Control Systems in Plants

Plant Hormones

Coordinates growth Coordinates development Coordinates responses to

environmental stimuli

Plant Hormones Auxin (IAA) Cytokinins Gibberllins Abscisic Acid Ethylene Oligogaccharins Brassinosteroids

Auxins Stimulates stem elongation Stimulates root growth Stimulates differentiation and

branching Stimulates development of fruit Stimulates apical dominance Stimulates phototropism and

gravitropism

Auxin Control Auxin stimulates

growth Auxin block on right

causes cells to elongate and the plant bends left

Auxin block on left causes cells to elongate the the plant bends right

Polar Transport Auxin is transported from apex

to shoot Cell wall is acidic

auxin ion picks up H+ diffuses across plasma membrane

Cytosol is neutral auxon loses H+ uses energy to pump out H+ to

maintain pH leaves cell through carrier proteins

Acid Growth Hypothesis Proton pump stimulated by auxin which lower pH of wall Hydrogen Ion activates Enzyme Enzyme breaks hydrogen bonds in cellulose Wall takes up water and elongates

Auxin Others Promotes secondary growth by

encouraging vascular cambium and secondary xylem

Promotes adventitious root at the base of a cut stem

Promotes fruit growth without pollination (seedless tomatoes)

Cytokinins Stimulates root growth Stimulates cell division and

differentiation (with auxins) more cytokinin - shoot buds develop more auxin - roots develop

Stimulates germination Delays Senescence

Gibberellins Promotes seed and bud germination Promotes stem elongation Promotes leaf growth Stimulates flowering and fruits

(with auxin)

Abscisic Acid Inhibits growth (with gibberellins) Closes stomata under water stress Permits dormancy

Ethylene Promotes fruit ripening Controls Abscission

(with auxin)

Oligosaccharins Triggers defense responses against

pathogens Regulates growth

Brassinosteroids Required for normal growth and

development

Signal-Transduction Pathways A hormone binds to receptor and stimulates secondary

messengers which Activates cell responses

Plant Movements

Phototropism Gravitropism Thigmotropism

Plant Movement

Rapid Leaf Movement drop in turgor pressure within

pulvini (at joints of the leaf) sent by action potentials

Sleep Movements cells on opposite sides of pulvinus

control the movement

Daily and Seasonal Responses

Circadian Rhythm Photoperiodism

controls flowering (short-day vs. long-day) critical night length

Photoperiodic Control

Flowering Hormones

Experiment indicates the presence of some type of flowering hormone

Phytochromes Function as photoreceptors / red (660nm) to far red (730nm) Activates kinases (regulatory proteins)

Red vs. Far Red Response

Plant Responses to Environmental Stress

Water Deficit Oxygen Deprivation Salt Stress Heat Stress Cold Stress Herbivores

Water Deficit

Slows Transpiration stomata close release of abscisic acid

Inhibits growth of young leaves Change leaf shape Deeper root growth

Oxygen Deprivation

Aerial roots Production of air tubes

Salt Stress

Salt glands Compatible solutes

Heat Stress

Heat-shock proteins

Cold Stress

Altering the lipid composition of their membranes

Changes in the solute composition of the cytosol

Responses to Herbivores Produce

Canavanine Recruitment of

predatory animals

Defense Against Pathogens Gene-for-gene

recognition

Defense Against Pathogens Hypersensitive response (HR)

phytoalexins are released PR proteins are released Seal off infected area

Systemic acquired resistance (SAR) Salicylic acid released due to death of cell Activates a Signal Transduction Pathway Activates SAR