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The process in which cells get aged and permanently stop division but does not actually die is called senescence.
Senescence is the process in which the important cellular blocks accumulated in the varying regions of plants, such as leaves, in the growth phase are recaptured. Thus, it is considered as the final stage of plant development. It is crucial for the plant’s survival and future generations to maintain a successful senescence process.
Senescence, or the irreversible cessation of cell division and withdrawal from the cell cycle, occurs throughout life, including during embryogenesis, growth and development, tissue remodelling, and wound healing.
Induction of Senescence
Plant hormones appear to have a significant impact on programmed senescence. Most specialists believe that abscisic acid, ethylene, jasmonic acid, as well as salicylic acid are the hormones that induce ageing; however, gibberellins, brassinosteroids, or even strigolactone are also implicated.
Leaf senescence is a well controlled decomposition and mobilisation process. Internal structures are broken down, macromolecules are broken down, and nutrients from the leaf are mobilised for use in the plant’s expanding parts or storage in the developing seed.
Difference between Ageing and Senescence
Both ageing and senescence are natural biological processes. They cause the physiological activities required for an organism’s survival to deteriorate, eventually leading to cell death.
Senescence is the process that cannot be reversed and is termed as the long-term arrest of the cell cycle. This can result from the excessive intracellular or extracellular stress experienced by the cell including cell damage, whereas ageing is an intrinsic part of human organisms caused by time, environmental factors, as well as genetic. This ultimately resulted in the gradual deterioration of physiological integrity, eventually leading to death vulnerability.
Effect of Nitric Oxide on Senescence
Senescence is the last stage of plant growth and development before death. Plants go through both age-related and stress-induced developmental ageing. Senescence is accompanied by considerable transcriptional, post-translational, and metabolomic alterations. Plants’ programmed senescence is also influenced by phytohormones. Nitric oxide (NO) is a gaseous signalling molecule in plants that regulates a variety of physiological activities.
NO is involved in seed germination, plant development, phytohormone perception and homeostasis, flower formation, reproduction, seed setting, fruit ripening, and plant defence against infection, as well as various abiotic stress.
Low ascorbic acid levels are thought to impact the long-day pathway by altering circadian rhythms or by increasing SA levels, resulting in early flowering and senescence under long-day conditions.
Nitrate Reductase Activity
One of the most significant enzymes in the assimilation of exogenous nitrate, which is the most common form of nitrogen available to green plants growing in soil, is nitrate reductase. The activity of this enzyme in plants provides an excellent assessment of the plant’s nitrogen status and is frequently linked to growth and yield.
Environmental elements such as light, nitrogen, and carbon availability have a strong influence on nitrogen reductase activity. Plant nitrogen reductase inactivation is reversible depending on phosphorylation state.
Eukaryotic nitrate reductases are sulphite oxidases that convert nitrate to nitrite as the first step in the nitrogen assimilation process. They’re found in plants and fungi, and in addition to the molybdenum active site, they have a heme and a FAD cofactor.
The initial process in nitrate assimilation, the reduction of nitrate to nitrite, is catalysed by nitrate reductase. Molybdenum is a cofactor for nitrate reductase.
Cadmium is a well-known heavy metal that has a number of negative impacts on plants. Cadmium poisoning affects nitrate reductase, an important enzyme involved in the synthesis of nitric oxide in plants.
Conclusion
Thus, it can be concluded that senescence is the withdrawal from the cell cycle that occurs throughout life, including during embryogenesis, growth and development, tissue remodelling, and wound healing.
Plant hormones appear to have a significant impact on programmed senescence.The plant hormones abscisic acid, ethylene, along with jasmonic acid, as well as salicylic acid increase the rate of the senescence process.
The activity of nitrate reductase in plants provides an excellent assessment of the plant’s nitrogen status and is frequently linked to growth and yield. The initial process in nitrate assimilation, the reduction of nitrate to nitrite, is catalysed by nitrate reductase. Molybdenum is a cofactor for nitrate reductase.
Environmental elements such as light, nitrogen, and carbon availability have a strong influence on nitrogen reductase activity. Plant nitrogen reductase inactivation is reversible depending on phosphorylation state.
