PGR 2

Question 1

discovery of auxin

Answer 1

All
this started with the observation of Charles
Darwin and his son Francis Darwin when they
observed that the coleoptiles of canary grass
responded to unilateral illumination by growing
towards the light source (phototropism). After
a series of experiments, it was concluded that
the tip of coleoptile was the site of transmittable
influence that caused the bending of the entire
coleoptile (Figure 15.10). Auxin was isolated by
F.W. Went from tips of coleoptiles of oat
seedlings.

precursor: tryptophan (zn2+)

1.Natural : IAA (Indole Acetic acid) & IBA (Indole Butyric acid)
2.Synthetic : NAA (naphthalene acetic acid), 2,4-D (2, 4-dichlorophenoxyacetic)
and 2,4,5-T (2, 4, 5-trichlorophenoxyacetic)

Question 2

discovery of giberellic acid

Answer 2

The ‘bakane’ (foolish seedling) disease of rice seedlings, was caused
by a fungal pathogen Gibberella fujikuroi. E. Kurosawa reported the
appearance of symptoms of the disease in uninfected rice seedlings when
they were treated with sterile filtrates of the fungus. The active substances
were later identified as gibberellic acid.

discoverer: precursor types
Yabuta & Sumiki Acetyl CoA GA1, GA2, GA3

Question 3

discovery of cytokinins

Answer 3

F. Skoog and his co-workers observed that from the internodal
segments of tobacco stems the callus (a mass of undifferentiated cells)
proliferated only if, in addition to auxins the nutrients medium was
supplemented with one of the following: extracts of vascular tissues, yeast
extract, coconut milk or DNA. Skoog and Miller, later identified and
crystallised the cytokinesis promoting active substance that they termed
kinetin.