Chlorophyll, carotene and xanthophyll are found in leaves, young stalks and unripe
fruits. Chloroplasts are found in cells along with chromoplasts, which especially contain
carotenoids and leucoplasts. These are without pigment and contain mostly starch.
Under certain circumstances, these plastids pass into each other. Their metamorphose is
induced by change of temperature and the amount of sun energy. Anthocyanins and betalains
(red, violet, purple) are in the cytoplasm. Their colour depends on the quantity of the
pigment and pH in the cells and change during the ageing of the cells. One of the
functions of these pigments is probably protection from the sun's rays, especially UV
rays. Plants in high mountains or arctic regions have larger quantities of these pigments.
When fruit is ripe, the chloroplasts change into chromoplasts. They have large quantities of carotenoids. These can crystallise and damage the tissue, which may cause rooting of the fruit.
We can observe the changing colours of the leaves every autumn. The chloroplasts decay, because of the lower temperature and a large quantity of the light at the same time. The colour of the leaves depends then on the pigments that were covered with the predominating chlorophyll. Plants with especially intensive colours have been attractive to mankind since ancient times. We breed them for decoration and give a great deal of our attention to the new sorts.