CYTOKININS

 

KINETIN WAS THE FIRST CYTOKININ DISCOVERED.

 

   1.   KINETIN DOES NOT OCCUR

      NATURALLY BUT IS                   SYNTHESIZED FROM HERRING

      SPERM DNA

 

      a.   DISCOVERED BY A GROUP

         LED BY FOLKES SKOOG IN

         THE 1950’S.

 

         1.   WERE TRYING TO FIND

            WAYS TO GET PLANT

            CELLS TO DIVIDE IN

            TISSUE CULTURE

 

         2.   FOUND THAT CELLS IN                CULTURES CONTAINING                VASCULAR TISSUE WOULD             DIVIDE BUT, THOSE                   LACKING VASCULAR                  TISSUE ONLY ENLARGED               BUT, DID NOT DIVIDE

         3.   EXTRACTS FROM

            VASCULAR TISSUES,

            COCONUT MILK, &

            YEAST ALL CAUSED                 CELLS TO DIVIDE

 

      b.   CARLOS MILLER ISOLATED

         THE ACTIVE PRINCIPLE

         FROM YEAST EXTRACT AND

         IDENTIFIED IT AS A                 PURINE WHICH IS A

         NUCLEIC ACID

 

      c.   OTHER NUCLEIC ACID

         PREPARATIONS WERE

         TESTED FOR CELL DIVISION

         PROPERTIES

 

         1.   “OLD” HERRING SPERM

            DNA WAS FOUND TO                   CAUSE CELLS TO DIVIDE

 

         2.   NEW HERRING SPERM DNA

            WAS FOUND TO HAVE NO

            EFFECT

 

            a. WHEN NEW HERRING

               SPERM DNA WAS AUTO-

               CLAVED, IT CAUSED

               CELLS TO DIVIDE

 

            b.   THE ACTIVE

               INGREDIENT WAS

               NAMED KINETIN AND

               LATER, SINCE IT

               CAUSED CELLS TO                      DIVIDE, WHICH IS

               CYTOKINESIS, THEY

               PROPOSED THE NAME

               CYTOKININ

  

      d.   NATURALLY OCCURING

         CYTOKININS WERE NOT

         KNOWN FROM PLANTS UNTIL

         THE EARLY 1960’S

 

         1.   ISOLATED FROM CORN

            (ZEA MAYS)                         INDEPENDENTLY BY                MILLER AND LETHAM

 

         2.   NAMED ZEATIN

THE PHYSIOLOGICALLY ROLES OF CYTOKININS

 

A.   CELL DIVISION AND    MORPHOGENESIS

 

   1.   CELLS THAT ARE NOT DIVIDING

      CAN BE MADE TO DIVIDE BY

      PROVIDED THEM WITH A

      CONTINUOUS SUPPLY OF             CYTOKININ

 

   2.   CELL CULTURES OF CALLUS

      CAN BE MAINTAINED WITH

      EQUAL AMOUNTS OF CYTOKININ

      AND AUXIN

 

      a.   WHEN CYTOKININ LEVELS

         ARE LOW AND AUXIN LEVELS

         ARE HIGH, ROOT DEVELOP-

         MENT IS FAVORED

 

      b.   WHEN CYTOKININ LEVELS

         ARE HIGH AND AUXIN LEVEL

         IS LOW, BUD DEVELOPMENT

         IS FAVORED

 

   3.   CYTOKININ IMPLICATED IN

      CROWN GALL FORMATION

 

      a.   CROWN GALLS ARE FORMED

         AT THE JUNCTION OF STEM

         AND ROOT DUE TO INFECT-

         ION BY AGROBACTERIUM

         TUMEFACIENS

     

      b.   INFECTED CELLS GAIN THE

         ABILITY TO PRODUCE CYTO-

         KININS

 

         1.   BACTERIA CAN BE                      KILLED BY HEATING

 

         2.   BACTERIA FREE TISSUES

            RETAIN THE ABILITY TO

            SYNTHESIZE CYTOKININS

 

         3.   THE BACTERIA CONTAIN

            A Ti OR TUMOR                      INDUCING PLASMID

 

            a.   THE PLASMID CAN BE

               INCORPORATED INTO

               THE NUCLEAR DNA OF

               THE HOST PLANT

 

            b.   THE GENES ON THE

               PLASMID ARE

               EXPRESSED

 

               1.   PLASMIDS USED

                  FOR GENETIC

                  ENGINEERING TO

                  INCORPORATE

                  GENES FOR                           CERTAIN                               CHARACTERISTICS

 

B.   NUTRIENT MOBILIZATION AND

   SENESCENCE

 

   1.   SENESCENCE - THE BREAKDOWN

      OF PROTEINS & NUCLEIC             ACIDS, THE LOSS OF CHLORO-

      PHYLL, AND THE ACCUMULATION

      OF AMINO ACIDS

 

  

2.   THERE ARE THREE KINDS OF    EVIDENCE THAT CYTOKININS HAVE    A ROLE IN DELAYING SENESCENCE

 

   a.   EXOGENOUS CYTOKININ

      APPLICATIONS TO DETACHED

      LEAVES WILL DELAY THE ONSET

      OF SENESCENCE, MAINTAIN

      PROTEIN LEVELS AND PREVENT

      CHLOROPHYLL BREAKDOWN

 

   b.   ENDOGENOUS CYTOKININ LEVELS

      HAVE BEEN CORRELATED TO THE

      ONSET OF SENESCENCE

 

      1.   DETACHED LEAVES,                   PROVIDED WITH AUXIN TO             PROMOTE   ROOTING, FAIL TO          SENESCE   AS NEW ROOTS

         PROVIDE CYTOKININ TO THE

         LEAF BLADE

 

   c.   WHEN THE GENE FOR CYTOKININ

      BIOSYNTHESIS IS LINKED TO A

      HEAT SHOCK PROMOTOR AND THE

      PLANT SUBJECTED TO ELEVATED

      TEMPERATURES, CYTOKININ IS

      PRODUCED IN HIGH AMOUNTS.

      BUDS ARE INDUCED TO DEVELOP

      SENESCENCE IS DELAYED

 

C. OTHER CYTOKININ EFFECTS

 

   WHEN APPLIED EXOGENOUSLY:

 

   1.   STIMULATE CELL ENLARGEMENT

      OF COTYLEDONS OF CUCUMBERS

      AND SUNFLOWERS

 

   2.   WILL RELEASE LATERAL BUDS

      FROM APICAL DOMINANCE

 

      a. “WITCHES BROOM” - DUE

         TO AN OVER-PRODUCTION OF

         CYTOKININ RESULTING IN

         RELEASE OF APICAL

         DOMINANCE AS SHOWN BY A

         A DENSE MASS OF SHORT

         BRANCHES