Botany: How Do Red Or Dark Brown Leafed Trees Produce What They Need To Grow And Produce Fruit ?
Posted by admin on February 23, 2010
I thought that the presence of chlorophyll was what make leaves green. I see that there are some cherry trees have dark colored leaves – so what happens with the chemistry of the plant in these cases?
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Those leaves still contain chlorophyll — at least as much as any other tree does. It’s just not visible because other pigments in the leaves overlay the green color, making the leaf look reddish. They’re doing perfectly ordinary photosynthesis under the cover of all that anthocyanin (the red pigment you’re probably seeing). In some cases, the pigment even protects photosynthetic tissue from being damaged by too much ultraviolet light — it’s the plant’s equivalent of the melanin in your skin, its “tan” preventing sunburn.
Photosynthesis involves an array of photosynthetic pigments, not just chlorophyll. There are, in fact, two kinds of chlorophyll (referred to as “a” & “b”), as well as another class of photosynthetic pigments called carotenoids. These molecules also absorb light for the photosynthetic process, but instead of using that energy themselves they pass on the energy to the chlorophylls. The various carotenoids (the main ones are carotene and xanthophyll) tend to reflect (waste) light in the yellow to red end of the spectrum. They would make leaves look yellow if they were the only pigments present. There can be a number of different photosynthetic pigments in a leaf at any one time, but chlorophyll is the most common, so we see most leaves as green in colour. Carotenoid molecules are large and complex, too, but they do not break down as fast as chlorophyll.
In addition to photosynthetic pigments (chlorophylls and carotenoids), there can be several kinds of non-photosynthetic pigments present in leaves. These are compounds that have varying functions in the leaf, but also act as pigments. The relative proportions and types of all these pigments present during the growing season will determine the colour and patterning of the leaves at that time. And they will all have an impact on the fall colours, as well. Plants that have reddish or purplish leaves during the growing season, such as Coleus or Shubert’s Chokecherry, have large concentrations of anthocyanins: a group of plant pigments that produce red, purplish or even blue colours. The anthocyanins are present is such concentrations that they swamp the green colour of the photosynthetic pigments. The chlorophylls are still there, but they are “out-shone” in the same sense that the carotenoids are normally “out-shone” by the chlorophylls. Each species of plant will have a unique array of pigments in it’s “colour palette”, based on the genetics of that species.