Ch#14 |Transportation| Lec #13 |Translocation Of Organic Solutes (Patterns of Transport Of Solutes)

Ch#14 |Transportation| Lec #13 |Translocation Of Organic Solutes (Patterns of Transport Of Solutes)

Patterns of Transport:
Phloem transport or translocation occurs from sources to sinks.
Sources are the areas of supply:
are the areas of metablism or storage.
Translocation does not occur totally in upward or in downward direction.
Similarly it has no effect of gravity.

Areas of Sources:
The areas of sources include:
(i) Any Exporting Organ For example a mature leaf, or

(ii) Storage Organ: That can store excess photosynthetic product and export it when other parts of the plant need.

Areas of Sinks:
Sinks are the areas of active metabolism or storage.
For example root, tubers, developing fruits, immature leaves and growing tips of stem and root.
Example:
In biennials (e.g. beet) root is a sink in first growing season but becomes source in the next growing season when the sugars are used in growth of new shoots.

Remember it !!!
The composition of materials flowing
in the phloem has been studied by
using aphids.
Aphids are the insects which are phloem
feeders. These insects insert their stylets
into stem or leaf and puncture a sieve tube.
A pressure is present in the sieve tube cell.
By this pressure sap enters the aphid's
digestive tract and come out of its posterior
end as droplets called "honey dew".
There is 10-25% dry matter. 90% or more
of dry matter is sucrose.
Nitrogenous compounds are about 1%.


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