Spectrophotometer shows Quercus coccinea absorbs more infrared light than Ferocactus wislezzni

By Chad Mackowiak, Kelly Gerbe, Evie Houghton, and Kristen Finos

Abstract:

The C₃ pathway is a type of photosynthesis in which CO₂ is first incorporated into a 3-carbon compound, i.e. oak tree. Crassulacean acid metabolism (CAM) photosynthesis is a variation found in plants in dry climate conditions. This pathway has a temporal difference from C₃ photosynthesis: the CO₂ necessary for photosynthesis is stored at night and released during the day for carbon fixation, i.e. cacti. C₃ and CAM plants store sugar in the form of glucose, use infrared wavelengths and contain the enzyme polyphenoloxidase (PPO), capable of catalyzing the oxidation of certain organic compounds. The question is, what is the major difference, if any, between the concentrations and comparisons of substances used in C₃ and CAM plants? To find our answers, these three similarities each involved a separate and specific test. The presence of glucose and starch were checked through a series of Benedict’s, Barfoed’s and Iodine tests. The findings of these tests determined that glucose was present in both plants and that it was not stored as starch in either plant and confirmed that the sugar was a monosaccaride. The comparison of wavelengths was determined by an absorption spectrum. The results indicated that C₃ plants absorbed more infrared light than CAM plants due to either a chemical or structural difference in chloroplasts. Finally, we tested for the presecnce of the enzyme polyphenyoxidase in the CAM plant. The test illustrated that our CAM sample did not contain PPO.

Discussion:

Ferocactu wislizenii (CAM - cactus) and Quercus coccinea (C3 – oak leaves) plants each differ in many ways. These differences are shown in many characteristics, such as sugar production, the presence of different enzymes and differences in photosynthetic pathways. Many factors affect the outcomes of these characteristics. During this research project, we predicted that CAM and C3 plants would have glucose present because this sugar is what is produced by the Calvin Cycle during photosynthesis. We then predicted that C3 would absorb more infrared light than CAM because C3 plants did not have an outer shell that reflected infrared red. Finally we predicted that PPO would be present in CAM because CAM plants needed it to oxidize other organic compounds that lived near the CAM. Thus, concluding that CAM and C3 had significant differences between each plant.

Based on our results from the sugar tests, Barfoed’s, Iodine, and Benedict’s, the CAM plant (Ferocactus wislizenii) and the C3 plant (Quercus coccinea) had glucose present. Plants produce sugar during photosynthesis by using light energy, water, and carbon dioxide to create their own food. The Benedict’s test showed that the cactus and the C3 produced a red precipitate confirming that it contained a free aldhyde or ketone group while Barfoed’s Test showed a red precipitate too. This test confirmed that the sugars are monosaccharides. The Iodine Test was used to show whether or not starch was present in each plant. The results of this test showed that starch was not present in either the CAM plant or the C3 plant. Both the CAM and C3 plants stored glucose because without glucose the plant would not receive nutrients that help it survive; glucose being a major nutrient to the plant. Despite different ways CAM and C3 plants fix carbon and opposite environments they live in, these plants produce and store the same sugar regardless of their diversity. We did not, however, get to determine the levels of glucose in each plant. The data would be more accurate and would give more information about the plants if we had tested the levels of concentration of glucose by centrifuging the precipitate and weighing it. This probably would tell us that CAM stores more glucose than C3 because CAM is exposed to harsher environments, therefore, causing it to stock more glucose.

The sun provides the Earth and all its inhabitants with light at all different wavelengths. Only a certain range of light can actually be seen by human eye. This is referred to as the visible light spectrum. But just because we can not see light at certain wavelength does not mean it is not there. Infrared rays exceed the visible light spectrum making it possible to see without the aid of technology. Plants can use this infrared, as was as visible light, to maximize their photosynthetic potential (Gibson, 1998). Unique pigments in the chloroplast of plant cells are responsible for soaking up and harvesting light at numerous wavelengths. In a study done by Arthur Gibson on the characteristics of CAM plants, he stated that desert plants, like the cactus, that are exposed to enduring days of intense sunlight soak up less infrared light than other non – desert plants (Gibson, 1998). This study inquired whether or not less infrared light was absorbed in the chloroplasts of desert plants because they lacked a sufficient amount of certain pigments, or other physical obstructions, like cactus hair, was absorbing some of the infrared light (Gibson, 1998).Our next test, photosynthesis, examines this hypothesis. In our photosynthesis test, we used infrared light to determine that C3 absorbed more light than CAM for wavelengths of light for centrifuged and normal solutions from 800nm to 900nm. The slight difference in absorbance of infrared light could be because the CAM plant has fewer pigments that absorb the infrared light than C3 plants.

Finally, our last test was an enzyme test. For this test we had to test different specie of cactus because our original solutions became rotten. This test tested CAM (Copiapoa) for the presence of polyphenoloxidase (PPO). Please note that this test was done with a different cactus because our first solution was rotting. PPO is an enzyme that catalyzes the oxidation of organic material. PPO was not, however, present in the CAM. Our original hypothesis that PPO was present in CAM was incorrect. When CAM was exposed to the catechol it did not turn an expected red/brownish color that shows the presence of PPO. We believe the reason for this was that polyphenoloxidase is “inhibited by compounds that complex with copper” and is “inhibited by benzoic acid with respect to catechol” (Bouchilloux, 1963). CAM plants are in such harsh environments that these enzymes are not necessary for it to live and grow.

We do, however, acknowledge that human error can affect the outcome of these tests. The correct substances or amounts of substance used for these tests could have been neglected. If the slightest amount was added or lost during any process then the results could be “royally screwed up.” Also the solutions could have been altered with the passing of time. It might have been beneficial to produce fresh solutions for each test. The temperature at which the solutions were stored could have been too cold or too warm for the solutions to be exposed to for a prolonged amount of time. If the refrigerator was not cold enough or if it was too warm then the solutions would react in a negative way, therefore, rotting and causing the results to be altered. Also, we are not endorsing that our constituent specimens represent all C3 and CAM photosynthetic plants, rather only the species we have referenced in this lab.

There are many tests we would have also like to do to further compare the differences in CAM and C3 plants, however, we were not able to these tests because of our laboratory constraints. If it were possible we would have liked to have tested for more enzymes other than polyphenoloxidase. An enzyme called DNA photolyase catalyses the repair of UV-induced DNA dimers. It would have been thrilling to see if CAM plants contained more of this enzyme because of there environment they are exposed to more UV light than C3 plants. We would have also liked to do more tests on the carbohydrates of the plants. It would have been exciting to test the concentrations of certain sugars and compare the results.

In conclusion, we determined that CAM and C3 had differing results for the infrared light; however, their results for the glucose test were similar. They both had glucose present in their system. They also both absorbed light; however, C3 absorbed more infrared light than CAM. The PPO test also concluded that polyphenoloxidase was not present in the CAM plant. Both plants are, obviously, very different in many ways while they are also similar in others. Each plant must adapt to their unique environment and live and grow accordingly. Without their differences then both plants would probably not survive their environments.