Post on 28-Jul-2015
Plant Responses & HormonesPlant Responses & Hormones
Course: B.Sc.(Biotech/Micro.) sem IISubject: Animal & Plant Physiology
Unit 1.2
PPlant lant HHormonesormones
HormoneHormone = Gr. “to excite” 1) active in small amounts 2) produced in one part of plant &
transported to another for action 3) action is specific for that site
EEach has a ach has a MMultiplicity of ultiplicity of EEffectsffects
Depending on site of action Developmental stage of plant Concentration of hormone
AAuxinsuxins stimulate growth but too much
inhibits growth functions: 1) root initiation, stem
elongation 2) retard abscission (loss) of
leaves & fruits (Figure 39.10) 3) stimulates cell differentiation 4) apical dominance (Figure
39.6)
GGibberellinsibberellins
discovered due to a fungus Giberella which causes Japanese “foolish” rice seedling disease
Figure 39.7 induces flowering stimulates growth by increasing
cell size & numbers (Figure 39.8)
CCytokininsytokinins
1) induces cell division (cytokinesis) 2) affects root growth &
differentiation 3) stimulates germination 4) delays senescence (aging); the
progression of irreversible change that eventually leads to death
AAbscisic bscisic AAcidcid
1) stimulates abscission and dormancy
2) converts vegetative buds (active) to dormant buds
3) stress hormones Closure of stomata. Differentiation of plant
EEthylenethylene
1) promotes fruit ripening 2) stimulates production
of cellulasecellulase Breaks the dormancy Breaks the dormancy
of bud and seeds.of bud and seeds. Helping in the plants to Helping in the plants to
increases their increases their absorption surface.absorption surface.
PhotochromesPhotochromes
Plant pigment Important in processes
where light is a critical factor, such as, flowering in long day short night plants
Figure 39.16
Plant Movements due to Plant Movements due to growthgrowth
Phototrophism – movement toward (positive) or movement away from (negative) light
Geotrophism – movement toward (positive) or away from (negative) center of the earth
ThigmotrophismThigmotrophism – directional growth responding to contact (tendrils)
Plant Movements not due to Plant Movements not due to GrowthGrowth
Thigmonastic response – touch stimulus, e.g. mimosa leaves
Photonastic response – shamrock
Sleep response – caused by change in osmotic pressure
Movement of materialsMovement of materials
Path from roots: 1) epidermis of root & root hair cells 2) roots absorb water, minerals, gases 3) stems conduct
Xylem & phloem are vertical conductors Parenchyma of cortex, pith, rays are
lateral conductors
MovementMovement Root pressure –osmotic pressure &
pressure created by active absorption & secretion by root cells; drives materials up xylem
Transpiration – evaporation of water through leaf stomata; cohesion of water molecules exerts a pull on columns of water in xylem
Guttation – release of water droplets at leaf tips; occurs when too much water is absorbed by plant & when humidity is high
Translocation – movement of material from one location to another
Fighting Back….Fighting Back…. Response to herbivory (animals eating
plants): 1) physical barriers – thorns & spines 2) chemical defenses – distasteful or toxic
compounds 3) chemical signaling – salivary enzyme from
herbivore triggers a pathway that produces a volatile attractant that recruits a parasitoid wasp. The wasp lays eggs within the caterpillar, and the larvae upon hatching destroy the caterpillar by consuming its tissues. (Figure 39.22)