Determining absorbance of various wavelengths of light for pigments present in Coleus plants

Determining absorbance of various wavelengths of light for pigments present in Coleus plants

Joseph Yung (King Yung)

212831426

Adrian Ionescu

Section M 11

February 5, 2014
Absorbance Table

Absorbance Spectra

Figure 1: Absorption spectra of pigments found, through chromatography, within Coleus plants. The different wavelengths of light were determined by the use of a spectrophotometer

Questions

1. The “total pigment” absorption spectrum provides us with the conclusive amount of light that was absorbed at that specific wavelength. Of which is made up through specific pigments that contribute to a segment of the total pigment absorption.
2. The maximum absorbance peaks for each pigment were dependent on the wavelengths of light they were exposed to. The green pigment had a maximum absorbance peak of 0.2 while the light purple pigment had a maximum of 0.11. The yellow pigment only had a maximum absorbance peak of 0.3 and lastly, the total pigment had a peak of 0.15.
3. The maximum absorbance peaks of the pigments found in my experiment and those in published in literature are very similar. Rabinowitch and Govindjee reported that the peak absorption rates for chlorophyll molecules have 435nm and 675nm peaks. This is very similar to the results found in my experiments as one pigment had absorbance peaks at 460-500nm and around 660nm. The same results were found in the other pigments with very similar wavelengths reported in publications and my results.
4. Based off of the results and observations that were also listed in question 3, we can determine the likely identity of the pigments. As previously stated, chlorophyll has a peak absorbance rate of approximately 435nm and 675nm (Rabinowitch and Govindjee 2013). In my experiment the green pigment reported very similar wavelengths and it can most likely be attributed to chlorophyll. As for the light purple pigment, absorbance peaks were reported in wavelengths 360nm and 580nm. This is almost identical to the absorbance peaks listed in Gould et. al literature of anthocyanin which were 370nm and 580nm. Lastly, the yellow pigment was more difficult to determine, as it had zero absorbance after 540nm in the spectrophotometer. By looking at the physical attribute of its color, one can assume that it is xynthophyll as that pigment is yellow in colour (Rabinowitch and Govindjee 2013). The physical attributes can also be used to support the identity of the other pigments in the experiment.
5. The most polar pigment is most likely the light purple pigment since it had the lowest Rf value. Also, because the chromatography paper is polar, and polar molecules are attracted to other polar molecules, this results in it moving less of a distance as compared to less polar molecules.
6. The least polar pigment is most likely the yellow pigment since it had the highest Rf value. The solvent is non-polar and non-polar molecules dissolves in a non-polar solution first. This further supports this point since it moved the furthest from the front, which must mean that it had dissolved the fastest out of the pigments.
7. Pigment differences exist between many plants due to the many different environments in which plant species grow. Seeman et. al reported that differences in chlorophyll ratios can be attributed to the amount and/or intensity of light that a plant gets. This can be easily seen in real world situations such as plants that live around the equator and those that are further away who do not get as intense and direct light. Taking an evolutionary standpoint, plants who have more of certain pigments within certain environments will have a higher fitness than those that do not. This leads them to have more ‘offspring’ passed down to the next generation. Also, it is important to note that types of pigments can very due to changing environments over the course of the Earth, which will potentially change the efficiency of a certain pigment that a plant may have. Once again, natural selection will take place and a specific pigment will become more apparent in a species.
8. If I were to use the tissue of a carnivorous plant as my sample, I would expect to see that there are not too many pigments within the plant, which also means that there would not be too much absorption of light in the spectra. Although there are still the presences of pigments, the amount of total pigments, I think, would be lower than a normal plant. This is because carnivorous plants largely get their nutrients for survival through small insects and bugs, as opposed to light (Slack 1988). This diminishes the need for a large amount of pigments within the plant, which can help determine the differences in pigments and absorption spectra.

References

Gould K, Kuhn D, Lee D, Oberbauer S. 1995. Why leaves are sometimes red. Nature. 378(241): 241-242

Rabinowitch E, Govindjee. 2003. Photosynthesis. New York: John Wiley & Sons. p. 102-123.

Seemann J, Sharkey T, Wang J, Osmond B. 1987. Environmental Effects on Photosynthesis, Nitrogen-Use Efficiency, and Metabolite Pools in Leaves of Sun and Shade Plants. Plant Physiology. 84(3): 796-802

Slack, A. 1988. Carnivorous Plants. Great Britain: First MIT Press. Print.

References: Gould K, Kuhn D, Lee D, Oberbauer S. 1995. Why leaves are sometimes red. Nature. 378(241): 241-242 Rabinowitch E, Govindjee. 2003. Photosynthesis. New York: John Wiley & Sons. p. 102-123. Seemann J, Sharkey T, Wang J, Osmond B. 1987. Environmental Effects on Photosynthesis, Nitrogen-Use Efficiency, and Metabolite Pools in Leaves of Sun and Shade Plants. Plant Physiology. 84(3): 796-802 Slack, A. 1988. Carnivorous Plants. Great Britain: First MIT Press. Print.