What is the proposed mechanism of wax biosynthesis to produc

What is the proposed mechanism of wax biosynthesis to produce the cuticle?

Solution

Cuticle is a waxy layer that is found in most of the terrestrial plants to prevent non stomatal water loss and gaseous exchanges from the surface.

Chemically cuticle is made up of verylong chain fatty acids or the VLFC and their derivatives ,aldehydes ,alkalies ,prmary and secondary alcohols and wax esters.

In some species lipophlic secondary metabolites like the flavonoids,tocopherols,and pentacyclic terpenoids are also associated.

the formation of wax from these compounds then follows two pathways viz.the alkane pathway or primary alcohol pathway.

The epidermal cells are known to be the sites of cuticular biosynthesis. It is initiated by the denovo synthesis of the  C16 and C18 fatty acid s which are then converted into CoA thioesters by along chain Acylcoenzyme synthatase(LAC) and are transferred to the E.r by an unknown mechanism.Then the  C16 acyl CoA forms the substrate for the fatty acid elongase (FAE) complesx which successively adds two carbons per cycle derived from the malonylCoA resulting in VLFCS.

The elongation can continue or is terminated by the the thioesters which then undergo modification to form primary alcohols and wax esters.