Food-Transport-Phloem | uksir-notes |Plant- Physiology
Plant Physiology:
 |
| transport |
Want to know about transport of Transpiration, stomata opening and closing, guttation in plants, Click the Link below:
Want to know about transport of water, osmosis in plants, Click the Link below:
Transport of food:
-
Transport of food from source/ production center to the sink/
consumption center is called as transport of food in plants.
-
Leaves are the food production center/ unit in plants, some
time young stem may contain chlorophyll and perform photosynthesis.
-
Consumption centers are mostly other parts like stem, apices,
root, fruits etc.
-
The transporting
tissue is phloem.
-
Phloem sap transport mostly water and carbohydrate.
-
90% of the solute is sucrose, as it is inactive highly
soluble.
-
Later sucrose converted to monosaccharide.
-
Phloem may transport- some minerals, amino acids, sugar
phosphate, potassium and phosphate ions etc.
-
It can also carry vitamins and phytohormones.
 |
| Phloem |
Routs of Translocation:
-
Solutes can be transported in various directions.
(a) Downward translocation:
-
Its the most common pathway.
-
Here food translocated from leaves to root and stem in
downward movement.
-
Food is utilized in
growth and storage.
(b) Upward Translocation:
-
In special condition food condition organic solutes and
mineral salts transported in upward direction.
-
Here from root storage transportation occurs to leaves as
well as apex.
-
During early stage of development, leaves are non functional.
At that time they need food.
-
Thus upward transport occurs.
(c) Lateral Translocation:
-
In woody stem lateral
translocation of food occurs.
-
It’s a very slow process.
-
Here food is supplied to the cortex and epidermal layer.
 |
| Translocation of plant |
Mechanism of Translocation:
-
Several theories have been put forwarded to explain the
solute movement:
- (a) Cytoplasmic streaming:
-
Proposed by Curtis in 1923.
-
Cytoplasm of living cell show streaming movement called as
cyclosis.
-
The cytoplasm transport organic food towards all direction.
-
But later it was rejected by Mason and Phyllis.
-
(b) Diffusion Theory:
-
Proposed by Mason and Maskell in 1928.
-
Due to diffusion of solute from higher conc. to lower conc.
-
Later this theory was modified to activated diffusion theory.
 |
| Translocation |
-
- (c) Trans cellular streaming Theory:
-
Proposed by Thaine in 1962.
-
According to him, sieve tubes contain proteinaceous tubular
strands.
-
These strands transport solute .
-
(d) Mass flow theory/ Pressure flow theory:
(Munch Hypothesis)
-
It was proposed by E.
Munch in 1930.
-
According to this theory organic solutes are translocated by
phloem sieve tubes.
-
The leaves are the sources
where as other parts are the sink.
-
The movement of
solutes can be upward or downward, that is bidirectional.
 |
| Pressure flow hypothesis |
Phloem sap move by
following steps:
1. Source: the part of plant where
food is prepared.
2. Phloem Loading: during photosynthesis,
mesophyll cells produce sugar.
-
This sugar dissolves
in cell sap and increase the conc.
-
Thus due to high osmotic pressure and turgor pressure,
dissolve sugar transported to companion cell of phloem tissue.
-
Later solutes are transferred to sieve tubes by active
transport.
-
This is called as phloem loading.
3. Transport of solutes: in side sieve tube,
pressure difference occurs.
-
Pressure is highest at source and lowest at sink.
-
Thus solutes are transported throughout the plant.
-
Necessary water is absorbed from xylem.
4. Sinks : they can be any part,
where food can be used.
-
Example: Stem, root, fruit and any storage organ.
5. Phloem unloading: at sink osmotic pressure
and TP is always low.
-
Here also solutes are unloaded by active transport.
 |
| source to sink |
Want to know about transport of Transpiration, stomata opening and closing, guttation in plants, Click the Link below:
Want to know about transport of water, osmosis in plants, Click the Link below:
Thank you for visiting.. feel free for asking doubt in comment session.... UK Sir
No comments