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How Plants Get Older
December 21, 2006 12:42


Department of geobotany of biology faculty of Moscow State University hosts a research on plant ageing and longevity evolution. Any study, which regards ageing, is subject to public interest – no matter which object is studied. Plants are perfect objects – they have both short-living ephemers and long-livers, which witnessed the downfall of the Roman Empire. Plants’ lifetime can change due to environmental impact and sets down as any adaptive trait in the course of evolution.

Common people regard ageing as an evident thing, but researchers claim ageing to be a very complex notion, difficult to define. From this point of view plants are perfect objects for a discussion, due to wide range of their lifetime.

 

Modern science suggests about 300 hypotheses of ageing, which, however, can be united onto three main fields. First group of hypotheses suggests ageing and death to be a process, which is coded in genome. Individuals, which have lived a long life, should give a living space (resources) to younger generations. That is why Mother Nature has taken care of continuity of life by putting in genes of living beings a special ageing programme, i.e. self-destruction order, which existence is confirmed by limited number of cell divisions and discovery of telomerase counter. However, the research fellow from the biology faculty of Moscow State University claims plants do not have many evidences for said programme of cell division counter. At the same time some plants have genes, responsible for ageing of leaves.

The second group of hypotheses links ageing process with slow accumulation of accidental mistakes during gene expression. Evolution has done its best to adapt an organism to environment, but the moment comes, and an organism becomes inadequate to its environment, which means that ageing is not an adaptive process but just a kind of accumulation of malfunctions of an organism. Arabidopsis thaliana, for example, becomes less resistant to diseases and less productive after mutations accumulate in its genetic pool. On the other hand, long-living plants are able to “repair” genes, which function improperly. Moreover, some plants show no signs of ageing even when their life cycle comes to an end – 5000 thousand-year-old pine Pinus longaeva is a bright example. Both groups of ageing hypotheses have logical explanations and enough facts, however they are strictly antipodal: first group considers ageing to be regular, the second – stochastic.

 

The third group of hypotheses considers ageing to be life period, which was missed by the natural selection. The selection is aimed at providing reproductive success of a species, thus it doesn’t care what happens after offsprings are successfully born and survived. The faster fruits ripen, the faster the plant grows old. This hypothesis has been approved by facts and calculations, as well as examples from plant’s life, with some exceptions, of course – Thuja occidentalis’s ageing depends rather on growing conditions than on seed maturation rate. Well, how does the evolution control plants’ ageing process? Plants often tend to die due to environmental changes, not due to organism’s natural die-off. In other words, ageing is evidently out of control of natural selection. Plant’s lifetime can be regulated only by air temperature fluctuations. Each plant species appears to have a wide range of life times, controlled by its environment.

Geobotanists have suggested a convenient classification, aimed at sorting a great variety of plant species. This classification considers correlation between life cycles, ageing and number of bloomings. Such a variety of “life styles” leads to a thought about numerous ways of ageing in the Plant Kingdom and origin of herbaceous plants.

Source:
    http://www.biology.fullerton.edu
    http://elementy.ru/
    http://www.ayurvedaplus.ru
    http://www.selnov.ru/

Kizilova Anna


Tags: Moscow State University Russian science Russian scientists Russian nature  

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