Do plants die of old age?

18 March 2014

Question

Do plants die of old age?

Answer

Chris - Let's have a straw poll if we can take the "planty" pun there. How old do you think the oldest plant is on Earth, Richard?

Richard - It's got to be thousands. I'm going to go, 10,000.

Chris - What do you think, Tamela?

Tamela - I'm definitely thinking thousands. I'm from the west coast of the US, we've got these giant sequoia trees and the redwoods are extremely old.

Ginny - Yeah, I don't know. If you start thinking about smaller things like algae-type things, I wonder if they can get technically even older than that.

Chris - Let's ask Tom as the geographer. What do you think?

Tom - I'm thinking thousands as well and the mind goes straightaway to redwoods, but I couldn't put a firm answer on it.

Chris - Would it surprise you then that actually, the oldest plant on Earth is at least 43,000. If not, 135,000 years old. It's a Lomatia, Kings Lomatia - it's found in south western Tasmania in the 1930s and the guy, King who found it sent it off to the Botanical Society and they called it King's Lomatia in his honour. It's subsequently been examined in more detail. This plant clearly cannot reproduce because it's got three copies of its genetic material in its cells which means it's genetically incapable of producing any seeds. So, the plant can only grow by effectively cloning itself. In other words, a bit of the plant digs into the ground and puts down some roots and makes another side spinoff plant. So, the tissue is slowly growing and growing from the same stock that's been there for all that time. How do they know how old it is? Because they have found in the same region, as the plants that are growing now in just one tiny part of Tasmania in south western Tasmania in Australia, they've found remnants in the fossil record going back at least 35,000. If not, 135,000 years of plant tissue resembling very, very precisely this existing plant. They've carbon dated it to those ages. So, it looks so similar that they're happy to conclude that it must be the same plant and therefore, it must have been growing there for at least 135,000 years, possibly longer. And there are some pine trees as you were saying Tamela which are in order of 4,500 years old. So, there's certainly a lot of old stuff in the plant world.

Ginny - That's pretty amazing, but actually, I was reading recently about an animal that scientists think may actually be effectively immortal. It's a kind of jelly fish. It has this weird life cycle where it can basically grow to its adult form, but then if times get a bit difficult and it's not getting enough food, it can revert back into its juvenile form. It seems to be able to do this indefinitely as long as it doesn't get eaten or die of disease or something. So, they actually think that this might be an immortal animal which is pretty incredible.

Richard - So, the trick here is it's got to be able to replicate its DNA, but without introducing errors along the way.

Chris - Yes and of course, plants, if they're that old, they have been replicating their genetic material for that long, but then a plant has a much lower metabolic rate than certainly I do. I can't speak for you Richard, but I'm guessing it's probably true. That being the case, when you copy your DNA and you grow your cells very, very rapidly, they're less likely to get damaged if they don't have this highly damaging environment that a fast metabolism like ours tends to breed. So, I think that's probably why the trees are able to be more resilient and live for these extended periods of time.

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