Tag: movement in plants

Scotopic in general means under low light conditions or night. For example scotopic stomata are stomata open during night and closed during day as against phototropic stomata, which are open during day but closed during night.

Nastic movements are generally observed in leaves, flowers, petals and bud scales. In these structures at some stage of development, growth in one surface is more than the growth on the other surface. There may be two types of such movements: epinasty and hyponasty. If the upper or inner surface has more growth, the movement is called as epinasty. An example for epinasty is the opening up of a flower and the drooping of a bud. In hyponasty, there will be more growth on the lower surface.

Semimonastic movement is the movement caused in response to touch or vibrations. The stimulus from the largely stimulated leaflets travels to other leaflets and their swollen base known as pulvinus. It further activates the leaf rachis and then runs through petiole and finally to the large pulvinus at the end of the petiole, where the leaf attaches to the stem. The potassium ions flows out from the vacuoles of cells in the various pulvini. This allows exit of water from various cells due to loss in turgidity the leaflet closes and the petiole collapses. So, the given statement is true.

Paratonic or induced turgor movements are turgor movements induced by stimuli, such as light, temperature and contact. These movements are also called as nastic movements and may be of various types, such as
(i) Siesmonasty
(ii) Nyctinasty
Siesmonasty means a response to shaking. The best example is Mimosa pudica ("Touch - me - not" plant) which is the sensitive plant. Such plants respond to stimuli, such as touch, blow or mechanical shock by folding their leaflets and lowering their leaves. This effect is caused by a change in the turgidity of the leaflets brought about by the movement of water into and out of the parenchymatous cells of the pulvinus or swollen leaf base.
Nyctinasty or sleep movements are caused by relative changes in cell size on the opposite sides of the leaf base called pulvinus. The movements are attributed to the amount of auxin, $K^+$ ions and therefore the movement of water. Entry of water to the lower side of the pulvinus causes the leaves to stand erect and the exit of water causes them to droop.

Seismonastic movement is a response to touch or blow. In Mimosa pudica plant, turgor movement is seen in leaflets in response to touch. When it is touched, it begins to fold up and droop. Nyctinastic movement is the response of a plant in response to darkness. In this, plant shows circadian rhythm that function on a 24 hour clock. It is seen in leaves of many legume plants. Thigmonastic movement is the response of a plant to touch or vibration. In Drosera, tentacles bend towards the insect's direction after coming in contact. Chemonastic movement is the response of a plant to chemical stimulus. An example is growth of pollen tube towards embryo sac due to presence of sugar in the style.

Mimosa pudica is well known for its rapid plant movement. Like a number of other plant species, it undergoes changes in leaf orientation termed "sleep" or nyctinastic movement. The foliage closes during darkness and reopens in light. The leaves also close under various other stimuli, such as touching, warming, blowing, or shaking. These types of movements have been termed seismonastic movements. The movement occurs when specific regions of cells lose turgor pressure, which is the force that is applied onto the cell wall by water within the cell vacuoles and other cell contents. When the plant is disturbed, specific regions on the stems are stimulated to release chemicals including potassium ions which force water out of the cell vacuoles and the water diffuses out of the cells, producing a loss of cell pressure and cell collapse; this differential turgidity between different regions of cells results in the closing of the leaflets and the collapse of the leaf petiole.

Answer is option A i.e. "Thigmonasty"
Movement in the leaves of mimosa while you touch is called “nastic” movement. Nastic movements are reversible. It means that after some time plant leaf will comes to its original position. Thigmonasty is the nastic response of a plant to touch or vibration.

Plants exhibit two types of induced movements of curvature. These are namely tropic and nastic movements. The directional growth movements in which direction of growth is determined by the direction of stimulus are known as tropic movements. Examples: thigmotropism, phototropism, chemotropism, gravitropism etc. This makes option A incorrect. The non-directive growth movements of plants, wherein the direction of stimulus is not the determinant of the direction of movement, are known as nastic movements. These movements always occur in one direction. Examples: Seismonasty, photonasty, thermonasty etc. This makes option B correct. Thus, the correct answer is B.

Movements in nyctinasty plants are not related to auxin levels.