General Question

Ltryptophan's avatar

How do seeds know when they have reached fertile soil?

Asked by Ltryptophan (10269points) June 8th, 2010

So a farmer drops a seed in a little hole, and covers up the hole with some dirt. Then he drizzles a little water, and the seed starts to grow… Fancy.

What did it? Was it the water that made the seed happy enough to sprout? Was it the weight of the soil? Do seeds feel?

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19 Answers

lilikoi's avatar

Nutrients dissolve in water thus allowing the plant to uptake them via roots. I don’t think plants know. There is no consciousness. If there is fertile soil and ample water (but not too much), conditions enable a plant to grow. If not, the seed will not grow. It’s not like it chooses. It’s like in people if you have food and water you grow, and if you don’t you starve and dehydrate and die.

gemiwing's avatar

Depends on the seed. Some seeds have a tough shell and won’t begin to germinate without quite a bit of water, for other seeds it’s heat. Once those basic requirements have been met, the seed sprouts and gives it a go. Whether it survives, of course, in another matter.

Ltryptophan's avatar

@lilikoi seeds got no roots! Egad!

lilikoi's avatar

Lol I was thinking about plants.

YARNLADY's avatar

It the same way ice knows to melt when it gets warm. There are certain chemical reactions that occur.

Ltryptophan's avatar

I was really wanting to know, what exactly is happening?

I can get a seed to grow as well as the next guy. Water, soil, miracle grow…bam, tomatos…

BhacSsylan's avatar

It depends highly on the seed, but the basic idea is as @gemiwing said, in that basic requirements must be met. Almost all seeds are to an extent water-soluble, and so water dissolves minerals and takes them into the seed. When enough water and nutrients have reached the seed (and the heat is sufficient, as well, as that will affect reactions), chemical reactions will start that will allow the seed to start growing.

As to exact processes, that’s tricky and highly dependent on the seed, as i said (and many times not well understood). Basically, the cells in the seed have receptors that will respond to various signals, such as water and heat and nutrients. Water and heat flow in, the receptors are activated, and the receptors send signals to the cells that starts them growing and replicating, and voila, you have a sprout.

Ltryptophan's avatar

@gemiwing great link, thanks!

ragingloli's avatar

How do engines know there is petrol in the lines and tank and oxygen in the air?

jaytkay's avatar

This fascinates me, too. A month ago I had a three-year old package of seeds in a drawer. Today I have little cilantro plants. Ta-da! Magic!

A real crazy seed story – some pine cones protect the seeds so well that only a fire will free them. So basically it takes a forest fire to let the seeds “know” it’s time.

marinelife's avatar

Obviously, from this picture, they don’t.

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ETpro's avatar

They don’t react to soil, they react to water filled with nutrients good soil provides. That’s why you can sprout seeds on a damp rag or piece of filter paper. Evolution has engineered them to react to conditions most likely to be encountered in nature in fertile soil in the presence of adequate water to grow. When the water soaks through the seed’s skin, that triggers a chain of chemical reactions that begins the seeds cell mitosis. Uptake of water and nutrients sustains the cell division, and the plant’s DNA maps out what becomes root, stem, leaf and so forth.

Because it takes water to trigger all this, the seed can lie in good soil without germinating and thus survive a drought, only going to work when water is present. You see this in the tremendous profusion of flowers that bloom in a desert after rains sweep through it.

Andreas's avatar

Another thought fellow Flutherites: Seeds seem to have inbuilt clocks so that even if the conditions for germination are right, not all the seeds will necessarily germinate at once. Just in case the right conditions don’t last and a dry spell happens before the seedling has a chance to establish itself. The wonders of the plant world never cease to amaze me. Incredible!

Andreas.

BhacSsylan's avatar

@Andreas Yep, though this is less to do with clocks and more to do with, essentially, the randomness of cellular processes (stochasticity, if you want to impress your friends). Conditions may be right, but receptors may not fire, or those receptors may not start the process, etc. This was selected for in evolution because, as you said, sometimes good times don’t last, and plants with a few extra seeds waiting until later will have a better chance of surviving potentially harsh early spring weather.

Interestingly, a very similar form of this can be found in some bacteria, most importantly tuberculous. Some cells will simply shut shut down for periods at a time, with almost no life processes. Then, randomly, they start up again. This is why it can be such a nasty disease to fight, because most ordinary medications can’t fight a cell with no metabolic processes.

Andreas's avatar

@BhacSsylan Great comment and addition to what I said. The “clock” point I made was how it was explained to me a number of years ago. Your answer is the correct technical one. Thank you.

Andreas

webserf's avatar

Although it has been covered in depth, WATER is the catalyst that causes seeds to sprout. IT is important to note that seeds WILL sprout without soil, but as many have pointed out, they will, at some point need nutrients.
For those who are questioning this fact, consider looking up “Hydroponics”, which is, in essence the science of growing plants in water/nutrient solution(s) as opposed to soil.

Moisture is what starts the chemical/cellular reaction, and the rest is “magic”!

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