Difference Between Abscission and Senescence

The key difference between abscission and senescence is that abscission is a fundamental process by which plants can shed their aerial organs such as a leaf, flower, fruit, seed, stem, or others from the parent plant while senescence is a biological ageing process in which cells irreversibly stop dividing and enter a state of permanent growth arrest without undergoing cell death.

Abscission and senescence are two cellular processes. Abscission is the separation of plant parts from the parent plant. Senescence is the cellular process in which cells show a permanent form of cell cycle arrest. Abscission occurs after the formation of an abscission zone at the point of separation. Senescence occurs at organ level as well as organism level. In plants, abscission allows shedding of senescent or physiologically damaged plant parts while senescence is important to increase fitness and survival.

CONTENTS

1. Overview and Key Difference
2. What is Abscission 
3. What is Senescence
4. Similarities Between Abscission and Senescence
5. Side by Side Comparison – Abscission vs Senescence in Tabular Form
6. Summary

What is Abscission?

Abscission is a fundamental process occurring in plants. It is a cell separation process. In fact, it is a tightly controlled cellular progression. Abscission can be defined as the separation of a plant part such as a leaf, flower, fruit, seed, stem, or others from the parent plant. Abscission takes place in groups of functionally specialized cells known as abscission zones. Abscission zones are located at specific sites of organ detachment in the plant. It is an important process by which plants can shed organs. Abscission allows the discarding of senescent or physiologically damaged organs.

Moreover, abscission is needed for highly efficient seed and fruit dispersal. Leaf abscission is a normal process during which old leaves are shed. Abscission occurs in young leaves when they are subject to leaf diseases or infestation. Furthermore, ripen fruits are dropped from the plants due to abscission. Plant hormones such as ethylene, auxin, and abscisic acid influence abscission in plants. Auxin is the main hormone that regulates the abscission.

Abscission is very common in lower plants. However, the occurrence of abscission differs within species and cultivars. Hence, manipulation of the abscission process is a common practice in agriculture. In crops like citrus, a high percentage of yield loss is due to abscission. Low crop yields are mainly due to the abscission of flower buds, flowers, and immature fruits.

Abscission occurs via three main steps: resorption, protective layer formation and detachment. During resorption, chlorophyll degrades in order to extract the majority of nutrients. A layer of cork cells forms under the abscission zone during the second step. Detachment takes place due to the secretion of cell wall enzymes by parenchyma cells to self-digest the middle lamella or due to imbibitions of water.

Abscission is not restricted to plants. Abscission is also referred to as intentional shedding of a body organ seen in certain animals. For example, tailless lizards intentionally shed their tails, in order to escape the clutches of a predator.

What is Senescence?

Senescence is a biological ageing process. It is the process by which cells irreversibly stop dividing and enter a state of permanent growth arrest without undergoing cell death. Hence, in plants, senescence can be considered as the last development stage. Several plant hormones such as ethylene and abscisic acid promote senescence in plants. Senescence can happen at various levels such as organ level, organism level, etc. Plants relocate nutrients from senescing leaves to stems or roots. Therefore, senescence is important for plants to increase fitness and survival.

Unrepaired DNA damage or other cellular stresses can induce cellular senescence. Certain features characterize senescence in cells. The cells show degenerative changes such as accumulation of breakdown products, cease of protein and nucleic acid synthesis, decline of cellular respiration, and release of enzymes through lysosomes, etc.

What are the Similarities Between Abscission and Senescence?

• Abscission and senescence are two processes occurring in plants.
• Plants or plant parts undergo abscission and senescence.
• Abscission allows for discarding senescent or physiologically damaged organs from the parent plant.
• Plant hormones promote both processes.

What is the Difference Between Abscission and Senescence?

Abscission is the natural detachment of plant parts from the parent plant while senescence is the biological ageing process in which cells undergo a stable growth arrest and other phenotypic alterations. So, this is the key difference between abscission and senescence. Abscission is important since it allows discarding senescent or physiologically damaged organs and highly efficient seed dispersal. Senescence is important in plants to increase fitness and survival.

Below infographic lists more differences between abscission and senescence.

Summary – Abscission vs Senescence

Abscission is the natural separation of plant parts such as flowers, fruits, leaves, etc. from the parent plant. Senescence is the biological ageing in which cells stop dividing and enter into a phase of cell cycle arrest. Thus, this is the key difference between abscission and senescence. Abscission is important for plants in order to discard senescent or physiologically damages plant parts. Senescence is essential for the survival of the plant or its future generations.

Reference:

1. Merelo, Paz, et al. “Cell Wall Remodeling in Abscission Zone Cells during Ethylene-Promoted Fruit Abscission in Citrus.” Frontiers, Frontiers, 20 Jan. 2017, Available here.
2. “Senescence in Plants.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., Available here.

Image Courtesy:

1. “Fall Leaves” By Symphony999 – Own work (CC BY-SA 3.0) via Commons Wikimedia

2. “Ginkgo senescence” By Bernskbarn – Own work (CC BY-SA 4.0) via Commons Wikimedia