Question: 100% NCERT covered from Particular Keyword.Explanations are 100% from NCERT | [Difficult level: Easy] From NCERT NEET Derived Question.
The hormone which controls xylem differentiation and helps to prevent fruit and leaf drop at
early stages, but promotes abscission of older mature leaves and fruits is
1. Gibberellin 2. Ethylene
3. Cytokinin 4. Auxin
Answer:(4)
Auxin control xylem differentiation and abscission of leaves and fruits at early stages.
Related points from NCERT
👉Zinc: Plants obtain zinc as Zn2+ ions. It activates various enzymes,
especially carboxylases. It is also needed in the synthesis of auxin.
👉Boron : Boron is required for uptake
and utilisation of Ca2+, membrane functioning, pollen germination, cell
elongation, cell differentiation and carbohydrate translocation.
👉Calcium is required by meristematic and differentiating tissues.
During cell division it is used in the synthesis of cell wall, particularly as
calcium pectate in the middle lamella. It is also needed during the
formation of mitotic spindle.and plays an important role in regulating metabolic activities.
👉Experiment used to demonstrate
that tip of the coleoptile is the
source of auxin :observation of Charles
Darwin and his son Francis Darwin when they
observed that the coleoptiles of canary grass
responded to unilateral illumination by
growing towards the light source
(phototropism)
👉Auxin was isolated by F.W. Went from
tips of coleoptiles of oat seedlings
👉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.
👉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 auxin
👉They help to initiate rooting in stem cuttings
👉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.
👉In most higher plants, the growing apical bud inhibits the growth of
the lateral (axillary) buds
👉It is widely applied in tea plantations, hedge-making.
👉Auxins also induce parthenocarpy, e.g., in
tomatoes.
👉They are widely used as herbicides.
2, 4-D, widely used to kill dicotyledonous
weeds
👉Auxin also
controls xylem differentiation and helps in cell
division.
Auxin works-
- Rooting in stem cutting
- Flowering in Pineapple
- Apical dominance,
- Parthenocarpy in tomato
- Weed free lawn,
- Xylem differenciation
- cell division
Gibberellin work
- Increase grape stalk,
- Elongate Apple
- Improve apple shape
- Delay senescence,
- Speed up Malting,
- Stem length increase in sugarcane,
- Hasten maturity period in juvenile conifers
- Early seed production
- Bolting in beet, cabbage( Rosette flowers)
Cytokinin works
- Rapid cell devision,
- New leaves
- lateral shoot growth
- Adventitious shoot formation
- overcome apical dominance,
- Nutrient metabolism
- Delay senescence,
Ehylene works
- Senescence tissue
- Ripening fruit
- Horizontal growth of seedling
- swelling of axis
- Apical hook formation
- Enhance respiration
- Respiratory climatic
- Break seed dormancy
- Break bud dormancy
- Initial germination in Peanut seed
- Sprouting potato sprouting
- Rapid internode/petiole elongation in deep water rice plant
- Root growth
- Root hair formation
- Increase absorption surface
- flowering of pineapple
- Synchronising fruit in pineapple
- Flowering in Mango
- Hasten fruit ripening in tomato and apple
- Thinning of cotton , cheery, walnut.
- Female flowering in cucumber
