One of Over 700 Sites
	with Guide Alan Bruzel, Ph.D. Bio | Contact

Subjects

Acids Bases pH Analytical Chem Ask an Expert Astrochemistry Atomic Structure Biochemistry Chemical Databases Chemical Warfare Chemistry Clip Art Chemistry History Chromatography Computational Chem Convert/Calculate Crystallography Electrochemistry Environmental Chem Fun Sites General Chemistry Graphics Software How Things Work Inorganic Chem K-12 Grade Lessons Organic Chemistry Periodic Tables Physical Chemistry Polymer Chemistry Spectroscopy Stoichiometry Terminology Toxic Chemicals Subject Library  All articles on this topic

More Sites On This Topic

Apply to become a partner for this site.

Autumn Leaf Chemistry

Dateline: 12/21/98

By Alan Bruzel

Green plants derive their green coloration from chlorophyll, the pigment used in photosynthetic reactions. Green plants are green because chlorophyll absorbs blue and red light. Thus, the light we see reflected from chlorophyll-containing leaves is enriched in green wavelengths because the chlorophyll molecule has removed the light's blue and red components. Carotene and zeaxanthin – molecules we shall discuss later in the context of their contributions to the color of autumn leaves – strongly absorb blue and green light. Here, it is the orange and yellow components of light that are reflected. These molecules are most familiar in their role as the orange pigment of carrot (Daucus carota) and the yellow pigment of corn (Zea mays).

Chlorophyll a (green)

The abundance of chlorophyll in most green plants masks the presence of these other interesting leaf pigments. Some of them – carotenes and their oxidized derivatives, the xanthophylls (such as zeaxanthin) – are lipid-soluble and reside in the chloroplasts along with chlorophyll. Other pigments – the anthocyanins – are water-soluble and are found in the fluid-filled vacuoles of the plant cell. Only during autumn, when approaching cold weather stimulates deciduous trees to begin the process of leaf abscission, do these secondary pigments make their brief, but dramatic, appearance.

ß-Carotene (orange)

Zeaxanthin (yellow)

During the course of leaf abscission (about a two week period), chlorophyll production slows. Now, the stage is set to display those more stable pigments that, during the summer, contented themselves with a subordinate role. Birches, elms, hickories, and willows, because of their carotene and xanthophyll content, unfurl a yellow-orange fall foliage display. Anthocyanins such as quercetin and its metabolic products pelargonidin, cyanidin, and delphinidin, provide the red-orange (and purple) portions of the fall spectacle. These anthocyanins range from the brown-orange in oaks to the scarlet, red, and purple in red maple, red oak, and sumac.

Quercitin (brown-orange)	Pelargonidin chloride (scarlet)

Cyanidin chloride (red)	Delphinidin chloride (purple)

Weather conditions enhance the intensity of these fall colors. Chlorophyll disappears fastest when exposed to bright sunlight and cold temperatures. Dry weather, which increases glucose concentration in the plant cells, accelerates anthocyanin production. (Anthocyanins are present as glucosides.) Therefore, to unleash the full potential of carotenes, xanthophylls, and the various anthocyanins, dry, sunny days must be followed by cool (but not freezing), dry nights.

Recommended Web resources for additional information:

Carotene
Information from Molecules of Life, Imperial College of Science, Technology, and Medicine.

Chemistry of Autumn Colors
Detailed explanation from Bassam Z. Shakhashiri, University of Wisconsin at Madison.

Leaf Colors
Structures of compounds responsible for plant leaf coloration. From the University of Maine at Orono.

Preserve Colorful Beauty of Autumn Leaves
Article by Marianne C. Ophardt for the Tri-City Herald, Washington State, USA.

Why Do Leaves Change Color in the Fall?
Autumn foliage explanations and projects. From Science Made Simple, Inc.

Why Do Leaves Turn? It's Chemistry
Feature on fall coloration by Suzanne Delcamp. From Destination: Maine.

Why Leaves Change Color
Article from the State University of New York, College of Environmental Science and Forestry.

Previous Features

Subscribe to The Chemistry Newsletter
Name	Email