James Madison University
BIO 480 Webposter
Introduction
Ribulose-1,5-bisphosphate carboxylase/oxygenase, also known as Rubisco, is found in plants, making up 40-80% of proteins found in leaf tissue. Rubisco plays an important role in the photosynthetic pathway. Rubisco acts as an enzyme which captures and fixes carbon at a slow rate. In addition, Rubisco can bind O2 instead of CO2. Since Rubisco is not an efficient fixer of CO2 and works slowly as an enzyme, Rubisco is abundant in plant tissue.
Photosynthesis is broken up into two stages, light dependent and light independent reaction. During light dependent reactions ATP and NADPH are produced. The light independent reactions utilize ATP and NADPH produced during light dependent reactions in the Calvin cycle (Figure 1). In the Calvin cycle, Rubisco fixes CO2, producing 3-carbon sugars which are used to make glucose (Alberts et al., 1998) (Figure 1).
Figure 1. Summary of the process for glucose production, including both light dependent and light independent reactions.
Image courtesy of: http://www.biologycorner.com/resources/photosynthesis-overview.gif
Rubisco is a useful protein to study since it is abundant and universally found in nearly all plants. The Rubisco protein is composed of eight large subunits and eight small subunits. The large subunits are encoded by the chloroplast genome. Rubisco large subunit (RBCL), 55 kDa, was the focus of this experiment (Rife, 2007).
Our experiment aimed to understand the changes of RBCL expression in Chrysanthemum x morifolium plants. Chrysanthemum x morifolium, commonly called chrysanthemums, are perrenial plants which flower in the fall. They bloom in a variety of flower styles and colors. For our study we chose yellow flowering Chrysanthemum x morifolium (Figure 2).
Figure 2. Chrysanthemum x morifolium.
Image courtesy of: http://images.inmagine.com/168nwm/photodisc/mi121/mi121079.jpg
Previous studies indicate that in rice leaves, RBCL DNA increases after leaf emergence, reaches a maximum before full expansion of leaves and declines to half the maximum during degradation (Suzuki et al, 2001). Also, in petunia and carnation petals, it was observed that RUBISCO and other chloroplast associated proteins show a rise in abundance during enlargement of flowers and lessen during degradation (Vainstein and Sharon, 1993).
Based on the literature describing RBCL DNA abundance for flowers and leaves during development, we can generate a hypothesis that in the leaves and stems of a Chrysanthemum x morifolium plant that is just beginning to bud, a low amount of RBCL DNA will be observed; in a plant that is growing some flowers, which are enlarging, levels of the protein and DNA will be great, and in a plant which has already bloomed and is beginning to degrade, levels of RBCL DNA will be about half the maximum. To test this hypothesis, leaf and stem tissues from Chrysanthemum x morifolium plants of increasing physical size and stage in growth will be analyzed for the presence of RBCL expression.