In this article we will discuss about the locomotion and curvature movements which arises in higher plants.
1. Locomotion in Plants:
a. Autonomic Movements:
Spontaneous movement arises automatically due to intrinsic reasons in the body. This is usually observed in unicellular organisms, for example, flagellar movement in Chlamydomonas.
They are mainly:
i) Movement of variation:
It is due to changes in cell because of pulsation easily found in Indian telegraph plant.
ii) Movement of growth:
Growing areas like root and shoot tips move upwards and downwards accordingly due to growth of organs. It is a slow movement observed in all plants and trees.
b. Paratonic Movements:
It is also known as lactic movements observed in complete cell or cell organelles in response to stimuli from outside the plant. It is chemo taxis for chemicals or photo taxis for light.
2. Movements of Curvature in Plants:
These movements are observed when changes in orientation of plant in response to external and internal stimuli. They can be growth or turgor, autonomic or paratonic which is tropic or nastic.
a. Tropic Movements:
Tropism is a plant movement that is determined by the direction of environmental stimulus. As soon as stimulus is received, specific part shows response by growth movements. This is due to unequal growth on its two sides by action of phytohormone. The movement of plant is towards the stimulus, then it is positive tropism and if it is against the stimulus, then they are negative tropism.
The locomotion is as follows:
i) Phototropism:
Stimulus is light movement of plant organs in response to the unilateral effect of light is called phototropism. Stems are positively phototrophic while rules are negatively phototropic. Leaves are transversely phototropic as they keep their faces at right angles to the direction of light.
ii) Geotropism:
The response is due to gravity if plant moves in the direction of gravity it is called positive geotropism and if opposite direction than negative geotropism. Roots are positively geotropic while the stem is negatively geotropic.
iii) Hydrotropism:
The movement is in response to water. Roots are positively hydrotropic. Positively hydrotropic response is stronger than geotropic one for roots i.e. they act for water on priority irrespective of gravity.
iv) Chemotropism:
This is response for chemical stimulus. This is visible in the growth of pollen tubes is style, ovary, and ovule. Here, every region products its own nutrients and chemotactic chemicals for growth and passage of pollen tube. Chemotropism is observed in germinating pollen grains. A drop of boron medium will result in bending of pollen tubes towards it from all directions.
v) Thigmotropism:
It is directional growth in response to the stimulus of contact. This is found in turners and tendrils. After the initial contact with support (wood or stick or another thick plant) due to notation turners and tendrils show less growth in the region of contact. The other side shows normal growth along with a bend over support.
b. Nastic Movements:
Reponses to stimuli where direction of the response is not determined is called nastic movement.
Examples of stimuli are heat, light, and torch. In nastic movements, from whichever direction the stimulus is applied, it affects all parts of the organ of a plant equally and they always move in same direction.
Types of Nastic Movements:
i. Photonasty:
Plant sleeps during the night as there is no sunlight.
ii. Thigmonasty:
This is in response to temperature movements, for example, tulip flowers open at high temperature.
iii. Nyctinasty:
Plants response to darkness, for example, opening and closing of stomata.
iv. Siesmonasty:
This is a plant movement in response to touch or shock, for example, Mimosa pudica or touch me not.
v. Hyponasty:
These are movements involving upward bending of the lower part of a plant.
c. Autonomic Movements:
Locomotion movements:
These are the movements of protoplasm. These are present in marine plant-sand are free, spontaneous.
Growth and curvature:
Plants are attached at one place, hence can charge only direction of their organs. These are nutation and nastic movements. The nutation movements are seen in turners and climbers, whereas and the nastic movements are due to differences in the rate of growth on opposite rides.
Variation movements:
These are due to changes in turgidity of cells, for example, the Indian telegraph plant.