PATTERNS IN PLANT DEVELOPMENT

 

OVER TIMES, PLANTS UNDERGO:

 

   1.   GROWTH - CHANGES IN SIZE       AND MASS.  IT IS AN                IRREVERSIBLE INCREASE IN          VOLUME OR SIZE

 

   2.   DIFFERENTIATION - WHEN A        CELL GIVES RISE TO TWO            DAUGHTER CELLS THAT EACH       BECOME SOMETHING DIFFERENT

 

      a.   CELLS CAN                           DEDIFFERENTIATE

 

      b.   PLANT CELLS ARE                     TOTIPOTENT

 

   3.   DEVELOPMENT - THE SUM OF          ALL THE CHANGES AN ORGANISM      GOES THROUGH IN ITS LIFE       CYCLE

 

 

 

CONTROL OF GROWTH AND DEVELOPMENT

 

   THERE ARE THREE LEVELS OF    CONTROL:

 

   1.   INTRINSIC

 

      a.   INTRACELLULAR

 

         CHANGES IN GENE                   EXPRESSION THAT                   INFLUENCE CELLULAR                  ACTIVITIES,BY ALTERING            THE KINDS OF PROTEINS IN          A CELL

 

      b.   INTERCELLULAR

 

         HORMONES AND THEIR ROLES

         IN COORDINATING THE

         ACTIVITIES OF GROUPS OF

         CELLS

 

 

 

   2.   EXTRACELLULAR

 

      a.   EXTRINSIC - ORIGINATE

         OUTSIDE THE ORGANISM AND

         CONVEY INFORMATION ABOUT

         THE ENVIRONMENT

 

ALL THREE LEVELS OF CONTROL INTERACT TO DETERMINE THE DEVELOPMENT OF A PLANT

 

GENETIC CONTROL OF DEVELOPMENT

 

CELLS DO NOT LOSE THEIR GENES

ALTHOUGH SOME MAY NOT BE EXPRESSED.  CELLS ARE TOTIPOTENT.

 

1.   DEVELOPMENT OF A PLANT MUST    FOLLOW A PROGRAMMED SEQUENCE    OF GENE ACTIVATIONS TO PRODUCE    THE REQUIRED GENE PRODUCT - A

   PROTEIN

 

 

 

2.   THE ORGANISM MUST BE ABLE TO

   RESPOND TO THE GENE PRODUCTS

   FORMED

 

GENES CONSIST OF SPECIFIC SEQUENCES OF NUCLEOTIDES IN THE DNA MOLECULE

 

GENE EXPRESSION DEALS WITH THE SYNTHESIS OF SPECIFIC PROTEINS ENCODED BY SPECIFIC GENES

 

   NO GENE IS TURNED ON ALL OF    THE TIME

 

   GENE EXPRESSION IS DIVIDED    INTO FIVE PRINCIPAL STAGES

 

   1.   GENE ACTIVATION

   2.   TRANSCRIPTION

   3.   RNA PROCESSING

   4.   TRANSLATION

   5.   PROTEIN PROCESSING

 

REGULATION CAN OCCUR AT ANY ONE OF THESE STAGES

 

1.   GENE EXPRESSION BEGINS WITH    THE PREPARATION OR ACTIVATION    OF THE DNA THAT MAKES UP A    GENE

 

   a.   REMOVAL OF HISTONES

   b.   EXTENSION OF DNA

 

2.   TRANSCRIPTION

 

   SYNTHESIS OF A MOLECULE OF          mRNA(RIBONUCLEIC ACID)FROM A    SEQUENCE OF DNA

 

   RNA POLYMERASE II

 

   DNA ---> mRNA

 

3.   RNA PROCESSING

 

      a.   MOLECULE OF 7-METHYL-

         GUANOSINE TRIPHOSPHATE

         (GTP) ADDED TO ONE END

         OF THE RNA MOLECULE.

         (CAPPING)

 

      b. POLYADENYLATED TAIL             ADDED TO THE OTHER END

         (AAAAAAAA)

 

      c.   INTRONS REMOVED AND               EXONS SPLICED TOGETHER

 

4.   TRANSLATION

 

   MODIFIED mRNA TRANSPORTED TO    THE CYTOSOL WHERE IT IS    ATTACHED TO A RIBOSOME

 

   a.   AMINO ACIDS ARE BROUGHT IN,

      ONE-BY-ONE AND BONDED           TOGETHER BY PEPTIDE BONDS

 

5.   PROTEIN PROCESSING (POST-

   TRANSLATIONAL MODIFICATION)

 

EACH STEP CAN BE A POINT OF REGULATION

 

HORMONAL REGULATION OF DEVELOPMENT

 

NON-DIFFERENTIATED CELLS CAN BE INDUCED TO DIVIDE AND DIFFERENTIATE, WITH HORMONES

 

ENVIRONMENTAL REGULATION OF DEVELOPMENT

 

ENVIRONMENTAL STIMULI

 

MOST ARE:

   1.   LIGHT

   2.   TEMPERATURE

   3.   GRAVITY

 

OTHERS ARE:

   4.   MAGNETIC FIELD

   5.   SOUND

   6.   WIND

   7.   SOIL MOISTURE

   8.   HUMIDITY

   9.   NUTRITION

   10.POLLUTANTS

 

 

ENVIRONMENTAL SIGNALS ARE EXTERNAL

 

SIGNALS MUST BE PERCEIVED AND TRANSDUCED INTO SOME METABOLIC ORBIOCHEMICAL CHANGE

 

ENVIRONMENTAL STIMULI ACT, IN PART, THROUGH MODIFYING GENE EXPRESSION OR HORMONAL ACTIVITIES

 

SURVEY OF PLANT DEVELOPMENT

 

SEED STRUCTURE AND DEVELOPMENT

 

   EMBRYO DEVELOPS IN THE OVARY

   OF THE FLOWER

 

   AN EMBRYO CONSISTS OF A(N)

 

   1.   EMBRYONIC ACCESS

      a.   PLUMULE AT ONE END

         (FORMS SHOOT - STEMS &

         LEAVES)

        

      b.   RADICLE AT THE OTHER END

         (FORMS ROOTS)

 

   2.   COTYLEDONS (SEED LEAVES)

     

      a.   MONOCOTYLEDONS - ONE

         COTYLEDON

 

      b.   DICOTYLEDONS - TWO

         COTYLEDONS

 

THE DEVELOPING EMBRYO IS SURROUNDED BY ENDOSPERM

 

   1.   A NUTRITIVE TISSUE

 

   2.   FORMED BY DOUBLE                 FERTILIZATION (THE FUSION

      OF A SPERM WITH TWO POLAR

      NUCLEI)

 

THE SEED IS SURROUNDED BY A TESTA OR SEED COAT

 

 

 

SEED GERMINATION

 

   1.   UPTAKE OF WATER