Autonomic Movements in Plants

Autonomic Movements in Plants:-

1. Growth movements

2. Variation movements

1. Autonomic growth movements:- These movements are due to unequal growth in different parts of an organ and are irreversible. They are independent of the surroundings of plants or external stimuli. They are further divided into types:

a. Nutation:- These movements occur in the growing stem of twiners (peas or beans). The stem exhibits a kind of nodding movements in two directions. As, the stem apex shows more growth on one side at one time and a little later there is a greater growth on the opposite side. It is called nutation. This circular movement of growing stem takes place always in the same direction for the same plant species. Since, the more rapid rate of growth travels around the tip which, as it grows upwards must therefore rotate.

b. Circumnutation:- In spirally growing stems and tendrils, the region of greater growth passes gradually around the growing point resulting in the spiral coiling of stem and tendrils. Such a movement is called circumnutation.

c. Epinasty and Hyponasty:- They are non-directional movements in which the response is determined by the structure of the responsive organ and not the direction of the stimulus. This kind of movement is exhibited mostly by young leaves, organs having dorsiventral symmetry.

> Epinasty is caused due to rapid growth on the upper surface (abaxial side), such as occurs at the time of the opening of leaves.

> Hyponasty is greater growth on the lower side (adaxial side) e.g., circinate coiling and closed sepals and petals in a floral bud.

2. Movements of variation:-

> They are autonomous curvature movements and are independent of external stimuli.

> They are not growth movements hence are reversible.

> These movements are also known as turgor movements because these are brought about by changes in the turgor pressure of certain sensitive cells of the plant organs. Such movements are exhibited by lateral leaflets in Desmodium gyrans.