Question

The abscission layer is covered by a leaf scar which is composed of:
A. Pectose and cellulose
B. Suberin
C. Pectin
D. Cutin

Answer 1

Hint: Suberin is a biomolecule (lipophilic and is made up of long-chain fatty acids) that is not easy to degrade and helps in protection from various kinds of stress.

Complete answer: Now, think of a real-life situation in which a leaf that is growing on the plants and performing photosynthesis but due to the mechanical injury or high winds or any other reason the leaf gets detached from the plant.
In this case, we can see when the leaf detaches then the petiole will also break or might not break but, in both cases, it will expose the internal tissues of the plant directly to the external environment.
Therefore, there are increased chances of the pathogen attack, formation of air bubbles (also called tyloses) in the water-conducting channels that is Xylem or increased oozing out of the water-rich in nutrients.

So, to prevent the loss incurred due to leaf detachment the plant develops the abscission layer and if we see the composition then it should be made up of a chemical substance that provides it protection both from the abiotic and biotic agents and it is only possible with a tough substance that is not easily degradable by the enzymatic actions of bacteria also.
Therefore, the abscission layer is made up of suberin or lignin.
Suberin is “an inert impermeable waxy substance that is found mainly in the cell walls of corky tissues.”

The correct option is B. Suberin.

Note: Suberin is unique and different from other non-carbohydrate cell walls biopolymers like lignin and cutin for several reasons:
(1) it is an assembly of two different polymeric domains, one poly(phenolic) and the other poly(aliphatic),
(2) each domain has a unique chemical constituent, and
(3) both domains are present in similar cells.