Tag: tropic and nastic movements in plants

Tendrils are the threadlike organs of plants which are actually specialized stem, leaf or petiole and used for climbing, support or attaching to another for parasitic growth. Most climbing plants such as vines develop tendrils that tend to coil around objects that support it. This feature of the tendrils is due to a phenomenon called thigmotropism - directional growth movement of curvature in response to stimulus or contact.

Auxin is a plant hormone that plays important role in the growth of stem and roots to gravity. Gravitropism is a plant growth response to gravity. Root shows positive gravitropism and shoot shows negative gravitropism. Auxin content is lower on the upper side and more concentration occurs in lower side of the root and stem. This stimulates stem elongation and thus stem grows upwards. In roots, higher growth on upper side occurs due to lower auxin content. This inhibits root elongation and thus root grows downwards showing geotropic response. 

Auxin is a plant hormone that plays important role in the growth of stem and roots to gravity. Gravitropism is a plant growth response to gravity. Root shows positive gravitropism and shoot shows negative gravitropism. When plant is placed horizontally, more concentration occurs in lower side of the root and stem. This stimulates stem elongation and thus stem grows upwards. This inhibits root elongation and thus root grows downwards. 

Turgor movement is a reversible change in position of a plant part due to a change in turgidity of cells. It is mostly caused by contact. Mimosa pudica shows dropping of leaves upon touching. In this sensitive plant, the pulvinus and pulvinnules are responsible for the folding of the leaves. In this, turgor changes occur in thin walled cells of pulvinus present on lower side and pulvinnules present on upper side. This results in folding of pinnules and pinnae comes together causing drooping of the compound leaves.

Nutation is the bending movements shown by some plant parts due to the unequal rate of growth of different parts of plants. Thigmonasty is the nastic response of a plant to touch. The movements of tentacles of Drosera when comes in contact with insect is due to thigmonasty. The movement of plant part in response to contact with a solid touch is called as thigmotropism. The curvature movements due to support seen in tendrils and twiners is an example of thigmotropism. The movement of parts of a plant in response to air current is called as anemotropism. 

Phototaxis is a movement of part of organism in response to the light. This phenomenon is exhibited by zoospores of certain algae like Ulothrix, Chlamydomonas, Volvox, Cladophora. They exhibit positive phototaxic movement in presence of diffused light and negative phototaxic movement in presence of intense light.

Nutation is the bending movements shown by some plant parts like root, stem, leaf due to the unequal rate of growth of different parts of plants. 

Centromere joins the microtubules of 'Chromosomal spindle fibres and helps in the movement of chromosome during cell division. Centromere also plays an important role in the polymerization of tubulin protein used in the formation of microtubules. Hence it is helpful in attaching the chromosome with spindle fibres.