Chemotropism

Chemotropism is defined as the growth of organisms such as bacteria, plants and fungi , navigated by chemical stimulus from outside of the organism or organism's 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. Chemotropism is defined as the growth of organisms such as bacteria, plants and fungi , navigated by chemical stimulus from outside of the organism or organism's 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. An example of chemotropic movement can be seen during the growth of the pollen tube, where growth is always towards the ovules. It can be also written that conversion of flower into fruit is an example of chemotropism. Fertilization of flowers by pollen is achieved because the ovary releases chemicals that produce a positive chemo-tropic response from the developing pollen tube. An example of positive and negative chemotropism is shown by a plant’s roots; the roots grow towards useful minerals displaying positive chemotropism, and grow away from harmful acids displaying negative chemotropism. Another example of chemotropic movement includes the growth of individual neuronal cell axons in response to extracellular signals. These signals guide the developing axon to innervate the correct target tissue. The neuronal growth cones are guided by gradients of chemoattractant molecules emanating from their intermediate or final targets. There is evidence that the axons of peripheral neurons are guided by chemotropism and the directed growth of some central axons is also a chemo-tropic response, it remains to be determined whether chemotropism also operates in the central nervous system. Evidence of chemotropism has also been noted in neuronal regeneration, where chemotropic substances guide the ganglionic neurites towards the degenerated neuronal stump.