Carbohydrate, Pigment and Enzyme Analysis Differentiates Lycopersicon esculentum Parts by Organic Function

By:

Team Wilford Brimley

Shawn Brandenburg

Zachariah Hicks

Lauren Polovich

Angela Wright

For:

LBS 145

Lab Section M2

Dr. Douglas Luckie

October 21, 2002

Abstract

By Lauren Polovich; revised by Zachariah Hicks

As in many living organisms, plants have certain structures that are specialized to perform specific tasks that are essential to the life and success of the plant. In many cases, however, people know relatively little about what makes these structures unique and able to perform their jobs well. In our investigation, we looked closer at the stem, leaf, and fruit of the Lycopersicon esculentum (Mueller, 2002), or common tomato plant, in order to determine what about their organic composition makes them uniquely designed for their particular job. To do this we performed a series of qualitative analyses to determine the carbohydrate content, photosynthetic pigments present, pH of each component, as well as the presence or absence of polyphenoloxidase. We predict that some common sugars will be found throughout the tomato plant, while other types of sugars will be found only in certain parts of the plant. We expect to find more types of storage specific sugars, such as starch, present in the fruit compared to the rest of the plant. Concerning the pigment aspect of our experiment, we feel that we will find varying concentrations of pigments in each of the three tomato plant components. With regards to enzymes, we hypothesize that PPO will be found in all parts except the fruit. Most of our results supported our hypothesis, showing that the different structures actually had organic compositional differences which would logically make them better suited for their specific tasks.

Discussion

by Shawn Brandenburg, Zachariah Hicks, and Lauren Polovich; revised by Shawn Brandenburg, Lauren Polovich, and Angela Wright

In our experiment, we set out to determine if the different organic compounds found within three different structures of a tomato plant accounted for the variation in physical form and specialization of function. We hypothesized that the stem, leaf, and fruit of the tomato plant contained some organic compounds that were present in all three structures while also containing a number of organic compounds which were unique to only one or two of the specimens. We predicted that reducing sugars would be found in all three structures, however because of our limited means of testing, we were unable to adequately determine exactly which specific reducing sugars were present in each component. Another initial prediction made involved photosynthetic pigments of each structure. We suggested the three structures contained different concentrations of pigments based on their specific functions and roles. We predicted that a similar distribution of the four main types of photosynthetic pigments would be present in both the stem and leaf components of the plant, however, only the carotenoid series of pigments would be present in the fruit. The final prediction we made involved the enzyme polyphenoloxidase (PPO). We predicted that the stem and leaf would contain small amounts of PPO while the fruit contained no PPO.

After performing the various carbohydrates tests, we were able to examine the data and draw conclusions based upon the color changes that occurred as a result of the various reactions that took place in each of the tests. In the case of the Benedict’s test, because each test tube produced an orange/red color precipitate, it supports the prediction that reducing sugars were present within each sample. The strength of the color of the orange/red precipitate varied from sample to sample, with the strongest color corresponding with the tomato sample. For Barfoed’s test, opposing observations took place in that none of the specimens formed an orange/red precipitate indicating that reducing sugars that are monosaccharides are not present within each solution. The results from Selivanoff’s test oppose our predictions as well, in that all of the solutions turned to red in approximately one minute, indicating the presence of disaccharide ketoses. Bial’s test suggests that the sugars within the stem are furanose sugars while the sugars in the leaf and fruit are pentose-furanose sugars because of the differing color changes observed in each test tube. The last carbohydrate test we performed, the iodine test, also did not verify our prediction that starch was present in all three structures because none of the solutions in the test tubes turned to a blue-black color (Luckie, 2002).

After extracting the photosynthetic pigments from each sample, we performed a paper chromatography test and prepared an absorption spectrum for each of the three samples. From the paper chromatography test, we thought that, due to the variations in band size and intensity of each pigment, each structure contains a different concentration of the photosynthetic pigments than the other two structures. Because of the lone presence of the orange-yellow pigment in the fruit chromatography strip, we can infer that only carotenoid pigments are present in this structure. However, in the stem and leaf chromatographs, there were thicker bands of pale green and blue green, verifying that there was a greater concentration of both chlorophylls a and b than carotene and xanthophyll. The absorption spectrum, however, did not seem to support these results. Because all of the plant components displayed peak absorbance readings within the same range, we cannot conclude any differences in the wavelengths of light most effectively absorbed for each structure. This is most likely due to the fact that we did not have the means to accurately separate the different photosynthetic pigments from our stock solutions for analysis, as well as the fact that our stock solutions were prepared from samples which were frozen and not fresh off of a living plant.

For our experiment involving testing for the presence of PPO in each of the samples, our data suggests that PPO is not present in any structure of the plant and thus it did not confirm our prediction. We derived this conclusion from the fact that the catechol did not cause a change in color in any of the samples (Luckie, 2002).

Based on our experimental results, some of our predictions were confirmed. Since our predictions were based upon our understanding of the symbiosis between the different parts of the tomato, our results confirmed that each part of the tomato plant is a specialized component integral to the successful operation of the whole. The stem for instance contains many carbohydrates and sugars. Xylose, a reducing sugar, which may be found in the stem, is mainly used for structural support (“Nutritional Information” 2002). The apparent presence of chlorophyll b in the stem seems to support the idea that in addition to providing structural stability, the stem also participates in photosynthesis, thus providing the plant with energy.

In contrast, the leaves seem to be specifically geared for photosynthesis. Our results were inconclusive with our hypotheses regarding the presence of starch within the leaf structure. This can possibly be explained by the fact that our respective plant structures remained frozen and unanalyzed for some time before we were actually able to complete our experiments, allowing time for any starch chains which might be present to be broken up into their glucose monomers, therefore producing negative results for the iodine test for starch. Despite these results, leaves are known to contain starch and chlorophyll, both of which are stored in the chloroplasts. The photosynthetic pigment analysis confirmed the presence of the chlorophyll, and further investigation using a more sensitive analysis than that of the iodine test could prove the existence of starch in the leaf structure.

Our negative iodine test results also seemed to disprove what we know of the presence of starch within the fruit structure of the plant as well. We know the fruit of the plant acts as a starch storage system for the seeds produced by the tomato plant. Because of the presence of starch and the lack of chlorophylls a and b, we can assume that the primary function of the fruit is to provide developing seeds with nutrients until they can germinate (Campbell, 2002). Once again, a more sensitive test for the presence of starch could provide more strength for our argument about the function of the fruit structure of the tomato plant. From our research we were also able to suggest that there are significant health benefits from the consumption of the fruit of the tomato plant. The presence of carotenoids, a family of photosynthetic pigments which includes lycopene which has been recently linked to cancer prevention, gives one example of just how nutritionally valuable tomatoes can be (Did You Know 2002).

Figure 12

Figure 12 - Absorption spectrum analysis for the fruit, stem, and leaf. This data set shows the level of absorbance present at the specified wavelength. The measurements were made using a photo spectrometer. The stock solutions were tested for transmittance at 445nm. The % transmittance found for the fruit, stem, and leaf was 27.2%, 16.1%, and 18.2% respectively. The general trend of a decrease in absorbance with an increase in wavelength remains the same for all three components, however, small perturbations make each absorption curve unique.

ã 2002 Team Wilford Brimley in conjunction with Zach Enterprises.