Question

9. Describe in full detail ONE of the plant hormones discussed in class. Support your description by discussing the chemical nature, site of biosynthesis, transport, effects, and practical uses.

Answer 1

There are many plant hormones we studied like GA2 cytokinines

On the molecular level, all auxins are compounds with an aromatic ring and a carboxylic acid group. The most important member of the auxin family is indole-3-acetic acid (IAA), which generates the majority of auxin effects in intact plants, and is the most potent native auxin.chemical structure of auxin IAA

Site of synthesis: The natural auxin found in plants is called IAA predominantly synthesized in the stem apexes like shoot and root.

Transport : Polar auxin transport is the regulated transport of the plant hormone auxin in plants. It is an active process, the hormone is transported in cell-to-cell manner and one of the main features of the transport is its directionality (polarity).

Effects

Auxins are a powerful growth hormone produced naturally by plants. They are found in shoot and root tips and promote cell division, stem and root growth. They can also drastically affect plant orientation by promoting cell division to one side of the plant in response to sunlight and gravity

Practical uses

1. Rooting: NAA and IBA are widely employed in initiating early and vigorous rooting in plants which are propagated by cuttings.

2.Prevention of Pre-Harvest Drop of Fruits: Premature falling of the fruits can be checked by the application of auxins such as 2, 4-D and 2, 4 6-trichlorophenoxy acetic acid.

3.Parthenocarpy: Parthenocarpic seedless fruits are obtained on commercial scale by the application of auxins in many plants.

4. Inhibition of Buds to Prevent Sprouting:Auxins like NAA prolong the dormancy of buds in potato tubers and thus are very useful in preventing the eyes of potato tubers to sprout during storage

5. Shortening of Internodes:In apples and pear the fruits are developed on dwarf spurs. Treatment of the other termi­nal shoots with a-naphthalene acetic acid prevents the elongation of their internodes so that they also become dwarf. The latter may also bear the fruits.

6.Selective Weed Killers:At higher concentrations the auxins may have profound herbicidal properties and are utilised in the eradication of the weeds like 2,4-D