Phototropism Prac - URGENT help needed!

[nerd]

We did a prac today regarding phototropism. We had a set of 8 coleoptiles, left 4 of them unchanged and cut the tips off the other 4. We exposed them to a light source from one side for a day and then checked on them again.

Now, as per the theory we learnt, we would expect the untreated shoots to bend towards the light and those with the tips cut off to not bend towards the light. By a stroke of luck, the prac actually worked and these were the results we observed.

My question is this: would the shoots that had the tips cut off still grow upwards, just not towards the light? Is the tip where the auxin is produced in the coleoptile or is the tip the receptor of auxin production?

Thanks in advance!

[Edmund]

Shoots with tip cut off will not grow towards light. Auxin is actually produced in the meristems, that is the shoot tips. Since source of auxin is removed, auxin cannot diffuse down to cause cell elongation...

[nerd]

But does that mean that when the tip is cut off, the shoots dont grow AT ALL or is it just that phototropism is stopped?

[Toothpaste]

Is the tip where the auxin is produced in the coleoptile or is the tip the receptor of auxin production?

Receptor of light (photoreceptor) at the tip --> (provided there's light) response = triggers production of auxin (signalling pathway) [signals from the tip to the part where elongation happens]

Brief answer, yes. Tip = receptor + production

But does that mean that when the tip is cut off, the shoots dont grow AT ALL or is it just that phototropism is stopped?

Growth would be inhibited, I think.

[nerd]

thanks!

[shinny]

Yeaaaaap; which is why people trim hedges. Auxin promotes vertical growth and inhibits lateral growth. By cutting the apical tip where it's synthesised, you inhibit vertical growth and promote lateral which is desired in bushy hedges and such.

[physics]

inhibition!!