This document discusses organogenesis and somatic embryogenesis in plant tissue culture. It defines organogenesis as the development of adventitious organs like roots or shoots from undifferentiated cell masses in tissue culture. Somatic embryogenesis is defined as the formation of embryo-like structures from somatic cells that can develop into whole plants similarly to zygotic embryos. The document outlines the different pathways of organogenesis, including indirect and direct organogenesis, and the stages and types of somatic embryogenesis. It also discusses factors that affect organogenesis and the applications and advantages and disadvantages of these processes.

1. ORGANOGENESIS AND SOMATIC
EMBRYOGENESIS
REEMA NAIK
FRUIT SCIENCE

2. PLANT TISSUE CULTURE:
PLANT TISSUE CULTURE IS THE ASEPTIC METHOD OF GROWING
CELLS AND ORGAN SUCH AS LEAVES, ROOTS, MERISTEMS, ETC
EITHER IN SOLID OR LIQUID MEDIUM UNDER CONTROLLED
CONDITION.
THE THREE COMMON PATHWAYS OF PLANT TISSUE CULTURE
REGENERATION ARE ;
1. PROPOGATION FROM PRE-EXISTING MERISTEMS(SHOOT
CULTURE OR NODAL CULTURE)
2. ORGANOGENESIS
3. NON ZYGOTIC (SOMATIC) EMBRYOGENESIS

3. ORGANOGENESIS
• A PLANT CONTAINS MANY ORGANS LIKE MERISTEMS ,CORTEX ,PHLOEMS,
EPIDEMIS ARE CONSIST OF STRUCTURAL UNIT CALLED CELL. BECAUSE AN CELL
HAVE TO NATURE OF CREATE WHOLE PLANT LIKE ANY ORGAN OR TISSUE OF
PLANT ALSO SHOW SAME NATURE MEAN THEY ALSO CREATE TO WHOLE PLANT
IN IN-VITRO CONDITION.
• IF PLANT ORGANS USED IN IN-VITRO CONDITIONS TO GENERATED NEW PLANT
THIS PROCESS CALLED ORGANOGENESIS.

4. ORGANOGENESIS
THE DEVELOPMENT OF ADVENTITIOUS ORGANS OR PRIMORDIA FROM
UNDIFFERENTIATED CELL MASS IN TISSUE CULTURE BY THE PROCESS OF
DIFFERENTIATION IS CALLED ORGANOGENESIS.
OR
“THE FORMATION OF ROOTS , SHOOTS OR FLOWER BUDS FROM THE CELLS IN
CULTURE IN MANNER SIMILAR TO ADVENTITIOUS ROOT OR SHOOTS FORMATION IN
CUTTINGS IS CALLED ORGANOGENESIS.
CAULOGENESIS:
IT IS A TYPE OF ORGANOGENESIS BY WHICH ONLY ADVENTITIOUS SHOOT BUD
INITIATION TAKE PLACE IN THE CALLUS TISSUE.
RHIZOGENESIS:
IT IS A TYPE OF ORGANOGENESIS BY WHICH ONLY ADVENTITIOUS ROOT FORMATION
TAKES PLACE IN THE CALLUS TISSUES.

5. TYPES OF ORGANOGENESIS
• IN PLANT TISSUE CULTURE, UNDIFFERENTIATED TISSUE IS REFERRED TO AS
CALLUS ALTHOUGH A CALLUS CAN CONTAIN MERISTEMATIC NODULE THAT MAY
NOT BE OBVIOUS TO THE NAKED EYE BUT WHICH NEVER DEVELOP FURTHER
UNLESS SUITABLE CONDITIONS ARE SUPPLIED.
DEVELOPMENT OF ORGANISED STRUCTURES CAN FOLLOW ONE OF THE THREE
PATHWAYS.
I. SHOOT REGENERATION , BASED ON A UNIPOLAR STRUCTURE WITH A SHOOT
APICAL MERISTEMS.
II. ROOT REGENERATION , ESSENTIALLY A UNIPOLAR STRUCTURE WITH A ROOT
APICAL MERISTEMS.
III. SOMATIC EMBRYOGENESIS IN WHICH THERE IS BIPOLAR STRUCTURE.

6. A)INDIRECT ORGANOGENESIS
• PLANT ORGAN FORMATION ON CALLUS TISSUES DERIVED FROM EXPLANTS.
PLANT GROWTH REGULATORS AND DIFFERENTIATION
THE CLASSIC OBSERVATION OF SKOOG AND MILLER THAT THE DIRECTIONS OF
DIFFERENTIATION COULD BE INFLUENCED BY THE RATIO OF THE EXOGENOUSLY
SUPPLIED GROWTH REGULATORS AUXIN AND CYTOKININ.
THEY OBSERVED IN TOBACCO STEM PITH CULTURES THAT A HIGH RATIO OF AUXIN TO
CYTOKININ LED TO INITIATION OF ROOTS WHEREAS A LOW RATIO LED TO
DEVELOPMENTS OF SHOOTS.
ALTHOUGH THERE ARE MANY SPECIES FOR WHICH THIS SIMPLE MANIPULATION WILL
NOT WORK, IN GENERAL AUXIN E.G. IAA, NAA WILL STIMULATE REGENERATION OF
ROOTS, AND CYTOKININS E.G. BAP WILL PROMOTE REGENERATION OF SHOOTS OR
EMBRYOS.

7. B) DIRECT ORGANOGENESIS
• FORMATION OF ORGANS DIRECTLY ON THE SURFACE OF CULTURED INTACT
EXPLANTS. THE PROCESS DOES NOT INVOLVE CALLUS FORMATION.
THE ROLE OF GROWTH REGULATORS
DIRECT ORGANOGENESIS BYPASSES THE NEED FOR A CALLUS PHASE.
A GOOD EXAMPLE IS THE FORMATION OF SOMATIC EMBRYOS.
MOST EVIDENCE SUGGESTS THAT DIRECT EMBRYOGENESIS PROCEEDS FROM
CELLS WHICH WERE ALREADY EMBRYOGENICALLY COMPETENT WHILE THEY
WERE PART OF ORIGINAL, DIFFERENTIATED TISSUE.

8. APPLICATIONS OF ORGANOGENESIS
• PLANT TISSUE CULTURE OR ORGANOGENESIS HAS DIRECT COMMERCIAL
APPLICATIONS AS WELL AS VALUE IN BASIC RESEARCH INTO CELL BIOLOGY,
GENETICS AND BIOCHEMISTRY.
• MICROPROPOGATION USING MERISTEMS AND SHOOT CULTURE TO PRODUCE
LARGE NUMBER OF IDENTICAL INDIVIDUALS.
• SCREENING PROGRAMMES OF CELLS, RATHER THAN PLANTS FOR
ADVANTAGEOUS CHARACTERS.
• LARGE SCALE GROWTH OF PLANT CELLS IN LIQUID CULTURE AS A SOURCE OF
SECONDARY PRODUCTS.
• REMOVAL OF VIRUSES BY PROPOGATION FROM MERISTEMATIC TISSUE.

9. FACTORS AFFECTING THE ORGANOGENESIS
IN VITRO ORGANOGENESIS IS CONTROLLED BY A NUMBER OF FACTORS OTHER THAN
PHYTOHORMONES THIS ARE AS FOLLOWS:
o SIZE OF EXPLANT: ORGANOGENESIS IS GENERALLY DEPENDENT UPON SIZE OF
EXPLANT. THE LARGE EXPLANT CONSISTING PARENCHYMA, VASCULAR TISSUES AND
CAMBIUM HAVE GREATER REGENERATIVE ABILITY THAN THE SMALLER EXPLANT.
o SOURCE OF EXPLANT: THE MOST SUITABLE PART OF THE PLANT FOR STARTING
CULTURE WILL DEPEND ON SPECIES. LEAVES AND LEAF FRAGMENT OF MANY PLANT
SPECIES LIKE BEGONIA, SOLANUM, NICOTINA, CREPIS, ETC. HAVE SHOWN CAPACITY
TO REGENERATE SHOOT BUDS.
o AGE OF THE EXPLANT: PHYSIOLOGICAL AGE OF EXPLANT IS IMPORTANT FOR IN
VITRO ORGANOGENESIS. IN NICOTIANA SPECIES, REGENERATION OF ADVENTITIOUS
SHOOT IS ONLY NOTED IF THE LEAF EXPLANT IS COLLECTED FROM VEGETATIVE
STAGE. I.E. BEFORE FLOWERING.

10. • OXYGEN GRADIENT : IN SOME CULTURES , SHOOT BUD FORMATION
TAKES PLACE WHEN THE GRADIENT OF AVAILABLE OXYGEN INSIDE
THE CULTURE VESSEL IS REDUCE. BUT ROOTING REQUIRE A HIGH
OXYGEN GRADIENT.
• QUALITY AND INTENSITY OF LIGHT: THE BLUE REGION OF SPECTRUM
PROMOTES SHOOT FORMATION AND RED LIGHT INDUCE ROOTING.
• TEMPERATURE : MOST TISSUE CULTURE ARE GROWN SUCCESSFULLY
AT TEMP. AROUND 250 C
• PH OF THE MEDIUM: THE PH OF THE CULTURE MEDIUM IS GENRALLY
ADJUSTED BETWEEN 5.6-5.8 BEFORE STIRILIZATION. THE PH MAY
HAVE DETERMINING ROLE IN ORGANOGENESIS.
• AGE OF CULTURE: A YOUNG CULTURES FREQUENTLY PRODUCES
ORGANS. BUT THE ORGAOGENIC POTENTIAL MAY DECREASE AND
ULTIMATELY DISAPPEAR IN OLD CULTURE.

11. EMBRYOGENESIS
SOMATIC EMBRYOGENESIS
“THE PROCESS OF A SINGLE CELL OR A GROUP OF CELLS INITIATING
THE DEVELOPMENTAL PATHWAY THAT LEADS TO REPRODUCIBLE
REGENERATION OF NON-ZYGOTIC EMBRYOS CAPABLE OF
GERMINATING TO FORM COMPLETE PLANTS.”
UNDER NATURAL CONDITIONS THIS PATHWAY IS NOT NORMALLY
FOLLOWED, BUT FROM TISSUE CULTURES SOMATIC EMBRYOGENESIS
OCCURS MOST FREQUENTLY AND AS AN ALTERNATIVE TO
ORGANOGENESIS FOR REGENERATION OF WHOLE PLANTS.

12. • IN SOMATIC EMBRYOGENESIS, EMBRYO LIKE STRUCTURES, WHICH
CAN DEVELOP INTO WHOLE PLANTS IN A WAY ANALOGOUS TO
ZYGOTIC EMBRYOS, ARE FORMED FROM SOMATIC TISSUES.
• THESE SOMATIC EMBRYOS CAN BE PRODUCED EITHER DIRECTLY OR
INDIRECTLY.
• TWO WAYS OF SOMATIC EMBRYOGENESIS:
• DIRECT EMBRYOGENESIS
• INDIRECT EMBRYOGENESIS

13. DIRECT EMBRYOGENESIS
IN DIRECT SOMATIC EMBRYOGENESIS, THE EMBRYO IS FORMED
DIRECTLY FROM A CELL OR SMALL GROUP OF CELLS WITHOUT THE
PRODUCTION OF INTERVENING CALLUS.
DIRECT SOMATIC EMBRYOGENESIS IS GENERALLY RARE IN
COMPARISON WITH INDIRECT SOMATIC EMBRYOGENESIS.
INDIRECT EMBRYOGENESIS
IN INDIRECT SOMATIC EMBRYOGENESIS, CALLUS IS FIRST PRODUCED
FROM THE EXPLANT.
EMBRYOS CAN THEN BE PRODUCED FROM THE CALLUS TISSUE OR
FROM A CELL SUSPENSION PRODUCED FROM THAT CALLUS.

14. IMPORTANCE OF SOMATIC EMBRYOGENESIS
• IN POLY EMBRYONIC CROPS LIKE CITRUS, ZYGOTIC AS WELLAS NUCELLAR
EMBRYONIC PLANTS ARE OBTAINED SEPARATELY.
• EMBRYOS OF BIG AND HEAVY FRUITS LIKE COCONUT CAN BE TAKEN OUT OF THE
FRUITS AND PRE-SERVE IN TUBE IN STERILE DISTILLED WATER FOR ABOUT TWO
MONTHS AND THEN CULTURED IN MEDIA.
• IN THIS PROCESS EASY INTERNATIONAL EXCHANGE OF GERMPLASM IS POSSIBLE.
• ONE MAJOR PATH OF REGENERATION.
• MASS MULTIPLICATION.
• PRODUCTION OF ARTIFICIAL SEEDS.
• SUITABLE IN SUSPENSION CULTURE.
• HIGHER PROPOGATION RATES.

15. STAGES OF SOMATIC EMBRYOGENESIS
• SOMATIC EMBRYOGENESIS ENCOMPASSES VARIOUS STAGES SUCH AS
1. CALLUS INITIATION
2. EMBRYO DEVELOPMENT AND MATURATION
3. PLANTLET FORMATION

16. ADVANTAGES
• IT IS OBSERVABLE, AS ITS VARIOUS CULTURE CONDITION CAN BE CONTROLLED
• LACK OF MATERIAL IS NOT A LIMITING IS NOT A LIMITING FACTOR FOR
EXPERIMENTATION
• HIGH PROPOGATION RATE
• SOMACLONAL VARIATION
• GERMPLASM CONSERVATION
• LABOUR SAVING
• ELIMINATION OF DISEASES AND VIRUS

17. DISADVANTAGE
S
• CONFINED TO FEW SPECIES
• THE SOMATIC EMBRYOS SHOW VERY POOR GERMINATION BECAUSE
OF THEIR PHYSIOLOGICAL AND BIOCHEMICAL IMMATURITY.
• INSTABILITY OF CULTURED CELLS IN LONG-TERM CULTURES IS A
MAJOR LIMITATION IN COMMERCIAL EXPLOITATION AND MASS
PROPOGATION.