Plant Physiology In order to enhance the efficiency with which turnips store ami
ID: 213154 • Letter: P
Question
Plant Physiology
In order to enhance the efficiency with which turnips store amino acids in their roots, you genetically engineer a plant that contains nitrite reductase in its roots instead of in its leaves as most plants do. Your reasoning is that if nitrite is reduced in the roots instead of the leaves, it will save the plant the cost of transporting the nitrite from roots to leaves, and then transporting the reduced form back to the roots. Instead you find that even though you succeed in getting nitrite reductase enzyme in the roots, little reduction actually occurs and nitrite accumulates in the roots to toxic levels. Meanwhile, the leaves begin to accumulate large amounts of starch and take on a yellowish color. Explain why these results have occurred.
Explanation / Answer
Nitrate Reductase is an enzyme which helps in assimilation of the exogenous nitrate and is one of the most important enzyme responsible for protein production in plants. The nitrate is the source of nitrogen being trapped from the fertilized soil which is reduced by the enzyme. However in this case it is seen that due to high nitrite accumulation it leads to toxic level in the roots. This is because the roots are able to assimilate the nitrate and converted into the reduced state. Since the roots are already getting the reduced form, the nitrogen is not sent to the leaves. However, in this due to reduced transport of the nitrate to the leaves via the roots, it triggers a reaction and biochemical pathway which increases the starch synthesis. Hence, reduced nitrate shifts a trigger in production of starch resulting in its accumulation.