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Why Leaves Turn Red.

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Darci Murakawa Bio 20 Lab Extra Credit 04/21/03 Why Leaves Turn Red 1. Until recently, a popular misconception concerning the functions of anthocyanins was the belief that by increasing the rate of metabolism in leaves, these pigment molecules are able to warm the leaves as well as protect photosynthetic structures from intense sunlight. In addition, it was also thought that anthocyanins are capable of protecting plant tissues against Ultraviolet (UV) radiation, based on observations that UV radiation has the ability to stimulate the synthesis of anthocyanin. However, in actuality these pigments are not well suited for functioning as protection against UV radiation, because they do not strongly absorb wavelengths (UV-B) ...read more.


However, anthocyanins can reduce photoinhibition by absorbing the wavelengths of light that are otherwise scantily absorbed by other pigments. Furthermore, while anythocyanins reside in the slightly acidic vacuoles of the cell, they remain very stable. Therefore, these resilient compounds can also protect the more fragile chlorophyll molecules within the chloroplasts. Besides serving as protection against photoinhibition, there is also evidence that anthocyanins inhibit superoxide production. When the leaves of plants absorb excess sunlight, the production of reactive oxygen species and free radicals is increased. Since free radicals are molecules with unpaired electrons, most are very reactive and unstable. When a point is reached where the naturally occurring antioxidants can no longer slake these free radicals, they can become destructive, obliterating the nearby biological equipment and may even result in the death of the cell. ...read more.


3. The colorful aspects of anthocyanins have been accentuated to serve as warning signals against predators such as insects and microbes. The red colors of the leaves alert predators and discourage them from consuming the leaves. However, this deterrence of herbivores during the autumn season would only be effective and provide a selective advantage to the plants if they could be protected in the following seasons as well. An experiment has shown that the autumn colors may serve as warning signals against autumn colonizing pests such as aphids. Therefore, the aphids do not lay their eggs on the trees containing the anthocyanins and thereby prevent the leaves from pest invasion the subsequent year, when the eggs would have hatched had the eggs been laid. ...read more.

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