This section is connected to exercise 3 Patterns in nature and 14 Colours of the forest
Many people’s favourite season is autumn because of the beautiful autumn foliage, i.e. colours of theleaves of trees . But why do the leaves all of a sudden change colours before they fall. During the summer growing season, leaves are packed with chlorophyll. That is the green, light absorbing pigment used for photosynthesis. The onset of autumn prompts chemical changes in the leaves of deciduous trees and shrubs as they prepare for winter dormancy, the respond on shorter and cooler days. As the chlorophyll breaks down, the green fades to reveal a bonfire of other colours.
- Yellow and orange: The appearance of yellow and orange shades in autumn leaves indicates the presence of carotenoids, pigments that all summer have been masked by the dominant green chlorophyll and are only revealed as the chlorophyll breaks down. Cartenoid pigments also make carrots orange.
- Reds: Unlike other colours, reds and purples are not always present in autumn leaves. These shades are made from anthocyanins, pigments produced from sugars trapped in the leaves before they fall. Some plants are bred to have red leaves all year round, hiding the green chlorophyll in the leaves.
Different plants have different pigments. Other than being beautiful to look at, they fulfil extra important functions from plants. They protect them from harmful UV radiation, help to limit the damage caused by stresses such as salt and dryness, and are present in fruit and flowers, to attract specific animals, including humans!
- Anthocyanins: are water soluble pigments that depending on their pH, may appear red, purple or blue. Food plants rich in anthocyanins include blueberries, raspberries, black rice and black soybean,
along with many others that are red, blue, purple or black. Some of the colours of autumn leaves are also derived from anthocyanins.
- Carotenoids: are organic pigments that are produced by plants, that tend to be coloured yellow, orange or red. These compounds are the dominant pigment in autumn leaf colouration in about 15 – 30% of tree species, but are also important in colouring the flowers of many species.
- Betalains : are pigments derived from the amino acid tyrosine. They are familiar as the colour of beetroot, but can also take yellow and orange hues. In flowering plants they are unique to the order caryophylales which contains beetroot but also spinach, bougainvillea and cacti.