MadSci Network: Botany

Re: Why do plants that are growing in the dark turn yellow?

Date: Wed Feb 1 19:53:33 2006
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 1138655118.Bt

Yellowing of leaves is called chlorosis. The green pigment in plants is
chlorophyll. In most plants, chlorophyll synthesis requires light. Gymnosperms,
such as pines, are an exception and can form chlorophyll in the dark.

For most plants, no new chlorophyll can be made in the dark. The existing
chlorophyll has a limited life and eventually degrades. When the chlorophyll
degrades, it reveals the yellow cartenoid pigments that were there all along but
just masked by the green chlorophyll.
The degradation of chlorophyll is also the reason why tree leaves change color
in the fall.

If you need details of the biochemistry of chlorophyll synthesis, do a search for chlorophyll biosynthesis.


 Why do the leaves change color in the fall?

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