CYTOKININS

CYTO = CELL
KINESIS = DIVISION

CYTOKININS PROMOTE CELL DIVISION

HISTORY

1913 - HABERLANDT FOUND THAT PHLOEM CELLS COULD CAUSE POTATO
       PARENCHYMA CELLS TO DIVIDE

1940’s
1950’S FOLKES SKOOG OBSERVED -

                 a. PLANT TISSUE CULTURE CELLS FAILED TO DIVIDE
                 b. ADDED COCONUT MILK TO THE CULTURE AND OBSERVED
                        THAT THE CELLS DIVIDED.
                 c. CARLOS MILLER, IN SKOOGS LAB IDENTIFIED THE
                        ACTIVE INGREDIENT AS A PURINE

1956 - CARLOS MILLER

                  a. FOUND THAT WHEN HERRING SPERM WAS ADDED INSTEAD OF
                         COCONUT MILK THE CELLS DIVIDED
                  b. HERRING SPERM IS RICH IN NUCLEIC ACIDS. WHEN DNA IN
          HERRING SPERM BREAKS DOWN ADENINE, A PURINE, IS RELEASED

NATURALLY OCCURING PLANT CYTOKININ IS ZEATIN.

NAMED ZEATIN BECAUSE IT WAS ISOLATED FROM CORN (Zea mays)

WHERE FOUND IN NATURE

                 ANGIOSPERMS, GYMNOSPERMS, MOSSES, FERNS

WHERE FOUND IN PLANTS

FOUND IN ROOTS, SEEDS, FRUITS, YOUNG LEAVES

EFFECTS ON PLANT GROWTH

1. STIMULATES CELL DIVISION
        a. WORKS IN CONJUNCTION WITH AUXIN
        b. HAVE NO EFFECT ON ANIMAL CELL DIVISION

2. STIMULATES CELL EXPANSION OF CELLS IN COTYLEDONS
        a. INCREASE CELL WALL PLASTICITY
        b. INCREASE THE AMOUNT OF SUGARS IN CELLS INCREASING THE
      INFLUX OF WATER INTO THE CELL

3. WORK WITH IAA TO INFLUENCE ORGANOGENESIS
        a. HIGH CYTOKININ/LOW IAA = FAVORS SHOOT FORMATION
        b. LOW CYTOKININ/HIGH IAA = FAVORS ROOT FORMATION

4. DELAY SENESCENCE
       a. DELAY THE BREAKDOWN OF CHLOROPHYLL IN DETACHED
              LEAVES

ABSCISIC ACID

1. A SINGLE COMPOUND THAT REGULATES SEED GERMINATION, STORAGE
   PROTEIN SYNTHESIS, AND MODULATES WATER STRESS

2. ORIGINALLY THOUGHT TO HAVE A ROLE IN ABSCISSION AND BUD DORMANCY
   BUT, NOW KNOWN TO HAVE LITTLE TO DO WITH EITHER ONE.
       a. TWO GROUPS WERE WORKING ON THE SAME COMPOUND AT THE SAME TIME.
      ONE GROUP CALLED THE COMPOUND ABSCISIC ACID AND THE OTHER
      CALLED IT DORMIN

3. TWO MAJOR AREAS OF ABA ACTION ARE KNOWN:
        a. MOBILIZATION OF FOOD RESERVES DURING SEED DEVELOPMENT AND
      GERMINATION
        b. RESPONSE OF LEAVES TO WATER STRESS
               1. PRODUCED IN LARGE AMOUNTS IN WATER STRESSED LEAVES TO
         REGULATE STOMATAL OPENING

PHYSIOLOGICAL ROLES OF ABSCISIC ACID

1. SEED MATURATION
       a. CYTOKININ LEVELS INITIALLY HIGH AS CELLS ARE RAPIDLY DIVIDING
       b. CYTOKININ LEVELS DROP AND GA AND IAA LEVELS INCREASE AS THE
      EMBRYO DEVELOPS
       c. AT THE LATER STAGE OF DEVELOPMENT, GA AND IAA LEVELS DECREASE,
      AND ABA LEVELS INCREASE
       d. ABA LEVELS INCREASE UNTIL THE EMBRYO IS MATURE
       e. EMBRYO LEVELS OF ABA REMAIN HIGH AFTER GROWTH STOPS
             1. HIGH LEVELS OF ABA HELP TO PREVENT VIVAPARY

                    VIVAPARY = EARLY GERMINATION OF SEEDS BEFORE THEY HAVE BEEN
                    RELEASED FROM THE OVARY

                    FLURIDONE INHIBITS ABA SYNTHESIS AND FAVORS VIVIPARY.

            2. STOMATAL OPENING
                   a. ABA IS PRODUCED BY THE ROOTS OF WATER STRESSED
                          PLANTS AND TRANSPORTED TO THE LEAVES
                  b. LEAVES PRODUCE LARGE QUANTITIES OF ABA AND STOMATES CLOSE

ETHYLENE

ETHYLENE IS THE ONLY GASEOUS PLANT HORMONE THAT IS A GAS

          
             H    H
              \   /
                C=C              C2H4
              /   \
             H    H

1. PRODUCED BY TISSUES UNDER STRESS
2. ETHYLENE TRIGGERS PLANTS TO PRODUCE MORE ETHYLENE
       a. WHEN A PIECE OF FRUIT IN AN ENCLOSED SPACE PRODUCES ETHYLENE,
      OTHER FRUIT IN THAT SAME SPACE BEGINS TO PRODUCE ETHYLENE

"ONE BAD APPLE SPOILS THE BARREL"

ETHYLENE IS COMMONLY USED TO ENHANCE RIPENING IN BANANAS

DISCOVERY

1800’S - PLANTS AROUND STREET LAMPS HAD SHORT THICK STEMS AND LEAVES
         FELL EASILY. LAMPS FUELED BY "ILLUMINATING" GAS.

1901  -  DIMITRY NELJUBOW FOUND THAT ETHYLENE WAS THE PRODUCT OF
         ILLUMINATING GAS THAT PROMOTES DEFOLIATION AND STUNTED
                      GROWTH

1910  -  JAPANESE DEPT. OF AGRICULTURE SAID NOT TO STORE ORANGES
         WITH BANANAS BECAUSE SOMETHING PRODUCED BY THE ORANGES
         CAUSED THE BANANAS TO RIPEN

1934     R. GANE SHOWED THAT ORANGES PRODUCED ETHYLENE GAS AND
         COULD BE CLASSED AS A HORMONE

PRODUCTION OF ETHYLENE

ETHYLENE MADE BY ALL PARTS OF AN ANGIOSPERM BUT ESPECIALLY BY;

1. ROOTS
2. SHOOT APICAL MERISTEM
3. NODES
4. SENESCING FLOWERS
5. RIPENING FRUITS

FFECTS OF ETHYLENE

1. FRUIT RIPENING
2. FLOWERING
       a. INHIBITION OF BUD OPENING (CARNATIONS)
       b. STIMULATION OF FLOWER INITIATION (PINEAPPLE, MANGO)

THE PHYSIOLOGICAL ROLES OF ETHYLENE

AFFECTS VIRTUALLY EVERY ASPECT OF PLANT GROWTH AND DEVELOPMENT

DIFFICULT TO WORK WITH BECAUSE IT IS A GAS
       1. ETHYLENE IS A BYPRODUCT OF INCOMPLETE COMBUSTION OF
              HYDROCARBONS
             a. TREES AROUND GAS LIGHTS WERE FOUND TO DROP THEIR
                    LEAVES, HAVE THICK STEMS AND BE STUNTED
             b. ORANGES STORED IN GAS HEATED GREENHOUSES RIPENED
                    1. THOUGHT TO RIPEN DUE TO HEAT BUT, WHEN PUT
                           IN ELECTRUCALLY HEATED GREENHOUSES FAILED TO RIPEN
                    2. TWO DISCOVERIES MADE ETHYLENE RESEARCH POSSIBLE
                           a. GAS CHROMATOGRAPHY
                                  1. MADE IT POSSIBLE FOR SMALL AMOUNTS OF ETHYLENE GAS
                TO BE MEASURED
                          b. ETHYLENE RELEASING AGENTS
                                 1. ETHEPHON (2-CHLORO-ETHYLPHOSPHONIC ACID
                                        - AT BASIC pH IT DECOMPOSES TO PRODUCE ETHYLENE

VEGETATIVE DEVELOPMENT

1. STIMULATES ELONGATION OF STEMS, PETIOLES, ROOTS AND FLORAL
   STRUCTURES OF AQUATIC PLANTS
2. PROMOTES GIBBERELLIC ACID SYNTHESIS IN RICE
3. IN PEAS, ROOT AND STEM ELONGATION ARE INHIBITED BY ETHYLENE
       a. STEMS SWELL
       b. LEAVES CURVE DOWNWARD, EPINASTY
4. PROMOTE SEED GERMINATION
5. INHIBIT BUD BREAK
6. REDUCE APICAL DOMINANCE

FRUIT DEVELOPMENT

1. PROMOTE FRUIT RIPENING
       a. KIWI
       b. BANANA
       c. AVOCADO
       d. APPLES

2. ETHYLENE RELEASE CORRESPONDS WITH INCREASED RESPIRATION
   AS SEEN BY AN INCREASE IN CO2 PRODUCTION CALLED THE CLIMACTERIC
   RISE
       a. ETHYLENE’S EFFECT IS AUTOCATALYTIC
              1. ETHYLENE RELEASED BY RIPENING FRUIT WILL STIMULATE A
        PREMATURE CLIMACTERIC IN OTHER NEARBY FRUITS
                    a. HYDROLYSIS OF STARCH TO SUGAR
                    b. SOFTENING OF TISSUE BY THE ACTION OF CELL WALL DEGRADING
                           ENZYMES
                   c. SYNTHESIS OF PIGMENTS AND FLAVOR COMPONENTS

    2. ETHYLENE EFFECTS ARE ECONOMICALLY IMPORTANT
                 a. FRUITS ARE PICKED GREEN FOR SHIPPING AND THEN GASED FOR
          COLOR DEVELOPMENT

       b. USED TO ASSURE UNIFORM RIPENING

       C. CAUSE FLOWERING IN PINEAPPLES