The Pigmentation of Fall Color
Question: Plant leaves are different colors because of pigments but why are some trees yellow in the fall, some are orange, some are red, and others have a combination of all these colors?
Answer: Leaf color is the product of the interaction of various pigments within a leaf. The color that we see is based upon two factors:
Types of pigments within a leaf
Amount of pigments present in the leaf.
Question: How do these pigments work and interact in such a way that they create such stunning colors?
Answer: It’s all about chemistry! Three classes of pigments determine leaf color:
Porphyrins
Carotenoids
Flavonoids
All three of these pigments have different chemistries which give them their differences in color. Within each pigment class there are certain compound types that reveal different colors.
Throughout the growing season leaves are typically green because the chlorophyll masks all the other pigments present in the leaf. As the chlorophyll breaks down in the fall, some of the other colors are revealed. Just like chlorophyll masks pigments, anthocyanins can mask carotenoids, making those pigments not visible. Plants whose leaves have high anthocynanin content will appear red. Orange colors tend to be caused by the presence of both anthocyanins and carotenoids. Leaves that have carotenoids but few anthocyanins will have a yellow color. So, this is the reason why your red maples turn red and your American beech trees turn yellow.
An interesting fact: Variegated leaves of certain plant varieties are due to the concentration of certain pigments in certain parts of the leaf. Basically, certain pigments gather near the edge while others gather in the middle and others group together here or there. Aren’t pigments cool?
