Introduction
Ribulose bisphosphate carboxylase (RUBISCO), an abundant protein found in plant tissue, acts to capture and fix atmospheric carbon in the photosynthetic pathway to produce the sugars required for metabolism in plants and animals. The large subunits of the RUBISCO protein are encoded by chloroplast DNA. It has been demonstrated that RUBISCO concentration correlates positively with chloroplast number in leaf tissue (Hew et al, 1998).
Chloroplasts are a specialized plastid responsible for the mechanism and production of the chemicals required for photosynthesis. They are differentiated from the precursor proplastid. Two other differentiated forms of the plastid that have been observed are chromoplasts and leucoplasts. These three forms of plastids are capable of re-differentiation back to a proplastid, and then converting to another form, given environmental cues or stressors. In particular, chromoplasts are involved in the production and storage of pigment such as carotenoid, which is observed in leaves and flowers of plants.
A relationship between petal pigmentation and chlorophyll/carotenoid content has been illustrated in recent studies. For example, during development of the yellow-flowered, Lilium longiflorum, chlorophyll and carotenoid concentrations demonstrated an inverse relationship with chlorophyll content decreasing and carotenoid concentration increasing as the petals transitioned from green to yellow coloring (Juneau et al, 2002). In mature petals of chrysanthemum, the carotenoid content was elevated in the yellow-pigmented cultivar, but reduced in the white, colorless cultivar (Kishimoto & Ohmiya, 2006). We believe that the observed declines in chlorophyll content and increases in carotenoid content in the petal are associated with the re-differentiation and conversion of plastids from chloroplasts to chromoplasts. Moreover, this relationship between chloroplast and chromoplasts can be quantified by the abundance of RUBISCO protein in the petals of chrysanthemum. Specifically, we hypothesize that white chrysanthemum petals containing low-carotenoid will have high levels of RUBISCO protein, while orange and purple chrysanthemum petals containing high-carotenoid will have low levels of RUBISCO protein. We predict no variation in the RUBISCO protein levels in tissue extracts from the leaves of the individual plants. Furthermore, there will not be any difference in RUBISCO DNA levels in the tissues of the three plants as all have the same plastid genome, and will contain the equal number of plastids in both the leaves and petals..