Speed read: Revealing Plant’s Colour Complexity

There’s more to chlorophyll than simply providing plant leaves with their natural green colouring. Chlorophyll is part of the engine that drives photosynthesis, possibly the most important reaction on earth, in which light is absorbed from the sun and converted into chemical energy to fuel the growth of plants.

Our understanding of the chemistry of chlorophyll owes much to Richard Willstätter’s extensive investigations of the structures of natural pigments. By succeeding in preparing chlorophyll in a pure state and in large quantities, Willstätter could begin to unlock the secrets of its complex chemical structure. Chief amongst his discoveries was that there are two main parts to chlorophyll: a component called ‘chlorophyllin’ that houses the natural green pigment and a previously unknown alcohol called ‘phytol’. Willstätter also provided the first conclusive proof that there are two types of chlorophyll, called ‘blue-green’ and ‘yellow-green’ on the basis that each absorbs slightly different wavelengths of light.

Willstätter was the first to provide conclusive evidence for the chemical relationship between chlorophyll and a vital component for life in animals — the red oxygen-carrying pigment in blood called haem. He showed that chlorophyll shares a similar structure to haem, with its essential chemical element magnesium held tightly within the heart of a chlorophyll molecule in the same way in which iron is held within haem.

Branching out into other colours on the plant palette, Willstätter uncovered the chemical structures of the anthocyanins, a family of blue and red pigments that are found in a variety of flowers and fruits. Willstätter proved that these anthocyanins are closely related to the yellow pigment found in many leaves, and his systematic analysis of pigments in several plants allowed him to formulate a scheme for how different combinations of anthocyanins in particular environments can account for the many different colours of flowers found in Nature.

First published 2 April 2009

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