Plant Regulation Chapter 39

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

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 Plasticity (soften) of plant Elongation of plant

Auxins Auxin moves from light exposed side To the shady side Promotes growth & elongation Helps plants response to environment Promotes activity of vascular cambium Promotes lateral root growth Found in pollen, fruit development

Auxins Synthetic auxins Prevent apples from dropping early Berries on holly Seedless tomatoes (green house tomatoes) Control weeds (higher dose, prevents axial growth)

Cytokinins Purines Similar structure to adenine 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 Found 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. Stem elongation slows, Stem thickens, Curvature causes the stem to start growing horizontally.

Ethylene Commercially sprayed on green tomatoes Hastens ripening

Light response Certain wavelengths of light Initiate biological change Phytochrome: Pigment containing protein Two forms P r (inactive form) and P fr (active form)

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

Light response Inter-conversion acts as switching mechanism Controls various light-induced events P fr form triggers plant’s developmental responses to light. Exposure to far-red light inhibits the germination response.

Light response

Seeds exposed to sunlight Phytochrome exposed to red light P r is converted to P fr Triggering germination.

Light response Determine spacing between plants P fr plant grows tall P r plant branches

Circadian clocks

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

Response present at germination Stem Greater concentration of a elongation hormone on the under side Cells grow more then upper side Root Upper cells grow more rapidly Root grows down

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 In 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)

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

Turgor movement Stimuli such as wind, touch, heat Rapid loss of K + out of half the pulvini cells Water follows Causes cells to be flaccid Leaves fold in Mimosa Reverses in approx minutes

Dormancy Survive environment extremes Plant have a dormant stage Temperature, light & water 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 Nematodes, fungi, bugs still penetrate these defenses

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

Secondary metabolites Soy products produce Phytoestrogens Similar in structure to human estrogen Decreased prostate cancer in Asian men Help minimize menopausal symptoms

Secondary metabolites Pacific Yew produces Taxol Helps fight cancer especially breast cancer Cinchona tree bark Quinine Anti-malaria drug Designed to harm herbivores

Plant defenses 1. Toxin in membrane-bound structure 2. Poison toxic when metabolized by herbivore

Allelopathy Chemical secreted by roots of one plant Inhibits growth of other plants Black walnut trees

Plant response Plant is injured Cell death at location Prevents further spread of pathogen H 2 O 2 & NO can be produced Can cause harm to invader Chemicals released to warn other plants of an invasion

Wasps