Introduction
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Photosynthesis is the process by which plants change light energy into usable chemical energy. Photosynthesis occurs in chloroplasts, where the Rubisco enzyme captures carbon dioxide and fixes it into molecules used in the photosynthetic pathway. Rubisco is a protein made up of eight small subunits and eight large subunits, where the smaller subunits are encoded by the nuclear genome and the larger subunits are encoded by the chloroplast genome. Since the turnover rate at which Rubisco catalyzes fixed carbon dioxide into carbohydrates is very slow, the amount of Rubisco enzyme in plants builds up, therefore making Rubisco is the most abundant protein on earth (Lodish et al, 2007)
Rubisco DNA can be found in chloroplasts, chromoplasts, and leucoplasts, which are located in different parts of the plant. Chloroplasts are plastids containing the green pigment chlorophyll and are found in green plant parts used for photosynthesis, such as stems and leaves. Chromoplasts are pigmented plastids used for flowers and are found in petals. Leucoplasts are colorless plastids that are found in plant parts that are unexposed to the sun, such as seeds (“Plastids”). Since these plastids are found throughout the plant, we hypothesize that Rubisco DNA will be found in similar amounts in the leaves, stems and petals.
We hypothesize that Rubisco would be more expressed in the plants’ leaves when compared to the plants’ petals and stems, since their major role is to capture sunlight used in photosynthesis. Smith et al. also states that the primary function of leaves is to absorb and process sunlight for photosynthesis. Previous studies with the pea plant, Pisum sativum, have also shown that the mRNA for the Rubisco enzyme is greatly abundant in leaves when comparing it to stems, petals, and pods (Gutteridge and Gateny, 1995). Since it has been found that more mRNA was present in the leaves, there would be a greater likelihood of finding protein in the leaves since mRNA is used in protein synthesis. We also hypothesize that there would be the least amount of Rubisco protein in petals. Stems also contain chloroplasts and are capable of photosynthesis, along with leaves (Davidson, 2004). Therefore, we believe that Rubisco protein would be more abundant in stems than in petals.
The focus of this study is to understand the many changes of genetic expression of the larger subunits of Rubisco in a flowering plant, mainly leaves, stems, and petals. In this experiment, we will be using samples of petals, stems, and leaves from plants of the genera Chrysanthemum and Dianthus. The concentrations of DNA will be studied using Real-Time PCR and gel electrophoresis analysis. The concentrations of protein will be studied using Western Blot analysis. By comparing the concentrations of protein and DNA in the petals, stems, and leaves of each plant, it can be determined whether the data supports our hypothesis.