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PRESENTATION BYKARTOORI SAISANTHOSHPh.D. SCHOLAR UASD.

•PATHWAY OF MOVEMENT OF ASSIMILATESIN DEVELOPING GRAINS OF MONOCOTSAND DICOTS

•CHEMICAL COMPOSITION OF SEEDS

•STORAGE OF CARBOHYDRATES, PROTEINSAND FATS IN SEEDS AND THEIRBIOSYNTHESIS

Pathway of movement of assimilates in developing grains of monocots and dicots

•Shot distance transport system

•Long distance transport system

•Shot distance transport system:

• Intracellular transport- diffusion, protoplasmic streaming,transporters

• Inter cellular transport-through apoplast and symplast

•Transfer cells: a group of specific cells exist in the terminal inconduct tissue, flower or fruits

•Companion cells and intermediary cells are considered as transfercells

•Main function: loading assimilates into phloem from source andunloading assimilate into sink cell from phloem to other conducttissue

•Long distance translocation of photo assimilates occurs viaphloem

•Apoplastic pathway: movement of water from cell to cell viacellulose cell wall

•Symplastic pathway: movement of water from cell to cell viaplasma membrane or plasmodesmata

•Active transport requires energy and moves particles up theirconcentration gradient. Passive transport does not requires energyand moves particles down their gradient energy

•Passive transport is a process which is carried out along theconcentration gradient.

Chemical composition of seeds

About 70% of all food for human being comes from seed andremaining 30% from animals indirectly

In addition to the normal chemical constituents found in planttissues seed contains extra substances, food reserves to supportearly seedling growth

The major food reserves

1. Carbohydrates

2. Proteins

3. Fats and oils

The minor food reserves

• 1. phytin and some nutritionally undesirable or even toxicsubstances like

• 2. raffinose and oligosaccharides

• 3. Proteinase inhibitors

• 4. Lectins

• 5. Alkaloids

Chemical composition of seed is determined by

• 1. Genetic factors

• 2. Agronomic practices

• 3. Environment

Average per cent compositionCrops Protein Oil Carbohydrates Major storage

organs

Barley 12 3 76 Endosperm

Maize 10 5 80 Endosperm

Oats 13 8 66 Endosperm

Rye 12 2 76 Endosperm

Wheat 12 2 75 Endosperm

Broadbean 23 1 56 Cotyledons

Garden pea 25 6 52 Cotyledons

Peanut 31 48 12 Cotyledons

Soybean 37 17 26 Cotyledons

Castor bean 18 64 Negligible Endosperm

Oilpalm 9 49 28 Endosperm

Rapeseed 21 48 19 Cotyledons

From Bewley and Black. 1994. Seeds: Physiology of development and germination

Carbohydrates

•Major storage substances in seed

•Cereal and grasses are rich in carbohydrates and low in proteinsand fats

•Major forms of carbohydrate storage in seed are

•A. starch

•B. hemicellulose

•Amyloids and raffinose series oligosaccharides are present asminor carbohydrate reserves

•Sometimes non storage forms like cellulose, pectins and mucilagesoccur

Carbohydrate storage in seeds•Starch Polysaccharide (…-glucose-glucose-glucose-…)

•Two forms: 1. Amylose, 2. Amylopectin

• 1. amylose structure

From Horton et al. 2002. Principles of Biochemistry

2. Amylopectin

From Horton et al. 2002. Principles of Biochemistry

Starch grains in starchy endosperm cells of rye.

• 50-75% amylopectin

• 20-25% amylose

•Sl: large starch grain

•Ss: small starch grain

•p: protein matrix

•w: cell wall

From Bewley and Black. 1994. Seeds: Physiology of development and germination

Amaranth starch(Bar: 1 µm)

Arrowroot starch(Bar: 20 µm)

Buckwheat starch(Bar: 5 µm)

Cassava starch(Bar: 10 µm)

Corn starch(Bar: 10 µm)

Oat starch(Bar: 5 µm)

Potato starch(Bar: 50 µm)

Rice starch(Bar: 2 µm)

Kidney bean starch(Bar: 20 µm)

Hemicelluloses

•Found in cell wall of plants and seed as reserves

• It is the major storage carbohydrate in endospermic legumes

•Many hemicelluloses are mannans with B(1-4) linkage betweenmannose units

•Galactomannans have a (1-6) linkage at galactose side chains

•Xyloglucans are known as amyloids

Hemicelluloses

•Large heteropolymers of several sugars

•Chemical structure of galactomannan

From Bewley and Black. 1994. Seeds: Physiology of development and germination

•Mucilages: are complex carbohydreates consisting of polyuronidesand galacto uronides that chemically resemble pectic compoundsand hemicelluloses

•Pectic compounds

•Found in primary cell wall and middle lamella

•Occurs as pectic acid pectin and propectin

•During ripening of fruits propectin is converted into pectins

•Free sugars

•Main storage carbohydrate in sugar maple disaccharides andoligosaccharides are common minor reserves in embryo andreserve tissues

Lipids –(triacylglycerides/fats/oil)

•Simple lipids- fats, fatty oils and waxes-major

•Compound lipids-phospholipids, glycolipids

•Derived lipids- cholesterol

•The predominant FA in seeds are unsaturated FA (UFA)

•Lipids are stored in oil storage bodies called spherosomes whichrange in size 0.2 to 6.0 microns diameter.

•Enzymes for lipid synthesis & hydrolysis are present inspherosomes

•During germination lipids disappear and sucrose content inincreases

•Lipase activity increases and hydrolysis tryglycerides to di andmonoglycerides

•High lipid content is associated with low protein content

PROTEINS

•Osborne classified proteins into 2 categories

•Metabolically inactive

•Prolamine

•Glutelin

•Metabolically active

•Albumin and globulins

•Albumins and globulins are not deficient in specific amino acids sothey are good sources of dietary protein

•Storage proteins are oligomeric

•Most storage proteins are not single but bounded together byintermolecular disulphide groups, hydrogen bonding ionicbonding and hydrophobic bonding

• In legumes the major storage protein is globulins, which accountfor 70% of total seed nitrogen

• In addition to these proteins glycoproteins like lectins are presentin seeds

•Some proteins are part of defence mechanism against pests andpredators

•Arcelin- conifers resistance against bruchid beetles

•Chitinase increases resistance to fungal attack

•Seed storage proteins are deposited in protein bodies

CENTRAL DOGMA OF MOLECULAR BIOLOGY DNA

RNA

Protein

transcription

translation

PROTEIN SYNTHESIS

TRANSCRIPTION

THE PROTEINS ARE MADE IN THE

CYTOPLASM IN THE RIBOSOMES

THE INFO FROM THE DNA IS

COPIED INTO m RNA, WHICH CAN

LEAVE THE NUCLEUS AND GET TO

THE RIBOSOMES IN THE

CYTOPLASM.

THE INFORMATION FOR PROTEIN

SYNTHESIS IS IN THE DNA IN THE

NUCLEUS.

DNA INFO COPIED TO mRNA

GROWING CELL

Before cell division the

cell’s DNA has to

duplicate

(DNA

REPLICATION)

While the cell is

growing it needs

enzymes and extra

proteins…

TRANSLATION

DNA

M RNA

PROTEIN

transcription

DNA info is copied into to RNA code, which

is still in the “language” of nitrogenous

bases, except that adenine on the DNA pairs

with uracil (in place of thymine) on the

RNA. HAPPENS IN NUCLEUS.translation

The RNA code is then translated to protein

code, which is a different “language.”

(nitrogenous bases to aminoacids.

This process involves ribosomes and two

kinds of RNA: mRNA and tRNA.

HAPPENS IN CYTOPLASM

INFORMATION IN THE mRNACodon: sequence of 3 nucleotides on

m-RNA that codes for one amino acid.

The GENETIC CODE states which codon

stands for which aminoacid.

1 aminoacid

1 aminoacid

TRANSLATION LOADED tRNA

RIBOSOME

mRNA

COMPONENTS PRESENT

IN THE PROCESS

anticodon

Aminoacid

carried

codon

TRANSLATIONThe newly made mRNA (transcription) leaves the nuceus and binds with the

ribosome in the cytoplasm.

ONE codon is exposed at site P and

another codon at site A

A tRNA with a complementary codon in

its anticodon site will bind with the

codon at site P, bringing an aminoacid.

1º AMINOACID:

Methionine (AUG)

in site P.

TRANSLATION

Even though every protein begins with the

Methionine amino acid, not all proteins will ultimately

have methionine at one end.

If the "start" methionine is not needed, it is

removed before the new protein goes to work (either

inside the cell or outside the cell, depending on the

type of protein synthesized)

TRANSLATION

A

2º AMINOACID: Glycine (only in this case) in site A.

PEPTIDIC BOND IS FORMED

TRANSLATION

STOP codon NO aminoacid is added. Its the

END of the polypeptide!

Growing polypeptide

POLYSOMES

Fatty Acids

• Building blocks for triglycerides and phospholipids

• A chain of carbon and hydrogen atoms with a carboxyl group at the alpha end and a methyl group at the omega end

Figure 5.1

Saturated and Unsaturated Fatty Acids Help Shape Foods

Figure 5.3

•Sucrose entering the developing oil seed is used mainly for synthesisof storage triacylglycerols and proteins.

The triacylglycerols synthesis can be considered in three parts:

The production of the glycerol back bone.

The formation of fatty acids.

The esterification of glycerols with fatty acids components to give triacylglycerols.

Sucrose is translocated into the developing seed and converted tohexose phosphates and triose phosphates by the reaction of glycolysis.

Fatty acid synthesis occurs in the plastids utilizing acetyl-coA, whichcan be generated by glycolytic reactions in the organelle.

Portion of Figure 5.7

Triglycerides

• Three fatty acids connected to a glycerol backbone

Summary of Lipogenesis

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