Reference no: EM132934787

Increasing the efficiency of photosynthesis is one way to increase crop yield and help to feed human populations. One enzyme vital to the Calvin-Benson cycle of photosynthesis is Rubisco. Rubisco catalyzes the fixation of atmospheric CO2 into organic molecules so that the carbon atoms can be used to produce carbohydrates. Rubisco is composed of two different types of polypeptide subunits: large subunits and small subunits. It is hypothesized that another protein called Rubisco assembly factor (RAF) is needed to help the polypeptide subunits fold together to form a functional enzyme.

Researchers engineered three genetically modified strains of maize (corn). Strain X was modified to produce additional Rubisco polypeptides of both types in the cells. Strain Y was modified to produce additional RAF protein. Strain Z was modified to produce both additional Rubisco polypeptides and additional RAF protein. The Rubisco content of each of the maize strains studied is shown in Figure 1.

The researchers then grew plants of each strain at a light intensity of 500μmol of photons⋅ m-2⋅ s-1 and a temperature of 25°C. After 40 days, the amount of Rubisco activity (as determined by the rate of carbon fixation) in each modified strain was determined (Figure 2).

Researchers also evaluated several characteristics of the plants of each strain: the height, the fresh mass of the plants, and the mass of plants dehydrated in an oven (dry mass). The data are presented in Table 1.

Researchers engineer a strain of maize with a mutation that results in a decrease in the expression of RAF. Predict the most likely effect of this RAF mutation on CO2 consumption in plants grown under the same conditions as those of the experimental strains. Justify your prediction. In addition to binding CO2, Rubisco can bind O2 when CO2 is not readily available. Once Rubisco binds to O2, an energetically wasteful cycle called photorespiration must be completed before Rubisco can bind CO2 again. Predict the initial effect of a higher than normal O2:CO2 ratio in the atmosphere on the rate of carbon fixation in most plants.