1. MECHANISAM OF LOADING AND UNLOADING OF PHOTO ASSIMILATES
BY,
NAME- VAISHNAVI B. ATAGRE
CLASS- MSC BOTANY (SEM –II)

2. Mechanism of loading and unloading of photo assimilates
Plants are amazing organism that can not only create their own food but also move it around.
They have tube like transport structures that allow them to move nutrients to different organs.
Plants make their own food by the process of photosynthesis.

3. Photosynthesis – Photosynthesis is the process by which plants use sunlight, water and carbon dioxide to create oxygen and energy in the form of sugar.

4. Translocation
Translocation – Transport of assimilates from source to sinks in plants is called as translocation.
The products of photosynthesis that are moved around are called Assimilates.

5. The location where the assimilates (THE PRODUCT OF PHOTOSYNTHESIS) are produced is called the source.
Sources are the area in a plant where sugars are produced or stored and the starting point of translocation
During translocation the assimilates are moved to a location called the sink.
Sinks are the areas in a plant where sugars are transported to be used or stored and the destination points of translocation

6. The phloem tissue consist of two main type of living cells -
Translocation occurs in the phloem tissue which consist of tube like structure called phloem vessle.
These phloem tissue run from the leaves into every other part of the plant and are responsible for transporting dissolved organic solutes such as sucrose and amino acids from the source to the sinks.
The phloem tissue consist of two main type of living cells -
Sieve tube elements- Stacks of these Cylindrical cells called sieve tube elements.
(The sieve tube has holes in it like a slice of swisschesse allowing for translocation.)
Companion cells – It appears to check the activity of the adjacent sieve element and participates in loading and unloading of the sugar into the sieve element.
( Companion cells function to load and unload sugars into the cavity of sieve tube members.)

7. Translocation of organic solutes such as sucrose takes place through sieve tube elements of phloem from source to sink.
But, before this translocation of sugars could proceed the soluble sugars must be transferred from mesophyll cells to sieve tube elements of the respective leaves.
( Mesophyll cells – It is a type of ground tissue found in the plants leaves. The most important role of the mesophyll cell is in photosynthesis. Mesophyll cells are large spaces within the leaf that allow carbon dioxide to move freely.)

8. Mechanism for Translocation
The glucose prepared in the leaves is converted into sugar.
The sugar in the form of sucrose is moved into the companion cells and then into the living phloem sieve tube cells by Active transport.
This creates a Hypertonic condition in the phloem. (Hypertonic condition- The solution with the higher concentration of solutes.)
Water in xylem tissue adjacent to phloem moves Endosmosis.(Endosmosis – It is the movement of solvent into the cell)

9. Osmotic pressure rises and phloem sap moves from an area of higher osmotic pressure to the area of low pressure.(sap is a sugary liquid filled with water and nutrients.)
Osmatic pressure is maintained low at the sink.
At the sink again atp is required to move the sugar out of the phloem sap into the cell where the sugar is used to relaese energy by the process of respiration.

11. Loading and Unloading
Loading – Transfer fo sugar ( photosynthetic) from mesophyll cells to sieve tube elements in the leaf is called as phloem loading.
Unloading – On the other hand the transfer of sugar from sieve tube elements to the receiver cells of consumption end (sink ) is called as phloem unloading .
Both are energy requring processes.

12. Thanku