Plant Growth and Development Test - 43

Avena sativa stem tip test or Avena curvature test is a diagnostic test for auxin. In this test auxins accumulate on the dark side (not exposed to light) of oat coleoptile and cause more growth on the darker side than the exposed side. Thus, causing a curvature stem towards the source of light.

The tropic movement taking place as a response to the light stimulus is called as phototropism. Some of the plant parts such as stems, branches, leaves and pedicels of flowers move towards the stimulus of light and are said to be positively phototropic while others such as roots and rhizoids which move away from the stimulus of light are said to be negatively phototropic. Phototropism was first studied by Charles Darwin in 1880, in canary grass and oat coleoptiles. Later on F. W. Went in 1923, suggested the involvement of auxins in this phenomenon.

Ethylene is a simple gaseous plant growth regulator (PGR). It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called as respiratory climacteric.

Auxin promotes cell growth and elongation of the plant. In the elongation process, auxin alters the plant wall plasticity, making it easier for the plant to grow upwards. Auxin also influences rooting formations. By applying NAA or IBA to a plant cutting from a parental plant, rooting takes less time for the new plant greatly increasing its chance of survival. Auxin is responsible for apical dominance and phototropism. Apical dominance means that a plant has the tendency to grow quickly up the central shaft without properly filling in the plant with smaller limbs and leaves. Phototropism is a process by which auxin on the exterior of a plant is degraded to cause a slope of the plant towards the light.

Therefore, the correct answer is option D.

D- Continuous exposure to ethylene results in inhibition of growth and therefore prevents sprouting. 

Ethylene is a simple gaseous plant growth regulator (PGR). It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called as respiratory climacteric.

A.Correct option B

B.Explanation for correct option:

Cytokinins are a group of plant growth regulators which are primarily involved in performing the function of cell division in plant roots, shoot system. This hormone helps in promoting the cell's growth, development, differentiation, affecting apical dominance and delay in leaf senescence.