phototropism

I tried to do some research on phototropism and phototropin 1 and 2, but I'm kind of confused with something. ' the direction of light is detected at the tip of the shoot. it's absorbed by phototropin 1 & 2, they are autophosphorylating protein kinase's and once activated (by blue light) they unfold and begin phosphorylating'. Why do they phosphorylate? Before I though it's to carry phosphate groups to the shaded side, for the ATPase enzymes. But according to my book 'phototropin 1 and phototropin 2 are more active on the light side'

So what is the purpose of phototropin 1 and 2 phosphorylating?

+rep

I've looked into this as well, and it's really complicated, plus scientists still don't know for sure what's going on.

Okay, this is what I think might be the case. due to the blue light in the visible spectrum, the phototropin enzymes autophosphorlyate and this introduces the presence of a negatively charged phosphoryl group. This could produce a conformational change, which causes repulsion of the auxins. (In my book it says there is a gradient, so possibly the large number of phototropin enzymes causes a large repulsion, hence the distribution of many auxins towards the shaded side.) the repulsion might be, if actually the case, due to the effect of pH on auxins (phosphoryl groups can undergo hydrogen bonding so that might increase the pH and reduce the auxin uptake by cells), or maybe charge (although I think it's neutral), but for whatever reason, auxins might be repelled by the activity of phototropins on the light side. The presence of many auxins on the shaded side could increase phosphorylation of the (H+) ATPase enzymes on the plasma membranes of the surrounding cells, and this would in turn increase proton extrusion and increase activity of the cells, which would ultimately elongate.

I cannot confirm that this is correct by any means, but it is a theory that I have produced based on my knowledge of biology, information from the Internet, together with my text book that could answer your question, and potentially explain what is going on. I may, however, have missed or misinterpreted something so it might be completely wrong. But let me know if you find out otherwise, because I'd be interested to know!

Thank you for the response! I agree with everything you said, and I never really thought about the negative charge of the phosphate group causing repulsion. But the auxin molecules are carried by PIN proteins. So maybe these PIN proteins have an excess of positive charges (tried to find the structure to confirm this but I couldn't find it), so therefore they repel each other, and the degree of repulsion causes the auxin to redistribute in the manner that it does.

What do you think?