Plant Regulation Chapter 39

Plant growth Plants respond to environment Growth response to abiotic factors Water, wind & light

Plant responses Light Gravity Touch Water Temperature

Plant hormones Internal signal (developmental) Environmental signal Chemical binds receptor Physiological response Developmental response Reception-transduction-response Regulate growth & development New protein or activation of protein

Signal transduction pathway CELL WALL CYTOPLASM 1 Reception 2 Transduction 3 Response Receptor Relay proteins and Activation of cellular responses second messengers Figure 39.3 Review of a general model for signal transduction pathways Hormone or environmental stimulus Plasma membrane

Potato plant de-etiolation (greening) Figure 39.2 Light-induced de-etiolation (greening) of dark-grown potatoes (a) Before exposure to light (b) After a week’s exposure to natural daylight

De-etiolation (greening) response proteins Potato response 1 Reception 2 Transduction 3 Response Transcription factor 1 CYTOPLASM NUCLEUS Plasma membrane cGMP Protein kinase 1 P Second messenger produced Transcription factor 2 Phytochrome activated by light P Cell wall Protein kinase 2 Transcription Light Translation Figure 39.4-3 An example of signal transduction in plants: the role of phytochrome in the de-etiolation (greening) response (step 3) Ca2+ channel opened De-etiolation (greening) response proteins Ca2+

Light response Photomorphogenesis: Nondirectional light-triggered development Change in form Flower formation Phototropisms: Directional development Trope (turn)

Plant hormones Auxin Cytokinins Gibberellins Brassinosteriods Ethylene Abscisic acid

Auxin First plant hormone (IAA) Indoleacetic acid Found in apical meristems of shoots Promotes activity of vascular cambium Promotes lateral root growth Found in pollen, fruit development

Auxins Plasticity (soften) of plant Elongation of plant Auxin moves from light exposed side To shady side Bends towards light

Auxins Synthetic auxins Prevent apples from dropping early Berries on holly Seedless tomatoes Control weeds

Cytokinins Similar to adenine (purines) Cell division & differentiation Found in root apical meristems Transported through plant Lateral buds into branches Inhibit lateral roots (auxin promotes)

Cytokinins Remove terminal bud Plant becomes bushier Promotes lateral buds into branches Auxin on cut surface Inhibits lateral buds

Cytokinins Applied to cut leaves prevent aging Florists spray on fresh cut flowers Crown gall Tumor growth on trees Bacteria causes increased production of auxin & cytokinins

Gibberellins Stem elongation Enhances if auxin present Found in apical portions of stems & roots Apply to dwarf plants restores normal growth

Gibberellins Stimulate enzymes that utilize food during germination Hastens germination Fruit development Helps space grape leaves (internodes) Fruits have more space to grow

Brassinosteriods Similar in structure to testosterone, estradiol, cortisol Elongation & cell division Bending of stems Reproductive development Delays senescence

Abscisic Acid In mature green leaves, fruit & root caps Formation of winter buds Induce seed dormancy Controls stomata open/close

Ethylene Gas Suppresses stem & root elongation Hastens fruit ripening Response to stress Leaf abscission Programmed cell death

Ethylene Mechanical stress on stem tip. Triple response Enables a seedling to avoid an obstacle.

Ethylene Commercially sprayed on green tomatoes Hastens ripening

Light response Certain wavelengths of light Initiate biological change Phytochrome: Pigment containing protein Pr (inactive form) Pfr(active form)

Light response Inter-convertible forms Pr absorbs red light (660nm) Converts to the active form Pfr Pfr absorbs far red light (730 nm) Converts to the inactive form Pr

Light response Acts as switching mechanism Controls various light-induced events Phytochrome exposed to red light Pr is converted to Pfr Triggering germination Far-red light inhibits germination

Light response

Light response Determine plant spacing Pfr plant grows tall Pr plant branches

Circadian clocks

Gravity response Gravitropism Response of plant to gravitational pull Shoot negative gravitropic response Roots positive gravitropic response

Gravity response Amyloplasts: Starch containing organelles Maybe involved in sensing gravity Stem located in the endoplasm Root located in the root cap Root cap is involved in sensing gravity

Touch response Thigmotropism Directional growth response Direction of touch Object, animal, wind Thigmonastic Responds in one direction Despite where the contact is

Touch response Tendril touches an object Uneven growth Wraps around the object Fly trap Touch hairs, closes (0.3 sec)

Turgor Movement Touch induces change in turgor Cells collapse Causes leaf movement Pulvini: Multicellular swellings Located base of leaf or leaflet

Turgor movement Environmental stimuli Rapid loss of K+ out of half the pulvini cells Water follows Causes cells to be flaccid Leaves fold in Reverses in approx 15-30 minutes

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Dormancy Survive environment extremes Signals that initiate or terminate dormancy Temperate regions dormancy occurs during winter (day-length) Dry climates dormancy comes in summer (rainfall)

Plant defense First defense Dermal tissue system Cutin, suberin Bark, thorns, trichomes

Plant defense Poisons Cyanide-containing compounds Stops electron-transport Cassava (African food) Secondary metabolites Alkaloids (caffeine, nicotine, cocaine, and morphine)

Plant defense Soy products produce Phytoestrogens Similar in structure to estrogen Decreased prostate cancer in Asian men Help minimize menopausal symptoms

Plant defense Pacific Yew produces Taxol Fights cancer especially breast cancer Cinchona tree bark Quinine Anti-malaria drug

Plant defenses Toxic when metabolized by herbivore

Plant defense Allelopathy: When a chemical secreted by roots Inhibits growth of other plants Black walnut trees

Plant defense Plant is injured Cell death at location Prevents further spread of pathogen H2O2 & NO can be produced Can cause harm to invader Chemicals released to warn other plants of an invasion

Wasps