Aging in plant

In some essential respects, green plant ageing varies from that of animals. A combination of the determinate or indeterminate status of meristems and the cell death and disposal techniques used by plants to develop well-adapted anatomies and morphologies governs a plant’s seasonal cycle and persistence. The balance between exploratory development and the wave of tissue death that follows it determines the degree of perenniality, and extremes of lifespan can result from relatively slight alterations in the quantitative relationship between growth and death.

Senescence and elimination of organs and tissues are related to internal resource reallocation, but they are programmed phases in the overall evolution of the plant and do not represent stress or starvation-induced ageing. Long-lived plants’ meristems acquire genetic damage, yet the organism has selection mechanisms in place to manage genetic load and even utilise somatic mutations that give adaptive benefits. Most plants do not age in the strict gerontological sense, and particularly long-lived forms such as trees and clonal creeping perennials are supported through selection and correction at the level of semi-autonomous cell lineages.

Cycle of Aging

• Senescence

Senescence has a specialised meaning in plant biology, and it is one of a slew of phrases related to the process or condition of aging. Words like maturity, ripeness, seniority, and longevity appear in a Thesaurus search for senescence,’ but the most common links are with decay, decline, gerontology, illness, and mortality. This reflects the word’s etymological background (from the Latin senescere, “to grow old”), as well as its relationship with senility and medical issues associated with human ageing.

Senescence is defined as a phase of development that: (1) is a transdifferentiation episode following the completion of growth; (2) may or may not be followed by death; and (3) is absolutely dependent on cell viability and the expression of specific genes, according to current physiological understanding of the senescence condition and its positive roles in plant growth, differentiation, adaptation, survival, and reproduction.

• Growth and development

Growth and differentiation result in changes in shape, which are referred to as development. Growth is not always connected with an increase in dry mass because post-mitotic expansion mechanisms in plants are mostly driven by water. Growth is a scaled trait of populations, ranging from cells to phytomers to individuals to complete biomes and floras. The essential characteristics of population growth are consistent across species and organisational levels. In biological systems, the pattern of rising and then declining proliferation is usually determined by density.

When population size is modest, growth begins slowly, reaches a maximum rate when density meets metabolic and environmental restrictions, slows as limiting external and internal factors become more important, and finally approaches maximum size asymptotically . The evolution of optimal life histories, lifespans, and senescence is also influenced by density dependency, which interacts with demographic structure.

• Mortality, life expectancy, lifespan

The current article is primarily concerned with the physiological aspects and mechanisms of ageing and senescence. Scaling up these processes to the population level and beyond leads us into demographic and evolutionary studies, which have their own conventions and definitions  in which terms like mortality (chance of death at a given age),expectancy life  (time to death at a given age), and lifespan (maximal life expectancy at birth) are quantifiable actuarial parameters. These terms are used empirically where they appear in this essay.

• Turnover

Molecules, cells, phytomers, individuals, and even entire floras all turn over on a regular basis (Leopold, 1975). The term “turnover” refers to the flow of people through a pool. The canopy is the pool in the case of leaf turnover (Hikosaka, 2005). Newly started leaves are attracted to the canopy, where they grow and mature, eventually becoming senescent and dying and leaving the pool. The combined S–V curve depicts the turnover kinetics of phytomers or other structural entities within a biological system in this way. The plant is growing if the rate of organogenesis and recruitment outnumbers the rate of death.

• Ageing

Ageing, like senescence, is a term that has come to be associated with degradation. True, mistakes will accumulate over time, and living tissues will show symptoms of wear and strain. In a broad biological sense, aging refers to changes that occur over time, and hence includes the time-dependent processes of growth and differentiation, as well as maturity, senescence, and mortality (Fig. 1). In this context, aging does not just refer to a loss of vitality. The idea that we begin to die the moment we are born is a lovely poetic thought, but it isn’t helpful in understanding the biology of aging.

• Death

Death is a state or circumstance that occurs at the end of the dying process but is distinct from it. ‘Death is not an event in life,’ said the philosopher Ludwig Wittgenstein. Post-mortem and nonbiological alterations occur in dead cells by definition. Biologists examining developmental endpoints must distinguish between the controlled activity of viable biological structures and the disastrous consequences of organic collapse.

Conclusion

A combination of the determinate or indeterminate status of meristems and the cell death and disposal techniques used by plants to develop well-adapted anatomies and morphologies governs a plant’s seasonal cycle and persistence. The balance between exploratory development and the wave of tissue death that follows it determines the degree of perenniality, and extremes of lifespan can result from relatively slight alterations in the quantitative relationship between growth and death. A combination of the determinate or indeterminate status of meristems and the cell death and disposal techniques used by plants to develop well-adapted anatomies and morphologies governs a plant’s seasonal cycle and persistence. The balance between exploratory development and the wave of tissue death that follows it determines the degree of perenniality, and extremes of lifespan can result from relatively slight alterations in the quantitative relationship between growth and death.