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)

39.11 Effect of Gibberellin39.11 Effect of Gibberellin

1

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)

Photoperiodic control of Photoperiodic control of FloweringFlowering

2

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

3

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

4

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)

References:References:Image1:http://postimg.org/image/oca4wl4xl/Image 2:

http://postimg.org/image/bfs7genuh/Image 3: http://postimg.org/image/tjv811lix/Image 4:

http://postimg.org/image/5vfq5rozd/Book:Plant Physiology by H. S. Srivastava.