Question

Hello! Please help me with this question...

Suppose a researcher is carrying out studies in which she adds a nonphysiological electron donor to a suspension of chloroplasts. Illumination of the chloroplasts yields oxidation of the donor. How could she tell whether photosystem I, II, or both are involved? EXPLAIN IN DETAIL...

Answer 1

You have not mentioned about the nonphysiological electron donor that you are using. I hope it is some dye that changes color after oxidation. Firstly, we have to think what an electron donor can do in the suspension of chloroplast and what can be its effect on the electron transport system? Then we can further think about, which photosystem it is affecting? Usually in there are some electron donors in the photosystem we can see. But major electron donors required in the electron transport chains are P680 in PSII and P700 in PSI. Electron donor is the source which provides electron to the electron transport chain in photosynthesis. Continuous supply of electrons are provided by splitting of water molecule in oxygen evolving complex. The nonphysiological electron donor can act as source of electron supply to the transport chain by oxidising itself. As I hope it could be some dye, so we can visually see the oxidation happening.

We have to see whether our donor donates its electron to which system?

For this First we have to generate transgenic plants with knocked out gene for P680. Another plant with knocked out gene for P700 and isolate chloroplast from those plants for our experiments. Also we have to see some chromogenic electron acceptor specific for particular photosystem. The chromogenic dye will dont show flouroscence upon reduction when added in suspended chloroplast. eg, dichlorophonellindophenol. Hence, in 1st transgenic plant where we have knocked out gene for P680(primary electron donor for PSII) shows deduction in flourescence for the electron acceptor specific to PSII in suspended chloroplast, then we can say that the given electron donor donates its electron to PSII. Similarly, for 2nd transgenic plant, where we knockout gene for P700(primary electron donor for PSI) if we get reduction in flourescence for the chromogenic electron acceptor specific to PSI, then we can say the given electron donor donates its electron to PSI. In another experiment, we can knock out genes for both P700 and P680, and we see reduction in the flouroscence for both the electron acceptors specific to PSI & PSII, then we can say the donor, donates its electron to both the photosystem.

I hope you get the answers.

Things you have to search for are,specific electron acceptors for respective photosystems which are also chromogenis upon reduction.