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In this heretofore long-winded explanation of what happens when a plant “rests” for a season, we’ve reviewed some basic molecular biology.  Hopefully concepts like cells, molecules, DNA, and enzymes are more clear now.  If not, here’s a one sentence refresher:

Cells are biological units containing many kinds of molecules, DNA being a specific kind that tells the cell how to make enzymes, the molecules that do the work of a cell.

One thing that cells (and hence the organism they are a part of) do is adjust to changing conditions.  And in nature, nothing is more constant than the changing of seasons.   When winter approaches, certain enzymes of the cell monitor the shortening of days and the drop in temperature marking the approach of cooler weather.

Your typical enzyme molecule works with others of its same kind in a sort of gang on an assembly line, getting handed some tweaked molecule from the enzyme upstream,  which they then tweak themselves, and then passing it to the next guy down the line.  Sometimes, believe it or not, the enzymes tweak themselves and pass themselves down the assembly line!

Here’s a classic clip from I Love Lucy that I hope will illustrate the assembly line-like nature of biological processes:

Of course, if you’ve read my previous post, you’ll know that the assembly line analogy falls apart at some point, too, since what you really have are swarms/clouds of a specific enzyme type overlapping in 3-dimensional space other clouds of enzymes or reactants, all carrying on their highly specific work by randomly bumping into each other.  Yes, biology is very, very complex.  (And that’s why there’s still no cure for cancer despite the billions and billions of dollars spent on research.)

Anyways, back to the weather: how do enzymes “know” that seasons are changing?  After all, they don’t actually think, do they?  No, enzymes don’t think.  But they do react — and by react, I mean they are involved in chemical reactions.  And when, say, the temperature-monitoring enzymes experience a change in temperature, they fail to react in the way they usually do.  This makes all the difference in the world.

You can think of the cell as a vast array of different assembly lines/swarms manufacturing and reacting and moving all manner of molecules.  The temperature induced change in reaction rate gets transmitted down the line in what is like a giant Rube Goldberg contraption of mind-boggling complexity, until it reaches some central switch enzyme that controls the change-of-seasons genetic program.  In other words, the information about changing seasons is conveyed to this central switch enzyme, which then turns on all the enzymes that are needed for colder (or warmer) weather or when it’s time to put up a flower.  Just as a football team changes from offense to defense to special teams, so a plant has enzymes for spring, and enzymes for winter (or their relative equivalents in tropical slipper orchid country).

So back to the original question: what happens when you let your plants rest?

My answer is that the plant changes a genetic program.  It’s not because you might otherwise grow them to death.  Plants are designed to grow: that’s what they do.  But part of their growth cycle requires a switch to a different seasonal genetic program, which entails production of a bunch of different enzymes.  And the plant likely needs those enzymes to get made and do their thing for long-term health.

It’s kind of like those claims that your plants (or you) need trace elements such as selenium or molybdenum for health.  Some species of orchids need the change in seasons to cause the change in genetic program to cause the production of certain enzymes to do specific things so they’ll grow well and put up a flower for you.