PGR -1 Flashcards
give an intro to auxins
Auxins (from Greek ‘auxein’ : to grow) was first isolated from human urine.
The term ‘auxin’ is applied to the indole-3-acetic acid (IAA), and to other
natural and synthetic compounds having certain growth regulating
properties. They are generally produced by the growing apices of the stems
and roots, from where they migrate to the regions of their action.
examples of auxins
Auxins
like IAA and indole butyric acid (IBA) have been isolated from plants.
NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic)
are synthetic auxins. All these auxins have been used extensively in
agricultural and horticultural practices.
what are some functions of auxins
They help to initiate rooting in stem cuttings, an application widely
used for plant propagation. Auxins promote flowering e.g. in pineapples.
They help to prevent fruit and leaf drop at early stages but promote the
abscission of older mature leaves and fruits.
what is apical dominance
The process in which the shoot apex of a plant grows faster and prevents the growth of lateral buds present at the lower position along the shoot is known as apical dominance.
Control of apical dominance:
The shoot apex releases a hormone called auxin.
Auxin promotes the growth of the shoot apex in the apical region while suppressing the growth of the lateral buds.
what is decapitation? why is it used in growing tea
1: Apical dominance
The phenomenon in which the growth of lateral buds gets inhibited due to the growth of apical bud is known as apical dominance. This is attributed to the action of auxin present at the apical regions of roots and shoots.
2: Decapitation
This is a process in which apical bud is removed to promote the growth of lateral bud by removing the effect of apical dominance.
3: Shoot decapitation in tea plantation
Shoot decapitation helps to remove the influence of auxin on the lateral buds. Hence, the dormant lateral buds become active and proliferate laterally making the plants bushy. This is widely used in hedge-making and tea plucking.
what induces parthenocarpy
Auxins also induce parthenocarpy, e.g., in
tomatoes. They are widely used as herbicides.
2, 4-D, widely used to kill dicotyledonous
weeds, does not affect mature
monocotyledonous plants. It is used to prepare
weed-free lawns by gardeners. Auxin also
controls xylem differentiation and helps in cell
division.
intro to gibbereleins
Gibberellins are another kind of promotery
PGR. There are more than 100 gibberellins
reported from widely different organisms such
as fungi and higher plants. They are denoted
as GA1
, GA2
, GA3
and so on. However,
Gibberellic acid (GA3
) was one of the first
gibberellins to be discovered and remains the
most intensively studied form. All GAs are
acidic.
explain effects of gibberellins
Their ability to cause an increase
in length of axis is used to increase the length of grapes stalks. Gibberellins,
cause fruits like apple to elongate and improve its shape.
Sugarcane stores carbohydrate as sugar in their stems. Spraying
sugarcane crop with gibberellins increases the length of the stem, thus
increasing the yield by as much as 20 tonnes per acre.
how gibberellin help extend market period
Senescence is a process in which cells reach permanent growth arrest without the death of cells as the whole cell division process comes to a halt.gradual deterioration of functional characteristics in living organisms.
They also delay
senescence. Thus, the fruits can be left on the tree longer so as to extend
the market period. GA3
is used to speed up the malting process in brewing
industry.
other physiological effect of gibberellins
Spraying juvenile conifers with GAs hastens the maturity period, thus
leading to early seed production. Gibberellins also promotes bolting
(internode elongation just prior to flowering) in beet, cabbages and many
plants with rosette habi(circular arrangement of leaves or of structures resembling leaves)t.
how were cytokinins discivered
Cytokinins have specific effects on cytokinesis, and were discovered as
kinetin (a modified form of adenine, a purine) from the autoclaved herring
sperm DNA. Kinetin does not occur naturally in plants. Search for natural
substances with cytokinin-like activities led to the isolation of zeatin from
corn-kernels and coconut milk. Since the discovery of zeatin, several
naturally occurring cytokinins, and some synthetic compounds with cell
division promoting activity, have been identified.
where are natural cytokinins formed
Natural cytokinins are
synthesised in regions where rapid cell division occurs, for example, root
apices, developing shoot buds, young fruits etc. It helps to produce new leaves, chloroplasts in leaves, lateral shoot growth and adventitious shoot
formation. Cytokinins help overcome the apical dominance. They promote
nutrient mobilisation which helps in the delay of leaf senescence.
