Introduction

         Ribulose bisphosphate carboxylase (Rubisco) is made up of small and large subunits, eight of each. These aid in obtaining carbon for the photosynthetic pathway. Rubisco is the most abundant protein on Earth and is found mostly in plant leaves. The nuclear genome encodes the small subunits and the chloroplast genome encodes the large subunits of Rubisco. The expression of both genes is influenced by light.

Figure 1: The Reactions Catalyzed by Rubisco

Rubisco can catalyze a reaction by using oxygen instead of carbon dioxide, as shown in figure 1. However, this does not work in all scenarios, e.g. hot climates, so some plants fix carbon dioxide on their own to avoid this problem. (Introduction to the Rubisco Lab Project)

            Rubisco is located in the pyrenoid in the chloroplast of plants. It is regulated by varying CO₂ levels. When CO₂ levels vary, the Rubisco amounts change in the pyrenoid. With higher levels of CO₂, 40% of the Rubisco is associated with the pyrenoid. At ambient levels of CO₂, 90% of the Rubisco becomes localized with the pyrenoid. All of the pyrenoid Rubisco should be active in order to account for the amount of CO₂ fixation occurring.

         Colocasia esculentum, due to its leaf shape, is generally known as the elephant ears plant. It is of the Araceae family and is a type of monocot, known as the Cocoyam. This plant grows from three to seven feet tall and the leaf blades can reach a width of up to two feet (60cm). The environment best suited for growth of Colocasia esculentum is at tropical temperatures with warm, moist soil. An abundant water supply must be available with suitable drainage. If ingested without being cooked, Colocasia esculentum can cause burning and swelling of the lips, mouth, tongue, and throat, thus leading to difficulty with speech. The toxic principle found in this plant is calcium oxalate crystals (Poisonous Plants of North Carolina). It is eaten in countries such as India and Nigeria. In the south eastern part of Nigeria, Colocasia esculentum is a major arable crop. Cocoyam serves as a good source of energy with an abundance of carbohydrates (Pakistan Journal of Nutrition). We chose to use this plant for our experiment out of sheer intrigue. When full grown, the leaves are beautifully enormous and are quite appealing to the eye.

            It was hypothesized that various parts of Colocasia esculentum (elephant ear) would contain different amounts of Rubisco. The first hypothesis was that the leaf would contain the most chloroplast DNA, followed by the stem and root, respectively. Since the leaves receive the most light and most photosynthetic activity occurs there, it was hypothesized that they would contain the most Rubisco followed by the stem and root in protein amounts.

Methods                                        Results                                        Discussion

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