Chapters
In this article, we will discuss the rapid response of the Venus fly trap to the stimulation of hairs on the lobes of modified leaves and discuss how the closure of the trap is achieved. Moreover, we will also discuss the role of auxin in elongation growth by stimulating proton pumping to acidify cell walls. So, let us get started.
Although the plants do not possess nerves and muscles, still their movements are well-coordinated and well-controlled. One of the critical features of all living beings is that they undergo constant shifts and changes. These changes may take place because of their growth or conversions in the body components. The changes or movements in living beings are not isolated, rather they are highly controlled and coordinated.
Now, let us formally define coordination:
The ordered working of distinct, but interrelated parts, so that they can perform one or more activities smoothly is known as coordination
Now, the question arises that how different parts of the plants coordinate with each other as they do not possess a nervous system. Well, the answer is quite simple. Plants use a chemical system for this purpose.
Chemical Coordination in Plants
Plants are active living beings; therefore, they respond to abiotic stimuli in terms of directional growth. This is known as tropism. Since plants cannot move like animals and do not have a nervous system, hence they employ hormones secreted from cells to respond to their environment.
The nervous system in animals responds much more quickly to external stimuli. The hormones in plants respond slowly as compared to the nervous system in animals, however, their effects are long-lasting as compared to the nervous system. Plants use their hormones for multiple purposes which include protecting themselves from pests, chemical defences against herbivores, communicating with other plants, etc.
Plants have different hormones that enable them to coordinate and respond to the environment. Hormones in plants are chemical compounds that are released by stimulated cells and are diffused around the cell.
In the next section of the article, we will discuss the quick response of the Venus fly trap to the stimulation of hairs on the lobes of modified leaves and discuss how the closure of the trap is achieved.
Anatomy of the Venus Fly Trap
The following structures are found in the Venus fly trap:
- Midrib = hinge
- 2 lobes (Three sensory hairs are present on each lobe that respond when they are deflected)
- Glands secreting digestive enzymes
- Glands that secrete nectar to attract insects
- Stiff outer edges that are interlocked so that they can trap insects
Electrical Communication in the Venus Fly Trap
- Plants have communication systems that allow them to coordinate various parts of their bodies
- The Venus fly trap refers to a carnivorous plant that takes its nitrogen compounds supply by trapping and digesting small animals, usually insects
- It is a highly specialized leaf that is divided into two lobes on either side of the midrib
- The interior of the lobes is red and contains glands that secrete nectar on the edges to attract insects
- Three stiff sensory hairs are present on each lobe that respond when they are touched
- If an insect, for example, a fly comes in contact with one of these hairs with sufficient force, action potentials are stimulated. These action potentials are then transmitted rapidly across the leaf
- Due to these action potentials, two lobes are folded together along the midrib, thus trapping the insect
How the Closure of the Trap is Achieved?
- Calcium ion channels in cells at the base of the hair get activated when one of the sensory hairs is touched with sufficient force
- As these calcium ion channels open, calcium ions flow in and produce a receptor potential
- If two of the three hairs are stimulated within 30 seconds, or a single hair is stimulated two times within this period, then action potentials transmit across the trap and close it
- The lobes of the leaf have a convex shape when the trap is open. On the other hand, the lobes have a concave shape, when the trap is stimulated. The concave shape of the lobe implies that they bend downwards, and the trap shuts down. It is thought that this happens because of the release of elastic tension in the cell walls
- Continuous activation of the sensory hairs is needed to seal the trap. This stimulation is provided by the prey that is trapped inside which generates more action potential
- More stimulation of the sensory hairs triggers calcium ions to enter gland cells where they trigger the exocytosis of vesicles that contain digestive enzymes
- After that, the trap remains shut for up to a week so that the prey can be digested, and the plant can absorb nutrients from it
In the next section of the article, we will discuss the role of auxin in elongation growth by stimulating proton pumping to acidify cell walls.
The Role of Auxin in Elongation Growth
- Plant hormones which are also called plant growth regulators enable the majority of the communication within plants
- Auxins are a type of plant hormone or plant growth regulators that affect several aspects of a plant’s growth including elongation growth. The overall length of roots and shoots is determined by the elongation of growth
- The primary chemical in the auxins group made by plants is IAA (indole 3- acetic acid). In simple terms, this chemical is known as auxin
- Auxin gets synthesized in the meristems, where cells divide. Meristems are the growing tips of roots and shoots
- In these meristems, the growth occurs in the following three stages:
- Cell division through mitosis
- Cell elongation by absorbing water
- Cell differentiation
- Auxin (IAA) plays its role in controlling the growth by elongation
How Does Auxin Control Growth by Elongation?
- On the cell surface membrane, the auxin molecules bind to the receptor proteins
- The plant growth regulator auxin triggers ATPase proton pumps so that they can pump hydrogen ions from the cytoplasm into the cell wall (across the cell surface membrane)
- It lowers the pH of the cell wall, i.e., it acidifies it
- As a result, proteins called expansins get activated, which help loosen the bonds present between cellulose microfibrils
- Simultaneously, potassium ion channels are also stimulated to open which results in an increase in potassium ion concentration in the cytoplasm, which decreases the water potential of the cytoplasm
- Consequently, the cell absorbs water through osmosis which increases the pressure inside the cell.
- As the internal pressure of the cell increases, the cell wall stretches, and the cell elongates
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