Thursday, 14 April 2011

Plant movements

Plants are stuck in one spot, rooted to the ground, and they don't usually move their parts around much either.  But there are a surprising number of plants that move a bit, although it's often rather slow.  Charles Darwin wrote a book about them.  Many flowers and some leaves fold up at night, for example, and there are seed pods that open quite quickly when a shower of rain comes along to splash the seeds out (especially in the ice-plant family Aizoaceae).  Plants don't have nerves to transmit impulses, nor do they have muscles.  Much of their movement is achieved by changes in turgor pressure, which is the pressure of sap inside the cells.  If cells suddenly swell, or collapse, they can force a leaf or pod to open or close.  Sometimes this works even if the cells are dead, as in some old seed pods.
Perhaps the most spectacular are the traps of the Venus fly trap, Dionaea muscipula, which catch and digest insects in their nitrogen-poor environments.  The traps are specialised leaf tips, and they look for all the world like the gin traps we used to use to catch possums when I was a boy (now illegal, because they're cruel).  They snap shut quickly enough to catch flies and other small insects, which they they digest for their nitrogen.
Our Venus fly trap made a double trap this week. Normally there's just one trap at the end of a leaf, but this leaf has two. I guess something went wrong with the developmental controls, or the patch of cells destined to become the trap got split in two.
Anyway, it seemed a good opportunity to test the signal that shuts the trap. The traps are triggered by a few small hairs on their surfaces. Do the triggers act directly (like a gin trap), or is there a signal sent from the hairs to the closing mechanism? If the latter, then maybe triggering one trap would close them both...


1 comment:

  1. What a great, clear description of how the plants move.