What is Senescence?
- Senescence is a deteriorative process
- It is process which naturally terminates the functional life of an organ or organism
- It represents the aging process
- All the metabolic processes in senescence is are catabolic in nature
- It is not confined only to whole plant
- At one time, it may not be for entire plant but may be limited to a particular plant
- Organ such as leaf and flowers or cells or cell, organelles
- Leaf fallling form a tree is an excellent example of senescence
Why is the phenomenon of Senescence important?
The phenomenon of Senescence is significant because of the following –
1. The process of senescence helps the mobilization of nutrients and of the vegetative parts of the plant into the fruits
2. Plants escape the influence of seasonal adversity by undergoing senescence of its
organs. Eg – Leaf fall in deciduous trees reduces the rate of transpiration to survive under
What are the different types of senescence?
The scientist who mainly studied senescence and proposed various types of senescence in 1961 is Leopold
Types of senescence
a) whole plant senescence
- It is also called as Overall Senescence
- In this tyoe of senescence entire plant is affected.
- This type of senescence occurs in annual plants
- Here, the entire plant dies after the development of fruit and seedsThe best examples of this type of senescemce are annual crops like wheat, tur, moong, gram, paddy, soybean etc.
b) Shoot senescence
- It is also called as Top Senescence
- In this type of senescence, the parts of the plant which are above the ground die but the root system continues to remain viable and live
- It is observed in perennial herbs
c) Deciduous Senescence
- It can be observed in deciduous woody plants
- Although, all the leaves die but the bulk of the stem and root system remains viable
- It is also called as synchronous senescence.
- The best example of decidious senescence is the Leaf fall in deciduous trees
d) Progressive Senescence
- This is also called as sequential senescence
- In this type of senescence, the death of leaves occurs gradually from the bottom to the top of plants.
- The best example of this type of senescence is the leaf fall in a coconut tree.
What are the physiological changes that occur during senescence?
The following physiological changes occur during senescence
- There is stoppage of the total process of Photosynthesis
- The colour of leaf changes from green to yellow resulting from the degradation of chlorophyll
- Redding of leaves occurs due to the accumulation of Anthocyanin pigments
- The lysosomes start to function to digest the cellular materials
- The starch content, RNA and proteins are decreased
- DNA molecules are degraded by the enzyme DNase and growth promoting hormones such as cytokinin decrease and ethylene and abscissic acid (ABA) content are increased
Ethylene and Abscissic acid are called Senescence promotors