explain pressure flow hypothesis of translocation of sugar in plant
Answers
it is the most accepted mechanism for translocation
it was proposed by MUNCH in 1930
also called as mass flow hypothesis.
by p-h-o-s-y--n-t-h-e--s--i-s sugar is prepared at source i.e leaves
then converted into sucrose a d-i-s-a-c-r-i-d-e compound
then sucrose is moved into a-d-j-e-s-e-n-t companion cells into sieve tubes by active transport.
and this process of loading at the source produces a h-y-p-o-t-o-n-i-c condition in p-h-o-l-e-m.
water in a-d-j-u-s-e-n-t xylem moves into p-h-o-l-e-m by osmosis.
as osmotic pressure builds up the p-h-o-l-e-m sap moves towards low pressure.
at the sink the osmotic pressure must be reduced.
again active transport is necessary to move the sucrose of the phloem sap and into the cells .
which will use the sugar converting into energy\ starch \cellulose .
as sugars are removed the osmotic pressure of phloem decreases and water moves into the phloem.