Is phloem unloading symplastic or apoplastic?

Is phloem unloading symplastic or apoplastic?

ADVERTISEMENTS: As with the phloem loading process, sucrose unloading also occurs through symplast via plasmodesmata or through apoplast at some point en route to sink cells. Phloem unloading is typically symplastic in growing and respiring sinks such as meristems roots, and young leaves etc.

Is phloem loading apoplastic?

Phloem Loading Mechanisms In apoplastic loading, sucrose produced in mesophyll cells enters the cell wall space (apoplast) and is taken up into the minor vein phloem by transporters. This is a thermodynamically active process that uses the proton gradient as an energy source.

What is the difference between symplastic and apoplastic unloading of phloem in sink tissue?

In several species, apoplastic loading of solutes appears to occur in the source leaf, whereas symplastic unloading occurs in the sink leaf. On the other hand, in the sink leaf, phloem loading is insensitive to PCMBS and anoxia, indicating a symplastic-unloading pathway (Turgeon, 1987).

What is unloading of phloem?

Phloem unloading is the movement of phloem sap constituents, principally nutrients (sugars, amino-N compounds, ions), signalling molecules (RNAs, proteins, phytohormones) and water, from sieve element-companion cell (SE-CC) lumens (SE-CC unloading) with subsequent cell-to-cell delivery to non-SE-CC vascular or ground …

Is phloem loading active or passive?

Most herbaceous plants employ thermodynamically active mechanisms of phloem loading, whereas in many trees, the mechanism is passive, by diffusion.

Why phloem unloading is active transport?

Unloading at the sink end of the phloem tube can occur either by diffusion, if the concentration of sucrose is lower at the sink than in the phloem, or by active transport, if the concentration of sucrose is higher at the sink than in the phloem.

What is apoplastic transport?

Inside a plant, the apoplast is the space outside the plasma membrane within which material can diffuse freely. The apoplastic route facilitates the transport of water and solutes across a tissue or organ. This process is known as apoplastic transport.

Is phloem translocation active or passive?

Münch theory and tall trees

What is the difference between Symplast and apoplast?

Symplast refers to the continuous arrangement of protoplasts of a plant, which are interconnected by plasmodesmata. Apoplast consists of non protoplasmic parts such as cell wall and intracellular space. Apoplast composed of nonliving parts of a plant.

What causes unloading of sucrose at sink cell?

Sucrose concentration in the sink cells is lower than in the phloem STEs, so unloading at the sink end of the phloem tube occurs by either diffusion or active transport of sucrose molecules from an area of high concentration to one of low concentration.

What is the process of phloem?

Phloem (/ˈfloʊ. əm/, FLOH-əm) is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as photosynthates, in particular the sugar sucrose, to parts of the plant where needed. This transport process is called translocation.

Is phloem loading is a passive process?

Phloem loading is the process of loading carbon into the phloem for transport to different ‘sinks’ in a plant. Passive phloem loading transports solutes freely through plasmodesma in the symplast of the minor veins of leaves. Active transport occurs apoplastically and does not use plasmodesmata.

Which is a symplastic of phloem loading and unloading?

Phloem unloading is typically symplastic in growing and respiring sinks such as meristems roots, and young leaves etc. in which sucrose can be rapidly metabolized. (Young leaves act as sink until their photosynthetic machinery is fully developed, at which point they become sources).

How is phloem unloading performed in potato tubers?

However, according to Oparka (1986), phloem unloading in potato tubers from sieve elements to cortical cells is a symplastic passive process. Because, there are wide varieties of sinks in plants which differ in structure and func­tion, no one scheme of phloem unloading is available.

How are sugars stored and unloaded from the phloem?

Finally, sugars are stored or metabolized in the cells of the sink. As with the phloem loading process, sucrose unloading also occurs through symplast via plasmodesmata or through apoplast at some point en route to sink cells.

Where does the loading and unloading of organic solutes take place?

The below mentioned article provides an useful note on the phloem loading and unloading in plants. Translocation of organic solutes such as sucrose (i.e., photosynthetic) takes place through sieve tube elements of phloem from supply end (or source) to consumption end (or sink).