Phloem

June 9, 2005 at 2:26 pm #1118

Navin

Participant

Hi

I want to know is there is Starch present in the phloem.

From what I know, the phloem transports sucrose.

So, would the phloem turn blue-black when flooded with iodine solution?

Also, would the pith of a stem turn blue-black when added with iodine solution?

June 9, 2005 at 3:10 pm #24115

James

Participant

Sucrose is transported in the phloem, and converted to starch at sink cells. The phloem doesn’t contain starch, but the pith does.

June 9, 2005 at 4:24 pm #24124

ERS

Participant

they should stain blue-black or thereabouts.
ERS

June 9, 2005 at 8:01 pm #24138

MrMistery

Participant

Actually it is a bit more complicated than that… Starch can not disolve into water, so it is moved around under the form of sucrose(or zaharose). Now the floem contains 25% organic substances and 75% water. From the total of organic substances, 90% is sucrose, the other 10% is made up of other sugars, aminoacids and lipids. So it is false to say that the role of the phloem is to transport sucrose, as some textbooks say.
Now, the phloem does not contain starch, if you put Lugol on it it will not turn blue.
I tried to do the experiment to test this last year, but no book tells us how to isolate the phloem from the plant. The pith will no doubt turn blue as there is starch present there

June 10, 2005 at 2:43 am #24162

lohita

Participant

and also phloem doesn’t carry only starch. it carries all the products of photosynthesis, this process is called translocation.

June 10, 2005 at 3:38 am #24165

Navin

Participant

Hey thanks a bunch!

June 10, 2005 at 8:29 pm #24227

MrMistery

Participant

quote lohita:

and also phloem doesn’t carry only starch. it carries all the products of photosynthesis, this process is called translocation.

Actually the phloem doesn’t carry starch at all because starch is not water-soluble. The stuff stranslocated through the phloem is called sucrose or sacharose

June 10, 2005 at 10:54 pm #24279

b_d_41501

Participant

It carries disaccharides, correct? It doesn’t carry polysaccharides (starches) due to this insolubility, right?

June 11, 2005 at 4:30 pm #24340

MrMistery

Participant

Yes that is true… It also carries fructose(something like 0.000001% but it is there) and other molecules such as aminoacids

June 11, 2005 at 6:37 pm #24370

b_d_41501

Participant

I thought so