Question

The natural plant hormones were first isolated from
(a) Corn germ oil and human urine
(b) Cotton fruits, spinach leaves and rice plants.
(c) Avena coleoptiles, spinach leaves and fungus Gibberella
(d) Human urine and rice seedlings

Answer 1

The natural plant hormones, Auxin or Indole- 3 Acetic acid (IAA) was first isolated from human urine by Charles Darwin. Although cytokinin was first isolated from herring sperm DNA, it does not occur naturally in plants. Later, Zeatin, a cytokinin-like hormone was first isolated from corn-kernels (corn germ oil) and coconut milk.

Complete answer: Apart from light, water oxygen, minerals and nutrients plants also require some organic compounds to signal, regulate and control the growth of plants which are collectively called as plant growth regulators or plant growth hormones.
There are five types of plant growth hormones: auxins, cytokinins, gibberellins, ethylene and abscisic acid which are responsible for growth and development of the plant.
Auxin or indole-3 acetic acid – IAA was first discovered by Charles Darwin. It was isolated from human urine. They facilitate flowering in plants ,used in the process of plant propagation etc.
Cytokinin on the other hand are involved in cytokinesis and were first isolated from herring sperm DNA as Kinetins. It does not occur naturally in plants. Later, it was isolated as zeatin (showing cytokinin like activity) from corn-kernels (corn germ oil) and coconut milk.

Thus the correct answer is Option A.

Note: In plant tissue culture experiments, auxin to cytokinin ratio is very important to favor plant growth. High auxin to cytokinin ratio favours roots development and high cytokinin to auxin ratio favours shoot development.