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            Carbon fixation occurring during the photosynthetic processes of plants is catalyzed by the enzyme Ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco). Rubisco, a multimeric complex, is comprised of 8 small subunits encoded within nuclear DNA,  and 8 large protein subunits, encoded with chloroplast DNA (Rodermel). The large Rubisco subunit (RBCL) is encoded within the chloroplast genome (Biology 480, 2008). Nassuth et al., (2005) have shown RBCL to be expressed in both the fruit and leaves of field and greenhouse grown tomato plants using reverse transcriptase-PCR. However, the level of RBCL expression was not quantified. The presence of RBCL in tomato plant tissues is indicative of Rubisco presence in the tissues.

During the maturation of the tomato fruit, chloroplasts within the fruit differentiate into chromoplasts while maintaining the same genetic information (Boyer et al., 1986). If the Rubisco gene levels remain the same in chloroplasts and chromoplasts, a varied amount of Rubisco protein indicates variation in gene expression. This study was designed to identify whether the expression of Rubisco differs in the tomato fruit of field grown Lycopersicum pimpinellifolium as they mature. Our hypothesis is that as tomato fruit ripen the amount of plastid DNA will remain the same throughout the differentiation process, but less Rubisco protein will be produced in the mature fruit. Rubisco expression and chloroplast DNA levels of the tomato leaf tissue was analyzed to compare the photosynthetic ability of tomato fruit with that of a highly photosynthetic tissue such as the tomato leaf.

To identify the levels of Rubisco protein present within the tomato plant tissues during each stage of the tomato ripening process, protein was extracted from the tissues during each stage of the ripening process, subjected to SDS page electrophoresis, and then either comassie blue staining or western blotting. To quantify the number of copies of the Rubisco gene in each of the tissues, during the ripening process, DNA was extracted from the tissues, and the relative levels of the Rubisco gene in each of the tissues quantified using real time PCR.

Data obtained from this experiment was used to characterize the amount of Rubisco produced during the tomato ripening process, due to up-regulation of the Rubisco gene, or due to increased copies of the Rubisco gene being present in the tomato tissues. It is hoped that the knowledge gained from this analysis can used to identify when Rubisco expression in the tomato plant decreases and how it decreases. This knowledge may be applied to indoor farming of tomatoes, allowing for the adjustment of artificial light levels, as the Rubsico levels, and the photosynthetic capacity of the plant decrease. This would allow for indoor farmers to efficiently use artificial lighting, and save money on yearly electric costs.