Biology How Can Dry Seeds Still Germinate After Long Periods of Desiccation?

[musicgold]

Homework Statement

It is my understanding that DNA exists only in living cells. When a grain of wheat is dryed in the sun for days, how can it still act as a seed the next season? Wouldn't all cells be dead in a dry seed?

Relevant Equations

How does the process of life restart once a seed gets wet?

Thanks

 

[phinds]

What research have you done on this so far? What have you found out?

 

[musicgold]

What research have you done on this so far? What have you found out?

From my research I learned that a seed begins to grow when it absorbs moisture, triggering the cells and enzymes within the seed to multiply, and that an embryo can wait inside a seed for decades in some cases.

But my question is about the stage before that. If a seed is bone dry, no cell can survive. If no cell is live, there can't be DNA in its nucleus. Without its DNA and genes, how can a cell create enzymes when it gets moisture?

Also, I forgot to mention that this is not a homework question. It is something I am curious about.

 

[jim mcnamara]

An observation: so-called 'Anasazi beans' were found in US SW Indian ruins that were abandoned around 1100CE. They were in pots. The settlers in Dove Creek Utah germinated the beans 800 years later and have been growing them ever since. See the link below for details.

So your observation needs revision. IMO. How do you know that the seeds are bone dry? And what is the moisture content of 'bone dry?' Zero? The testa (skin) of beans resists water moisture movement somewhat.
It takes about 8-12 hours of cool water immersion to completely rehydrate dried beans - see any recipe for preparing dry beans.

Some pictures and some history:
https://www.anasazibeans.com/beans.html

 

[musicgold]

Thanks. That reminds me that, many archeological finds include DNAs from ancient remains such as plants and animal bones. So I am not sure now.

Also, the reason, I used the term "bone dry" is because I have seen how wheat grains are dried. They are left in the hot sun for days to remove moisutre. Could there still be moisture at their core? Don't know.

 

[TeethWhitener]

What makes you think that DNA magically disappears when a seed dries out?

 

[musicgold]

What makes you think that DNA magically disappears when a seed dries out?

I don't mean to say that DNA disappears. I feel a cell wouldn't be able to survive after the seed is dried so much. So I am wondering how the process of life kick starts again one the seed gets some moisture.

It is well known that if you roast a seed, it will not germinate. So when do we cross the line that the seed can't start life again.

 

[TeethWhitener]

I feel a cell wouldn't be able to survive after the seed is dried so much. So I am wondering how the process of life kick starts again one the seed gets some moisture.

https://en.wikipedia.org/wiki/Desiccation_tolerance

It is well known that if you roast a seed, it will not germinate. So when do we cross the line that the seed can't start life again.

Roasting involves raising the material to a high temperature. This is different from dehydrating a material.

 

[256bits]

If a seed is bone dry,

How dry is "bone dry"? I guess no moisture content.

When a grain of wheat is dried in the sun for days,

There is moisture in the air as humidity, which would be in equilibrium with the moisture within the seed. Although, as one heats the seed, either with the sun or through artificial methods, more of the water s driven out of the seed. Too much of a high temperature for too long a time and all the moisture could be driven out.

 

[Bystander]

https://en.wikipedia.org/wiki/Grain_drying

EDIT: Incidental/anecdotal note on dehydration survival among plants, animals, tardigrades can survive very dry conditions, much more so than plant seeds;
https://en.wikipedia.org/wiki/Tardigrade#Survival_after_exposure_to_outer_space

 

[BillTre]

It is my understanding that DNA exists only in living cells.

This is just not true.
DNA is isolated all the time in labs.
It is also found by archeologists and paleontologists, in not living cells.
On the other hand, DNA by itself is just a macromolecule, not a living thing and it won't by itself come back to life.

When a grain of wheat is dryed in the sun for days, how can it still act as a seed the next season? Wouldn't all cells be dead in a dry seed?

Rather than considering whether something is strictly alive or dead and thinking that once it is not living it is irreversibly dead, you might want to consider the process of being alive and how that process could be suspended.
You could consider seeds as being in suspended animation (where the living processes of the cell(s) are not ongoing, but where they could be started up again.
This is similar to cells frozen down for preservation in a lab (typically in liquid nitrogen).

How can this happen? Plants evolved this ability over millions of generations because it allowed them to better survive (this is an ultimate type explanation, one of why the process evolved).
As long as the organization of a seed's cells is not irreversibly disrupted (such as membranes busted open and dissociated) a proper rehydration might allow it to return to normal living functioning. The highly evolved structure of the seed is there to allow this rehydration to happen (this is an adaptive trait for the plant).
A seed smashed by a hammer will not be able to do this because its structure has been irretrievably scrambled.

Are seeds lacking in all water? I am guessing not.
There are probably water molecules tightly associated with other molecules, like proteins.

Heating to too high of a temperature could destroy the cell structure or denature proteins. Either could result in death.