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I am doing an experiment about the growth of onion roots.

I put onion plants in different solutions of sucrose in water — 0.1M, 0.2M, 0.3M, 0.4M, 0.5M — with the root touching the water.

Measurements of root growth tells me that the presence of sucrose in the solution inhibits root growth.

Why does this happen? Does sucrose affect the root's mitosis? If so, how?

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  • $\begingroup$ Have you used the same onion for all the experiments? If not, it could be due to the onions themselves rather than the enviroments they are in. $\endgroup$ Mar 30, 2018 at 13:04
  • $\begingroup$ A formula does not identify a compound as many compounds have the same formula. This is an old question but I have edited it to replace the formula with the name of the compound I assume is being referred to. $\endgroup$
    – David
    Jan 6 at 9:30

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tl;dr you are using a lot of sucrose. You would need to show us the data, but I'm not surprised if the plant gets confused / dies/ doesn't know what to do when you add so much.

An important aspect of experiments in biology is calibrating the treatment you're applying to the biological system. If you give a plant way more of an important signalling molecule than it would usually expect in nature, it may respond in a way that doesn't make any sense.

1M sucrose would be a 34% solution of sucrose (molar mass of sucrose is 342.3 g / M, in 1 L of solution).

If you look at papers or even at hobbyist forums where people add sucrose to stimulate root growth, they seem to usually be adding a 5% solution or less (50g / 1L ~ 0.16M), which is described as "high". So at the highest level you are adding more than 3X as much sucrose as people usually do.

I'd look at your data and try to understand whether the inhibition happens in a dose responsive fashion, and further whether the dose response is linear or whether it just gets weird at the higher concentrations.

As for the expected response, you will see in published work that sucrose or other sugars tend to encourage, rather than inhibit, root growth in most plants. Here for example is Figure 4 from a paper:

enter image description here

The left panel has no sucrose added and the right panel has 30mM sucrose added. You can clearly see longer roots in the presence of sucrose, at least in these young Arabidopsis seedlings.

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  • $\begingroup$ tl;dr is not standard English but internet slang. Please replace it. $\endgroup$
    – David
    Jan 6 at 9:35
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    $\begingroup$ @David part of inclusiveness is tolerance - not insisting things be just the way you personally think they should be. We're all just individual users here. The community has embraced tl;dr, it's here to stay. Also, cf. OED and Merriam-Webster $\endgroup$
    – uhoh
    Jan 6 at 16:01
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    $\begingroup$ @David "tl;dr" is perfectly fine in ALL Stack Exchange sites. There's no basis to go around suggesting here and there that people shouldn't use it. If you'd like to start a new site policy, go to meta and ask "Shall we ban tl;drs in Biology SE?" and see what the rest of the community thinks. $\endgroup$
    – uhoh
    Jan 7 at 14:35
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    $\begingroup$ To get back to the topic - surely the problem with the higher concentrations is osmotic effects rather than an inhibition of growth as such. $\endgroup$
    – bob1
    Jan 7 at 21:01
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    $\begingroup$ @uhoh wrote “tl;dr is perfectly fine”… …except that it is unnecessarily incomprehensible to a section of native English-speaking qualified biologists. I have not sought to ban anything, nor would it be within the remit of this site to do so. If I migrated this topic to Meta it would not be to micromanage people’s vocabulary, but to explain my view of the practical implications of the principles already adopted by SE to help them implement them theirselves. I have already made myself clear in this particular case, and SE Biology will not disintegrate if the poster chooses to persist. $\endgroup$
    – David
    Jan 8 at 9:03

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