core t - crop plants

7/28/2019 Core T - Crop Plants

1/83

Core T

Crop plants


2/83

Contents

1. Crop plant reproduction.

2. Crop adaptations.

3. Methods to improve crops.


3/83

Lesson objectives 1

Students should be able to:

1. explain the significance of the grains of cerealcrops in the human diet.

2. compare the outcomes of self-pollination andcross-pollination in terms of genetic variations.

3. describe and explain the structural features of anamed, wind-pollinated plant.


4/83

Crop plants

Definition:

Plants that are cultivated for the purpose ofharvesting its seeds, roots, leaves, etc. thatare useful to humans.

Many crop plants are grown as foods.

They may also be used for other purposes,e.g. as feeds (to livestock, etc.), biofuel, etc.


5/83

World distribution of crop plants


6/83

Many of these crop plants grown as staplefoods (foods that are eaten regularly andbecome a dominant food part in the diet).

cereal crops

belongs to grass family harvest and eat the grains

rice, eaten in many parts of easternAsia.


7/83

starchy stem or root vegetables

e.g. yam or taro in New Guinea. e.g. potatoes in the US.

starchy fruits

dates in the Middle East. banana in the New Guinea.

These staple foods are eaten mainly because ofthe carbohydrate (therefore, energy) content thatthey contain per unit mass.


8/83


9/83

Significance of cereal crops in

the human dietCereal crops contain:

a lot of energy per unit mass (more than 1400 kJper 100 g.

highcarbohydrate (starch and sugar) content.

relatively low fat content.

no cholesterol.


10/83

high in dietary fibre.

significant amount of protein (except essentialamino acids, like those found in fish, eggs, etc).

rich in vitamin B.

the other vitamins (A, C, D, etc.) needs to beobtained from fresh fruits, leafy vegetables and dairyproducts.

sufficient calcium.

Cereal crops are also relatively cheaperfor theirhigh energy values.


11/83

Pollination

Pollination:

the transfer of pollen grains (malegametes) from the anther (malereproductive organ) to the stigma (receptivestructure of the female reproductive organ).


12/83

Self- and cross-pollination

Self-pollination:

pollination of a flower by pollen from thesame floweror from another flower on thesame plant.

results in inbreeding (sexual reproductionbetween closely-related individuals).


13/83

Cross-pollination:

pollination that occurs between diff. flowersof the same plant or from diff. plants belongingto the same species.

results in outbreeding (sexual reproductionbetween unrelated or distantly-related

individuals).


14/83

Agents of pollination:

1. Animal.

2. Water.

3. Wind.

most cereal crops, e.g. Zea mays arewind-pollinated.

General structural features of a flower


15/83

General structural features of a flower

The structural features

of the flower exhibitsdifferent adaptations,

depending on the type of

the pollinating agent.


16/83

Wind-pollinated plants

Example: Zea mays (a.k.a. maize or corn).

tall, fruiting grass.

grows best in climates with long, hot summers(originally grown in Central and South America,but now become staple food in some regions ofAfrica, etc. now also grown to make biofuel).

fruits in cobs.

Zea mays


17/83

Zea mays

Fruits of maize

in cob

each is from

fertilisation of

diff. ovules by

diff. pollen

grains.

each isgenetically

different from the

others.


18/83

Structural features ofZea mays

Zea mays have structural features that

encourages cross-pollination to occur.

Cross-pollination results in outbreeding,therefore enhancing genetic variation in the

population.


19/83


20/83


21/83

Q: Tabulate the structural features ofZea

mays and their respective functions thatenables effective cross-pollination (andthus, outbreeding) to occur.


22/83

Structure Functions

Anther dangling fromfilament.

pollen grains

are very smalland light.

enables pollen grain to be exposedto the wind.

easily carried by the wind to settle

on the stigma of another plant whichare further away.

Stigma long andfeathery. protrudesfrom the flower.

enables the stigma to 'catch' thepollen grains.


23/83

Structure Functions

Height tall and sturdy

plant.

holds the male flowers high andupright for good exposure to thewind.

Separate male andfemale flowers male flower at the

apex ('top') of plant. female flower atlower part of plant.

encourages cross-fertilisation tooccur (lower likelihood for themale flowers to pollinate thefemale flowers of the same plant).


24/83

Advantages of outbreeding

1. Results in heterozygosity (possess diff.alleles of a gene).

2. Reduces the chance of offspring receiving2 recessive alleles of the same gene, whichmay become harmful to the plant.

3.Avoids inbreeding depression (weak andstrain dying out).


25/83

4. May conferhybrid vigour(strength and vigour

found in many heterozygous organisms; usuallystronger than the parents).

5. May result in genetic and phenotypic variation

amongst offspring.

6. Variation increases likelihood of at least someindividuals surviving in difficult conditions.

7. Variation allows adaptations to change inenvironment.


26/83

Lesson objectives 2


4. describe the structure of the fruit in maizeand explain the function of the endosperm.


27/83

Fertilisation

Definition:

The fusion or union of the male and the femalegametes during sexual reproduction to form azygote.

In Zea mays, just like in other angiosperms

(a.k.a. flowering plants), double fertilisationoccurs.

doesn't occur in gymnosperms.


28/83


29/83

Structure ofZea mays ovule

embryo sac

egg cell (n)

synergids (n)polar nuclei (2n)

antipodal cells (n)integuments


30/83

Steps in double fertilisation ofZea mays:

Once pollination has occurred,

1. Pollen tube grows through the style.

there are 3 haploid nuclei in a pollen grain:

1 pollen tube nucleus.

2 male gametes (initially a haploidgenerative cell that eventually dividesinto 2 haploid male gametes).


31/83

2. Pollen tube enters the ovule through themicropyle.

*micropyle = small opening in the surface ofa plant ovule.

the pollen tube move towards the ovule

by chemotaxis (response to chemical stimuli).


32/83

3. Pollen tube penetrates through the embryo sac.

pollen tube nucleus cause disintegration of 1of the synergid cells.

1 male gamete fuses with the egg cell

becomes the embryo (2n).

the other male gamete fuses with the polarnuclei (a.k.a. primary endosperm nucleus).

forms the endosperm nucleus (3n).

the remaining synergid and antipodal cellswill eventually disintegrate.


33/83


34/83

So, double fertilisation is:

a process that occurs only in flowering plants(angiosperms) whereby 2 male gamete nucleiseparately fuse with different nuclei in the embryosac.

A male gamete nucleus fuses with the egg cellto form a 2n zygote which eventually becomesthe embryo.

The other male gamete nucleus fuses with 2polar nuclei to eventually form 3n endosperm.


35/83

Useful links (double fertilisation):

http://www.youtube.com/watch?v=bUjVHUf4d1I

http://bcs.whfreeman.com/thelifewire/content/chp39/3902001.html
http://www.youtube.com/watch?v=bUjVHUf4d1Ihttp://bcs.whfreeman.com/thelifewire/content/chp39/3902001.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp39/3902001.htmlhttp://www.youtube.com/watch?v=bUjVHUf4d1Ihttp://www.youtube.com/watch?v=bUjVHUf4d1I


36/83

Structural features of Zea mays fruit


37/83

Structural features ofZea mays fruit


38/83

*endosperm = tissue or part of a fruit that acts as afood store for developing embryo.

Role of endosperm:

contains a lot of starch and protein for growth anddevelopment of embryo.

Other uses of endosperm (to human):

important source of carbohydrate and protein inthe human diet. to make flour, e.g. wheat flour. to make alcoholic beverages, e.g. beer (usingbarley endosperm).


39/83

Lesson objectives 3


5. explain how the anatomy and physiology of theleaves of C4 plants such as maize or sorghum areadapted for high rates of carbon fixation at hightemperatures in terms of:

(i) the high optimum temperatures of the enzymes

involved, and

(ii) the spatial separation of initial carbon fixationfrom the light-dependent stage.


40/83

C4 plants

Recall that in Calvin cycle in (light-independent

reaction of) photosynthesis,

RuBP (5C) + CO2(1C) unstable intermediate

(6C) 2 GP (3C).

These plants are called C3 plants.


41/83

However, in maize the first molecule to beformed by combination with CO

2is oxaloacetate

(4C).

Therefore, maize is a C4 plant.

Q: Why is the photosynthetic pathway different?


42/83

A: Rubisco catalyses the reaction ofRuBPwith O

2instead of with CO

2when:

1. temperature is high.

2. light intensity is high.

Photorespiration takes place.

Zea mays, sorghum and sugar cane areexamples of C4 plants.

e.g. in Africa


43/83

Photorespiration is a wastage of RuBP.

less RuBP will be available forphotosynthesis, to make important molecules,e.g. starch, etc.

Q: How to avoid photorespiration from takingplace?

A: By separating RuBP and rubisco in plant cellsfrom the air spaces (high O

2concentrations) by

keeping them in bundle sheath cells.

Bundle sheath cells


44/83


45/83


46/83

Bundle sheath cells prevent any directcontact between rubisco and RuBP with air.

Bundle sheath cells are surrounded by

mesophyll cells.

the mesophyll cells carry out normal light-dependent reactions.

CO2

absorbed by the mesophyll cells.


47/83

Mesophyll cells around the bundle sheathcells have PEP carboxylase enzymes.

*PEP = phosphoenolpyruvate

1. PEP carboxylase catalyses the reaction btw.CO

2and PEP to form oxaloacetate.

CO2(1C)+ PEP (3C) oxaloacetate (4C)


48/83

2. Oxaloacetate (4C) converted to malate (4C).

3. Malate transported to bundle sheath cells.

malate converted to pyruvate (3C) and releasesCO

2

normal Calvin cycle occurs

RuBP + CO2 unstable 6C intermediate 2x GP

pyruvate is transported back to mesophyllcells (regeneration of PEP).


49/83


50/83

Useful link (photorespiration):

http://www.wiley.com/college/boyer/0470003790/animations/photosynthesis/photosynthesis.swf

More animations can be found on

http://www.learnerstv.com/animations.php
http://www.wiley.com/college/boyer/0470003790/animations/photosynthesis/photosynthesis.swfhttp://www.wiley.com/college/boyer/0470003790/animations/photosynthesis/photosynthesis.swfhttp://www.learnerstv.com/animations.phphttp://www.learnerstv.com/animations.phphttp://www.learnerstv.com/animations.phphttp://www.wiley.com/college/boyer/0470003790/animations/photosynthesis/photosynthesis.swfhttp://www.wiley.com/college/boyer/0470003790/animations/photosynthesis/photosynthesis.swfhttp://www.wiley.com/college/boyer/0470003790/animations/photosynthesis/photosynthesis.swf


51/83

Important characteristic of C4 plant enzymes:

higher optimum temperatures than C3 plantenzymes.

e.g. PEP carboxylase has optimum temp.at 45 degrees celsius.

inactive at low temperatures.


52/83

Sorghum

grown in very hot and dry environment,e.g. India, East Africa, the USA, etc.

Uses of sorghum:

1. food for people.

2. fodder for livestocks, e.g. dried hay, etc.3. sweet syrups, etc.

Sorghum


53/83

Sorghum

Sorghum grains


54/83

Sorghum grains


55/83

C4 plant, like maize. But sorghum is able tosurvive better in drier areas, i.e. more drought

resistant than maize. Drought resistant sorghum isknown as milo.


56/83

Summary of sorghum adaptations


57/83

Summary of sorghum adaptationsFeatures Adaptations

1. Roots deep and widely spreading

able to reach for deeper H2O in the soil.

2. Leaves

very thick and waxy cuticle prevent evaporation of H

2O through the

epidermis. diff. cell sizes at upper epidermis

enables rolling up of leaves when H2O is deficient.

--- prevent loss of H2O by transpiration.

3. C4plant

diff. photosynthetic pathway than C3 plant. prevent wastage of RuBP by photorespiration. more efficient photosynthesis.

have enzymes with higher optimum temp. do not denature easily in very hot environment.


58/83

Rice (Oryza spp.)

Cultivated rice:

1. Oryza sativa a.k.a. Asian rice. grown in many parts of Asia.

easy to genetically modify, esp. as modelorganism in cereal biology.

2. Oryza glaberrima a.k.a. African rice.

grown in parts of Africa. more brittle & have lower yield than O. sativa. more tolerant to severe climatic conditions,iron toxicity, infertile soils, etc. than O. sativa.

Adaptations of rice for wet


59/83

Adaptations of rice for wetenvironments

Rice are usually grown in flooded plains or soil.

Problems with flooded soils:

1. Water contains very low dissolved oxygenand carbon dioxide.

difficulty for gaseous exchange to occur. needed for aerobic respiration andphotosynthesis.

Paddy field in Chieng Mai,Th il d


60/83

Thailand


61/83


62/83

2. Presence of ethanol as a result of


63/83

anaerobic respiration (recall Core

L). ethanol is toxic.

Solutions:

1. Rice root cells produces alcoholdehydrogenase enzymes that can break downethanol in the water.

2. Rice root cells also have higher toleranceto ethanol.

3. Partial submergence in water causes


64/83

gdifficulty to photosynthesise.

Solution:

Rice produces a gas called ethylene a.k.a.ethene that stimulates the production ofgibberellins.

gibberellin stimulates cell division and cellelongation in rice stem.

rice grow taller.

*ethylene (an alkene) also stimulates ripening offruits, e.g. bananas.

C i t


65/83

Crop improvement

Crops are improved in 2 ways:

1. selective breeding (recall Core P).

2. genetic engineering (recall Core R).

H b idi ti f h t


66/83

Hybridisation of wheat

Hybridisation:

crossbreeding individuals from differentspecies or different varieties.

if diff species: usually produces infertile

offspring.


67/83

Wheat (Triticum aestivum) was first

cultivated app. 10,000 years ago in the so-called 'fertile crescent' in the Middle East.

selective breeding was done then.

more yield.--- shorter stem.--- larger or more grains per plant.

more pest- and disease-resistant.


68/83

Development of wheat


69/83

2n = 14

n = 7(AA)

2n = 14

n = 7(BB)

2n = 14n = 7(AB)

The hybrid is INFERTILE. the chromosomes cannot pair up to form bivalents duringMEIOSIS. male and female gametes cannot be formed.

(wild wheat)


70/83

The hybrid from einkorn and wild goat grass

is infertile.

Wheat has not been formed yet.

The hybrid has to become fertile first so thatit can crossbreeding again to eventually formwheat (T. aestivum).

But how?

(Recall polyploidy

Core P on sympatric speciation)


71/83

Polyploidy

Caused by mutationthat might haveoccurred duringattempted meiosisor mitosis.


72/83

Inbreeding and hybridisation


73/83

Inbreeding and hybridisation

Recall that maize is adapted to cross-pollination.

However, if maize is to be uncontrollablycross-bred, the grown maize will not beuniform, e.g. some producing lower yield than

the others, less-pest-resistant, etc.

too much variation between the maize.


74/83

If inbreeding is to be done, homozygositybtw the maize will increase. hybrid vigour decreases. inbreeding depression occurs over

several generations (becomes weaker, etc.).

So, how to maintain heterozygosity, yet atthe same time make the maize grow and

produce yields uniformly?


75/83

Hybrid vigour inmaize


76/83

Inbreeding depressionin maize

1. Inbreeding done by crop breeders to make


77/83

them homozygous for specific phenotypes.

2. Farmers can buy the seeds of the inbredmaize plants

depends on the maize phenotypes that

they want.

3. Farmers can cross-breed these plants andgrow them.

the maize will produce uniform productswith the desirable traits/phenotypes.

Production of golden rice


78/83

Like most cereal grains, rice lacks vitamin A, whichis very important in the human diet.

Vitamin A:

found in carotene (yellow pigments found inoranges, etc.).

in cereals, e.g. rice, vit. A is found in thealeurone layer but these are removed.

endosperm do not have vit. A.

So, how to produce rice that contains Vit. A?


79/83

The vitamin A productiongene is cut using restrictionenzyme. 'Sticky ends' are formed.


80/83

the same restriction enzyme isused to cut the vitamin A productiongene. the DNA are joined together by

li ase enz me


81/83

Plasmids inserted into bacteria by:1. electroporation OR

2. chemical means, e.g. NACl solution.


82/83

Issues with golden rice production


83/83

g p

There are unprecedented problems that mayarise from GMOs, e.g. golden rice.

Main problem of vitamin A deficiency isundernutrition due to poverty.

need to overcome this problem.

Nevertheless, golden rice can be fed to childrenwith vitamin A deficiency while solving theproblem of poverty.

core t - crop plants

Documents