Abscission in Plants : Introduction

By
Abscission in Plants : Introduction
Abscission in Plants : Introduction

Introduction
  • In many woody plants, the leaves fall from the tree at the end of autumn. Some evergreen plants do not shed all the leaves at once but fall at different times or new leaves emerge before the old leaves fall. Such plants always look lush green. Sometimes flowers, different parts of the flower and fruits also shed. This action is called abscission. The plant is not injured in this process.

This fall usually occurs due to the formation of a special type of layer on the petiole of the leaf or at the base of the flower and fruit pedicel. This type of layer is called Abscission layer. 

Before shedding, the leaves turn yellow due to loss of chlorophyll, which is called senescent stage. 

Many waste products also get accumulated in the leaves. In this way, by the separation of leaves, those leaves which are not capable of photosynthesis are separated from the plants. 
Along with this, plants also get rid of excretory substances by this process. In many plants, pollination becomes easier due to the fall. 
Due to the absence of leaves, flowers are easily pollinated by wind, such as pears, almonds, etc. 
Sometimes, due to environmental changes such as extreme cold or dryness, plants become deficient in water, because they are not able to absorb sufficient amount of water. In such a situation, the leaves also fall to prevent the loss of water by transpiration.
  • The Abscission layer is made up of two strips of cambium type parenchyma cells. 
  • These cells are different from the cells of other tissues of the petioles. 
  • The cells of this layer are smaller and contain a higher amount of protoplasm and starch. 
  • Gum accumulates in the cells below the dissociation layer in the petiole and tyloses are formed in the vessels and the food transfer stops due to the formation of a callose plug on the sieve septum of the phloem. 

  • The middle lamella and outer walls of the senescent cells of the dissociation layer swell and become succulent and finally separate from each other. Now the leaf is attached to the mother plant only by convective bundles and when touched lightly or by a slight gust of wind, this vascular bundle breaks and the leaf falls down. 

A layer of cork cells forms just below the detachment layer and, thus, acts as a protective layer over the wound due to leaf drop. Later, a periderm is formed over this lesion, which is attached to the earlier periderm. The main causes of decomposition are the low absorption of nutrients from the soil and the production of growth inhibitors, such as abscisic acid (ABA).

Abscission in Plants : Introduction
The hormones that affect the abscission are as follows:

  1. Abscisic Acid - Abscission of leaves - Spraying of abscisic acid solution on the leaves causes them to disintegrate soon.
  2. Ethylene – Ethylene accelerates the dissolution of leaves, fruits and flowers.
  3. Auxin - In many plants, some fruits fall from the tree before they are fully mature and cannot be used for food, such as in apples and pears etc. This separation occurs due to the formation of an abscission layer on the underside of the inflorescence. If a solution of a particular concentration of auxin is sprayed on such trees, then these immature fruits do not disintegrate. The shedding of leaves and fruits can also be stopped for a long time by spraying auxin.



No comments:

Post a Comment