Saturday, October 9, 2010

Fall Color Pigmentation

Nature Watch
By Susan Thurn,
Cable Natural History Museum

As we go through another peak season of autumn colors, the mornings begin with a blaze of color as the sun shines on the leaves, and the night’s silence brings comfort and solace. The colors this year were golden! But just what do all those colors do?

First we have the magical chlorophyll, the special ingredient that converts sunlight into sugars. Chlorophyll absorbs red and blue parts of the light spectrum, so it reflects to our eyes as green. Just as sunlight can fade our fabrics colors, or damage our skin, sunlight also causes chlorophyll to break down. Green plants continually create new chlorophyll throughout the warm summer. Fall’s cooler temperatures slow down chlorophyll production, which is when leaves begin showing other colors than green.

The orange color we have seen so much of this fall season is the same color of many fruits and vegetables such as tomatoes, carrots, sweet potatoes, marigolds, pumpkins and even egg yolks and butter. These orange pigments are called carotene. In our bodies, carotene is essential for normal vision, for healthy skin and organs. It is believed to have protective properties against some types of cancer, and against ultraviolet rays of the sun. In plants, carotene absorbs sunlight energy, but instead of photosynthesizing like chlorophyll, it just passes the energy on to the chlorophyll. Carotenes are not damaged as easily by sunlight, so when chlorophyll disappears from the leaves in the fall, the carotene color is left behind for a longer time.

Finally, there are the anthocyanins, which show red and purple colors. These pigments are formed when plant proteins interact with sugars inside the plants cells. The colors formed are based on their acid levels. If the sap in the cells is acidic, the red colors will be brighter, and if less acidic, the color will show more purple. Anthocyanins do not play a part in photosynthesis, so there is some debate over what their purpose is in the leaves. Some believe that they provide a sunscreen for the leaves, allowing the leaves to reabsorb nutrients before they drop to the ground. Anthocyanins are also water-soluble, so can change the freezing point in the leaves, and so may protect a plant’s water supply. Blueberries and so many other fruits and vegetables are filled with anthocyanins, and also have healing powers. Whatever their role, they bring beauty to the colored autumn horizon.

Such a treat another fall has brought us. It brings joy to our eyes, and the rustle of the drying leaves brings a different music to our ears. Additionally, they can bring a variety of colors in our yard, gardens, and kitchens! Enjoy the benefits of these pigments in our foods, and enjoy the wonder of the seasons from our own back yards!

For over 42 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and new exhibit, On Lake Owen: The Art of Walter Bohl, in Cable at 13470 County

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