During the previous two parts I have mentioned two common patterns in negligible and negative senescence species that escape senescence:
1. dormancy
2. modular growth
Although such species are encountered in the animal as well as in the plant kingdom, traditionally there has been a lack of interest in studying plants in the gerontology field. Since the tacit purpose of trying to comprehend aging is to find ways to at least slow down if not escape aging altogether in our own species, plants seem to be too distantly related to us to show them any interest. But are we wise for doing this? Is there something plants can teach us that animals can’t? Aren’t they cheaper to study, both on the necessary instruments and the ethical problems their study may presume?
Let’s start with what sets annual plants apart from perennial ones.
Annual plants undergo their whole life cycle – from germination to the formation of the next set of seeds – in up to one year – examples include peas, lettuce, watermelon and many others.
Perennial plants on the other hand are plants that survive more than two years. How do they do this? Well, they leave behind not only their seeds like the annual plants do, but part of their roots as well! They reproduce not only through seeds, but through vegetative/asexual reproduction as well – for example, if you cut one such rhizome in half (a specialized type of root) and you plant each half in appropriate soils, two individual plants will be born. It is not only the root that can produce new individuals, but part of their underground stems as well – and the two of them are called rootstock.
Such perennial plants can be:
-herbs – like alfalfa, red clover
-trees and shrubs – like the maple, the apple, the evergreen trees, the sequoia
Perennial plants have varying lifespans; they can be either:
1. non-clonal plants
2. clonal plants
The longevity record for a non-clonal (perennial) plant belongs to the Great Basin bristlecone pine (Pinus longaeva) at 5,062 years, while the one for a clonal (perennial) plant is set at 43,600 years for Lomatia tasmanica!
If we were to compare life with a chess game where the king must be defended at all costs, then:
-the meristem (the plant tissue of undifferentiated cells) is the actual king
-the plant’s growth modules are the chess boards
-the plant’s vascular tissues, leaves and flowers are the chess functional pieces
We could easily see why it pays to switch from an annual plant to a perennial one. Annual plants play short chess games, at the end of which all kings are dead (no more meristematic cells here!), while perennial plants risk more complexity for the sake of asynchronous chess games – their games start and end in different parts of the plant at different times – they always have a supply of kings available so they are able to go through another winter.
So what can we learn from these surviving plants then?
Three things:
1. Meristematic cells are the plant’s equivalent to our stem cells and it is in such cells that the key to long lifespans reside.
2. It pays to take it slowly and we can’t but hope that suspended animation in humans will become as reliable as dormancy is in plants
3. These plants survive through their ability to form new roots. As for a far-fetched comparison to my human pacients, what sets the optimist 90-year old – who survived two world wars and the death of several family members and friends – apart from the complaining 50-year old – with no serious diseases to battle – is the ability to form new roots: new friendships, new relationships, new hobbies, plans and hopes!
Bibliography:
The OldList database of ancient trees
Lynch et al, 1998, “Genetic evidence that Lomatia tasmanica is an ancient clone” (original paper here)
Bunne-Bosch S., 2014, “Perennial roots towards immortality” (original paper here)
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