Differences in Carbohydrates, Polyphenoloxidase, and Photosynthesis Between Pinus strobus and Malus domestica.
 
 
 
 
 
 
 
 
 
 
 
By:
Brian Pillar
Roger Jump
Jason VanDenBrink
 
 
 
 
 
 
 
 
 
 
 
LBS 145 Biology II: Cell and Molecular Biology
Lab section Thursday 8:00-11:00 pm
Jeff Quinn and Rick Chalmers
Douglas Luckie, Ph.D.
10/17/02

Abstract:

Author: Brian Pillar

Our experiment revolved around a question. What differences exist between coniferous and deciduous trees? To answer the question, we looked for the carbohydrates present in the two tree species, the photosynthetic rates and pigments of each, and tested for the existence of polyphenoloxidase (PPO) in both coniferous and deciduous trees. For our coniferous sample, we used the needles of Pinus strobus, while Malus domestica, an apple tree, was the deciduous choice. As carbohydrate tests, we used a combination of Benedict’s, Barfoed’s, Selivanoff’s, Bial’s, and an Iodine test. Paper chromatography was used to test for the presence of photosynthetic pigments in the samples, and spectroscopy was used in comparing the photosynthetic rates of the species. To test for the presence and amount of PPO in the samples, an absorbance spectrum was taken at time intervals during a Catechol reaction. Benedict’s and Barfoed’s tests gave negative results with each sample, while Selivanoff’s test gave positive results after 1.5 minutes with both samples. A positive Iodine test result in the apple tree leads to the belief that starch is present, while negative results with the conifer implies the opposite. Bial’s test supported the existence of pentose-furanose rings in Malus domestica and hexose-furanose rings in Pinus strobus. Paper chromatography suggested the presence of chlorophyll b, carotene, and xanthophyll in both species, while photospectroscopy verified that Malus domestica had the higher photosynthetic rate. Our PPO tests seem to indicate that the enzyme is present in the apple leaf, but not in the pine needle.

Discussion:

Author: Brian Pillar

A number of questions regarding the differences between coniferous and deciduous trees stood as the foundation of our experiment. Do the two tree types produce the same sugars? Do deciduous trees have higher photosynthetic rates to be able to store energy for the winter? Are pine cones to be considered fruits? To simplify our experiments, we chose one type of pine tree, Pinus strobus, and one deciduous tree, Malus domestica, an apple tree, to use as our samples. We predicted that identical carbohydrates would be present in the two tree species, that our deciduous tree would indeed have a higher photosynthetic rate than our coniferous sample, and that the pine sample would contain enzymes found in fruits, supporting the idea that pine cones could be considered a type of fruit. We began our experimentation with carbohydrate tests.

Our first carbohydrate test was Benedict’s test, which tests for the presence of reducing sugars in a sample (sugars containing a free or potentially free aldehyde or ketone group). Upon completing the procedures for Benedict’s test, we found no presence of a red precipitate in any sample of either Malus domestica or Pinus strobus, indicating that neither sample contained a reducing sugar. (Course Pack, 64)

Barfoed’s test was our second carbohydrate test, which looked for the presence of monosaccharides in our samples. As in Benedict’s test, a red precipitate would result from the experiment to show a positive result (presence of a reducing monosaccharide), and none of our tree samples showed even a slight amount of precipitate. These results make perfect sense, since Benedict’s test lead to the belief that no reducing sugars were present in the samples, so it would be expected that no reducing monosaccharides would be present. (Course Pack, 64)

The next carbohydrate test run in our experiment was Selivanoff’s test, which determines if a ketose is present in the solution. A red color change in under a minute would indicate the presence of a monosaccharide ketose, a change in approximately one minute indicates that a disaccharide ketose is present, and a change in over a minute signifies that an aldose is present. In the two trials run, both the samples of Malus domestica and Pinus strobus turned a red color in approximately 1 minute, 30 seconds, leading to the belief that only aldose is present in the leaves of each tree. (Course Pack, 65)

After Selivanoff’s test, an Iodine test was run to test for the presence of starch in either solution. Our controls indicated that a change from the original color of the solution to a blue-black color would confirm the presence of starch in the solution. The addition of Iodine solution to our pine sample showed no change, but addition to the apple sample turned the solution a red-brown color. We consider this to be a positive change and confirm the presence of starch in the leaves of the apple tree, and relate the difference in color (red-brown instead of blue-black) to the difference in color between our sample solution and control solution. (Course Pack, 65)

Our final carbohydrate test was Bial’s test. Bial’s is a test of furanose rings, in which a color change to green/olive demonstrates the presence of a pentose-furanose, a muddy brown color signifies a hexose (or higher)-furanose, and no color change for a pyranose sugar. Our sample for Malus domestica turned an olive color, indicating that a pentose-furanose sugar was present, and the Pinus strobus sample turned muddy brown, the color change for a hexose-furanose or higher chain. After this final carbohydrate test, we moved into the photosynthesis tests. (Course Pack, 66)

In the photosynthesis portion of our experiment, we first used paper chromatography to determine which photosynthetic pigments were present in our samples. Both Malus domestica and Pinus strobus had similar results, and when compared with the results for our controls, it was determined that each contained chlorophyll b, xanthophyll, and carotene. (Course Pack, 72)

We then tested the absorbance spectrum of our samples to determine if either species had a higher photosynthetic rate. Throughout the visible spectrum, our apple tree sample had a higher absorbance than our pine tree sample, indicating a greater concentration of photosynthetic pigments in the deciduous sample than in the coniferous sample. When looking at this information and taking into account that apple leaves have a much greater surface area than do pine needles, we are led to the belief that there is a higher rate of photosynthesis in Malus domestica than in Pinus strobus. (Course Pack, 73)

Our final experiment was to determine whether or not the enzyme polyphenoloxidase (PPO) was present in either sample, and how much of the enzyme was in each sample relative to the other sample. To do this, we tested the absorbencies of both samples over time during a reaction with Catechol, known to react with PPO. The absorbency of the apple solution increased with time, denoting that a reaction was taking place and confirming the presence of PPO in the solution, while the absorbency of the pine solution jumped around sporadically, leading to the belief that polyphenoloxidase was not present in the solution. (Course Pack, 82)

The results of our experiments provide evidence that some of our predictions were correct, while other predictions were the opposite of what was found. Different types of carbohydrates were found in the two tree species, contradicting our prediction that Malus domestica and Pinus strobus would contain the same types of sugars. In regard to photosynthesis, our prediction that the rate in the apples trees would be higher than the rate in the pine trees was supported by our tests with absorbencies and our comparison of surface areas. This further confirms our belief that the efficiency of apple trees is what gives them enough energy to survive the winter and re-bud in the spring, while pine trees must carry out photosynthesis throughout the year. Our predictions dealing with polyphenoloxidase were also refuted by our findings. We had originally believed that the enzyme would be found in both samples and show that the pine cone could in fact be considered a fruit. Lack of the presence of PPO in Pinus strobus, however, negates this belief, leading to the conclusion that pine cones, unlike apples, cannot be considered fruits.

Figure 11:

This is a graph of light absorption versus time. This graph is very important because we believe it represents the visible effects of the reaction of Catechol with PPO thus verifying the presence of PPO in the apple tree leaves. were used to help us determine which wavelengths were most useful to the chlorophyll in the leaves. It is to our understanding that the higher absorption readings mean that these wavelengths are most useful to the apple tree leaves.