APOPLASTIC PHLOEM LOADING " SUCROSE-H IONS SYMPORTER"
Channel: YashFame
Date: 2020-09-24

Translocation of solutes in plants (Angiosperms) from source to sink. Here we need to understand what is source and sink. Source is the region where photosynthates are produced or from where translocation starts and ended to sink. On the other hand, sink is the part where in solutes are stored and consumed dominantly. So as an example, we can say leaves are the source and roots and other developing parts of the plants.

In this video, we will study translocation of photosynthates, primarily sucrose via vascular tissue i.e. PHOLEM.

Involvement of phloem components like CC (companion cells) and Sieve tubes (in Angiosperms) to transport sucorse to sink tissue.

Translocation may be via plasmadesmata (PD) or without them. With PDs it is called Symplastic and without PDs, Apoplastic (away from protoplast).

Apoplastic pathway does require ATP molecule, thus it is a active process and selectivity to sucorse transport is assured by H+ Sucrose Pump. 

In Symplastic,  no involvement of ATP molecules, it's a passive process but selectivity to sucrose is assured by diameter and number of PDs present in the cells involved in translocation. This Symplastic selectivity was well explained through a model, called "Polymer Trap Model). 


Munch Hypothesis also explains how passive or bulk flow of sucorse is done.

Loading of Sucorse and Unloading of Sucorse via Apoplastic and Symplastic are explained in detail.