MadSci Network: Botany

Re: How is it that a carnivorous plant can take nourishment from an insect.

Area: Botany
Posted By: Evelyn Tsang, Grad student Molecular Evolutionary Biology, McGill University
Date: Thu Dec 12 18:48:53 1996

Hello Katie, neat question. Let's break it down into sections:

Plants don't actually have nerves. What you're seeing is called seismonasty (or thigmonasty). Seismonastic movements are the result of a plant's ability to transmit a stimulus from touch-sensitive cells in one part of the plant to responding cells located elsewhere. The Venus-flytrap uses seismonastic movement to gather nutrients for itself.

As most plants are unable to move around to forage for food, they rely on their leaves to produce simple sugars through photosynthesis, and on their roots to absorb mineral nutrients from the soil. Nutrient availability happens to be dependent on the soil pH, and in areas such as acid or peaty bogs, there aren't very many nutrients at all. This is where you would find insect-catching plants such as the Venus-flytrap, the sundew and the pitcher plant. These plants have modified their leaves from photosynthetic to insect-catching functions.

In the case of the Venus-flytrap, the end of a leaf consists of two lobes joined along the central axis. Each lobe contains tiny trigger hairs attached to "motor" cells in the epidermal (outermost) layer of the leaves. When two or more hairs (or if one hair is touched twice) in succession, then the motor cells are stimulated to move positive ions from within the cell to the cell wall. This occurs all along the outer surface of the central portion of the lobes of the trap. This change in pH expands the outer epidermal cells along the central portion of the leaf, and since the inner epidermal cells have not changed in size, the flytrap snaps shut. **This takes about 1-2 seconds and a LOT of energy to accomplish.** Once shut, glands touching the insect secrete digestive enzymes- and thus the prey is dissolved and absorbed by the plant. When empty, epidermal cells along the midrib of the inner surface of the leaf expand and the leaf opens once more. This less strenuous activity takes about 8-12hrs to accomplish.

Hope this answers your question!

Evelyn E. Tsang
Biology Graduate Student
McGill University

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