GIBBERELLINS

 

1.   NAMED BECAUSE OF THEIR    CHEMICAL STRUCTURE, NOT THEIR    BIOLOGICAL ACTIVITY

 

   ent-gibberellane structure

 

 

 

 

 

 

 

 

2.   MORE THAN 80 KNOWN AND MORE    ARE BEING FOUND EVERY YEAR

 

3.   EACH ASSIGNED AN “A” NUMBER

 

   GA1, GA3, ... ROUGHLY IN THE

   ORDER THEY WERE DISCOVERED

 

 

 

 

 

4. GA3 WAS ONE OF THE FIRST

   GIBBERELLINS DISCOVERED AND IS

   READILY EXTRACTABLE FROM    FUNGI. IT IS KNOWN AS    GIBBERELLIC ACID

 

5. GA1 AND GA20 ARE THE MOST    ACTIVE AND ARE MORE IMPORTANT    TO PLANTS

 

6.   NOT ALL GA’s ARE BIOLOGICALLY

   ACTIVE. SOME ARE PRECURSORS TO

   BIOLOGICALLY ACTIVE GA’s.

 

PHYSIOLOGICAL ACTION OF GIBBERELLINS

 

   THE DISCOVERY OF GA

 

   1.   RICE PLANTS WITH A FUNGAL        INFECTION HAD EXCESSIVE          STEM    ELONGATION CAUSING             THE STEMS TO BE TALL AND         WEAK

 

   2.   THE SEEDLINGS FELL OVER          INTO THE WATER AND WERE          SAID TO HAVE “FOOLISH            SEEDLING” DISEASE

 

   3.   THE DISEASE WAS CAUSED BY A    FUNGUS THAT PRODUCED               GIBBERELLIC ACID

 

   4.   THIS COMPOUND COULD BE             ISOLATED FROM FUNGAL              CULTURES AND WHEN PUT ON A       NONINFECTED PLANT CAUSED        STEM ELONGATION.

 

GA CAUSES ELONGATION OF INTACT STEMS UNLIKE AUXIN WHICH CAUSES ELONGATION OF EXCISED STEMS

 

DWARF PLANTS

 

WHEN GA IS PUT ON DWARF PLANTS THEY REACH NORMAL HEIGHT.  WHEN IT IS APPLIED TO NORMAL HEIGHT PLANTS THERE IS NO AFFECT

 

  

 

 

   DWARF CORN AND DWARF PEAS ARE

   DWARFS BECAUSE THEY LACK GENES

   NECESSARY FOR GA SYNTHESIS

 

   ASSAYS FOR GA CONTENT SHOW THE

   NATURAL LEVEL OF GA TO BE LOW    IN   THESE PLANTS

 

ROSETTE PLANTS

 

   1.   ROSETTE PLANTS HAVE ALMOST        NO   ELONGATION OF INTERNODES

 

   2.   IN ALMOST ALL CASES, WHEN       GA IS APPLIED, INTERNODES          ELONGATE

 

   3.   ROSETTE PLANTS GENERALLY       “BOLT” PRIOR TO FLOWERING.        APPLICATIONS OF GA CAUSE          BOLTING

 

 

 

      a.   BOLTING IS OFTEN BROUGHT

         ABOUT BY DAY-LENGTH              (PHOTO-PERIOD)

 

         1.   GA19 IS BIOLOGICALLY                INACTIVE

 

         2.   GA20 IS BIOLOGICALLT

            ACTIVE

 

         3.   IN RESPONSE TO LONG             DAYS, GA19 IS                         CONVERTED TO GA20

 

INHIBITION OF STEM GROWTH

 

STEM GROWTH CAN BE INHIBITED BY CHEMICALS THAT BLOCK GA BIOSYNTHESIS

 

   INHIBITORS:

 

   1.   AMO-1618

  

   2.   CYCOCEL (CCC)

 

   3.   PHOSPHON-D

 

   4.   ALAR (B-NINE)

 

   INHIBITORS BLOCK CERTAIN GENES

   FOR GA SYNTHESIS

 

INHIBITORS USED COMMERCIALLY TO:

 

   1.   PRODUCE MORE COMPACT PLANTS

 

      a.   POINSETTAS

 

      b.   LILIES

 

      c.   CHRYSANTHEMUMS

 

   2.   HELP GROW SHORTER WHEAT

      PLANTS TO INCREASE YIELDS        AT HARVEST

 

   3.   USED ON APPLES AND CHERRIES

      TO ENHANCE FRUIT COLOR AND

      PRODUCE A FIRMER FRUIT

 

SEED GERMINATION

 

GA HAS A ROLE IN GERMINATION OF CEREAL GRAINS

 

   1.   GERMINATING CEREAL GRAINS

      SECRETE HYDROLYTIC ENZYMES

 

      a.   a-amylase -   STARCH

                        BREAKDOWN

 

      b.   PROTEASE    -   PROTEIN

                        BREAKDOWN

 

   2.   THE EMBRYO SECRETES GA

 

      a.   GA INDUCES THE ALEURONE

         LAYER TO PRODUCE a-                AMYLASE

 

      b.   ENDOSPERM IS BROKEN DOWN

         TO NOURISH GERMINATING

         SEED

 

 

 

FLOWERING

 

   1.   GA HAS A ROLE IN BOLTING

      WHICH IS FOLLOWED BY

      FLOWERING

 

   2.   GA INDUCES FLOWERING SOON

      AFTER GERMINATION OF SOME

      PLANTS

 

   3.   GA CAN INDUCE ADULT PLANTS

      TO REVERT TO A JUVENILE

      STAGE

 

   4.   GA CAN CAUSE PINE TREES TO

      PRODUCE CONES EVEN IN THE

      JUVENILE STAGE

 

   5.   GA PROMOTES FORMATION OF

      MALE FLOWERS IN Cucumis AND

      Cannabis sativa