Question

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?
A. Auxin and abscisic acid
B. Gibberellin and abscisic acid
C. IAA and gibberellin
D. Auxin and cytokinin

Answer 1

Hint: Plant growth regulators are simple molecules having diverse chemical composition.
They could be indole compounds, adenine derivatives, terpenes or gases.
Plant growth regulators are also known as plant hormones or phytohormones.

Complete answer:
The plant growth regulators are divided into further of two categories:
1. Plant growth promoters
2. Plant growth inhibitors
Plant growth promoters are plant hormones that help in regulation of growth by promoting the growth of the plant.
For example: Auxin, Gibberellin and cytokinin.
Plant growth inhibitors are plant hormones that help in regulation of growth by inhibiting the excessive growth of the plant.
For example: Abscisic acid.
Auxin is the plant growth hormone that promotes lengthening and coordinates with other growth hormones to regulate growth.
It also causes apical dominance.
Cytokinin is the plant growth hormone that promotes cell division in shoot apical meristem and differentiation in root apical meristem.
It works antagonistically to auxin to balance the growth with development in shoot and root apex.
Gibberellin: They also act as the promoters.
There are more than 100 gibberellins found in different types of organisms such as fungi and higher plants.
They produce physiological responses and have the ability to cause an increase in the length of the axis.
Abscisic acid: It is also known as stress hormone.
It inhibits the seed germination and increases the tolerance of plants to various kinds of stresses.

So, the correct option is option D. Auxin and Cytokinin.

Note:
> Auxins also induce parthenocarpy for example in tomatoes.
> It is also used as herbicides.
> 2,4-d used to kill dicotyledons weeds, but does not affect mature monocotyledonous plants.
> It also controls Xylem differentiation and helps in cell division.