Passage II

G. soja (a wild soybean) produces γ-tocopherol (a type of vitamin E). It then converts some γ-tocopherol into α-tocopherol (another type of vitamin E). In G.soja, the enzyme TMT catalyzes this reaction:

γ-tocopherol α-tocopherol

A. thaliana (a mustard plant) produces γ-tocopherol, but lacks TMT, so it produces only a small amount of α-tocopherol.

Because α-tocopherol is more effective at reducing cellular damage than is γ-tocopherol, a scientist tried to transfer G. soja's TMT gene into A. thaliana.

Experiment 1

Four versions of G. soja's TMT gene (TMT1-TMT4) were cloned. Each gene was incorporated into a vector (a biological structure that carries a gene and transfers it into the cells of an organism).

Six genetically identical lines of A. thaliana were developed (L1-L6). As shown in Table 1, L1-L4 were each exposed to a vector carrying 1 of the 4 cloned genes; L5 was exposed only to the vector; and L6 was left untreated.

Next, 10 plants from each line were grown. Table 1 gives the tocopherol concentration and the percent (%) by mass of the 2 types of tocopherol in the plants.

Experiment 2

Four genetically different strains of A. thaliana were grown (S1-S4), S1-S4 were each exposed to a vector carrying TMT1.

Next, 10 plants from each strain were grown. Table 2 shows the tocopherol concentration and the percent by mass of the 2 types of tocopherol in the plants.

Tables adapted from D. Shintani and D. DellaPenna, “Elevating the, Vitamin E Content of Plants Through Metabolic Engineering.” ©1998 by the American Association for the Adviancement of Science.