigate further the fate of chlorophyll in higher plants and to provide chemical evidence for possible physiological activity of some of its tetrapyrrolic breakdown products.