Phyllobilins--the abundant bilin-type tetrapyrrolic catabolites of the green plant pigment chlorophyll.

The seasonal disappearance of the green plant pigment chlorophyll in the leaves of deciduous trees has long been a fascinating biological puzzle. In the course of the last two and a half decades, important aspects of the previously enigmatic breakdown of chlorophyll in higher plants were elucidated. Crucial advances in this field were achieved by the discovery and structure elucidation of tetrapyrrolic chlorophyll catabolites, as well as by complementary biochemical and plant biological studies. Phyllobilins, tetrapyrrolic, bilin-type chlorophyll degradation products, are abundant chlorophyll catabolites, which occur in fall leaves and in ripe fruit. This tutorial review outlines 'how' chlorophyll is degraded in higher plants, and gives suggestions as to 'why' the plants dispose of their valuable green pigments during senescence and ripening. Insights into chlorophyll breakdown help satisfy basic human curiosity and enlighten school teaching. They contribute to fundamental questions in plant biology and may have practical consequences in agriculture and horticulture.