Why Do Geranium Leaves Turn Yellow?

The reason why some plants get yellow or reddish leaves is due to the presence of certain chemicals in their leaves called carotenoids. Carotenoids are pigments found naturally in many fruits and vegetables such as carrots, apples, spinach, strawberries, tomatoes and others. They give these foods color and make them attractive to eat.

Carotenoids are present in the leaves of all plants including those that have been genetically modified (GMO). When they come into contact with sunlight, ultraviolet rays from the sun cause these carotenoid molecules to absorb energy which causes them to change shape. These changes result in the formation of different colored pigments. Some of these colors include yellow, orange, red and purple.

Yellow and Red Leaf Color

When the carotenoids react with oxygen, they form hydrogen peroxide which reacts with water to produce free radicals. Free radicals are unstable compounds that can damage cells and DNA. This reaction produces reactive oxygen species (ROS) which can lead to cell death. ROS may also contribute to other harmful effects such as skin cancer, cataracts, heart disease, diabetes mellitus and Alzheimer’s Disease.

Many different factors affect the oxidation of carotenoids. These factors include:

Amount of Water – The more water that is available to a plant, the less carotenoid it contains and the paler it appears. In fact, some plants need to dry out in order to maintain their bright color. If too much water is present, then the cells are unable to draw in large amounts of oxygen necessary for carotenoid oxidation.

Sources & references used in this article:

Gender variation and sexual differences in reproductive characters and seed production in gynodioecious Geranium maculatum by J Steinbeck – 1945 – World Publishing Company

On the bionomics of a primary parasite and of two hyperparasites of the geranium aphid by J Ågren, MF Willson – American Journal of Botany, 1991 – Wiley Online Library

Why Mothers Get Gray by GH Griswold – Annals of the Entomological Society of America, 1929 – academic.oup.com

Rose-scented geranium (Pelargonium spp.) herbage yield, essential oil yield and composition as influenced by nitrogen nutrition and liming by JL Williams – 1918 – Scribner



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