Plant Growth and Development
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F.W. Went isolated auxin (Greek ‘auxein’: to grow) from tips of coleoptiles
of oat seedlings.
Auxin was first isolated from human urine.
Auxins are produced by the growing apices of stems
& roots, from where they migrate to regions of their
action.
TÝPËS ØF ÅÜXÏÑS
ÑÅTÜRÅL
E.g.Indole-3-acetic acid (IAA) and
indole butyric acid (IBA). They are
isolated from plants.
SÝÑTHËTÏÇ
E.g. NAA (naphthalene
acetic acid) and 2, 4-D (2,
4-dichlorophenoxyacetic).
(AIPMT 2009)
FÜÑÇTÏØÑ ØF ÅÜXÏÑS
Initiate rooting in stem cuttings for plant propagation.
(AIPMT 2010,
NEET - II 2016)
Promote flowering. E.g. in pineapples.
(NEET 2019)
Prevent fruit and leaf drop at early stages.
Promote the abscission of older leaves and fruits.
Induce parthenocarpy. E.g., tomatoes.
(AIPMT 2006)
Used as herbicides. E.g. 2, 4-D is used to kill dicot weeds. It does not affect
mature monocot plants. It is used to prepare weed free lawns.
Controls xylem differentiation and helps in cell division.
In most higher plants, the growing apical bud inhibits the growth of
lateral (axillary) buds. It is known as apical dominance. Removal of shoot
tips (decapitation) results in the growth of lateral buds. It is applied in
tea plantations & hedge-making.
(AIPMT 2006, AIPMT Mains 2010)
2 Gibberellins
These are acidic PGR.
E. Kurosawa treated the sterile filtrates of Gibberella fujikuroi (a fungus
that causes ‘bakane’ disease or foolish seedling in rice) to healthy rice
seedlings. As a result, it showed the symptoms of ‘bakane’ disease. Later,
the active substances were identified as gibberellic acid.
Movement of Auxin
Auxin moves away
from the light
Concentration
increases
Stem grows
faster on
dark side
Light
Direction
Seedling
Stem grows
towards
the light
Light causes
destruction of
auxin