Why Do Leaves/Fruits Change Colors in the Fall?
Did you know where the gorgeous coloring of the leaves in the fall comes from and why nature makes her annual art display in the autumn woods?
The leaves of trees and other plants contain three main pigments: carotene, anthocyanin, and the photosynthetic pigment, chlorophyll, which captures the sun’s energy to make food for plants. In plants growing season, chlorophyll is the most abundant pigment what gives leaves their green hue in spring and summer.
In summer days leave makes more glucose than the plant needs & the excess glucose is stored as a starch and used as they need.
Another chemical in leaves, auxin, controls a special band of cells at the base of each leaf stem, called the abscission layer. During the growing season, auxin prevents this layer from fully developing and blocking the tiny, internal tubes that connect each leaf to the rest of the tree’s circulatory system.
In fall, however, cooler and shorter days trigger an end to auxin production, allowing the abscission layer to grow and cut off the circulation of water, nutrients and sugar to the leaves. When this happens, chlorophyll disintegrates rapidly, letting carotene shine through as the yellow in maple, aspen and birch leaves.
However the red and purple colors, though, are not hiding in the leaves and they are not carotenoid. They are the colors from the anthocyanins.
Anthocyanins, is newly created in the late summer or early fall with bright sunny days & cool night from the trapped glucose which produce nice bright color with the complex interactions of many influences both inside and outside the plant. Their formation depends on the breakdown of sugars in the presence of bright light as the level of a certain chemical (phosphate) in the leaf is reduced. During the summer growing season, phosphate is at a high level. It has a vital role in the breakdown of the sugars manufactured by chlorophyll. But in the fall, phosphate, along with the other chemicals and nutrients, moves out of the leaf into the stem of the plant. When this happens, the sugar-breakdown process changes, which stimulates the signal and leading to the production of anthocyanin pigments. The brighter the light during this period, the greater the production of anthocyanins and the more brilliant the resulting color display that we see. When the days of autumn are bright and cool, and the nights are chilly but not freezing, the brightest colorations usually develop.
Why plants are producing anthocynins: Anthocyanins apparently play a major role in pollination by attracting insects in flower, protection from ultraviolet (UV) light, protecting the plant’s DNA from damage by sunlight defense against pathogens and insect attack and resistance to a variety of biotic and abiotic stress conditions.
When there’s less sun, anthocyanin isn’t as chemically active and leaves are more orange or yellow than red.