How would you like to live for 5,000 years, or even longer?
There’s only one catch.
You can’t move from the exact spot where you were born, for your entire life.
And so it is for the Earth’s oldest known individual organisms: ancient trees. (FYI, here’s a list of longest-living organisms.)
Probably the most well-known of such trees are the Bristlecone pines that have lived for millennia in the high deserts of western North America. (Although trees such as the King’s Holly – the world’s oldest living tree (43,000 years)? may even be older, they are clonal colonies, that is, a group of genetically-identical individuals that have grown vegetatively from a single ancestor.)
But even discounting the ancient plants from clonal colonies, some plants are orders of magnitude older than the oldest known animal.
Why can some plants live thousands of years, and we can’t? (Let’s not get into the biological theories about why we age here, because it’s discussed so well elsewhere online – here, for example. Instead, let’s see how some plants manage to live so long.)
Ageing as a Time-Stress Response
First, let’s acknowledge that most plants, like animals, age and die. In plants, this is called senescence, and for a brief introduction, please see the essence of senescence, by Professor Howard (Sid) Thomas.
In an excellent review of the subject (see Ref. 1 below), Prof. Thomas likens aging in perennial plants to an environmental stress response. But instead of heat or cold or drought, the environmental stress in this case is the passage of time.
Thus, the strategies that some plants use to resist ageing are the same responses, in general, that apply to environmental stresses: avoidance, resilience or adaptation.
“In the specific case of time-stress, the options are: (1) to outrun it – in other words, to grow, develop and differentiate; (2) to resist it – through building in structural and functional durability and by repairing wear and tear; or (3) to pre-empt it – using programmed senescence as a developmental and adaptive resource so that ageing and death take place on the organism’s own terms, so
to speak.” (from: Ref. 1 below)
Keys to Potential Immortality: Stem Cells, Modular Development, Dormancy
Apparently, one of the keys to long life is to have long-lived stem cells, which are crucial for the continuous generation of new cells.
A recent report about why plants usually live longer than animals shows that “…certain organizing stem cells in plant roots are less sensitive for DNA-damage. Those cells hold an original and intact DNA copy which can be used to replace damaged cells if necessary. Animals rely on a similar mechanism but most likely plants have employed this in a more optimized manner. This could explain why many plants can live for more than hundreds of years, while this is quite exceptional for animals.”Longevity in animal stem cells has also recently been implicated in
solving the mystery of the lack of ageing in the tiny freshwater polyp Hydra.
Another key to extraordinary long life = “modular development”. What the heck is this?
Look at a tree. See how new branches are produced near the top? And how the developmental pattern seems to be repeating, over and over? Each module consists of a stem, a leaf, and a bud, which contains a potential growth center, or meristem. Somewhat the same thing is happening underground, that is, new branch roots are being produced, over and over. These are examples of so-called “modular development” that occur in most plants and some animals.
The third key to potential immortality is dormancy, the ability of some living organisms to temporarily shut down or greatly decrease growth and metabolic activity. For animals, think hibernation…like in scifi movies when the astronauts are put into “suspended animation” to endure extremely long spaceflights. In plants, think about how deciduous trees lose their leaves to overwinter. Such plants are in a state of dormancy, and they are, in a way, slowing down biological time, thus slowing down ageing.
“The unique combination of modular development and dormancy evolved by perennial plants allows them to defy aging. The field of aging and regenerative biomedicine could find inspiration in this combination, which makes the probability of death owing to external factors higher than death caused by physiological deterioration associated with aging at the plant organism level.” (from Ref 2 below)
1. Thomas, H. (2013) “Senescence, ageing and death of the whole plant.” New Phytologist, Vol. 197, pp. 696-711. (PDF)
2. Peñuelas, J. and S. Munné-Bosch (2010) “Potentially immortal?” New Phytologist, Vol. 287, pp. 564-567. (Full Text)
3. Borges, R. M. (2009) “Phenotypic plasticity and longevity in plants and animals: cause and effect?” Journal of Biosciences, Vol. 34, pp. 605–611. (PDF)
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