Question

Low concentration of auxin inhibits growth in
(a)Stem
(b)Roots
(c)Leaves
(d)Flowers

Answer 1

Hint: Auxins are a powerful growth hormone produced naturally by plants. Auxin is found in shoots and root tips. The presence of auxin promotes cell division, stem, and root growth. Hence, the plant becomes shorter as a low concentration of auxin hampers their growth.

Complete answer:
Apical dominance is a phenomenon in which the central stem is dominant and lateral stems are suppressed. It promotes stem elongation and inhibits the growth of lateral buds. Hence, a low concentration of auxin inhibits growth in the stem.
It is seen that in response to sunlight and gravity, auxin can also drastically affect plant orientation by promoting cell division to one side of the plant. High or low concentrations of auxin are already classified as toxic and often retards protoplasmic streaming which may also inhibit the morphological growing parts of the plant where it was applied.

Additional Information: -The first major plant hormones discovered is auxin. In the coordination of many growths and behavioral processes in plant life cycles, Morphogen-like auxins play a cardinal role. They are very essential for plant body development.
-Auxin is present in all parts of a plant in very different concentrations. The concentration of the auxin is crucial developmental information in each position, so it is subject to tight regulation through both metabolism and transport.
-In-plant bodies, auxin creates "patterns" of auxin concentration maxima and minima, which in turn guide further development of respective cells, and ultimately of the plant as a whole.
- A scientist named Kenneth V. Thimann (1904-1997) first isolated one of these phytohormones and determined its chemical structure as indole-3-acetic acid (IAA).
-Five naturally occurring (endogenous) auxins in plants include indole-3-acetic acid, 4-chloroindole-3-acetic acid, phenylacetic acid, indole-3-butyric acid, and indole-3-propionic acid.
-The Dutch biologist Frits Warmolt Went first described auxins and their role in plant growth in the 1920s.
-Auxin induces the formation and organization of phloem and xylem. The auxin may induce the cell differentiation and regeneration of the vascular tissues when a plant gets wounded.
So, the correct answer is, ‘Stem’.

Note: The plant originated hormone auxin participates in phototropism, geotropism, hydrotropism, and other developmental changes. Cell elongation is stimulated by auxin through stimulating wall-loosening factors, such as elastins, to loosen cell walls. The presence of gibberellins makes this effect stronger, also in the presence of cytokinins auxin stimulates the cell division. If the auxin concentration is higher than cytokinin concentration when auxin and cytokinin are applied to callus, it can generate rooting. And when the auxin concentration is equal to the cytokinins, xylem tissues can be generated.