Growth regulators
Bioassay
for different growth regulators
Auxin:
- Split
pea test
- Avena
coleoptile test
- Rice
root inhibition test
Gibberellin
- Barely
endosperm test (production of reducing sugars)
- Elongation
of dwarf seedlings
Cytokinin
- Chlorophyll
retention test
- Root
inhibition test
Abscisic Acid (ABA)
- Inhibition
of alpha amylase enzyme
- Rice
seedling growth inhibition test
Ethylene
- Triple
pea test (special thickening, horizontal nutation, rate of reduction of
elongation)
- Pea
stem swelling test
Senescence
“The process of deterioration that
accompany aging and that lead to death of an organ or organism are called as
senescence”. Meristematic regions do not senesce but non-meristematic regions
senesce
Ex. Decidous plants drop old leaves
every year
Reason:
Senescence occurs due to loss of
chlorophyll, RNA and proteins including many enzymes. This is brought out by
two ways,
- Slower
synthesis of vital plant components due to diversion or deficiency of
nutrients
- Breakdown
of vital components by hormone induced process or by any means
Role of hormone in Senescence
- ABA
and Ethylene induce senescence
- Cytokinin,
givverellic acid and auxin prevent senescence.
Therefore the change in
the status of these hormones affects the onset of senescence.
Advantages of senescence
- Fruit:
dispersal of seeds
- Flower:
prevents diversion of excess nutrients to flower, avoid shadding and new
infection sources.
- Leaves:
reduce transpiring surface and more nutrients are diverted to fruits and
other vital parts of the plant
- me mother cell
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