HORMONE PHYSIOLOGY AND SIGNAL TRANSDUCTION Huseyin Tombuloglu, Phd. GBE 304 Spring 2015.

HORMONE PHYSIOLOGY AND SIGNAL TRANSDUCTION

Huseyin Tombuloglu, Phd.GBE 304 Spring 2015

Growth and DevelopmentGrowth: irreversible increase in size (net

increase in protoplasm) brought about by increases in cell size and number.

Development: which includes…Morphogenesis: creation of pattern and shape

resulting in morphological and anatomical development.

Differentiation: physiological and biochemical specializations.

Specialization of Cells Coordination/Cooperation between specialized cells

for survival. Development involves a specific, logical sequence of

events…. Life Cycle (highlights):

Fertilization Embryo development Germination Vegetative growth Reproductive Growth Gametogenesis Senescence Plant Death

Plant HormonesCoordinateCoordinate complex steps in growth and complex steps in growth and

development.development.Play key roles in Play key roles in signal transductionsignal transduction.. IntegrateIntegrate many different plant parts. many different plant parts.Coordinate “Coordinate “timingtiming” of growth and ” of growth and

development.development.Very potent at Very potent at lowlow concentrations. concentrations.

Plant Hormones Definition of a Plant Hormone:

1. Naturally occurring organic substance.2. Affects plant growth and development.3. Operates in very low concentrations.4. Actions may involve sites far removed from

hormone origin.

Hormones elicit a wide range of responses….Hormones elicit a wide range of responses….from growth to dormancy.from growth to dormancy.

Hormones Classes Commonly grouped into five (5)

categories…but they have multiple, overlapping, and interacting functions:

1. AUXINS2. GIBBERELLINS3. CYTOKININS4. ETHYLENE5. ABSCISIC ACID

AUXINS

Auxins [indoleacetic acid (IAA)]

first plant hormone to be discovered.early on it was believed to be the “master”

plant hormone.studies date back to the time of Charles

Darwin (1880s).very simple chemical structure….dramatic

influences on growth.“growth promoting hormone”

Cell elongation is controlled by IAA

believed to cause release of H+ protons from protoplast into cell wall.

acidic protons weaken cell wall structure which softens the wall and allows for expansion from turgor pressure.

Thus, auxin promotes cell elongation.

Auxin-induced cell wall expansion.Auxin-induced cell wall expansion.

Functions of Auxins Elongation of stems and roots. Responsible for tropisms….phototropisms. Enlargement of fruits and tubers. Promotion of cell divisions in cambium

tissues. Vascular cambium…auxin signal in Spring

from buds. Secondary xylem initiation.

Taiz and Zeiger. 2002. Plant Physiology, 3rd Ed.

Auxin and root formationAuxin and root formation

Taiz and Zeiger. 2002. Plant Physiology, 3rd Ed.

Auxin and GeotropismAuxin and Geotropism

Functions of Auxins Wound healing.

Promotes pith and cortex cells to differentiate into sclerenchymatous xylem to cover wounds.

Promotes rooting of plant cuttings. Promotes rooting of soft wood cuttings.

Inhibits growth in areas other than root tissues.

Shorten stems and retards growth. Apical dominance…function of auxin distribution.

Functions of Auxins Inhibits abscission of leaves and fruit.

Prevents leaf and fruit drop. Tissues send continuous auxin signal to prevent

abscission layer development.

Auxin release and movement to zones of abscission is halted by:

Disease Injury…lighting strikes Natural/Seasonal development

Auxins and Leaf Abscission In the Fall, leaves fall from the trees because

the leaf tissues STOP producing auxins. Same mechanisms in place for fruit drops

(apples).Auxins are in highest concentrations in the

stem apex of plants. Such high concentrations inhibit the growth of axillary buds….apical dominance.

Pruning, or removing the auxin signals results in elimination Pruning, or removing the auxin signals results in elimination of apical dominance and a flush of later meristematic growth. of apical dominance and a flush of later meristematic growth.

Auxins function best at very Auxins function best at very lowlow concentrations. concentrations.

Auxins and HorticulturePractical applications in agriculture and

horticulture:Useful in propagating/rooting of plant tissues

cuttings.As a herbicide.Prevention of fruit drop.Thinning of fruits….depending on the

concentration.

Auxins and HorticultureMost often, synthetic auxins are preferred

over natural IAA.2,4-D = 2,-4-dichlorophenoxacetic acidHerbicide which mimics the activity of IAA.Plant Growth Regulators are often synthetic auxins.

Remember that plant hormones are most effective in SMALL quantities.

Low concentrations…stimulate growth.High concentrations…herbicidal.

Auxins and Horticulture2,4-D is very effective at controlling broadleaf

dicot plants. It has no effect on grass monocots.Differences in control represent metabolic

differences between the dicots and monocots.

This fact is utilized successfully by agriculture and horticulture professionals.

Agent Orange

U.S. Army Huey helicopter spraying Agent Orange over Vietnamese agricultural land.

 U.S. Air Force's herbicide program in Vietnam

MOVIE SPRAY

http://upload.wikimedia.org/wikipedia/commons/transcoded/1/15/US-troops-spray-Agent-Orange-from-riverboat-Vietnam.ogv/US-troops-spray-Agent-Orange-from-riverboat-Vietnam.ogv.360p.webm

GIBBERELLINS