Contents Introduction Structure of seed Types of germination Physiology of seed germination Physiological condition of quiescent seed Physiological Biochemical & other changes Accompanying seed germination Emergence of seedling out of the seed coat Factors affecting germination 

1. SEED
GERMINATION
PRESENTED BY
:-
SHAH BHOOMI A.
M.SC.

2. CONTENTS
 INTRODUCTION
 STRUCTURE OF SEED
 TYPES OF GERMINATION
 PHYSIOLOGY OF SEED GERMINATION
 PHYSIOLOGICAL CONDITION OF QUIESCENT SEED
 PHYSIOLOGICAL BIOCHEMICAL & OTHER
CHANGES ACCOMPANYING SEED GERMINATION
 EMERGENCE OF SEEDLING OUT OF THE SEED
COAT

3. INTRODUCTION
 GERMINATION IS THE PROCESS BY WHICH A
PLANT GROWS FROM A SEED.
 GERMINATION IS EMERGENCE OF NORMAL
SEEDLING FROM THE SEEDS UNDER IDEAL
CONDITION OF LIGHT, TEMPERATURE,
MOISTURE, OXYGEN AND NUTRIENTS.
 GERMINATION IS EMERGENCE OF RADICLE
AND PLUMULE THROUGH SEED COAT.

4.  A SEED IS A MATURE OVULE, WHICH IS
FORMED AFTER THE FERTILIZATION.
THE OUTER COVERING OF A SEED IS CALLED
SEED-COAT WHICH IS A PROTECTIVE
COVERING AND IS KNOWN AS TESTA.
 SEEDS CONTAIN A SMALL OPENING CALLED
MICROPYLE THROUGH WHICH WATER ENTERS
INTO THE SEED.

5. STRUCTURE OF SEED
 SEEDS ARE OF TWO TYPES
ACCORDING TO THE
NUMBER OF COTYLEDONS.
A. MONOCOTYLEDONOUS
SEEDS:
THESE SEEDS CONTAIN
ONLY ONE COTYLEDON;
FOR EXAMPLE, WHEAT,
BAJRA, MAIZE AND RICE.
Fig: Maize seed
Source:-
www.biologydiscusion.com

6. B. DICOTYLEDONOUS SEEDS:
THESE SEEDS CONTAIN TWO COTYLEDONS;
FOR EXAMPLE, MANGO, GRAM AND PEA.
Fig: Gram seed
Source:-

7. TYPES OF GERMINATION
 THERE ARE TWO TYPES OF GERMINATION:
1. EPIGEAL GERMINATION:
- IN THIS, THE COTYLEDONS ARE RAISED
OUT OF THE SOIL AND GENERALLY
BECOME GREEN AND PHOTOSYNTHETIC.
- IN DICOTS, THEY ARE PUSHED UP BY RAPID
EXTENSION OF HYPOCOTYL BEFORE GROWTH
OF THE EPICOTYL.

8. FIG.:- EPIGEAL GERMINATION OF COMMON BEAN
Source :-
www.Scienceinhydrophonics.com

9. 2. HYPOGEAL GERMINATION:-
- IN THIS TYPE OF GERMINATION, THE COTYLEDONS
REMAIN UNDERGROUND.
- HYPOCOTYL GROWTH IS RESTRICTED.
- THE EPICOTYL GROWS TO RAISE THE FIRST LEAVES OUT
OF THE SOIL.
- HYPOGEAL GERMINATION OCCURS IN DICOTYLEDONS
SEEDS OF GRAM, MANGO, PEA, GROUNDNUT, ETC AND IN
MONOCOTYLEDONS LIKE RICE, MAIZE, WHEAT ETC.

10. SOURCE:- WWW.EASYELIMU.COM
Hypogeal
germination

11. PHYSIOLOGY OF SEED
GERMINATION
ALL THE VIABLE SEEDS WHICH HAVE OVERCOME
DORMANCY (IF ANY) EITHER NATURALLY OR
ARTIFICIALLY WILL READILY GERMINATE UNDER
SUITABLE ENVIRONMENTAL CONDITIONS
NECESSARY FOR SEED GERMINATION I.E.,
WATER, O₂, TEMPERATURE AND IN SOME CASES
LIGHT.
 SUCH SEEDS WHICH JUST WAIT FOR SUITABLE
ENVIRONMENTAL CONDITIONS TO GERMINATE

12.  THE PROCESS OF SEED GERMINATION STARTS
WITH THE IMBIBITION OF WATER BY SEED COATS
AND EMERGENCE OF GROWING ROOT TIP OF
EMBRYO.
IT ENDS WHEN THE EMBRYO HAS DEVELOPED
INTO A SEEDLING WHICH IS OUT OF BOUNDS OF
SEED COATS AND HAS ITS OWN
PHOTOSYNTHETIC SYSTEM.
 THE PHYSIOLOGICAL AND BIOCHEMICAL
CHANGES ACCOMPANYING THE SEED

13. PHYSIOLOGICAL CONDITION OF
QUIESCENT SEED
 BEFORE GERMINATION SEED IS A DRY
STRUCTURE WITH VARIOUS METABOLIC
ACTIVITIES REDUCED TO A MINIMUM.
 IT HAS DRY, COMPARATIVELY HARD SEED
COAT CONSISTING OF USUALLY NON-LIVING
CELLS.
 THIS SEED COAT AND THE CELLS OF
ENDOSPERM WHEN PRESENT FORM A BARRIER

14.  MOREOVER, IN CERTAIN SEEDS THE SEED COAT IS IMPERMEABLE
TO WATER AND O2 AND ACTS AS BARRIER BETWEEN EMBRYO AND
THESE SUBSTANCES.
 THEREFORE, THE CELLS OF THE SEED COAT AND ENDOSPERM
(WHEN PRESENT) MUST BECOME PERMEABLE TO WATER AND
OXYGEN, ALSO THESE MUST BECOME PENETRABLE TO THE
GROWING ROOT TIP OF THE EMBRYO IF GERMINATION IS TO
OCCUR.
MOST PART OF THE EMBRYO (EXCLUDING COTYLEDONS) CONSISTS
OF POTENTIALLY MERISTEMATIC CELLS.
 BUT STILL THESE CELLS DO NOT DIVIDE AND ENLARGE AND HAVE
MINIMUM RESPIRATION RATE IN DRY SEED.

15. IT IS CHIEFLY DUE TO THE FOLLOWING REASONS :-
(I) IN ABSENCE OF SUFFICIENT AMOUNT OF WATER, THESE CELLS
ARE UNABLE TO MAINTAIN TURGOR SO THAT THEIR
GROWTH IS CHECKED.
(ii) THESE CELLS DO NOT HAVE SUFFICIENT AMOUNT OF
SOLUBLE RESPIRABLE FOOD.
 THE RESERVE FOOD STORED IN COTYLEDONS OR ENDOSPERM
IS IN INSOLUBLE FORM AND IS NOT AVAILABLE TO THESE
CELLS.
(III) AEROBIC RESPIRATION IN EMBRYO CELLS IS AT ITS MINIMUM.
 IT IS BECAUSE SEED COAT ACTS AS BARRIER TO O2.
OXYGEN UPTAKE IN DRY SEEDS IS REDUCED TO ABOUT 0.05

16. (IV) SEED COAT MAY CONTAIN INHIBITORS WHICH CHECK
GROWTH OF THESE CELLS.
(V) THE CONCENTRATION OF HYDROLYTIC ENZYMES IS
LOW IN DRY SEEDS.
(VI) HARD SEED COAT FORMS A PHYSICAL BARRIER TO
THE GROWTH OF EMBRYO.
ALL THESE ABOVE CONDITIONS ARE ADMIRABLY
OVERCOME IF SEEDS ARE PLACED UNDER SUITABLE
CONDITIONS ESSENTIAL FOR GERMINATION AND IN
MOST CASES SEED GERMINATION BEGINS JUST BY
PLACING THE DRY SEEDS ON A MOIST SUBSTRATE.

17. PHYSIOLOGICAL BIOCHEMICAL &
OTHER CHANGES ACCOMPANING SEED
GERMINATION
WATER UPTAKE:
 SEED GERMINATION, AS MENTIONED EARLIER,
STARTS WITH THE IMBIBITION OF WATER BY DRY
SEED COAT WHICH IS PURELY A PHYSICAL PROCESS.
VARIOUS HYDROPHILIC GROUPS SUCH AS —NH2, —
OH, —COOH ETC., OF PROTEINS, POLYMERIC
CARBOHYDRATES ETC., FOUND IN THE SEED COAT
ATTRACT DIPOLAR WATER MOLECULES AND FORM
HYDRATED SHELLS AROUND THEM RESULTING IN

18. THIS WATER UPTAKE BY SWELLING IS FOLLOWED BY
INTENSIVE WATER UPTAKE ASSOCIATED WITH
GERMINATION.
DUE TO IMBIBITION OF WATER THE SEED COATS
BECOME
(I) MORE PERMEABLE TO O2 AND WATER AND
(II) LESS RESISTANT TO OUTWARD GROWTH OF
THE EMBRYO.

19.  RESPIRATION:
THE UPTAKE IS ACCOMPANIED BY RAPID INCREASE IN
RESPIRATION RATE OF EMBRYO.
 INITIALLY THERE MAY BE ANAEROBIC RESPIRATION BUT
IT IS SOON REPLACED BY AEROBIC ONE DUE TO
AVAILABILITY OF O2.
 AS COMPARED TO DRY SEEDS, THE UPTAKE OF O2 IN
GERMINATION SEEDS MAY RISE IN CASE OF CEREALS
FROM 0.05 Μ 1/G TISSUE/HR TO 100 Μ 1/G TISSUE/HR
WITHIN VERY SHORT PERIOD AFTER GERMINATION
WHEN WATER CONTENT HAS REACHED ABOUT 40%.
 SUCROSE IS PROBABLY THE RESPIRATORY SUBSTRATE
AT THIS STAGE WHICH IS PROVIDED BY ENDOSPERM.

20.  MOBILIZATION OF RESERVE
MATERIALS:
 AS GERMINATION PROGRESSES THERE IS
MOBILIZATION OF RESERVE MATERIALS TO
PROVIDE :
(I) BUILDING BLOCKS FOR THE DEVELOPMENT
OF EMBRYO,
(II) ENERGY FOR THE BIOSYNTHETIC
PROCESSES, AND

21. (I) NUCLEIC ACIDS:
IN MONOCOTS DURING THE IMBIBITION STAGE OF SEED
GERMINATION THERE IS RAPID DECREASE OF DNA AND RNA
CONTENT IN THE ENDOSPERM WITH A SIMULTANEOUS
INCREASE IN THE EMBRYONIC AXIS PROBABLY DUE TO THEIR
TRANSPORTATION AS SUCH.
APPRECIABLE AMOUNT OF RNA APPEARS IN THE ALEURONE
LAYER AFTER ABOUT 16 HOURS WHICH IS PROBABLY DUE TO
ITS DE NOVO SYNTHESIS.
 HIGHER CONCENTRATION OF RNA (AND ALSO PROTEIN) IN
THE EMBRYONIC AXIS PRECEDES CELL DIVISION.
 DUE TO MORE CELL DIVISIONS THE DNA CONTENT IS
INCREASED.

22. (II)
CARBOHYDRATES:
INSOLUBLE CARBOHYDRATES LIKE STARCH ARE THE
IMPORTANT RESERVE FOOD OF CEREALS IN THE
ENDOSPERM.
 DURING GERMINATION STARCH IS HYDROLYSED FIRST
INTO MALTOSE IN THE PRESENCE OF Α-AMYLASE AND
Β-AMYLASE AND THEN THE MALTOSE IS CONVERTED
INTO GLUCOSE BY MALTASE.
THE GLUCOSE IS ABSORBED BY THE SCUTELLUM,
CONVERTED INTO SOLUBLE SUCROSE AND
TRANSPORTED TO GROWING EMBRYONIC AXIS.
DURING GERMINATION THE EMBRYONIC AXIS SECRETES
GIBBERELLIC ACID INTO THE ALEURONE LAYER WHICH

23.  THIS ENZYME IS NOT FOUND IN UN-
GERMINATED SEEDS.
 REMOVAL OF GIBBERELLIC ACID DURING THIS
PERIOD RESULTS IN RAPID FALL OF Α - AMYLASE
SYNTHESIS.
 THE LATTER CAN BE RESTORED BY SUPPLYING
EXTERNAL GIBBERELLIC ACID.
 THE GIBBERELLIC ACID INDUCED SYNTHESIS OF
Α-AMYLASE IS COUNTERED BY ABSCISIC ACID.
 IN CONTRAST TO Α-AMYLASE, Β-AMYLASE IS
ALREADY PRESENT IN THE SEED IN INACTIVE

24. (III) LIPIDS:
 MANY PLANTS LIKE CASTOR BEAN, PEANUT ETC.
STORE LARGE AMOUNT OF NEUTRAL LIPIDS OR FATS AS
RESERVE FOOD IN THEIR SEEDS.
 DURING GERMINATION THE MOBILIZATION OF THESE
FATS IS BROUGHT ABOUT BY HYDROLYSIS OF FATS TO
FATTY ACIDS AND GLYCEROL BY LIPASES AND Β-
OXIDATION OF FATTY ACIDS TO ACETYL-COA.
 THE ACTIVITY OF LIPASES IS GREATLY STIMULATED BY
IMBIBITION AND IN SOME CASES THERE MAY EVEN BE DE
NOVO SYNTHESIS OF THESE ENZYMES WHICH IS
PROBABLY TRIGGERED BY GIBBERELLIC ACID.

25. SOME OF THE ACETYL-COA IS CONVERTED INTO
SUCROSE VIA THE GLYOXYLATE CYCLE AND IS
TRANSPORTED TO THE GROWING EMBRYONIC
AXIS.
 SYNTHESIS OF THE TWO KEY ENZYMES OF
GLYOXYLATE CYCLE (I.E., ISOCITRATASE AND
MALATE SYNTHETASE) TAKES PLACE DE NOVO
DURING THE EARLY STAGES OF GERMINATION.
 THEIR CONCENTRATION IS INCREASED DURING
THE STAGE WHEN FATS ARE BEING ACTIVELY
CONVERTED INTO SUCROSE.
THEY DISAPPEAR WHEN ALL THE STORED FAT HAS
BEEN CONSUMED AND THE SEEDLING HAS

26. (IV) PROTEINS:
 SOME PLANTS STORE PROTEINS AS RESERVE FOOD IN
THEIR SEEDS IN THE FORM OF ALEURONE GRAINS.
 MOBILIZATION OF THESE PROTEINS INVOLVES THEIR
HYDROLYTIC CLEAVAGE INTO AMINO ACIDS BY
PEPTIDASES.
 THESE ENZYMES, IN PART, ARE SYNTHESIZED DE NOVO
AS THE GERMINATION STARTS IN THE SAME WAY AS Α -
AMYLASE IS SYNTHESIZED IN CEREALS.
 THE AMINO ACIDS MAY EITHER PROVIDE ENERGY BY
OXIDATION AFTER DEAMINATION OR MAY BE UTILISED
IN THE SYNTHESIS OF NEW PROTEINS.

27.  DURING SEED GERMINATION THERE IS ACTIVE
SYNTHESIS OF ENZYMES AND OTHER PROTEINS AND
ALSO THE FORMATION OF DIFFERENT RNA SPECIES FOR
THEIR SYNTHESIS.
 FOR THE SYNTHESIS OF THESE PROTEINS POLYSOMES
ARE INVOLVED.
 IT IS NOT DEFINITE WHETHER THESE ARE ALREADY
PRESENT IN THE SEED OR ARE SYNTHESIZED DURING
GERMINATION.
 MOREOVER, IT IS ALSO NOT CERTAIN WHETHER
POLYSOMES ARE SYNTHESIZED DE NOVO OR FROM

28. (V) INORGANIC MATERIALS:
A NUMBER OF INORGANIC MATERIALS SUCH AS
PHOSPHATE, CALCIUM, MAGNESIUM AND
POTASSIUM ARE ALSO STORED IN SEEDS IN THE
FORM OF PHYTIN.
 THESE MATERIALS WHICH MAY ACTIVATE A
NUMBER OF IMPORTANT ENZYMES ARE
LIBERATED DURING GERMINATION DUE TO THE
ACTIVITY OF VARIOUS PHOSPHATASES
INCLUDING PHYTASE.

29. EMERGENCE OF SEEDLING OUT OF
THE SEED COAT
 ALL THESE CHANGES DESCRIBED ABOVE
GRADUALLY RESULT IN SPLITTING OF SEED
COAT AND EMERGENCE OF THE GROWING
SEEDLING.
 FIRST, THE RADICLE COMES OUT AND GROWS
DOWNWARD, THEN PLUMULE COMES OUT AND
GROWS UPWARD.
 DUE TO CONTINUED GROWTH OF THIS
SEEDLING, THE LATTER COMES OUT OF THE

30.  THE SPLITTING OF SEED COAT MAY
TAKE PLACE EITHER:
(i) BY IMBIBITIONAL PRESSURE OR
(ii) BY INTERNAL PRESSURE CREATED BY THE
GROWING PRIMARY ROOT OR
(iii)BY HYDROLYTIC ENZYMES WHICH ACT ON
CELL WALL CONTENTS OF SEED COAT AND
DIGEST IT E.G., CELLULASE, PECTINASE ETC.
SOMETIMES THE SEED COAT MAY BE
EXTENSIVELY ROTTED BY THE ACTIVITY OF

31. FACTORS AFFECTING
GERMINATION
 SOME OF THE IMPORTANT FACTORS ARE:
(1) EXTERNAL FACTORS
 WATER,
 OXYGEN AND
 SUITABLE TEMPERATURE
 LIGHT
 SOIL CONDITION
(2) INTERNAL FACTORS
SEED DORMANCY DUE TO INTERNAL CONDITIONS AND ITS
RELEASE.

32. (1) EXTERNAL FACTORS
(I) WATER :
 THE WATER IS AN IMPORTANT FACTOR WHICH CONTROLS
AND ACTIVATES VARIOUS ENZYMATIC ACTIVITIES.
 A DORMANT SEED IS GENERALLY DEHYDRATED AND
CONTAINS HARDLY 6-15% WATER IN ITS LIVING CELLS.
 THE ACTIVE CELLS, HOWEVER, REQUIRE ABOUT 75-95% OF
WATER FOR CARRYING OUT THEIR METABOLISM.
 THEREFORE, THE DORMANT SEEDS MUST ABSORB EXTERNAL
WATER TO BECOME ACTIVE AND SHOW GERMINATION.
 IT HELPS THE SEEDS IN IMBIBITIONS CAUSING INCREASE IN
OSMOTIC EFFECTS.

33. (II) ATMOSPHERIC COMPOSITION (OXYGEN) :
 IT IS ALSO AFFECTS SEED GERMINATION.
 THE ATMOSPHERE CONSISTS OF SEVERAL GASES
LIKE O₂, CO₂ AND N₂ ETC. OXYGEN INCREASES
RESPIRATION.
 THE PERCENTAGE OF O₂ FOR GERMINATION
USUALLY VARIES FROM 8 TO 20.
 EXCESS OF CO₂ CONCENTRATION DECREASES
GERMINATION IN GENERAL BUT IN A FEW SEEDS
LIKE PHLEUM PRATENSE SHOW INCREASES IN

34. (III) TEMPERATURE :
 THE OPTIMUM TEMPERATURE FOR SEED GERMINATION
VARIES ACCORDING TO SPECIES.
 THE OPTIMUM TEMPERATURE FOR MOST SPECIES
RANGES BETWEEN 25-35 ⁰C.
 GENERALLY, THE GERMINATION IS INHIBITED AT VERY
LOW TEMPERATURE AND VERY HIGH TEMPERATURE(0°C
AND 45°C).
A FEW SEEDS OF CERTAIN SPECIES REQUIRE LOW
TEMPERATURE FOR GERMINATION.
TEMPERATURE MAY INTERACT WITH LIGHT AND
HUMIDITY CAUSING GERMINATION.

35. (IV) LIGHT :
 THE SEEDS OF MOST CULTIVATED PLANTS GERMINATE
EQUALLY WELL IN LIGHT AND DARK.
 PHOTOBLASTIC SEEDS CAN GERMINATE ONLY IN PRESENCE
OF LIGHT.
 THE LIGHT INDUCES PHYTOCHROME ACTIVITY.
 MAYER (1986) PROPOSED THE INVOLVEMENT OF CALCIUM
BINDING PROTEIN, THE CALMODULIN, WHICH STIMULATE THE
METABOLIC RESPONSES DURING GERMINATION.
INACTIVE PHYTOCHROME (PR) ACTIVE
PHYTOCHROME (PFR)
TRANSPORT OF CA2+ IONS CALMODULIN
MEDIATION
PRIMARY LIGHT REACTION SECONDARY LIGHT
Red
light

36. (V) SOIL CONDITIONS :
 THE SOIL CONDITION WHICH INDUCE
GERMINATION INCLUDE WATER HOLDING
CAPACITY, AERATION OF SOIL, MINERAL
COMPOSITION, SOIL – TEXTURE, PH OF SOIL AND
ORGANIC MATTER ETC.
 SALINE CONDITION OF SOIL INHIBITS
GERMINATION.
 OTHER SOIL CONDITION ALSO PLAY
IMPORTANT ROLE IN GERMINATION.

37. (2) INTERNAL FACTORS:
SEED DORMANCY DUE TO INTERNAL CONDITIONS AND ITS RELEASE:
IN SOME PLANTS THE EMBRYO IS NOT FULLY MATURE AT THE TIME
OF SEED SHEDDING.
SUCH SEEDS DO NOT GERMINATE TILL THE EMBRYO ATTAINS
MATURITY.
 THE FRESHLY SHED SEED IN CERTAIN PLANTS MAY NOT HAVE
SUFFICIENT AMOUNTS OF GROWTH HORMONES REQUIRED FOR THE
GROWTH OF EMBRYO.
THESE SEEDS REQUIRE SOME INTERVAL OF TIME DURING WHICH THE
HORMONES GET SYNTHESIZED.

38. THE SEEDS OF ALMOST ALL THE PLANTS REMAIN
VIABLE OR LIVING FOR A SPECIFIC PERIOD OF TIME.
THIS VIABILITY PERIOD RANGES FROM A FEW
WEEKS TO MANY YEARS.
SEEDS OF LOTUS HAVE THE MAXIMUM VIABILITY
PERIOD OF 1000 YEARS.
SEEDS GERMINATE BEFORE THE ENDING OF THEIR
VIABILITY PERIODS.
IN MANY PLANTS, THE FRESHLY SHED SEEDS
BECOME DORMANT DUE TO VARIOUS REASONS
LIKE THE PRESENCE OF HARD, TOUGH AND
IMPERMEABLE SEED COATS, PRESENCE OF GROWTH
INHIBITORS AND THE DEFICIENCY OF SUFFICIENT
AMOUNTS OF FOOD, MINERALS AND ENZYMES,
ETC.

39. REFERENCES
 PLANT PHYSIOLOGY – S.K.SINGH
(1ST EDITION IN 2005)
 A TEXTBOOK OF PLANT PHYSIOLOGY
BIOCHEMISTRY AND BIOTECHNOLOGY –
S.K.VERMA
- MOHIT VERMA
(6TH EDITION IN 2007)
 FUNDAMENTALS OF PLANT PHYSIOLOGY –
V.K.JAIN