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Abstract   Introduction    Materials & Methods    Results    Discussion    Literature cited

Ribulose 1,5-bisphosphate carboxylase (RuBisCO) is the most abundant protein in nature. RuBisCO is located in the cholorplast and functions heavily in photosynthesis. This protein is responsible for capturing atmospheric carbon dioxide and fixing it into the precursors of sugars via photosynthesis. Although the primary function of RuBisCO is to fix carbon dioxide, it has relatively low affinity for this substrate.  Due to the low affinity, a high concentration of this protein is necessary to be metabolically efficient for the plant (Lodish, 2007). 

The house plant Schefflera arboricola, commonly known as the dwarf umbrella tree, has both unvariegated and variegated leaves.  Vareigation in plants is a genetic anomaly resulting in white patches on normally green leaves. Chimeral variegation results from a nuclear, and recessive mutation that hinders the meristematic portion of the leaf from producing functional chloroplasts. Mutations in both nuclear and organellar genes can results in chloroplasts that do not reach functional maturity. Wild-type portion of the leaves are known to contain healthy chloroplasts (Wu, 1999).  The white portions of the variegated leaves contain chloroplasts with abnormal plastids void of all functional pigments.  The chloroplast deficiency noted in variegation leaves results in reduced photosynthesis in the lighter portions of the leaves (Aluru, 2001).  In green  areas of variegated leaves, we expect to see RuBisCO levels comparable to, if not higher than, normal green leaves to compensate for the pigment deficient regions of the leaves.   In the white portions of the variegated leaves, we expect reduced RuBisCO expression. There is an alternate type of vareigation which is caused by reflection of light, not a lack of pigment.

           In this experiment we will extract the proteins from the plant tissues by homogenization and centrifugation and determine total protein concentration using the DC protein assay system. With a Western blot we will determine which tissues express the RuBisCO protein. The DNA will be extracted and real time polymerase chain reaction (real time-PCR) will be performed on the isolated DNA.  The RuBisCO large subunit is encoded in the chloroplast genome and using real time-PCR we will be able to quantize how much RuBisCO DNA is in each plant tissue. We expect for the DNA extractions between the wild-type leaves, and variegated leaf portions to be comparable in quantity since we hypothesize that the chloroplasts are still present within the white portions, just non-functional.

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