Thigmonastic movements in Venus flytrap and Potometer-tool to measure traspiration

Thigmonastic movements are shown by some insectivorous plants such as Venus flytrap, Drosera, etc. These plants have tentacles, which are sensitive to the stimulus of touch.

In the herbaceous Drosera or Sundew each leaf is covered on upper surface by glandular hairs called as tentacles. Each tentacle bears a gland at its tip.Glands are reddish in color and secrete viscous fluid which glitters in sun like dew drops, hence called sundew. When any insect, mistaking the glistening substance as honey, comes in contact with leaf, gets entangled in viscous sticky fluid. Tentacles bend upon the insects and the lamina of leaf assumes cup-like structure. Digestive juices are secreted and digested  food is absorbed.

Dionaea muscipula or venus fly trap is a herbaceous plant and grows on damp mossy places.Each half of leaf blade bears three long pointed triggers hairs placed triangularly on the leaf surface. The midrib of leaf functions as a hinge between two lobes of the lamina. The upper surface of leaf bears reddish digestive glands. When the insect sits on the leaf, the sensitive pointed hairs bring about the sudden closure of leaf. Glands secrete the enzyme pepsin and hydrochloric acid, thereby digesting the protein contents of the trapped insect.

Thigmonastic in Venus flytrap

In Venus flytrap, the change in turgor pressure occurs.In this shift, the H+ ions are pumped into the walls of cells in response to the action potentials from the trigger hairs.

These protons loosen the cell wall in such a way that the tissue becomes flaccid, and because of this the cells quickly absorb water. That causes each leaf to expand from outside and the trap to snap shut.

P- proteins (Phloem Proteins) are components found in large amounts in phloem sieve tubes. The main function of these bodies is to seal off the sieve tube element or sieve cell by bringing about the blockage of sieve plate when the sieve element is injured. These bodies and callose together block the pores of sieve tube elements.P-protein bodies and callose from blocking plugs. P-protein bodies are assigned some functions in the translocation of food material in the sieve tubes, but it is not universally accepted.

The primary purpose of P-protein bodies is to seal off the sieve tube element or sieve cell by bringing about the blockage of sieve plate when the sieve element is injured. These bodies and callose together block the pores of sieve tube elements.P-protein bodies and callose forms blocking plugs.

P-protein bodies are assigned some functions in the translocation of food material in the sieve tubes, but it is not universally accepted.

Stomata are the primary organs for transpiration. The epidermis of stem and leaf are provided with numerous stomata. Diffusion of water vapor through the stomatal pores is known as stomatal transpiration. Transpiration occurs while the stomata are open for the passage of carbon dioxide and oxygen during photosynthesis.The movement of the guard cells regulates the opening and closing of the guard cells.

Stoma complex consisting of a pore surrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lack chloroplasts.

How guard cells differ from the epidermal cells:-

  • The guard cells are bean-shaped in surface view, while the epidermal cells are irregular in shape.
  • The guard cells can manufacture food by photosynthesis as they contain chloroplast. (The chloroplasts are absent in epidermal cells).
  • The guard cells are the epidermal cells that can make sugar.

Potometer

Potometer is an instrument of apparatus with the help of which, the rate of transpiration is measured, Main types of potometers are Simple potometer, Farmer’s potometer, and Ganong’s potometer.

The whole instrument is made of glass and is consisted of a long tube, having a side tube, bent at right angles. A fresh piece plant shoot is cut under water and then these pieces are inserted inside tube through a cork, the cork fitted into the mouth of this tube. The whole apparatus is filled with water and the joints are made air tight.

The apparatus is placed in the sunlight. The air bubble enters the tube and after this lower end of the tube is placed in the beaker, containing water, Water is absorbed by the shoot and transpired through the leaves. Transpiration pull is created and cause the movement of air bubble with it.Readings are taken for the air bubble and thus the amount of water absorbed and transpired is calculated.