Red leaves. Why do some plants have red leaves. Lush greenery is a delightful sight. The pigment chlorophyll is responsible for this green color. We can also find other colors – red, yellow, orange, purple, etc. in a plant’s flower or fruit. Even leaves that are commonly green, have variations at times. It is due to the increased presence of accessory pigments like carotenoids, xanthophyll, flavonoids, etc. Flavonoids like anthocyanin and betalain like betacyanin give the leaves its red-purple color. Red leaves appear chiefly in plants growing in acidic soil. Betalains are found only in some plants. E.g. Amaranth, beets, etc.
What’s in a Colour – Why do some Plants have Red leaves?
Chlorophyll is present in all the leaves to carry out photosynthesis. The accessory pigments like carotenoids aid in photosynthesis, act as antioxidants, help dissipate excess energy, and protect the leaves from adverse temperature conditions. Though they are always present in a leaf, their color becomes visible when the chlorophyll level in leaves decrease. E.g. Oak trees during fall. Certain species of plants, produce either anthocyanin or betacyanin, under a variety of conditions. These pigments serve the same purpose as the accessory pigments but do not directly participate in photosynthesis. Xanthophyll content is presumed to be less in such red-leaved plants.
Seasonal changes a reason for plants red leaves
Lack of sunlight and cold conditions in winter are not ideal for photosynthesis. So, some plants start losing their leaves in fall. To make that happen, chlorophyll production reduces in leaves and leaves are cut off from the tree gradually. The other colored pigments become visible during this time since chlorophyll is less. Extreme dry conditions or short sunny days with cold nights will be stressful for plants. Metabolism reduces, excess sugar accumulates in the leaves and causes the production of anthocyanin. Anthocyanin helps to protect the leaves from excess heat and light, UV radiation, etc. It helps trees recover whatever residual nutrients are present in the leaves.Nutrient deficiency induces red color
Deficiency & Stress can cause red leaves
Red leaves can also be caused by a deficiency of Phosphorus, Magnesium or Potassium. Magnesium is an integral part of chlorophyll and its deficiency affects photosynthesis. Such nutrient deficiencies decrease chlorophyll level. White spots appear on the leaves. When anthocyanin is present, the leaves turn red. Herbicidal spray can also cause a reaction and turn the leaves red. Leaf injury, the infection causes breakdown of chlorophyll. Leaves produce red pigments to repair the injury. E.g. Red Beet leaves produce Betacyanins
Extreme temperature can kill young leaves. Young leaves are yet to develop; hence, they have less chlorophyll to carry out photosynthesis. Hence red pigments are visible. E.g. Rose leaves in frost. Similarly, inside the canopy of the tropical rainforest, we can find many plants with red leaves. These are shade-loving plants. So excess sunlight can damage the leaves. Hence, plants produce anthocyanin to protect them from high-energy light.
Sometimes redness occurs as a result of cell mutation. Sometimes we culture plants with red leaves for various purposes. E.g. Japanese Red leave Barberry. Short-day plants like Poinsettia, survive with short-day and long nights. By artificially inducing long nights (12 hours of darkness), chlorophyll is decreased and we can trigger anthocyanin production in these type of plants. The Bracts of poinsettia bloom into red leaves.
Why do some Plants have Red leaves – Conclusion
In short, plants respond to changes in the environment, temperature, light, and other external conditions. The reddening of the leaves is an adaptive mechanism to cope with these changes. These are reasons why do some plants have red leaves?