What is Abscission?
- Abscission is a complex physiological process marked by the changes in colour of the
leaves, flowers and fruits due to degradation of chlorophyll and the synthesis of
- Abscission results in Shedding of leaves, flowers and fruits
- This process is different in Decidious trees in which all the leaves of decidious plants fall in autumm season while in evergreen trees, older leaves fall while new leaves are developed continuously throughout the year
- In many evergreen plants, leaves are not shed even after they die. In many cases leaves are retained in withered dry condition even after the whole shoot is dead
What is the significance of phenomenon of Abscission?
- It helps in diverting water and nutrients to the young leaves
- Abscission serves as function in removing plant parts containing waste materials
- It is a self pruning process through which fruits and injured organs are shed from the
- It helps in disseminating fruits and vegetative propagates
What is Abscission zone?
- The main site of leaf abscission is at the base of the petiole
- The site of abscission is internally marked by a distinct zone called abscission zone
- This zone is made up of one or more layers of cells arranged transversely across the petiole base called as abscission layer
- The Abscission zone is pale or brown in colour
How does the process of abscission take place?
- Several environmental factors such as drought and N deficiency promote abscission
- Abscission starts when the amount of auxin begins to decrease because Auxin is synthesized in growing leaf blades and it strongly retards senescence and abscission
- Abscission is caused by the formation of cell wall degrading enzymes in the abscission zone, due to ethylene production
- The cells of the abscission layer separate from each other due to the dissolution of middle lamellae and the primary cellulose walls under the influence of the activity of enzymes, pectinase and cellulase
- At this stage, the petiole remains attached to the stem by vascular elements only
- But due to its own weight and the wind force, the leaf is detached from the stem
- The broken vascular elements are soon plugged with tyloses or gums
- Wound healing in cells proximal to the breaking point involves formation of a corky layer that protects the plant from pathogen invasion and excess water loss
- Suberin and lignin are synthesized during healing
- Cytokinins and gibberellins arriving from the roots also delay senescence and abscission