Tag: coordination in plants

The area of the plant which perceives a stimulus is called as perceptive region. Tip of the stem is the perceptive region for the light. The area of the plant which shows the response is called as responsive region. 

Hydrotropism is the response of the plant towards the water stimulus. It was first demonstrated by Johnson in 1829. During the course of his experiments, he found that when the air into the roots of seedlings penetrated, the roots continued to grow downwards. Hydrotropism can be positive as in case of growth of roots towards the water and also negative which is shown by shoot growing away from the water source. 

Geotropism is the plant response to the stimulus of gravity. Plant growth away from the gravity is called as negative geotropism. Stem shows negative geotropism. Plant growth towards the gravity is called as positive geotropism. Root shows positive geotropism.

Auxin is the hormone that stimulates cell elongation and growth. In the shoot when light falls on it the hormone gets activated and also promote the movement of shoot towards the light.

Phototropism of shoot and geotropism of root are due to several hormonal action. The hormones responsible include auxin plant hormone. Auxin is responsible for the growth of shoot positively phototrophic. Auxin also induces apical dominance in shoots.

Pnuematophores are called as breathing roots. These are found in mangrove trees. These are the modifications in root which grows in the same direction as that of shoot. Thus, they are negatively geotropic as well as positively phototrophic.

Haptotropism or thigmotropism is known as the movement of parts of a plant in response to a touch stimulus. Chemotropism is the growth of organisms such as bacteria and plants, navigated by chemical stimulus from outside of the organism or organisms part. The response of the organism or organism part is termed 'positive' if the growth is towards the stimulus or 'negative' if the growth is away from the stimulus. Geotropism or gravitropism is a turning or growth movement by a plant in response to gravity. Phototropism is the movement of plants in response to light.

'The power of movement of plants' is a book by Charles Darwin on phototropism and other types of movement in plants. This book contains his works in producing evidence for his theory of natural selection. The power of movement of plants was published on 6th November 1880, and 1500 copies were quickly sold by publisher John Murray. This book stands at the culmination of a long line of study in plants and is immediately preceded by 'The different forms of flowers on Plants of the same species' (1877).

Charles Darwin studied phototropism by covering different parts of oat coleoptiles and subjecting them to light from one direction. When he covered or removed coleoptile tip, phototropic response did not occur and concluded that phototropic bending in the zone of elongation was controlled by the tip. The movements which allow organs of plants to move in or the other directions is called movements of curvature. His demonstration that the site of photoreception at the shoot tip and the location of curvature are separable. From his observations, Darwin was able to propose that a transmissible substance produced in the tip is responsible for inducing curvature in lower regions of the plant. This insightful discovery eventually lead to the discovery of first plant hormone - auxin.