How do seeds know when to grow?

Joe asks:

why are seeds able to wait for the proper condition to germinate?

Because that’s what seeds do.  Really. Now, HOW they do it, that’s a whole different question…..

Without getting into some fairly complex biochemistry, the answer is fairly simple. Seeds have a whole slew of little biological switches. They are turned on and off depending on the environment that the seed is exposed to. Some of them are fairly simple. For example, if it is very dry, the seed’s shell will stay hard, and keep what moisture there is inside the seed where it belongs – inside the seed. If the outer environment gets wetter, the seed shell will absorb some of the water and get softer. This is actually lot more complex than just soaking up water – the proteins and lipids in the shell actually change shape and go through a bunch of other changes as they absorb the water.

These changes do all sorts of things. When they change shapes, they expose different parts of the proteins to the inside of the seed. When this happens, the newly exposed parts can trigger other reactions inside the seed. Those changes trigger other changes, and if conditions are right, the seed may start to grow.

This is a very simplistic example – all we are looking at is the amount of water int he environment. Temperature, light, nutrients, and a whole slew of other factors can come into play, but the basic concept is the same. If all of these “switches” ‘turn on” (or off) in the right combinations, and in the right sequence, the seed will start to grow.

Sometimes, a seed can “turn on”, then if conditions don’t stay right, they can “turn off” again until conditions get better, but not always. Of course, the longer the seed has been growing, the less likely it will be to be able to return to being dormant. Some seeds are really incredibly good at waiting for the right conditions. A few years ago, a 2,000 year old date palm seed was successfully sprouted, and is still growing. Pretty cool by my book…..

So there ya go. Seeds are basically little environment computers waiting for conditions to be just right  before they launch their “grow” application.

See, science isn’t all that hard if you ask the right questions……

One Response to “How do seeds know when to grow?”

  1. Mrs. Chili Says:

    YAY!! Dr. Science is back! I MISSED you on the internet (though I’m really digging that I get to see you every work day!).

    Now, can you explain to me why honey never goes bad? (your 2000-year-old date palm story made me remember that I’d heard someone found a jar of honey in a tomb somewhere in Egypt and that it was still safely edible…).

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