Plant Growth and Development Test - 8

• Gibberellin is responsible for seed germination. The hormone ABA ( Abscisic acid) inhibits seed germination.
• It is a powerful inhibitor promoting seed dormancy. Hence ABA is antagonistic to gibberellin. 
  Thus the correct answer is option B.

Answer is option B i.e. "It is the basis for quantitative determination of small amounts of growth- promoting substances."
Dr F. Went isolated Auxin from Avena coleoptile tip. His experiment demonstrated the polar movement of auxins. Tryptophan is the precursor of Indole acetic acid (IAA, natural auxin). Important biassay of auxins are Avena curvature test and cross root inhibition test.

Phototropism is the growth of organisms in response to a stimulus. It is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light have a chemical called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the farthest side from the light. Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is called positive phototropism, while growth away from light is called negative phototropism. 

Correct Option: D

Solution

Correct answer is option A.

Explanation for correct option:

• Auxin is a plant hormone. IAA is a type of auxin present in the plant.
• Auxins help to initiate rooting in stem cuttings. This property is widely used for plant propagation by stem cuttings.
• Auxin also promotes apical dominance, hence its used in tea plantation.

Correct Option: C

The Avena geo-curvature test is a bioassay for auxin-type growth regulators. Etiolated oat coleoptiles are used and the test is conducted in special perspex trays under diffuse daylight. The coleoptiles, with the primary leaves intact, are arranged in grooves on the trays in 4 series of 6 coleoptiles each, and cut to a size of 10 mm. The test substance is applied on an agar strip covering only the lower halves of the apical cut surfaces of each series. After a 4-hour stay in the dark in moist Petri dishes the coleoptile cylinders are shadow graphed on a 35-mm photographic film. The curvatures are measured from an enlarged projection (10 times natural size) of the shadow graphs. The lowest IAA concentration which can be determined is around 30 to 60 μg/l IAA. The concentration response curves follow a logarithmic course up to 1,000 μg/l.

• Gibberellin - regulate various developmental processes, including stem elongation, germination, dormancy, flowering, flower development, and leaf and fruit senescence.
• Ethylene - majorly used for ripening fruits and for the production of more flowers and fruits.
• Abscisic acid - an inhibitory rather than stimulatory hormone. It is involved in the closure of stomata, bud and seed dormancy.
• Cytokinin - promote cell division, or cytokinesis, in plant roots and shoots. They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and leaf senescence.

Thus, the correct answer is option A. 

• Auxin is a plant growth regulator that promotes apical dominance.
• Bioassay is the method to find the potential effect of any hormone or enzyme on living tissues.
• Avena coleoptile curvature is the experiment done by Frits Warmolt Went in 1926 on avena sativa (oats).
• He checked the efficiency of the auxin hormone in the Avena plant by transporting the hormone in the coleoptile of it and then observed the increase in the length of the plant.