Are red pigments present on leaves all year round?


Marit Knudsen, Jessica Hoskins, and Sarah Finnegan


CU Boulder, Fall 2006


Have you ever wondered exactly when the red pigments in leaves arise? Are red pigments in leaves manufactured in the fall or are they present all year round? From previous lab experiments, we concluded that green leaves have Chlorophyll a, Chlorophyll b, Carotenes, and Xanthophylls. Depending on the pigments color, a wavelength can be measured using a spectrometer to determine the pigments exact name. So, if leaves have several pigments than the red pigments should be present all year.


To test our predictions, we used equal proportions (6.22g) of red and green leaves from a Maple tree. We began to extract the pigment from the leaves using a mortar and pestle plus water to attain an equal concentration of both pigments. Unfortunately, the concentrations were not concentrated enough so we proceeded with an alternative. We then placed the 6.22g of each color into a blender containing 20 mL of Methanol to extract the pigment. We applied the pigment using a pipette. 160microliters of pigment was applied to each chromatography paper to guarantee pigment equilibrium. The chromatography paper then sat in 5mL of Acetone for 15 min to allow pigment separation.


Our results indicated that the red pigment was not present all year round, since the red pigment could only be seen on the chromatography paper corresponding to the red leaves. The green leaf chromatography paper had mainly green pigments. One potential problem, however, was our decision to perform the experiment so late in the fall season. When viewing our chromatography paper, red pigment can be observed from the green leaf, meaning that there were no completely green leaves remaining; they had traces of red because they were altering due to the season. Another potential problem was the allotted amount of time. Since our experiment was put on hold due to trial and error on how to extract the pigments, we were not able to use the spectrometer to determine which wavelength and pigment the red corresponded to.


Red pigment presentation was not present all year round, meaning our results were not consistent with our hypothesis. If the experiment were to be repeated, we would modify our hypothesis to: Are the relative concentrations of pigments different in red leaves compared to green leaves? When reading our hypothesis it seems quite obvious that red pigment would not be present all year round because red pigment means red color and we cannot see red in leaves all year round. The experiment by, Harvey, on why leaves turn orange? can be compared to our experiment. They determined that leaves contain other groups of pigments, one of which is anthocyanins for the orange color. So, if we performed a relatively similar experiment next time, we could determine the wavelength of red pigment and place the chromatography paper in a spectrometer to compare the concentrations of pigments on red and green leaves and determine the pigments name. If we wanted to take it even further we could add temperature as a variable to see the senescence of red leaves.