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1. Mar. 2024
For centuries, people have been searching for a cure that would allow them to live forever. Or at least extend their lives to a hundred or a hundred and fifty years while maintaining a reasonable quality of life. Twenty-first century health care, new cures for previously fatal diseases, or the availability of nutritious food already allow people to live longer than they did a hundred years ago. But this is still nothing compared to the record-breakers in the plant kingdom, who have the potential to live hundreds or even thousands of years. Why can plants and we can't? That's what we talked about with Karel Říha and Darya Volkava from the CEITEC research institute at Masaryk University, who are trying to understand plants down to the last molecule.
The biblical Methuselah is said to have lived to be 969 years old. The Greenland shark can enjoy the currents of the sea for 400 to 500 years, and Jonathan, a nearly two-hundred-year-old celebrity turtle, walks the beaches of St Helena Island in the South Atlantic. What about longevity in plants?
Karel Říha (KŘ): The plant Methuselah, the oldest living tree and at the same time the oldest individual on Earth, is the bristlecone pine, which probably began to sprout sometime in the Bronze Age in the third millennium BC, i.e., a few hundred years before the erection of the Stonehenge stone circle. It would seem to be such a rare phenomenon that nature has "forgotten" about it. The truth is, however, there could easily have been more examples of ancient plants/trees like this had it not been for human intervention and the struggle of plants for light and nutrients, attacks by pests, or physical damage to plants in natural disasters.
So do plants, unlike animals, have some special life strategy coded into them to survive adversity and reach old age?
Darya Volkava (DV): In animals, the body form is pre-planned and arises during embryonic development. These 'pre-programmed' structures such as the head, limbs, internal organs and so on only get bigger over time, but animals are rarely able to regenerate them. In contrast, plants do not have a predetermined body plan. They are born as very simple structures; such newborns have only an embryonic root and an embryonic shoot, which harbour special clusters of stem cells called meristems. The division of these cells gives rise to new organs throughout the life of the plant, which allows to grow indeterminately.
KŘ: Another strategy to survive adversity is modular growth. Plant body is made up of repeating units, or modules, such as branches, leaves or flowers. These units are to some extent functionally independent of each other. For example, you can cut off a branch of a tree without significantly harming the tree, because other branches will replace its function or a new branch will grow. Together the ability to form new organs throughout the life and to sacrifice individual organs without detrimental effects on the whole organism help plants to adapt their growth to the surrounding conditions.
Some types of long-lived plants took these advances even further. The survival strategy of so-called clonal plants is to form communities of genetically identical clones, called ramets, linked by the root system into a single superorganism. If one clone dies, another can replace it, and the entire clonal colony can persist for many millennia – a good example is the Pando Forest in Utah, which consists of 47,000 clones of quaking aspen, and is estimated to be between 14,000 and 40,000 years old.
It would seem that humans have an advantage over plants: they have no root system and can move from place to place to escape life-threatening situations. How is it possible that plants can thrive in one place for hundreds of years?
DV: The very fact that plants cannot move contributes to training their longevity – they are forced to adapt to local environmental conditions and rebuild or regenerate their structures in response to damage caused by environmental influences, pests or diseases. However, not all of them manage to overcome destructive external influences – that is why ancient plants whose life spans over millennia are so rare to come across.
Diseases do not avoid either animals or plants. But can plants get cancer?
KŘ: Plants do not suffer from cancer. But why is that so? Animals and plants both are multicellular organisms; their cells grow and divide, which allows them to renew their tissues and regenerate the body. Disturbances in regulation of these processes can lead to various diseases, including tumours, where uncontrolled cell growth and division occurs. In animals, tumour cells can spread throughout the body, and therein lies their danger. However, this does not occur in plants because of their rigid cell walls that "concrete" cell in the same place and do not allow them to migrate. Uncontrolled cell division is therefore not a threat to plants.
This leads to an interesting trade-off in nature. Animal cells are programmed to be capable of only a certain number of divisions, which on the one hand minimises the formation of tumours, but on the other hand limits the regenerative capacity of organs. At the same time, plants do not run the risk of tumour formation, which enables their cells to undergo many more divisions. This gives plants enormous growth potential.
So, the plants do not have to worry about cancer, but is their life threatened by the annual autumn dieback, for example? Is it a sign of ageing?
DV: Plants have mechanisms that allow them to grow and regenerate continuously throughout their lives. The changes that we observe in nature in plants in autumn, for example, are not related to ageing, but are part of a natural cycle that involves both senescence – the death of old organs and tissues – and regeneration and growth of new structures. It is a controlled biological process designed to process the nutrients from the leaves produced during the growing season and mobilise them for seed production or to store them in the trunk and branches. These stored nutrients then facilitate the regrowth of leaves and flowers in the following season. Senescence in plants is therefore not a manifestation of ageing, but of a cycle of renewal.
So, can plants live forever?
KŘ: Trees have the potential for an indefinite lifespan, and their life and developmental strategies certainly suggest it. As long as they are able to manage the interplay between dieback and regrowth, to respond to various damages caused by natural disasters, pests or diseases through the regeneration process, they could theoretically be immortal. However, with increasing lifespan, they are also more likely to succumb to external influences, which is why long-lived trees are rare. But who knows, if we gave trees the utmost care and protected them from outside influences, they might live forever. After all, people have been experimenting with plant immortality in this way for a long time – as evidenced by bonsai plants, some of which are said to be around 1,000 years old. Considering the plant's prerequisites for longevity, this experiment still has a long way to go.
Karel Říha leads a research group at the CEITEC research institute at Masaryk University that focuses on plant biology, particularly the processes that regulate reproduction and their adaptation to stress.
Darya Volkava is a PhD student in Karel Říha's research group and is interested in how plants coordinate reproduction with vegetative growth, which has an impact not only on plant lifespan, but also on seed and fruit production, and therefore on the yield of some agricultural crops.
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