chapter 9 - 1.0(1)

unit twounit twoPlant Structure,Plant Structure,Chemistry, Growth, Chemistry, Growth, Development, Genetics, Development, Genetics, Biodiversity, and ProcessesBiodiversity, and Processes

6 Structure of Higher Plants

7 Plant Growth & Development

8 Plant Chemistry & Metabolism

9 Genetics & Propagation9 Genetics & Propagation

10 Cultivated Plants: Naming, Classifying, Origin, Improvement & Germplasm Diversity and Preservation

11 Photosynthesis & Respiration

12 Water Relations

13 Mineral Nutrition

© 2011, 2007, 2002, 1988 Pearson Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

Practical Horticulture 5th edition By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky

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Chapter 9 - Genetics and Propogation

1. There are 5 plant hormones, list 2.

2. Ribose, deoxyribose, and glucose are examples of what class of plant metabolites?

3. Phospholipids arrange in a _______ _________ to form plant cell membranes.

4. A plant has several meristematic regions, list 2.

5. How does light quality/quantity change as sunlight filters through a forest canopy to the forest floor?

Bonus (2 pt): What is the name of NC State’s football stadium?

Quiz 2 – Out of 15 (3 pts a question)Quiz 2 – Out of 15 (3 pts a question)



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• Explain how the basic concepts of genetics relate to the production and utilization of plants. Discuss how genetic engineering is used to introduce genetic traits into plants from unrelatedor distantly related organisms.

• Describe the common methods of plant breeding and sexual and asexual propagation.

KEY LEARNING CONCEPTSKEY LEARNING CONCEPTSAfter reading this chapter, you should be able to:



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Basic Genetic Concepts in Plant ScienceBasic Genetic Concepts in Plant Science

• Pants we cultivate all originated from wild plants, but most appear very different from their wild relatives.– Differences arise through recombination of genes

& redistribution of heritable traits.

Brassica oleracea (Cabbage)



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ChromosomesChromosomes• Plants are made of mostly living cells

• Not the xylem in woody perennials

• A living cell consists of– Cell wall – structure + containment – Cytoplasm - nucleus is suspended.– Chromosomes – Strands of DNA that carry most genetic information

• Stored in nucleus



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ChromosomesChromosomes• DNA: large molecule in form

of a double helix– Self–replication– DNA is a polymer: nucleotides

– Adenine, guanine, cytosine are in both DNA & RNA

– RNA replaces DNA’s thymine with uracil



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ChromosomesChromosomes

• Backbone of DNA is composed of sugar residues (S) linked by phosphates (P) on each side.• Each sugar also attached to a nucleotide



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• Nucleotides connect sugar residues via hydrogen bonds.• Adenine, thymine (Purines)• Guanine, cytosine (Pyrimidines)• Thymine replaced with uracil in RNA

• Nucleotide bond to sugar is stronger than bond to complementary nucleotide• Allows for un-zipping of double helix

• (enzyme promoted)



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ChromosomesChromosomes• DNA self-perpetuating genetic code.• Ribonucleic acid (RNA) actually controls cell growth.

• DNA is double-stranded—RNA is a single strand.– RNA sugars have 1 more oxygen atom than DNA sugars.

• RNA has uracil (U) as a base in place of thymine (T).

Ribose Deoxyribose



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• The DNA molecule acts as a template for RNA• Proteins are constructed from amino acids using RNA

as a template

• Directed, originally, by DNA

• Chromosomes are long, threadlike structures of deoxyribonucleic acid (DNA) plus associated ribonucleic acids (RNA) & proteins.



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ChromosomesChromosomes• Number of chromosomes is conserved within a species

– Usually diploid (2n), chromosome number.– Gamete cells – the number is reduced by half and is termed the haploid, or 1n, chromosome number.

• Will combine with other gamete to make 2n



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• Number and appearance of chromosomes vary considerably between species.



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ChromosomesChromosomes• During cell division:

• Chromosomes unravel• DNA separates into single strands

• (weak h-bonds)

• Once new strand is formed, like attracts like.• Complimentary bases

• A = T• C = G• Matches purine with pyrimidine



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Homologous ChromosomesHomologous Chromosomes

• Mitosis – Cell division in vegetative tissue

• Chromosomes split longitudinally, then replicate– One of each pair goes to

each daughter cell.– Each daughter cell has a

genotype identical to the mother



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• Meiosis – formation of reproductive cells.• Pollen grains and

embryo sac (contains egg)

• 1n gametes unite during fertilization to form 2n zygote



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• Maternal and paternal chromosomes divide randomly during meiosis

• This is called genetic segregation.



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Meiosis and FertilizationMeiosis and Fertilization

• During angiosperm fertilization: one male gamete (1n) unites with the two polar nuclei (1n each) to form endosperm– Endosperm = food storage tissue for developing embryo.– Endosperm = 3n

• Seed coat – developed by mitosis from the female parent – cover both the endosperm and the embryo.



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• Gymnosperm vs. Angiosperm• Same process, different

structures



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• Homologous chromosomes – pairs of chromosomes within a single cell (2n – diploid).– Must have genes affecting same traits in same positions.



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• Alleles – genes that occupy the same position on homologous chromosomes and affect the same trait.– Alleles can be the same/different & dominant/recessive.



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GenesGenes• Genes may act alone, or with an accomplice

– One gene (or several interacting genes) may determine plant height, leaf shape, flower color, or fruit size.– Any individual gene may have a large effect or a small effect.

• Genes on the same chromosome are linked—they move from one cell generation to the next as a unit.– Linkage is not perfect, as sometimes during meiosis, chromosomes break and exchange parts. (crossing over)



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• A dominant gene is one that causes a certain characteristic to be expressed whether the plantis homozygous or heterozygous.

• A recessive gene causes the character it controlsto be expressed only if both alleles are recessive.



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• Random segregation during gamete formation makes new combinations for a monohybrid & dihybrid crosses.

• Monohybrid cross : one gene, one characteristic

• In garden peas, tallness (D) isdominant over dwarfness (d).

• A tall pea plant is homozygous (DD)or heterozygous (Dd)

• Three genotypes occur in the second generation (F2).

• (DD, Dd, dd)



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Inheritance in a dihybrid cross of the peach (Prunus persica).

• Fuzzy skin (G) of a peach is dominantover the glabrous (smooth) skinof the nectarine (g).

• White flesh color (Y) is dominantover yellow flesh color (y).

• The phenotype of the F1 generationis different from either parent

• Segregation in the F2 generation produces nine genotypes & four phenotypes.



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GenesGenes

• A sequence of triplet organic bases along DNA make up a gene.– Three nucleotides code for an amino acid– Amino acids make up proteins– Proteins serve many functions within the cell



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MutationsMutations

• A few errors slip through during cell division.– Mutations may result in changes in plant characteristics.

• Most mutations don’t matter (deleterious).– Some are not – can be good, or bad.

• Mutations can be induced with chemicals & by ionizing radiation.



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PolyploidyPolyploidy

• Polyploidy – individual plants have more than two sets of homologous chromosomes in their somatic (vegetative) cells.– Duplication or combination

Many of the cultivated crop species evolved in nature as polyploids.



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Cytoplasmic InheritanceCytoplasmic Inheritance

• Mitochondria and chloroplast DNA control a few traits– Contributed only by the female parent – useful in

determining hereditary relationships among organisms.

Chloroplast – BASF Company



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Genotype and PhenotypeGenotype and Phenotype• Genotype – genetic makeup of the plant

– GCC-CGT-TGT-CTT-CCC-TCA– Alanine, Arginine, Cysteine, Leucine, Proline, Serine

• Phenotype – outward appearance, behavior, and chemical and physical properties.– Interaction of genes and environment



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BreedingBreeding

• Breeding: selecting a female & male parent with unique desirable traits & crossing them to produce offspring with both sets of desirable traits.

• DNA analysis speeds up breeding– Early confirmation of traits



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BreedingBreeding

In the breeding process, pollen is collected from the male plant and then used to fertilize the female plant

Left: Removing pollen from the male parent. Right: Applying pollen to the female plant.Figure 9-5



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BreedingBreeding

• Unintentional fertilization makes breeding difficult– The female must be kept from receiving unwanted pollen.

• Pollen producing structures must be removed in monoecious self-fertile plants– Male-sterile plants eliminates the problem



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BreedingBreeding• Single gene traits are the easiest to breed for.

• It is possible to develop a homozygous line from a single, self-pollinating plant. – When a population becomes completely or nearly

homozygous, reduced vigor can occur.



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BreedingBreeding• Production hybrid seeds allows for very uniform offspring

– F1 generation from a cross of two different—yet homozygous—parents.

• Almost all corn is now produced from hybrid seed

• Seed from hybrid crop cannot be saved and used to produce future crops.– F2 generation segregates into several different genotypes and phenotypes



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BiotechnologyBiotechnology

• Biotechnology -- developing organisms by molecular biology & genetics, using advanced genetic engineering techniques.

• Enhanced traits:– dietary attributes, resistance to insects, herbicides, certain

environmental stresses, etc.



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BiotechnologyBiotechnology• Genetic engineering -- Introducing a new gene into a species

– A genetically engineered plant is a transgenic plant.

• Genetically modified organism (GMO) vs. genetically engineered plants,– Genetically engineered is a more accurate term.



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• A GMO is created during sexual reproduction.

• Not all genetically engineered plants are the result of gene transfer — sometimes endogenous genes alter.



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• Genetic engineering starts with identification of a gene – trait relationship.– The gene is removed from cells of the host organism.– Then introduced into nucleus of “target cells”– Typically accompanied by a marker gene



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Steps of Genetic Engineering



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Steps of Genetic Engineering

Reproduction



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• Technology isn’t there to fabricate genes

• A promoter is often attached to turn the gene “on”– Can be constant or only under specific conditions– Genes often respond differently in different environments



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Propagation of PlantsPropagation of Plants

Propagation – increasing plant numbers

• Plants are propagated bysexual (seed) or asexual (vegetative) methods.

• Depending on the species, some techniques work better than others.



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• Successful propagation transmits desirable characteristics between the original and the progeny.

• Propagation while maintaining specific characteristics often drives commercial propagation methods.



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• If the plant group reproduces “true” by seeds—with no characteristics changed—the cultivar is a line.– A line is homozygous and, if self-pollinated, seed

propagation yields progeny like the original plant.

– Many crops are lines.



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PropagationPropagation

• Inbred lines,used to produce hybrid cultivars.

• Hybrids i.e. hybrid corn



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• Control of seed source is essential.

• Cultivars must be separated to prevent contamination



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• Seed certification programs to protect and maintain the genetic quality of cultivars.

• Government agencies set the standards for seed quality and characteristics.



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Seed ProductionSeed Production

• U.S. seed certification programs recognize four classes of seeds in agronomic crops:– Breeder seed—produced in small amounts, under the

control of the plant breeder, to produce foundation seed.– Foundation seed—multiplied from breeder seed, available

in limited amounts, planted to produce registered seed.• Controlled by public/private foundation seed stock

organizations.

– Registered seed—seed source for growers of certified seed, under the control of the registered seed producers.

• The progeny of either breeder or foundation seed.

– Certified seed—is of known genetic identity & purity, available in large quantities, sold to farmers for general crop production.



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Seed FormationSeed Formation

• A seed has three essential parts:– The embryo, which develops into the new plant.– Food storage material -- endosperm.– Seed coverings – seed coat.

Parts of the seed as they develop from the parts of the flower:



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Seed Storage and Viability TestingSeed Storage and Viability Testing

• For a seed to germinate, the embryo must be alive.

• Length of viability can depend on storage conditions.

– Some are very short-lived, viable only a few days/months.

– Others generally remains alive for a great many years.

• Testing viability:– In a cut test, seeds are cut in half to see if there is an embryo inside– Float – they float, they’re not live seed



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• The germination test useful without dormancy– Viability calculated as the percentage of seedlings

developing from numbers planted.



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• Tetrazolium Test—2,3,5-triphenyl tetrazolium chloride, colorless in water, turns to a red-colored chemical when it contacts living, respiring tissue.– Seeds are usually soaked, then cut lengthwise to expose

the embryo and placed in a tetrazolium solution.• If the embryo turns red, the seeds are viable.



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Seed DormancySeed Dormancy

• Dormancy is a survival mechanism for some species

• Causes for dormancy can persist and have several requirements

• Dormancy can be structural or physiological conditions in seed coverings, the embryo, or both.



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• Seed Coat Dormancy—Seed coats or other tissues may be impermeable to water & gases which cannot penetrate to the embryo and initiate germination.

• Artificial methods of softening seed coats:– Scarification—the surface of the seed is mechanically

scratched or ruptured.– Heat treatment—exposure to heat, usually boiling water,

sufficiently disrupts the seed coat to permit passage of water and gases.

– Acid scarification—soaking seeds in concentrated sulfuric acid etches their coats enough for germination.



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• Embryo Dormancy—physiological conditions or germination blocks in the embryo prevent growth, though environmental conditions are favorable.– Dormant seeds will germinate in spring if they are allowed

to winter outdoors while being kept moist.• From this arose the practice known as stratification.

• Critical conditions in seed stratification are:– Chilling temperatures; Moisture ; Adequate oxygen; Time.

• There is evidence stratification increases growth-promoting hormones (gibberellins & cytokinins).– Growth-inhibiting hormones (abscisic acid) decrease.

• The term after-ripening is often used to describe the changes in the mature seed that allow germination.



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• Seeds of some species have both seed coat and embryo dormancy—Double Dormancy. – To obtain germination, seeds should be first treated to

soften the seed coats, and given cold stratification.



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Seed GerminationSeed Germination

• Three phases of seed germination:– Imbibition of water by seeds—cells get turgid, coverings

soften, rupture & permit passage of oxygen & CO2.

– Activation of hormones/enzymes—after water is absorbed, various enzyme systems are activated or synthesized as a result of stimulation by hormones.

• Food materials are translocated to root/shoot growing points.

– Embryo growth/development—the root-shoot axis (plumule, epicotyl, hypocotyl, and radicle) grows by cell division and enlargement.



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Seed GerminationSeed GerminationThe seed coats rupture and photosynthetic tissueemerges into the light to carry on photosynthesis.

The embryonic root (radicle) emerges and grows intomoist soil to supply the newly developed leafy tissues

with water for growth and transpiration.



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Seed GerminationSeed Germination

• Environmental Factors Influencing Germination: – Moisture—essential to initiate physiological & biochemical

processes.– Temperature—influence percentage and rate of seed

germination– Aeration—respiration rates are high in germinating seeds.

– Low O2 limits germination

– Light—essential for some kinds of seeds, such as lettuce, celery, most grasses & many herbaceous garden flowers.

– Freedom from pathogenic organisms—seedlings can after germination from damping off, caused by fungi.

– Freedom from toxic amounts of salts.

chapter 9 - 1.0(1)

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