Chapter 34, Problem 1Q

Summary Introduction

To review:

The role of tonoplast intrinsic protein (TIP) and the importance of the two mentioned conditions by the researchers in the experiment.

Given:

In the first case, researchers injected the oocytes of the frog Xenopus laevis which are large in size with a low osmotic cell permeability with the messenger ribonucleic acid (mRNA) of plant TIP. In the second case, the oocytes were injected with mRNA of a protein which does not help in transport whereas, in the third case, researchers kept the oocytes uninjected. They were observed after incubation of 2 days in isotonic medium and treatment with hypotonic solution.

The following graph was plotted showing the changes in relative volume of the different oocytes of the three cases over time:

It was also observed that the oocytes which were injected by TIP mRNA bursts after sometime while others do not. The following table depicts the osmotic water permeability of the three conditions as calculated by the researchers:

Introduction:

TIP is a transport protein present in the tonoplast of the plant cell. It helps in transport of molecules just like the other aquaporins. Also, hypotonic solution is that solution which has higher water potential than the cell so that due to the difference in water potential, the water moves inside the cell and swells up.

Explanation of Solution

From the graph, it can be concluded that with time, there is a significant increase in the volume of the oocytes that were injected with the mRNA of TIP. On the other hand, there is a very little increase in the relative volumes of the oocytes which were injected with mRNA of nontransport protein and the oocytes that were not injected at all. This happened due to the fact that when the oocytes were kept in the hypotonic solution, entry of water inside the cell took place because of the difference in water potential. The movement was rapid and in large quantity in the first case as compared to the second and the third case. The entry in the first case was rapid as TIP which is a transport protein increased the osmotic permeability of the oocytes, allowed the entry of more water and lead to the increase in volume of the oocytes.

Also, for the interpretation of the experiment the other two conditions were important as they proved that in absence of TIP the transportation occurs in a normal way and there is a little change in the volume of the oocytes.

Conclusion

Hence, it can be concluded that the TIP which is a transport protein is responsible for the increment in the relative volume of the oocyte cells as it increases their permeability and hence leads to their bursting.