BRIDGE COURSE BRIDGE COURSE PROGRAMPROGRAM

Vikasana – Bridge Cource 2012

INTRODUCTION:

Plant begins its life from a singleg gcelled zygote after fertilization. It followsmany successive events to form a complexy pbody, having root, stem, leaves flower. Theformation of plant parts are controlled andp pmaintained by developmental processes.The growth and the differentiation are thegtwo important process for development.

GrowthThe fundamental characteristic of living being.gIt’s a metabolic process – anabolic and catabolic.catabolic.It requires energy.P  i    INTUSUSSEPTION i i  Process is a INTUSUSSEPTION‐ increasing the protoplasm of a plant body.

Definition of Growth

Growth is an irreversible, permanent, increase in size  volume or mass of an organ or its part or an in size, volume or mass of an organ or its part or an individual cell.

Growth results:Increasing dry weight.Takes place in certain parts root and shoot apexTakes place in certain parts‐ root and shoot apex.Increase in length‐Meristematic cells at apex.Girth/diameter increase due to secondary Girth/diameter increase due to secondary meristem.

PLANT PARTS‐SHOWING GROWTH

How growth takes place?g p

Division of Meristematic cells.

Mitotic cellular divisionMitotic cellular division.

Cell increase in number. 

Length increase by root and shoot apex.

GROWTHGROWTH

UNLIMITED LIMITED GROWTH GROWTH

UNLIMITED GROWTHIndeterminate type Ex: Root and shoot systemContinuous growth.Seed germination to death.Capacity of cell division is restricted to locations.p yNew cells are added.Apical meristems causing primary growth.p g p y gLateral meristems‐ vascular and cork‐cambium, causing secondary growth in dicot and g y ggymnosperms.

LIMITED GROWTHDeterminate typeEx: Leaves, Flowers, Fruits.Ex: Leaves, Flowers, Fruits.

St   i   ft   i i  Stop growing after gaining certain size.

Plant also exhibits two kinds of growth:Plant also exhibits two kinds of growth:

Vegetative growth:‐ Begins from the seed germination. Plant 

body  having, stem, leaves and branches.

Reproductive growth:‐ Begins after vegetative p g g ggrowth‐ produce 

flowers,  ends in seed production.

How to measure growth?g

At cellular level, growth is an increase in amount of protoplasm. It is measured by different  means:

1. Increase in dry/fresh weight.2. Increase in length.2. Increase in length.3. Increase in area.

I  i   l4. Increase in volume.5. Increase in cell number.

PHASES OF GROWTHRoot and the shoot apex region are studied tounderstand the phases of growth. Period of growthcan be divided into Three phasescan be divided into Three phases.

1 Meristematic phase: region of cell division1. Meristematic phase: region of cell division.

2. Elongation phase: region of cell elongation.2. Elongation phase: region of cell elongation.

3. Maturation phase: region of differentiation.3 p g

Root apex showing growth regions

MERISTEMATIC PHASECells are rich in protoplasm.Nucleus is large and prominent.Nucleus is large and prominent.Cell walls are primary in nature.C ll  ll i  thi   d  t i   ll lCell wall is thin and contains cellulose.Plasmodesmata are more in number.

ELONGATION PHASE:It is present next to Meristematic region.

Vacuoles are large in size.

Enlarged cells.

Results in new cell wall deposition.Resu ts e ce a depos t o .

MATURATION PHASE:The region is present away from the apex.It is close to the elongation region.It is close to the elongation region.Cell reach maximum size.W ll thi k i  t k   lWall thickenings takes place.Protoplasmic modification occurs.Different cell types‐ parenchyma, collenchyma, sclerenchyma, xylem and phloem.

GROWTH RATEI  i   th    it ti  i  Increase in growth per unit time is 

the growth rate. It may be arithmetic or geometricalgeometrical.

In arithmetic growth, only one d h   ll  i    di id   d  h  daughter cell continues to divide and others differentiates and matures.

In geometrical growth, growth increases rapidly, daughter cells continue mitotic divisions. All the cells divide.

SIGMOID CURVE/GROWTH CURVEWhen we plot growth against

time, a sigmoid curve or S‐ curve, isobtained. It is the common character of allliving organisms in nature.

Initial growth is slow and is in lag phase(l i h ) C ll di id i(lagging phase). Cells divide‐ increasesrapidly‐ follows exponential rate‐logarithmic phase The daughter cellslogarithmic phase. The daughter cellsundergo mitotic division‐ they retain thedividing ability‐ continue the division.d v d g ab ty co t ue t e d v s o .Growth slows down (diminishing)leading to a stationary phase. We get atypical sigmoid curve, similar in tissuesand cells of a plant.

DIFFERENTIATION:In three phases of cell growth, cell divides,

enlarges and differentiates. In division andl t h ll i i i b t l tenlargement phases, cell increases in size but later

differentiates and matures to perform a definitefunction. This maturity is the differentiation. Cellywall and protoplasm undergo changes and stop thedivision.C ll l i   h   l i   hCell loosing the protoplasm in trachearyelements of xylem.Cell gaining rigidity elastic  lignin depositionCell gaining rigidity elastic, lignin depositionsclerenchyma.

DE‐ DIFFERENTIATIONDE DIFFERENTIATIONIt’s the process where living, differentiated

cells regain the capacit of cell di ision It iscells, regain the capacity of cell division. It isresponsible for secondary growth. Theparenchyma cells are known for deparenchyma cells are known for de‐differentiation.

E  I  f i l   bi   d  k  biEx: Inter fascicular cambium and cork cambium.

RE‐ DIFFERENTIATION

Meristematic cells or tissues are able to divideand produce the cells that once again loose theand produce the cells that once again loose thecapacity to divide but matures. They do specificfunction after maturity and become a permanentfunction after maturity and become a permanenttissue, the process is re‐ differentiation.

E  T ll   d  ll  i  ti   ltEx: Tumour cells and callus in tissue culture.

Differentiation in plant is open, becauseCells of the same meristem have differentstructures at maturity.y

Structure at maturity is determined byStructure at maturity is determined bylocation of the cell‐ cells away from apicalmeristem develop as root cap in root apexmeristem develop as root cap in root apex.

ll h d hCell pushed to periphery mature as epidermis

DEVELOPMENT

Sum total of growth and differentiation.

It includes all changes in life cycle.

Starts from germination to senescence.g

Meristematic DifferentiationPlasmatic growth

cellDifferentiation

Expansion Maturation

M t llS Mature cellSenescence

DEATH

PLASTICITYDevelopment of a plant is influenced by Development of a plant is influenced by ENVIRONMENTENVIRONMENT.. TheyThey showshow differentdifferent kindskindsENVIRONMENTENVIRONMENT.. TheyThey showshow differentdifferent kindskinds

ofof structuresstructures OROR followfollow differentdifferent pathwayspathwaysinin responseresponse toto environmentenvironment.. ThisThis abilityability isisinin responseresponse toto environmentenvironment.. ThisThis abilityability isiscalledcalled PLASTICITYPLASTICITY..

Examples‐Coriander leaves –shapesY l h l di t d b t,Young leaves have less dissected butmature leaves show more dissected.

Heterophylly in water plant Limnophyllaheterophylla Leaves inside water showsheterophylla. Leaves inside water showsdissected leaves ,leaves above the water levelshows undissected leavesshows undissected leaves.

Growth, differentiation and development, pare related events in a plant.

D l t i t t l f th dDevelopment is a sum total of growth and differentiation .

Both are under the control of external and internal factors.

EXTERNAL FACTORS ‐EXTRINSIC FACTORS.INTERNAL FACTORS ‐INTRINSIC FACTORS.GENETICAL CAUSES.INTERCELLULAR FACTORS‐ CHEMICALS ,called GROWTH  REGULATERSGROWTH  REGULATERS

PLANT GROWTH REGULATERSThey are also called PHYTOHORMONES.They are simple chemicals.They are simple chemicals.They produce in small quantity.P t   th   i hibit  thPromote growth or inhibit growthProduce in certain parts of the plants.They are transported to the site of action.

ACCIDENTAL INVENTION OF GROWTH REGULATERSREGULATERS

Charles Darwin and his son Francis Darwinobserved grass coleoptiles tips moving g p p gtowards light.

F.W.Went continued the experiments in coleoptiles of oat and isolated the AUXIN.

E.Kurosawa reported an active substance from a fungus Gibberella fujikuroi causing Bakanedi (f li h  dli  di )disease (foolish seedling disease)

Skoog and Miller discovered action of coconut milkSkoog and Miller discovered action of coconut milkpromoting Callus formation in tissue culture.

Cousin confirmed the ripening of stored  unripened Bananas influenced by ripenedOranges.

GENERAL CHARACTERS OF PHYTOHORMONES

Phytohormones may promote the growth or i hibi   h   hinhibit the growth.Growth promoters involved in cell division, cell enlargement  tropic movements  flowering  enlargement, tropic movements, flowering, fruiting, seed formation, root formation.ex: auxins, gibberellins and cytokinins., g yGrowth inhibiters involved in dormancy, abscission wound response and stress.ex: ethylene and abscisic acid

AUXINS (auxein= to grow)Isolated from human urine.Chemically Indole‐ 3‐ Acetic acid and other y 3natural and synthetic compounds. Produced at growing root and shoot tips.g g pMove to the region of action.Indole Acetic acid and Indole Butyric acid Indole Acetic acid and Indole Butyric acid isolated from plants.Naphthalene Acetic acid and 2, 4, D are Naphthalene Acetic acid and 2, 4, D are synthetic auxins.

Functions and applications of Auxins:Functions  ApplicationsFunctions  ApplicationsInitiate rooting in tissue culture. stem 

cuttings ipropagation.

Promote flowering In Promote flowering. In pineapples.

P   l  d   f l f  d f iPrevent early drop of leaf and fruit.

Promote older leaves and fruits to fall off.Promote older leaves and fruits to fall off.

Apical dominance.Apical dominance.Induce parthenocarpy. Tomatoes.H bi id Killi   f di tHerbicides. Killing of dicot

weeds in l t ti   f plantations of 

coconut, areca‐t  tnut etc.

Prevents xylem differentiation.

GIBBERELLINS

Extracted from Gibberella fujikuroi‐ a fungus.There are more than 100 gibberellins  Denoted as There are more than 100 gibberellins. Denoted as GA1, GA2 , etc.GA3 was the first gibberellins to discover and GA3 was the first gibberellins to discover and study.All  ibb lli     idi  i  All gibberellins are acidic in nature.

FUNCTIONS AND APPLICATIONS OF GIBBERELLINS

increase the length of plant axis(elongation of grape stalk.)(e o gat o o g ape sta .)

elongation and proper shapeelongation and proper shape.(apple and other fruits)

delay senescence. prevent early fall.(All fruit plants‐ to retain them in tree)

promotes bolting.(Beet root  cabbage etc)(Beet root, cabbage etc)

S  i  i  l hStem increase in length.(sugar cane)

CYTOKININSEffect  specifically on cytokinesis.Discovered as kinetin ,not naturally Discovered as kinetin ,not naturally occurring.Coconut milk and corn kernel contain as Coconut milk and corn kernel contain as zeatin.S th i d i   t  d  h t    d Synthesized in root and shoot apex and young fruits.

Effects and applications

Cell division promoting activityCell division promoting activityHelp to produce new leaves, hl lchloroplast.Lateral growth and adventitious shoot gformation.Help to overcome apical dominanceHelp to overcome apical dominanceDelay leaf senescence

ETHYLENE.Growth inhibitorGrowth inhibitor

Gaseous hormone, produced in senescing , p gtissues and ripening fruits.Increases respiratory rate fruitIncreases respiratory rate fruit.Influence the swelling of plant axis.P  Promotes senescence.Formation of abscission layer in leaves and flowers.Increases respiration rate‐ripening.

APPLICATION OF ETHYLENEBreak seed dormancy  and bud dormancy.

Initiates seed germination‐Groundnut, sprouting of Potato tubers.p g

Promote internodes and petiole elongationPromote internodes and petiole elongationRice plants of deepwater cultivation

Promote root growth –root hair formation.g

Initiates flowering ‐Pineapple.Initiates flowering  Pineapple.

Flower induce –MangoFlower induce –Mango.

Eth h  f it  i T t  A l  Ethephon a fruit ripener –Tomato, Apple, Cherry, female flower production in cucumberscucumbers.

ABSCISSIC ACID‐growth inhibitor.Regulates abscission and  dormancy.Inhibits seed germination Inhibits seed germination Stimulate closing of stomata.I  t l   f  l t  t   t  Increases tolerance of plants to stress –STRESS HORMONE.d d d d l dInduces dormancy‐seed development and 

maturation.Withstand desiccation.

PHOTOPERIODISM.Li ht i flLight influence.

Flowering responses to relative length of g p gLIGHT and DARK period in 24 HOUR cycle –PHOTOPERIODISM.CRITICAL PERIOD‐for flowering.MORE – long day plants.g y pLESS‐short day plants.NEUTRAL day neutral plants not affected by U R day eut a p a ts ot a ected bylight exposure.

Above Above Above no

Criticalfloweringflowering

Above no flowering Flowering

after Critical photo period Below no Below

flo ering

vegetative maturityperiod

flowering flowering yLDP SDP DNP

Oat,rye,beetroot,pea

Tobacco, coffee, chrysanthemum

Tomato, sunflower, cucumbercucumber

EXAMPLES FOR LDP

OAT AND RYE

BEET ROOTBEET ROOT

PEA PLANT

EXAMPLES FOR SDP

COFFEECOFFEE

TOBACCO CHRYSANTHEMUM

EXAMPLES FOR DNP

TOMATO SUNFLOWER

VERNALISATION

Low temperature treatment  for flowering for a period.2 kinds of varieties winter and spring –p p gbarley ,rye.

Spring varieties –planted in spring –flower and grain production in SPRING

Winter varieties –planted in autumn‐flower in spring harvested in summer.Biennial plants –Monocarpic‐need a cold 

   f  fl i  temperature treatment for flowering.Ex,:Beet root, Cabbage ,Carrot  

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