LSM 3261 — Life Form and Function

R d i i PlReproduction in Plants

Lecture 5Lecture 5

Lecture 5 Topics• Reference • Pollination• Reference• Generalized life cycle of

plants• Flower

• Pollination• Double fertilization• Fruit

Fr it allFlower– Homology of flower parts– Structure and function of

flower parts

• Fruit wall• Fruit classification systems

• By numbers of carpelsand flowersflower parts

– Largest flower in the world

– Reproductive parts

and flowers• By various criteria

• Kinds of fruitsS dReproductive parts

– Homology of the stamen– Homology of the carpel

Advertising by flowers

• Seed• Seed and embryo

developmentS d– Advertising by flowers

• Mega- and micro-sporogenesisand gametogenesis

Pollen grains

• Seed parts• Seedling• Fruit and seed dispersal

– Pollen grains• Inflorescence

– Largest inflorescence in the world

• Asexual reproduction• Pando, largest plant in the

worldthe world • Why sexual and asexual

reproduction?

Reference• Solomon, E.P., L.R. Berg

and D.W. Martin. 2011. Biology. 9th ed. – Chapter 37p

Generalized Life Cycle of PlantsFl i l di l l i• Flowering plants display alternation of generations

• Alternation of generations = alternation of a haploid gametophyte p g p ygeneration with a diploid sporophytegeneration

Revision of LSM 1103 material

FlowerFlower =Flower

The typical flower is a shoot of limited growth, with much shortened internodes, which bears typically, yp ythese parts. These are, from the apex downwards, the:a. Essential organs

1) Carpels (collectively called the gynoecium)2) Stamens (collectively called the androecium)

b A ( i th tb. Accessory organs (= perianth segments, collectively called the perianth)1) If homogeneous = tepals (collectively called the1) If homogeneous tepals (collectively called the

perianth)2) If of two types, then

P l ( ll i l ll d h ll )

Magnolia grandiflora has

l– Petals (collectively called the corolla)– Sepals (collectively called the calyx)– Petals and sepals are collectively called the perianth; individual

l d l b ll d i th t

tepals

petals and sepals may be called perianth segments too

Homology of Flower Partscorresponds to carpels

correspond to stamens

corresponds to receptacle

corresponds to petals

corresponds to sepals

corresponds to pedicel

p p

Compare a typical flower with a branch of leavesItem Flower Leafy Branch

Apical meristem growth Determinate: growth stops Determinate or indeterminate: Apical meristem growth g pafter full development of the flower

growth proceeds for a long period

Leaves modified or not Modified or notLeaves modified or not

Axillary buds in the axils One or more axillary buds are found per leaf axil

Internodal lengths Usually elongated between nodes

Subtended by a leaf or not Yes

Arrangement of parts on the axis

Alternate, spiral, opposite or whorled or combinations

Trichomes or glands Present or absent

Will it root if a cutting is Possible

made?

Structure and Function of Flower PartsTh i f h (• The tip of the stem (numerous nodes and compressed internodes) can end in a receptacle– Gives rise to most of the flower

parts• Only the stamens (male) and

carpels (female) directly participate in sexual reproduction

• The calyx is made up of all of the y psepals– Outermost and lowest whorl on

a floral shoota o a s oo– Cover, protect developing bud

• The corolla is made up of all of the petals

Hawk moth

petals– Attract and provide platform

for pollinatorsl

Periwinkle – Can also select pollinators,

protect inner structure of the flower

(Catharanthus roseus)

Largest Flower in the World

l f ffl ld i h blFlower of Rafflesia arnoldii, with blooms up to 1 m across and 11 kg in weight! A charismatic species.

Reproductive Parts of the Flower• The stamens are inside the petals

– Are the male reproductive organs– Have thin stalk called a filamentHave thin stalk called a filament– End in the anther, which bears pollen

grainsC l b th l hi h• Carpels bear the ovules, which can develop into seeds– Female part called a pistil or

igynoecium– Can be made up of a single carpel, two

or more separate carpels, or fused carpels

– Has three parts:• Stigma, where pollen landsg , p• Style, the necklike structure• Ovary, contains one or more

ovules that can develop into aovules that can develop into a fruit

Homology of the Stamen

anther

Stamens ― or

microsporangium

microsporophylls

microsporophylls

Fern sporophyll

Homology of the CarpelCarpel

Fused margin

Ovules

Ovaryy

Style

Stigma

Stigmal f Styleovulesleaf

Ovules

Ovary

Ancestral condition

Advertising by FlowersM h tt ti l /• May have attractive colors / patterns (especially in UV light)

• May be food sourcesPollen– Pollen

– Nectar in nectaries• May have attractive odors• May aid pollination by shape of• May aid pollination by shape of

flower– May force pollinator to rub

against stamen UVg• May have shapes like animals’

mates ― form of mimicry• May release pollen to the wind or

water

Ophrys sp., the bee orchid

Megasporogenesis and Megagametogenesis 1Megagametogenesis 1

• Megasporogenesis: Each ovule contains a megasporocyte that undergoes meiosismegasporocyte that undergoes meiosis

1 megasporocyte 4 megaspores 1 megaspore + 3 dead cells Why?

M t i Th• Megagametogenesis: The megaspore undergoes mitotic divisions:

1 megaspore 2 nuclei 4 nuclei 8 nuclei walls form

micropyleg p

around the nuclei 6 uninucleate cells + 1 binucleate cell (central cell) = embryo sac or gametophyte or megagametophyte

• The egg and the polar nuclei participate in double fertilization

• Pollen derived tube cell will enter through• Pollen-derived tube cell will enter through micropyle

• Synergid cells die after a short timey g

Megasporogenesis and Megagametogenesis 2Polygonum hydropiper is the laksais the laksa leaf!

The pattern (in the previousThe pattern (in the previous slide) is the Polygonum 8-nucleate bipolar type, but there are at least 12 other types named after the genera in which they were first discovered (the otherwere first discovered (the other types not covered in this module)

Microsporogenesis and Microgametogenesis 3Microgametogenesis 3

• Microsporogenesis: Pollen sacs within the anther contain manywithin the anther contain many diploid microsporocytes which undergo meiosis

1 diploid microsporocyte 4 haploid1 diploid microsporocyte 4 haploid microspores

• Microgametogenesis: Each i di id b i i

Why not reduce to only 1 like in the megaspore?

microspore divides by mitosis

1 haploid microspore

1 h l id i ll1 h l id i ll

mitosis

1 haploid vegetative cell

growth

1 haploid generative cell

mitosis

1 haploid pollen tube1 haploid sperm cell

1 haploid sperm cell

Inflorescence 1Inflorescence =

A shoot which bears two or more flowers and typically has the leaves on this shoot reduced to yp ybracts. The pedicel of each flower lies in the axil of a bract and commonly bears bracteoles, both of y ,which may be absent. A solitary flower may also be considered an inflorescence.

Inflorescence 2

Maiden’s jealousy (Tristellateia australasiae)

There are many kinds of inflorescences

Inflorescence 3

Singapore daisy (Sphagneticola trilobata)

Inflorescence 4

ray floretsdisc floret o etbud

Singapore daisy (Sphagneticola disc floretstrilobata) inflorescence in half-

section

Largest Inflorescence in the World

inflorescence

Talipot palm, CoryphaCorypha umbraculifera, with inflorescences up to 8 m tall with class of 2005!class of 2005!

“Largest Flower” in gthe World

• Inflorescence of the titan arumInflorescence of the titan arum (Amorphophallus titanum)

• Inflorescence • Member of cocoyam family (Araceae)• Member of cocoyam family (Araceae)• Largest inflorescence of its family

members

Pollination• I fi t t t f tili ti• Is first step to fertilization• Cross pollination: pollen from a different

individual plant• Self-pollination: pollen from the same

flower or flowers of the same plantCan cause problems Wh t bl ?– Can cause problems What problems?

– Many plants have mechanisms to prevent self-pollination

– Some plants are dioecious: separate sexes on different plants (opposite = monoecious = unisexual flowers onmonoecious unisexual flowers on same plant)

– Many plants are self-incompatible i i kowing to genetic makeup ― prevents

self-pollination• Thus, reproduction only involves

pea

, p ymixing of genes from differentindividuals

Double Fertilization 1• Pollen lands on stigma• One of the pollen cells forms a pollen tubeOne of the pollen cells forms a pollen tube

– grows down the style and enters the embryo sac through the micropyle

S ll d l f h d ll• Sperm cells develop from the second pollen cell– Move down the pollen tube cellMove down the pollen tube cell– One sperm cell reaches the egg, unites and fuses– Second finds the 2 polar nuclei and they fuse to

f i l id dform triploid endosperm. – These two fusions are called double fertilization

• Ovule develops into a seed and ovary around• Ovule develops into a seed, and ovary around it develops into fruit

Suggest advantages of double fertilizationSuggest advantages of double fertilization

DoubleDoubleFertilization 2

F iFruit

Fruit =Ripened ovary or ovaries, sometimes associatedwith accessory parts such as the receptacle or perianth, generally containing one to many seeds insideinside

Fruit Wall1. Easy or not to distinguish layers

2 Layers of the fruit wall (pericarp)2. Layers of the fruit wall (pericarp)a. Epicarp (exocarp)b Mesocarpb. Mesocarpc. Endocarp

2 Classification Systems of Fruits1. Based on the no. of carpels and flowers the fruit is

derived fromderived from

2. Based on the following criteria:a. Fruit wall dryness of succulence (fleshiness) when ripeb. Dehiscence or indehiscence of the ripe fruitc. No. of seeds per fruitd. No. of carpels per fruite. Position of the ovary that forms the fruit

Fruit Types 11 Based on the no of carpels and no of flowers the fruit is1. Based on the no. of carpels and no. of flowers the fruit is

derived from2. Types:

a. Simple fruit: single carpel or syncarpous ovary of a single flowerb. Aggregate fruit: several ripened carpels from a single flower with an

apocarpous gynoecium

yp

p p gyc. Multiple (composite) fruit: ripened ovaries of the flowers of one

inflorescence (more than one flower)PineapplePineapple

(Ananas comosus)

Malayan cherry (Muntingia calabura)

Strawberry (Fragaria ananassa)

Fruit Types 21. Based on the following criteria:

a Fruit wall dryness or succulence (fleshiness) whena. Fruit wall dryness or succulence (fleshiness) when ripe

b Dehiscence or indehiscence of the ripe fruitb. Dehiscence or indehiscence of the ripe fruitc. Number of seeds per fruitd Number of carpels per fruitd. Number of carpels per fruite. Position of the ovary that forms the fruits

Fruit Types 32 Fruit types

pappus

2. Fruit typesa. Dry when ripe

i. Indehiscent (does not split)1) Thin fruit wall1) Thin fruit wall

a) Separate from seed coati) Without pappus: acheneii) With pappus: cypselaii) With pappus: cypsela

b) Fused to seed coat: caryopsis2) Thick and tough fruit wall: nut

a) With cupule: acorn) pii. Dehiscent (splits)

1) Made of 1 carpel (1 locule + 1 point of seed attachment)a) Splits on 2 sides: legume) p gb) Splits on 1 side only: follicle

2) Made of 2 carpels combined: capsuleb. Fleshy when ripe

i. With hard, bony endocarp: drupeii. Without hard, bony endocarp

1) Combined with accessory tissues (receptacle): pome2) Not combined with accessory tissues: berry

a) With juice vesicles and segments: hesperidiumb) Without juice vesicles and segments: pepo

Achene = Fruit which is dry when ripe one-seeded indehiscentFruit which is dry when ripe, one seeded, indehiscent and where the seed and the pericarp are fused only at the stalk of the ovule

carpelStrawberry flower

pedicel

receptacle

i i i

y

Diagrammatic representation of a flower with its sepals, petals, and stamens removed

Achene = Fruit which is dry when ripe one-seeded indehiscentFruit which is dry when ripe, one seeded, indehiscent and where the seed and the pericarp are fused only at the stalk of the ovule

Clematis sp.

stigma

style

St b

1 acheneseed

fruit wall (developed from ovary wall) Strawberry

(Fragaria ananassa)

wall)

Caryopsis (plural, caryopses) = Fruit which is dry when ripe, one-seeded, indehiscent and y p , ,where the seed and the pericarp are fused, i.e., like the achene except for the fusion between the seedcoat and the pericarp

Maize (Zea mays)

CypselaCypsela = Like the achene but is fused to the calyx (the fruit of members of the sunflower family [Asteraceae ormembers of the sunflower family [Asteraceae or Compositae]) with plumed tips which are the split calyx lobesy

Tridax procumbens

N tNut = Fruit with a dry, i d hi t llindehiscent wall, developing from a syncarpous gynoeciumsyncarpous gynoecium but becoming one-seeded by abortion of all but one carpel. The exocarp is usually hard

d th f it band the fruit may be subtended by a cupule (called an acorn in such(called an acorn in such a case)

Li hLithocarpus sp.

Capsule = pFruit with a dry, dehiscent wall, usually ytwo or more seeded, derived from a

isyncarpous gynoecium, and dehiscing along the septa (septicidalsepta (septicidal capsule) or between them (loculicidal (capsule)

Ladies’ finger (Abelmoschus esculentus) ripe

pericarpseptum

Ladies finger (Abelmoschus esculentus) ripe fruits

locule

Follicle = Like a legume except that it splits down one side rather than twoLike a legume except that it splits down one side rather than two

Star anise (Illicium verum)

Saga tree (Adenanthera pavonina)

Legume = Fruit with a dry dehiscent

pavonina)

Fruit with a dry, dehiscent wall, usually two or more seeded, derived from a singleseeded, derived from a single carpel, and dehiscing down two sides

Berry =Berry Fruit which is fleshy when ripe, with a fleshy pericarp right throughright through

B tTomato (Lycopersicon Berry types• Typical berry• Hesperidium

( y pesculentum)

Hesperidium• Pepo

Hesperidium = Fruit which is a special case of theFruit which is a special case of the berry; the pericarp is rather thick, the fruit is partitioned and filled with juice p jvesicles

Orange (Citrus sinensis)Orange (Citrus sinensis)

Pepo = Fruit which is a special case of the pberry; the pericarp becomes leathery when ripe, and this fruit

i f d l i h btype is found only in the cucumber family (Cucurbitaceae)

Luo Han Guo

Cucumber (Cucumis sativus)

Largest Pumpkin in the Worldg p

What kind of fruit is this?fruit is this?

The size has been increasing every year, but is there a limit?

The largest pumpkin for 2010 weighed 821.2 kg (1,810.5 pounds). It was grown by

is there a limit?

The largest pumpkin for 2010 weighed 821.2 kg (1,810.5 pounds). It was grown by Chris Stevens of New Richmond, Wisconsin, USA. (It’s still a little too early in the year for the 2011 pumpkin, since they are harvested in autumn, in October.)

DDrupe = Fruit which is fleshy when ripe, with a distinct epicarp,

d b d d th d dmesocarp and bony endocarp, and the seed or seeds surrounded by the bony endocarp called a pyrene which may be more than one per drupemay be more than one per drupe

Peach (Prunus persica)

Coconut (Cocos nucifera)

Coffee (Coffea arabica)

PPome = Fruit which is fleshy when ripe; derived from a combination of the thin, papery pericarp with the fleshy development of the hypanthium

Fruit Types 32 Fruit types

pappus

2. Fruit typesa. Dry when ripe

i. Indehiscent (does not split)1) Thin fruit wall1) Thin fruit wall

a) Separate from seed coati) Without pappus: acheneii) With pappus: cypselaii) With pappus: cypsela

b) Fused to seed coat: caryopsis2) Thick and tough fruit wall: nut

a) With cupule: acorn) pii. Dehiscent (splits)

1) Made of 1 carpel (1 locule + 1 point of seed attachment)a) Splits on 2 sides: legume) p gb) Splits on 1 side only: follicle

2) Made of 2 carpels combined: capsuleb. Fleshy when ripe

i. With hard, bony endocarp: drupeii. Without hard, bony endocarp

1) Combined with accessory tissues (receptacle): pome2) Not combined with accessory tissues: berry

a) With juice vesicles and segments: hesperidiumb) Without juice vesicles and segments: pepo

The SeedSeed = A matured, fertilised ovule

Seed and Embryo Development 1• The seed de elops from the• The seed develops from the

ovule• Seed nutrient endosperm used to

aid in germinationaid in germination– Also animal food source

• The basal and apical cells from the first division of the fertilized egg form an axis of development in the embryo

• The basal cell forms a suspensorapical cell

– Anchors the embryo– Provides nutrient flow

• Apical cell develops into the b zygoteembryo proper zygote

apical cell

basal cell

Seed and Embryo Development 2• The top cell divides to• The top cell divides to

form a cluster of cells called a proembryo

• Small spherical globular embryoformsforms – Differentiation into

specialized tissuesp– Two leaflets form ―

called cotyledons• Called heart stage ―• Called heart stage ―

looks like heart– In torpedo stage,

elongates starts toelongates ― starts to curve back on itself as it grows

Seed and Embryo Development 3

Parts of the Seed

1. Seedcoat2. Aril3. Endosperm3. Endosperm4. Embryo5 P i5. Perisperm

Seedcoat1. Derived from the integument(s) of the ovule2. Layers2. Layers

a. Testa: outer seedcoatb Tegmen: inner seedcoatb. Tegmen: inner seedcoat

Aril1. Structure which grows from some part of the ovule or ovule

stalk after fertilization and invests part of the whole of the seedseed

2. Often mucilaginous, gelatinous, or brightly coloured D i (D iDurian (Durio zibethinus)

Rambutan (Nephelium lappaceum)pp )

Nutmeg (Myristica fragrans)

Endosperm1 F d i hi h1. Food storage tissue which

develops from the primary d l ( dendosperm nucleus (second

fertilization event)2. Types of seeds

a. Endospermous or albuminous: Exendospermous seed

with endospermi. Ruminate: with remains of the

megasporangium in theNutmeg seedmegasporangium in the

endosperm

b. Exendospermous or

seed

pexalbuminous: without endosperm

Endospermous seed with ruminate endosperm

Embryo1. Rudimentary plant

which develops fromwhich develops from the zygote (first fertilization event)fertilization event)

2. Parts of the embryo• Cotyledon(s)• Cotyledon(s)• Axis• Shoot ape• Shoot apex

• Root

Perisperm1 P i i hi h1. Persistent megasporangium which serves as

nutritive tissue instead of the endosperm2. Primitive characteristic

Pepper

Pepper (Piper nigrumg

The Largest Seed in the World

Double coconut, Lodoicea maldivica, with each drupe (containing 1–3 d ) 27 k ! E h d b 50 l Y ill3 seeds) up to 27 kg! Each seed can be up to 50 cm long. You will see this tree at the Botanic Gardens.

Seedling1. Seedling =

Y l tYoung plant which

i t fgerminates from the seed

2. Partsa. Cotyledonsb. Epicotylc. Plumuled. Hypocotyle. Radicle

Fruit and Seed Dispersal• Seeds are carried by wind, water and

animal vectors– Fluffy components aid transport ―Fluffy components aid transport

e.g. milkweeds– Entire plant breaks at base and rolls

t bl d

milkweedtumbleweed

Cardamine― e.g. tumbleweed– Burrs catch in animal coats/feathers

(e.g. hedgehog plant)

Cardamine

– Some plants split open their ovaries ― some are explosive in doing so (explosive dehiscence)(explosive dehiscence)

– Dispersal by ingestion ― some have laxative characteristic to pass fig

quickly through tract– Some animals bury seeds

• SquirrelsSquirrels • Ants (seeds have oil body

called elaiosome) oak

Asexual Reproduction

Other Asexual Reproduction FormsPl tl t ti l t th t• Plantlets are tiny plants that grow off the mother leaves– Meristematic tissue on edges– Kalanchoe pinnata is one of

most common forms• Suckers are above ground

h t th t d lshoots that develop as adventitious buds on roots– Rhododendrons – Some trees do this ― ‘quaking

aspen’

Pando, largest plant in the world

• Latin Pando I spread• Latin Pando, I spread• Populus tremuloides, quaking aspen• 43 hectares in area• 43 hectares in area• 47,000 stems

6 000 t i t• 6,000 metric tons• Root suckers from one original

individual growing into one massiveindividual growing into one massive forest of trees connected by their rootsUSA postage stamp to

commemorate Pando

Why Sexual AND Asexual R d ti ?Reproduction?

1. SexualV i ti ia. Variation in progeny

b. Progeny can respond well to changes in environmentenvironment

c. Disadvantage is that costly, time-consuming method of reproduction

d. Does not always automatically produce better-adapted individuals; can be wasteful in a sense

2 A l2. Asexuala. If parent well-adapted, may work wellb Allows simple rapid growthb. Allows simple, rapid growthc. If environment does not rapidly change, can be

most effective form of reproductionp