Senescence

Senescence is the natural process of aging in plants, which involves changes that lead to the death of tissues, cells, and the entire plant body. This process can affect the whole plant or just a part of it, and occurs in various ways.

Senescence occurs in flowers, leaves, stems, fruits, and roots, but usually happens at different times in different organs. For example, in certain perennial herbs like alfalfa, the aboveground portion dies out annually, while the crown and root system remain largely intact. Leaves die in deciduous woody perennials, while most of the stem and root tissues remain alive.

Sensescence is responsible for the eventual deterioration and termination of the functional life of an entity or structure. Even though meristems are not subject to senescence and can be considered as immortal, the cells that are generated from them age gradually, ultimately leading to death.

#Types of Senescence

Depending on its role in the aging of plants, senescence can be grouped into these categories:

The process of shoot senescence occurs in some perennial plants with underground structures such as rhizomes, tubers, and bulbs. The shoot remains above the ground and dies each year after flowering; however, the underground structure survives, allowing for new shoots to emerge in the next season. Examples of such plants include ginger, banana, and gladiolus.

Whole plant senescence is a process that occurs in monocarpic plants, such as wheat, cabbage, mustard, and bamboos, that only produce fruits and flowers once in their lifetime. This has a significant effect on the entire plant, leading to its death after it has produced fruits and flowers.

Sequential senescence is a phenomenon commonly seen in most perennial plants, wherein the tips of the main shoot and engirdling branches grow and produce new leaves and bulbs, while the older leaves and lateral parts such as old branches experience senescence and die out. Examples of plants that display this phenomenon include Eucalyptus and Pinus.

Synchronous or simultaneous senescence occurs in deciduous trees such as the maple and elm, where the trees shed their leaves in autumn and produce new leaves in spring.

What causes Senescence?

The process of leaf senescence is accompanied by the early loss of chlorophyll, enzymes, and RNA.

As a result of either a faster breakdown or slower synthesis, there is a decrease in the cellular constituents.

Competition between Reproductive and Vegetative Structures for Nutrients

Long-night and short-day conditions induce leaf senescence and flowering

The secretion of senescence factor in the fruits of soybean causes senescence in the leaves.

The process of senescence is also regulated by hormones.

Loss of integrity in food storage cells and degradation of food reserves

Physiological Changes Occurring During Senescence

Chlorophyll Degradation

Decrease in starch content

Decrease of proteins and RNA

The process of photosynthesis ceases

Enzyme DNase breaks down DNA molecules

Decrease in growth-promoting hormones such as cytokinin

Functioning of Vacuoles as Lysosomes and Digestion of Cellular Matter

The accumulation of Anthocyanin pigments in leaves causes the reddening of leaves.

An increase in the content of deteriorative hormones such as abscisic acid and ethylene

Abscission

Abscission is the process of a plant shedding its flowers, leaves, and fruits, such as ripened fruits or old leaves. This is important for the plant’s normal life, as it seals off the vascular system to prevent nutrient or water loss, and also protects the plant from fungal or bacterial infections. This shedding typically takes place at the time of autumn, with the shedding of old leaves at the base of the petiole.

Leaves of deciduous plants in autumn fall simultaneously, giving the plants a bare look. In contrast, evergreen plants experience an eventual abscission of their leaves, as older leaves fall and new leaves continuously develop throughout the year. However, the majority of herbaceous species do not shed their leaves even after the plant dies, with leaves sometimes remaining in withered, dry conditions even after the shoot has died.

The process of abscission is a complex physiological process. During abscission, the color of flowers, leaves and fruits changes due to the breakdown of chlorophyll and the production of the anthocyanin pigment.

At the base of the petiole, leaf abscission occurs. This site is marked internally by zones known as abscission zones, which consist of one or more layers of cells that are arranged across the petiole’s base. This is known as the abscission layer.

The abscission zone is typically brown or pale in colour. The cells of this layer separate from one another due to the dissolution of the middle lamellae and primary cellulose walls, which is caused by the action of enzymes such as cellulase and pectinase. At this stage, the petiole is only attached to the stem by the vascular elements.

Abscission is a result of the formation of cell wall degrading enzymes in the abscission zone due to the production of ethylene.

The Importance of Abscission

The process helps to direct nutrients and water towards the younger leaves

Helps to spread vegetative and fruit propagation

As it is a self-pruning process, damaged structures and fruits are shed from the parent plant.

It is effective in eliminating plant structures that contain unwanted substances.

Important Notes on Plant Growth and Development - Check this out for more information.

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![Senescence and Abscission]()

#Differences Between Senescence and Abscission

Senescence and abscission are two different processes that occur in plants. Senescence is the process by which a plant’s organs and tissues age, while abscission is the process by which a plant’s organs and tissues are shed.

Senescence is a gradual process that occurs over time, while abscission is a sudden process that occurs in response to environmental changes. Senescence is characterized by a decrease in the production of hormones and other molecules, while abscission is characterized by the production of hormones and other molecules that cause the shedding of the organ or tissue.

Senescence can also be triggered by environmental changes, while abscission is almost always triggered by environmental changes. Senescence results in the death of the organ or tissue, while abscission results in the shedding of the organ or tissue.

Following are the differences between senescence and abscission:

| | | |

| — | — | — |

| Attributes |

| Senescence |

| Abscission | represents a table

| Death of Plant |

| It ultimately leads to the demise of the plant.

| It does not cause the death of a plant, but instead eliminates old and unwanted parts of plants. character represents a table cell

| Association with Aging |

| No |

| Not Associated represents a table column

Minimizing Nutrient and Water Loss

| Does not minimize |

| Minimized represents a table

Protection of Plants from Fungal and Bacterial Infections

| Does not protect |

| Protects the plants

This is a table

| Self-Pruning Process

| Not a process at all

| It is such a process.

This is a table

|This is a table|

| Removal of Plant Parts

| Removed due to Aging

Unwanted parts of plants are removed to promote better growth.

This table shows the number of books read by each student:

This table shows the number of books read by each student:

| Function |

Mobilizes required nutrients to flowers, resulting in the conversion of flowers into fruits

| Aids in directing essential nutrients and water to developing or younger plant parts

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Survey Results

| Role in Distribution of Vegetative Structures or Fruits All Over Plant Body

| Does not help |

| Helps |