Which of the following is not an inhibitory substance governing seed dormancy? [2020]
Gibberellic acid
Abscisic acid
Phenolic acid
Para-ascorbic acid
(1)
Gibberellic acid is involved in growth promoting activities, such as cell division, cell enlargement, pattern formation, tropic growth, flowering, fruiting, and seed formation, and is called a plant growth promoter. It breaks seed dormancy, which is antagonistic to abscisic acid.
It takes very long time for pineapple plants to produce flowers. Which combination of hormones can be applied to artificially induce flowering in pineapple plants throughout the year to increase yield? [2019]
Cytokinin and Abscisic acid
Auxin and Ethylene
Gibberellin and Cytokinin
Gibberellin and Abscisic acid
(2)
Synthetic auxins like NAA and 2, 4-D are often employed for inducing flowering in pineapple. Ethylene also stimulates flowering in pineapple and related plants. Hence, both auxin and ethylene can be applied artificially to induce flowering in pineapple plants throughout the year to increase yield.
Fruit and leaf drop at early stages can be prevented by the application of [2017]
ethylene
auxins
gibberellic acid
cytokinins
(2)
In low concentrations, auxins such as 2,4-D (2,4-Dichlorophenoxy acetic acid) are useful in preventing pre-harvest fruit drop and leaf drop.
You are given a tissue with its potential for differentiation in an artificial culture. Which of the following pairs of hormones would you add to the medium to secure shoots as well as roots? [2016]
IAA and gibberellin
Auxin and cytokinin
Auxin and abscisic acid
Gibberellin and abscisic acid
(2)
Cytokinin and auxin are two plant hormones that are supplied to the tissue culture medium in definite proportions. They bring about cell division and differentiation of callus. A low auxin to cytokinin ratio promotes shoot formation whereas a high auxin to cytokinin ratio promotes rooting of callus.
The Avena curvature is used for bioassay of [2016]
IAA
ethylene
ABA
(1)
Avena curvature test is a test based on the experiments of Went (1928) which can measure auxin up to 300 mg/litre. Indole-3-acetic acid (IAA) is a universal natural auxin and Avena curvature test serves as an accurate bioassay for this plant hormone.
Auxin can be bioassayed by [2015]
potometer
lettuce hypocotyl elongation
Avena coleoptile curvature
hydroponics
(3)
Auxin bioassay is a quantitative test as it measures concentration of auxin to produce the effect and the amount of the effect. Avena curvature is based upon experiments of Went (1928). 10° curvature is produced by auxin concentration of 150 mg/litre at 25°C and 90% relative humidity. The test can measure auxin up to 300 mg/litre. Auxin from a shoot tip or any other plant organ is allowed to diffuse in a standard size agar block (generally 2 × 2 × 1 mm). Auxin can also be dissolved directly in agar. 15–30 mm long oat coleoptile grown in dark is held vertically over water. 1 mm tip of coleoptile is removed without injuring the primary leaf. After 3 hours a second decapitation is carried out for a distance of 4 mm. Primary leaf is now pulled loose and agar block supported against it at the tip of decapitated coleoptile. After 90–110 minutes, the coleoptile is found to have bent. The curvature is measured. It can also be photographed and the curvature known from shadow graph.
What causes a green plant exposed to the light, on only one side, to bend towards the source of light as it grows? [2015]
Light stimulates plant cells on the lighted side to grow faster.
Auxin accumulates on the shaded side, stimulating greater cell elongation there.
Green plants need light to perform photosynthesis.
Green plants seek light because they are phototropic.
(2)
Auxins induce cell elongation. In a differentially illuminated plant, they accumulate in the shaded part, causing elongation of the cells in the shaded part. This unequal elongation on two sides causes the plant to curve or bend towards the light source, i.e., phototropic curvature.
Dr. F. Went noted that if coleoptile tips were removed and placed on agar for one hour, the agar would produce a bending when placed on one side of freshly-cut coleoptile stumps. Of what significance is this experiment? [2014]
It made possible the isolation and exact identification of auxin.
It is the basis for quantitative determination of small amounts of growth-promoting substances.
It supports the hypothesis that IAA is auxin.
It demonstrated polar movement of auxins.
Which one of the following growth regulators is known as ‘stress hormone’? [2014]
Abscisic acid
Ethylene
Indole acetic acid
(1)
Abscisic acid prepares plants to cope with stress conditions like drought, etc. by inducing stomatal closure and other reactions. Hence, it is named stress hormone.
