Chap 5. DIFFERENTIATION AND DEVELOPMENT

  1. INTRODUCTION
    2.

    Differentiation-Differential growth in cell and tissues.

    -Orderly and systematic in mitotic cell division

    Mitotic-somatic Meiotic-reproductive

    -Genetically controlled development by gene activation and deactivation

    -Tissue organ differentiation controlled by plant growth hormones

    that are produced in different parts of the plants

  2. PLANT GROWTH HORMONES (Plant Growth Regulators)

Phyto-hormones

Auxins, Gibberellins (GA), Cytokinins, Ethylene, Abscisic Acid (ABA)
    1. Auxins
    1. Function

      2. -Promote cell growth and elongation, alters cell wall plasticity

      -Responsible for apical dominance and phototropism

      -Promote calusing and rooting

      -Directing movement (shoot apex----downward)

    2. Bioassay

      3. -Split pea stem curvature study

      -Oat coleoptile test for photoropism

    3. Site of Synthesis

      4. -Stem apex (growing point)

      -Present abundantly in actively growing shoot tips

    4. Chemistry

    IAA- Indoleacetic Acid (Natural)

    NAA- Naphthaleneacetic Acid (synthetic)

    IBA- Indolebutyric Acid (synthetic)

  1. Application

-Pruning-Removal of Apical dominance

-Rooting cuttings (IBA dip)

-Callus induction invitro

 
    1. Gibberellins (GA)

About 45 different forms
    1. Function

      2. -Stimulates stem elongation (by cell enlargement and division)

      Cabbage-----------GA-------- 6 foot tall

      Bush bean---------GA---------Pole bean

      -Breaks seed and bud dormancy

      -Substitutes cold treatment effect (Azalea, Easterlily)

      -Induces flowering and converts sex expression from female to male

      flowers (in cucurbits)

      Cucumber-monoecious (male female)------GA3--à Androecious (male)

      Muskmelon-Andromonoecious (male male/female)

      ----------GA3--à Androecious (male)

      -Induces parthenocarpy (seedless grapes)

      fruit set without pollination

      -Stimulates a -amylase activity (in barley seed germination)

    2. Occurrence

      3. -First isolated from rice plant infected by Gibberella (1926, Japan)

      -Concentrated in Shoot apex (more in leaf primordia)

      -Present in leaf, stem, roots (non-directional movement)

    3. Chemistry

      4. -Diterpenoids

      -About 45 different forms (GA1, GA2…GA45)

       

       

       

    4. Application

-Production of seedless grapes (Thompson seedless)

-Increases malt content in beer making

-Flower induction in azaleas (mimic vernalization)

-Overcomes dwarfism

-Cut flower stem elongation

used for long-stem mums, alstroemeria, columbine

commercial- ProgibbÒ

    1. Cytokinins
    1. Function

      2. -Stimulates active cell division (cytokinesis)

      -Induces shoot differentiation in tissue culture

      -Regulates synthesis of DNA, RNA, Protein

      -Shoot multiplication (commercial cloning labs)

      Also transgenic plants (Ti plasmids)

    2. Occurrence

      3. -Present in actively dividing embryos, seed, fruit

      -Mostly synthesized in root tissues (upward translocation)

       

       

    3. Chemistry

      4. -Purines and their derivetives

      -Natural: Zeatin (Expensive)

      -Synthetic: Kinetin

      Benzylamino purine (BA)- Benzyl Adenine (BA)

      2-ip

       

    4. Bioassay

      5. -Tobacco pith cell culture

      -Shoot induction from callus (Plant regeneration)

    5. Application

-In vitro plant regeneration (Micropragation)

-Increasing flower yield (Multiple branching)
    1. Ethylene
    1. Function

      2. -Causes fruit ripening and plant senescene

      -Causes leaf abscision

      -Stimulation of early flower induction (pineapple, bromeliads)

      -Converts flower sex from maleness to femaleness

      Cucumber: Monoecious (male, female) ------Eth---à gynoecious (female)

      Muskemlon: Andromonoecious (male, female)----Eth-à gynomonoecious (male/female)

    2. Occurrence

      3. -Found in all tissues

      -Abundant in ripening fruits (apple), rotting tissues

    3. Chemistry

      4. -Ehylene gas- natural

      -Ethepon (Ethrel)- synthetic

       

    4. Bioassay

      5. -Flower petal shattering –snapdragon-sensitive to CH4

      -Other assays -Epinasty

    5. Application

-Flower induction (Pineapple, Silver vase, bromeliads)

-Increase rubber yields in Hevea (up to 6500 16/AC)

-Fruit ripening (banana) Defoliation (cotton)
    1. Abscisic Acid ABA (Growth Inhibitor)
    1. Function

      2. -Causes bud and seed dormancy

      -Causes leaf abscision (Abscisin)

      -Counteracts with GA, Cytokinin

    2. Occurrence

      3. -Tissues of stressed plants

      -Senescing plants

    3. Chemistry

      4. -Isoprenoid compound

    4. Bioassay

      5. -Stomatal closure

    5. Application

-Research (Reversal of GA, Cytokinin activities)

-Drought Tolerance
    1. Growth Inhibitors
    1. Natural

      2. -Coumarin--------à prevents seed germination (tomato) watermelon

      -Benzoic Acid

      -Chlorogenic Acid

    2. Synthetic

-Maleic Hydrazide (MH 30)

Phosphon (B-9)

CCC (Chlormequat)

Ancymidol (A-Rest)

  1. VEGETATIVE PHYSIOLOGY
    1. Seed Germination
    1. Seed a ripened ovule

      2. Seed= Embryo (young plant) + food supply (edosperm,

      Cotyledon) + protective covering (seed coat)

    2. Three steps of germination

1) Imbibition of water

2) Enzyme synthesis and activation

3) Radicle emergence and shoot development
    1. Seed Dormancy
    1. Physical dormancy (Seed coat dormancy)

-Seed coat is impervious to water

-Can be removed by
    1. Microbial decomposition (in nature)
    2. Scarification

-Acid (sulfuric acid) treatment

-Hot water

-Mechanical (scoring, cracking)
    1. Physiological dormancy (Embryo dormancy)

-Inhibitor substances present in embryo (ABA, Coumarin)

Last about 1-6 months

-Can be eliminated by:

Stratification-most cold storage (4-6 months)

Some seeds require warm and cold treatments (i.e. peony)

-for embyo maturation
    1. Double Dormancy

-Both seed coat and embryo dormancies exist (Redbud)

-Can broken by:

Scarification (or seed coat decomposition by microorganism)

Stratification (or winterizing for 2nd year)

-deactivates physiological dormancy

    1. Juvenility
    1. Juvenility and maturity phases are genetically controlled

      2. -some trees (apple, pear) start fruiting after 4-8 years

    2. "Juvenile factors" may b transferred to different tissues

      3. Hedera helix (English Ivy)-Rejuvenation possible by grafting

    3. Involvement of GA

Onset of maturity can be delayed by GA application
    1. Bud Dormancy
    1. Buds are formed in the summer months and stay dormant although environmental conditions are favorable for growth.

      2.  

    2. Bud dormancy is broken by low temperature

Peach: 350-1200 hrs chilling at below 45°

 

 

 
  1. REPRODUCTIVE PHYSIOLOGY
    1. Flowering
    1. Effect of C/N ratio (Nitrogen to Carbohydrate ratio)

      2. -High C/N ratio-----more reproductive

      -High N/C ratio-----more vegetative (High nitrogen supply----more vegetative growth)

    2. Effect of Photoperiod
    1. Photoperiodism- Plant growth response to the length of the day

      2. Long-day plants (Short night plants) LDS (SNP)

      -Flower initiate when days are longer than 16 hours

      (shorter than 8 hour nights)

      -oat, spinach, rudbeckia, clover, radish

      Short-day plants (Long-night plants) SDP (LNP)

      -Flower initiation takes place when days are shorter than 13 hours.

      -coffea, chrysanthemum, poinsettia, kalanchoe

      Day-neutral plants

      -Flower initiation is not affected by day lengths

      -Many plants (Rose, carnation, citrus)

    2. What growth hormones are involved?

-"Florigen"…has not been substantiated

- Phytochromes…pigment receptor of photoperiodic response;

they exist in two different forms

 

4. Application of photoperiodism

-Year round production of short-day flowering plants by black-clothing

-Marketing of poinsettia for both Thanksgiving and Christmas

-Flower induction in breeding programs
    1. Vernalization (Springtization)

      2. -Theory advanced by Klippart and Lysenko "Vernal" (spring)

      -Low temperature induced "programming" of flowering

      winter wheat, azalea, tulips, easterlily

      -Devernalization- deprogramming of vernalization

      important in onion stage

    2. Sex Expression

-The sequence of flowering (Influenced by photoperiod and temperature)

-The ratio of female: male flowers