Autumn leaf color is a phenomenon that affects the typical green leaves of many deciduous trees and shrubs, causing them to turn various hues of yellow, orange, red, purple, and brown for a few weeks throughout the autumn season. In British English, the phenomena are known as autumn colors or autumn foliage, whereas in American English, it is known as fall colors, fall foliage, or simply foliage.

The pigment chlorophyll, which is found inside a chloroplast organelle, is responsible for the color of a green leaf. When chlorophyll is plentiful in the leaf’s cells, as it is throughout the growing season, the green color of the chlorophyll dominates and obscures the colors of any other pigments present in the leaf. As a result, summer leaves are distinctively green.

Chlorophyll serves an important role in the plant’s metabolism: it absorbs sun rays and converts the energy into simple sugars, which are made from water and carbon dioxide. These sugars are the plant’s primary source of carbohydrates, which are required for growth and development. Chlorophylls break down throughout the food processing process. Thus they are constantly “used up.” The plant, on the other hand, refills the chlorophyll during the growing season to keep the supply high and the leaves green.

The veins that transport fluids into and out of the leaf progressively seal off as a layer of unique cork cells develops at the base of each leaf when daylight hours shorten and temperatures fall as autumn approaches. Water and mineral input into the leaf is decreased as this cork layer grows, initially slowly and later more rapidly. The quantity of chlorophyll in the leaf begins to diminish at this time. After the tissues between them have nearly entirely changed color, the veins are frequently remaining green.

Photosystem II (light-harvesting complex II or LHC II), the most prevalent membrane protein on the planet, contains a lot of chlorophyll. In photosynthesis, the LHC II catches the light. It is found in the chloroplast’s thylakoid membrane and is made up of an apoprotein and many ligands, the most significant of which are chlorophylls a and b. This complex is dismantled in the fall. The breakdown of chlorophyll is considered to happen first. According to research, chlorophyll b reductase catalyzes the first step in chlorophyll degradation, reducing chlorophyll b to 7hydroxymethyl chlorophyll a, which is eventually reduced to chlorophyll a. This is thought to disrupt the complex, causing the apoprotein to break down. FtsH6, a member of the FtsH family of proteases, is a key enzyme in the apoprotein’s degradation.

Chlorophylls break down into nonfluorescent chlorophyll catabolites, which are colorless tetrapyrroles. The hidden pigments of yellow xanthophylls and orange beta-carotene are exposed when the chlorophylls decay. These pigments are present all year, but the red pigments, known as anthocyanins, are produced from scratch once around half of the chlorophyll has been destroyed. The amino acids produced during the decomposition of light-harvesting complexes are retained in the tree’s roots, branches, stems, and trunk throughout the winter until the following spring, when they are recycled to relieve the tree.

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