PLANT HORMONES

        WHAT IS A HORMONE?

             AN ORGANIC COMPOUND MADE IN ONE PART OF A PLANT AND
            TRANSPORTED TO ANOTHER PART WHERE IT ELICITS A RESPONSE.

WHAT HORMONES ARE PRESENT IN PLANTS?

        AUXINS
        GIBBERELLINS
        CYTOKININS
        ABSCISIC ACID
        ETHYLENE

AUXIN

1870 - CHARLES AND FRANCIS DARWIN STUDIED PHOTOTROPISM
 
               PHOTOTROPISM IS A PLANTS MOVEMENT IN RESPONSE TO LIGHT

QUESTION ASKED BY DARWIN - HOW DO PLANTS GROW TOWARD LIGHT?

HOW DID THEY STUDY THIS?

STUDIED COLEOPTILES OF CANARY GRASS AND OATS

   WHAT IS A COLEOPTILE?

        COLEOPTILE = SHEATH COVERING THE EMERGING SHOOT OF A MONOCOT

BOTH GREW TOWARD LIGHT COMING FROM ONE DIRECTION.

STEM BENDS TOWARD LIGHT SEVERAL CM BEHIND THE TIP.

EXPERIMENT DONE BY THE DARWINS

1. COVERED TIPS OF GROWING PLANTS WITH METAL FOIL
2. LEFT REGION OF CURVATURE EXPOSED TO LIGHT
3. EXPOSED PLANT TO UNIDIRECTIONAL LIGHT
4. PLANT DIDNíT BEND TOWARD
LIGHT
5. REMOVED FOIL CAPS AND PLANT GREW TOWARD LIGHT
6. NEXT THEY LEFT THE GROWING
TIP EXPOSED TO LIGHT AND
       COVERED THE REGION OF CURVATURE AND THE PLANT GREW TOWARD LIGHT
7. CONCLUSION: GROWTH OF COLEOPTILES TOWARD LIGHT CONTROLLED BY THE
   TIP OF THE COLEOPTILE

DARWINíS SAID PHOTOTROPISM WAS DUE TO AN "INFLUENCE" PRODUCED IN THE TIP.

STUDIES HALTED BY THE DEATH OF CHARLES IN 1882.

THE "INFLUENCE"

POSSIBILITIES:

1. CHEMICAL
2. ELECTRICAL
3. ????

FRITZ WENT

1. ISOLATED THE SUBSTANCE RESPONSIBLE FOR THE CURVATURE OF STEMS
   TOWARD LIGHT

EXPERIMENT

1.  CUT OFF TIPS OF COLEOPTILES AND PLACED ON AGAR BLOCKS
2.  LET SIT ON AGAR FOR SEVERAL HOURS
3.  REMOVED COLEOPTILES FROM BLOCKS
4.  PLACED BLOCK ON SIDE OF DECAPITATED COLEOPTILE STEM
5.  STEM BENT TOWARD SIDE OF STEM WHERE AGAR BLOCK WAS PLACED

THE AGAR BLOCK CONTAINED THE "INFLUENCE" NAMED AUXIN

NATURALLY OCCURRING AUXIN

INDOLE-3-ACETIC ACID (IAA)

ASPECTS OF PLANT GROWTH AND DEVELOPMENT REGULATED BY AUXIN

1. PHOTOTROPISM
2. INHIBITION OF ABSCISSION ZONE
FORMATION
3. INHIBITION OF LATERAL BUD DEVELOPMENT (APICAL DOMINANCE)
4. MAINTNANCE OF TISSUE POLARITY

   ROOTS FORM FROM THE BOTTOM OF A STEM CUTTING AND SHOOTS FROM THE
   TOP.

5. LEAF BLADE EXPANSION
6. LATERAL ROOT INITIATION

SITE OF SYNTHESIS

APICAL BUDS AND YOUNG LEAVES

GIBBERELLINS

HISTORY

DISCOVERED BY KUROSAWA IN JAPAN IN THE 1926.

1. JAPANESE FARMERS NOTICED THAT SOME OF THEIR RICE HAD A
       "PROBLEM".
       a. PLANTS HAD WEAK, ELONGATED STEMS.
       b. PLANTS FELL OVER EASILY.
       c. CALLED CONDITION "FOOLISH SEEDLING" DISEASE OR bakanae.
       d. WERE FOUND TO BE INFECTED WITH A FUNGUS CALLED
              Gibberella fujikuroi

2. FUNGUS WAS GROWN IN CULTURE
       a. CULTURE SOLUTION CAUSED SYMPTOMS IN DISEASE FREE
              PLANTS.
       b. ACTIVE SUBSTANCE WAS NAMED GIBBERELLIN
       c. 80 TO 100 NOW KNOWN; GA3 MOST ACTIVE

3. CHARACTERIZED BY 1938
       a. NOT KNOWN IN THE WEST UNTIL 1945 BECAUSE OF,
              1. WORLD WAR II
              2. LITTLE COMMUNICATION
              3. PUBLISHED IN LITTLE READ JOURNALS

4. EFFECTS ON PLANT GROWTH
       a. ELONGATION OF INTERNODES OF DWARF PLANTS AND
              ROSETTE PLANTS
       b. STIMULATE SOME SEED GERMINATION
               1. STIMULATES AMYLASE PRODUCTION
               2. -AMYLASE DIGESTS ENDOSPERM
               3. SEED GERMINATES
       c. FLOWERING PROMOTED

5. COMMERCIAL EFFECTS
       1. GRAPE
              a. CAUSE ELONGATION OF GRAPE "BERRIES"
              b. CAUSES PEDICEL ELONGATION
                     - LESSENS LOSS BY FUNGUS