Plant Abscission: The Art of Letting Go II Free Study Material II Easy notes #biology #botany #plantphysiology #plantbiology

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In the autumn season due to several factors the cells of this zone start secreting some enzymes that weaken their walls, and the leaf fall by flutter of wind.

The nearby cells of this zone swell out and secrete a material to cover the wound

Environment factors such as low temperature and short days are important for Abscission in plants.

Abscission can be defined as shedding of leaves, fruits and flowers in plants due to physiological and anatomical changes.

Before the leaves fall a region or site is Biochemically, anatomically and cytologically prepared for separation of leaf. The changes took place in this site or zone called as Abscission zone.

Abscission zone can be defined as- Leaf abscission starts with the formation of a specialized separation layer of mitotically active cells called an abscission zone

Differentiation of this zone may be early, or it may start just before activation. 

In a leaf at the leaf base there is an Abscission Zone perpendicular to Petiole of leaf, the cells of this zone are involved in cutting off leaf.

CHARCTERSTICS OF ABSCISSION ZONE

  • The cells of this zone are parenchymatous but smaller in size compared to nearby cells.
  • They have dense cytoplasm and complex plasmodesmata.
  • The cells are Mitotically Active.
  • The vascular bundles in this zone are thin and short.
  • Chloroplast breakdown to Gerontoplast for recovery of proteins.

STEPS INVOLVED IN ABSCISSION



1.Abscission Zone:
The location where abscission occurs is called as Abscission zone that is determined in early stage of plant development.

2.Differentiation of Abscission zone: Differentiation of this zone may be early, or it may start just before activation. A set of genes are involved in this process.

3.Activation of process:

Phytohormones also plays important role in abscission in plants. One of the phytohormone that is ETHYLENE is found to be effective in abscission in plants.

4.Cell Detachment:

Ethylene leads to cell detachment 

The cells of the abscission zone then began to detach from each other in this zone due to secretion of cellulases, Polygalacturonases, Hydrolases that modify the cell wall, dissolve middle lamina and result in cell detachment. Vascular bundles are reduced in diameter.

ET promotes abscission, whereas auxins inhibit this process.

As the process proceeds the abscission zone is further divided into Separation layer. Actual breakdown of leaf occurs at this layer.

Separation layers comprise of corky layer at both its sides. This corky layer secretes a protective chemical called Suberin that forms a protective layer and prevent injury to living tissue of stem.

Ultimate abscission of leaf from stem left a leaf scar. The scar on the stem left by the leaf will be sealed by the corky layer, which will prevent desiccation and block microbial invasion.

Abscission and Crop yield

There were several chemicals that inhibits action of Ethylene and modify the process of Abscission.

Hexanal a compound that heals plant injuries used to stop fruit abscission, hexanal applied to apple fruit plant delay its abscission and improve crop yield.

Ethephon an ethylene used to promote flower abscission in tea plants so as to get more yield.

Two phytohormones thus plays important role in abscission one is Auxin and other is Ethylene.

Role of Auxin:

  • Concentration of Auxin plays important role in regulating Leaf Abscission.
  • Experiment by Addicot and Lynch
  • Low auxin level promotes abscission while high auxin concentration suppress abscission.

Auxin and Higher Ethylene promotes abscission in leaves.

QUESTION PRACTICE

Leaf fall occurs in tree when there is increase in concentration of  (KVS)

Ethylene

Cytokinin

Gibberellin

Auxin

Reference:

https://link.springer.com/article/10.1007/s44307-024-00033-9

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