Control Systems in Plants

Plant Hormones l Coordinates growth l Coordinates development l Coordinates responses to environmental stimuli

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

Auxins l Stimulates stem elongation l Stimulates root growth l Stimulates differentiation and branching l Stimulates development of fruit l Stimulates apical dominance l Stimulates phototropism and gravitropism

Auxin Control l Auxin stimulates growth l Auxin block on right causes cells to elongate and the plant bends left l Auxin block on left causes cells to elongate the the plant bends right

Polar Transport l Auxin is transported from apex to shoot l Cell wall is acidic l auxin ion picks up H+ l diffuses across plasma membrane l Cytosol is neutral l auxon loses H+ l uses energy to pump out H+ to maintain pH l leaves cell through carrier proteins

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

Auxin Others l Promotes secondary growth by encouraging vascular cambium and secondary xylem l Promotes adventitious root at the base of a cut stem l Promotes fruit growth without pollination (seedless tomatoes)

Cytokinins l Stimulates root growth l Stimulates cell division and differentiation (with auxins) l more cytokinin - shoot buds develop l more auxin - roots develop l Stimulates germination l Delays Senescence

Gibberellins l Promotes seed and bud germination l Promotes stem elongation l Promotes leaf growth l Stimulates flowering and fruits l (with auxin)

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

Ethylene l Promotes fruit ripening l Controls Abscission l (with auxin)

Oligosaccharins l Triggers defense responses against pathogens l Regulates growth

Brassinosteroids l Required for normal growth and development

Signal-Transduction Pathways l A hormone binds to receptor and stimulates secondary messengers which Activates cell responses

Plant Movements l Phototropism l Gravitropism l Thigmotropism

Plant Movement l Rapid Leaf Movement l drop in turgor pressure within pulvini (at joints of the leaf) l sent by action potentials l Sleep Movements l cells on opposite sides of pulvinus control the movement

Daily and Seasonal Responses l Circadian Rhythm l Photoperiodism l controls flowering (short-day vs. long-day) l critical night length

Photoperiodic Control

Flowering Hormones l Experiment indicates the presence of some type of flowering hormone

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

Red vs. Far Red Response

Plant Responses to Environmental Stress l Water Deficit l Oxygen Deprivation l Salt Stress l Heat Stress l Cold Stress l Herbivores

Water Deficit l Slows Transpiration l stomata close l release of abscisic acid l Inhibits growth of young leaves l Change leaf shape l Deeper root growth

Oxygen Deprivation l Aerial roots l Production of air tubes

Salt Stress l Salt glands l Compatible solutes

Heat Stress l Heat-shock proteins

Cold Stress l Altering the lipid composition of their membranes l Changes in the solute composition of the cytosol

Responses to Herbivores l Produce Canavanine l Recruitment of predatory animals

Defense Against Pathogens l Gene-for-gene recognition

Defense Against Pathogens l Hypersensitive response (HR) l phytoalexins are released l PR proteins are released l Seal off infected area l Systemic acquired resistance (SAR) l Salicylic acid released due to death of cell l Activates a Signal Transduction Pathway l Activates SAR