PFF---Exam Three

Saints be with ye

Flowering Plants

There are over 300,000 (500,000?) known species; provide countless products: 11 species provide 80% of the world’s food.

Unique flowers: The corpse flower; produces a corpse-like odor that attracts carrion beetles (pollinators).

Bonus: An underground-flowering orchid was discovered accidentally in Australia!

Variety of Flowers

Can be any color or combination of the colors of the rainbow, virtually any texture (filmy to thick and leathery), inconspicuous or impressive, odorless to overwhelming (scents can range from seductive and exhilarating to putrid); habitats are also varied (soil-bound to underground to epiphytic); can be found virtually anywhere (where they receive their basic needs of sunlight, moisture, and a minimal supply of minerals).

Categories of Flowering Plants

Annuals - cycle completed in one growing season (seed germination to mature plant producing seeds).

Biennials - cycle completed in two growing seasons.

Perennials - cycle takes several to many growing seasons or plant produces flowers on new growth, while other plant parts persist indefinitely.

Two classes:

Magnoliopsida - dicots (approx. ¾ of all flowering plant species; includes many annuals and virtually all flowering trees and shrubs).

Liliopsida - monocots (primarily herbaceous; includes bulb plants, grasses and allies, orchids, irises, and palms; palms do not have a vascular cambium → become large through a primary thickening of cells that occurs just below the apical meristem).

Structure of Flowers

Flowers begin as embryonic primordium that develops into a bud; occur as specialized branches at the tips of peduncles (may have branchlets of pedicels → stalk of a single flower); peduncle or pedicel swells at the tip into a small pad known as a receptacle; other parts of the flower attach to the receptacle—often in whorls (sepals, petals, stamens, and pistil).

The Main Whorls(TM)

Sepals - outermost whorl; collectively referred to as a calyx; protects flower while in bud; usually three-to-five, small, green, and leaflike

Petals - nextmost whorl; collectively known as the corolla (you have to put your foot on the pedal [petal] of your Toyota Corolla); can be showy (to attract pollinators) or inconspicuous or missing (in many trees, weeds, grasses, and wind-pollinated plants); usually three-to-many; can be distinct units or fused into a single sheet of tissue; the calyx and corolla collectively form the perianth.

Stamen - nextmost whorl; attached to the receptacle and typically situated in the center of the flower; each stamen consists of a slender filament with a sac called an anther at the top; anthers develop and release pollen grains (usually through either lengthwise slits or anther pores).

Pistil - innermost whorl; often shaped like a tiny vase that is closed at the top; consists of three regions: the stigma (the top), the style (the slender, stalklike portion), and the ovary (the swollen base that later develops into a fruit); the stigma can vary among species (from a narrow point, to a bulb to a set of broad arms or branches).

Ovaries

Contains ovules; develop from specialized, ovule-bearing leaves called carpels whose margins roll inward; carpels may be fused together into a compound ovary; pistil can consist of one to several carpels; the number of carpels is often reflected by the number of lobes or divisions of the stigma (each segment of a mature ovary—such as a tomato or an orange—represents a carpel).

Superior Ovaries

The calyx and corolla are attached to the receptacle at the base of the ovary; peas and primroses.

Inferior Ovaries

The receptacle grows up around the ovary (so that the calyx and corolla appear to be attached at the top); apples, cacti, and carrots.

Inflorenscence

Flowers can be produced singly or in inflorescences (groups of flowers that may all open at the same time or follow an orderly progression to maturation).

Fruits

Developed and matured ovaries and their accessory parts; usually contain one or more seeds that develop from fertilized ovules within the ovary; only produced by flowering plants; highly variable: can consist of only ovary and seeds or contain adjacent flower parts, can be fleshy or dry, may split or not, may be derived from one or more ovaries.

Fruit Regions

Exocarp - the skin of the fruit.

Mesocarp - the often-fleshy tissue between the exocarp and the endocarp.

Endocarp - the inner boundary around the seed(s).

Collectively known as the pericarp.

Simple Fleshy Fruits

Simple fleshy fruits develop from a flower within a single pistil; ovary may be superior or inferior; ovary may be simple (from a single carpel) or compound (consisting of two or more carpels)

Drupes

Simple fleshy fruits with a single seed enclosed by a hard, stony endocarp (or pit); usually develops from flowers with a superior ovary containing a single ovule; mesocarp is not always obviously fleshy (coconut husks consist of mesocarp and exocarp).

Examples: apricots, cherries, peaches, plums, olives, almonds, coconuts.

Berries

Usually develop from a compound ovary and commonly contain more than one seed; entire pericarp is fleshy; may be difficult to distinguish between the mesocarp and endocarp.

Three types are recognized:

True berries - fruit with a thin skin and a pericarp that is relatively soft at maturity; most contain more than one seed (there are exceptions); tomatoes, grapes, peppers, blueberries, bananas, dates, avocados.

Pepos - berries with relatively thick rinds; pumpkins, cucumbers, watermelons, squashes, cantaloupes.

Hesperidiums - berries with a leathery skin that contains oils; numerous outgrowths from the inner lining of the ovary wall become saclike and swollen with juice as the fruit develops; all members of the Citrus Family: oranges, lemons, limes, grapefruit, tangerines, and kumquats.

Pomes

Simple fleshy fruits for which most of the flesh comes from an enlarged floral tube or receptacle that grows up around the ovary; the endocarp is papery or leathery; apples, pears, quinces (in apples, the ovary consists of the core and a little adjacent tissue; the remainder of the fruit is developed by the floral tube).

Dry Fruits

Fruits whose mesocarp is definitely dry at maturity

Dehiscent Fruits

Fruits that split at maturity; fruits in this group are distinguished by the way they split.

Follicles - split along one side/seam (suture), exposing the seeds within; larkspur, columbine, milkweed, peony

Legumes - split along two sides; peas, beans (garbanzo and otherwise), lentils, carob, kudzu, mesquite.

Siliques - split along two sides, but the seeds are borne on a central partition, which is exposed when the two halves separate; silicles = siliques that are less than three times long as they are wide; broccoli, cabbage, radish, shepherd’s purse, and watercress.

Capsules - most common; consist of at least two carpels and split in a variety of ways (along the partitions between carpels, through cavities in the carpels, through a cap toward one end that pops off and releases seeds, from a row of pores through which the seeds are shaken out); irises, orchids, lilies, poppies, violets, snapdragons.

Indehiscent Fruits

Dry fruits that do not split at maturity; the single seed is united with the pericarp.

Achenes - only the base of the single seed is attached to its surrounding pericarp; husk is easily separated from the seed; sunflower “seeds,” buttercup, buckwheat.

Nuts - similar to achenes, but larger, with a harder and thicker pericarp, and a cluster of bracts at the base; acorns, hazelnuts, and hickory nuts.

Grain - pericarp is tightly united with the seed and cannot be separated from it; grasses (corn, wheat, rice, oats, barley).

Samara - pericarp extends out as wings for dispersal; maples (in pairs), ashes, elms, tree of heaven.

Schizocarp - twin fruit that breaks into one-seeded segments called mericarps; Parsely Family: carrots, anise, dill.

Aggregate Fruits

Derived from a single flower with several to many pistils; the individual pistils develop into tiny drupes or other fruitlets, but they mature as a clustered unit on a single receptacle; raspberries, blackberries, strawberries.

Multiple Fruits

Derived from several to many individual flowers in a single inflorescence; each flower has its own receptacle, but as the flowers mature separately into fruitlets, they develop together into a single fruit; mulberries, Osage oranges, pineapples, figs.

Fruit and Seed Dispersal

Important that seeds are carried away from the mother plant before they germinate to prevent competition and inbreeding.

Dispersal by Wind

Several fruits and seeds have a variety of adaptations for wind dispersal; hop hornbeams, the seed is enclosed in an inflated sac that gives it buoyancy in the wind; some members of the Buttercup and Sunflower Families have plumed fruits; Willow Family seeds are comose (hairy); seeds of button snakeroots and Jerusalem sage are too large to be airborne, but spherical enough to be rolled along; some seeds (e.g., orchids) are so tiny and light that they can be blown great distances; some seeds may be winged (catalpa and jacaranda); Dandelion fruitlets are plumed; in tumbleweeds, the whole above-ground portion of the plant may be abscise and blown away by the wind—releasing seeds as it endlessly bumps along.

Dispersal by Animals

Birds, mammals, and ants all act as seed dispersal agents; some seeds may pass through a digestive tract (and may not germinate unless they have); some may be adapted to adhere to fur or feathers (bedstraw, bur clover, unicorn plants, twinflowers, flax); Bleeding hearts and trilliums have appendages on their seeds that contain oils attractive to ants (elaiosomes).

Dispersal by Water

Some fruits contain trapped air (sedges have inflated air sacs); others have waxy materials on the surface of their seeds; some plants have seeds and fruits that have thick, spongy pericarps that absorb water slowly (adapted to ocean currents).

Other Dispersal Mechanisms and Agents

Fruits of some legumes, touch-me-nots, and others mechanically eject seeds—sometimes with considerable force (splitting action of witch hazel capsules may fling the seeds over 12 meters; dwarf mistletoes violently release fruits in response to a warm-blooded animal coming close to the plants); in Geraniums, each carpel of the fruit splits and curls back from a central axis → each fruitlet consists of a single, pointed seed with a long, slender tail that is sensitive to changes in humidity (at night, when the humidity increases, the tail is relatively straight, but, in the sun, it coils up like a corkscrew—drilling the pointed seed into the ground and planting it in the process).

Humans may intentionally or unintentionally transport seeds.

Seed Structure

Ovules develop into seeds.

Cotyledons - food storage organs that function as “seed leaves.”

Embryo - cotyledons and the plantlet.

Plumule - embryo shoot.

Epicotyl - stem above cotyledon attachment.

Hypocotyl - stem below cotyledon attachment.

Radicle - tip of embryo that develops into the root.

Hilum - attachment scar (where the ovule used to be attached to the ovary); plant belly button!!!

Micropyle - small pore that allows water to enter the seed during imbibtion.

Germination

Beginning or resumption of seed growth; some seeds require a period of dormancy (brought about by mechanical and/or physiological circumstances → thick/tough seed coats, growth-inhibiting substances present in the fruit or seed coat, one-way valves, etc.); dormancy may be broken via mechanical abrasion, thawing and freezing, bacterial action, or soaking rains; scarification = artificially breaking dormancy.

The embryo is composed of only a few cells when the fruit ripens; seeds will not germinate until embryo develops (after-ripening).

Epigeous Germination

Hypocotyl lengthens, bends, and becomes hook-shaped; top of hook emerges from the ground, pulling the cotyledons above ground; once above ground, the hook straightens out.

Hypogeous Germination

Hypocotyl remains short and cotyledons do not emerge above the surface.

Conditions for Germination

Favorable environmental factors are needed for germination:

Water and oxygen (essential for all seeds).

Light or its absence (some varieties of lettuce will not germinate without light; the California poppy will only germinate in the dark [emo]).

Proper temperature range (varies; most crops have an optimum germination temperature of between 20 and 30 degrees Celsius).

Enzymes in cytoplasm begin to function after water is imbibed.

Longevity

Seed viability varies (depends on species and storage conditions); some (willow, cottonwoods, orchids, and tea) only remain viable for a few days or weeks; period of viability of most seeds is extended by months or even years when they are stored at low temperatures and kept dry; wheat seeds, when stored properly, can maintain 30% viability even after 30 years.

Vivipary - No period of dormancy; embryo continues to grow while fruit is still on parent.

Genetic Variation

Differences in alleles of genes found within a population; Darwin’s theory relies on the presence of genetic variation → provides raw material for natural selection to act upon.

Asexual Reproduction

Any form of reproduction not involving the union of two gametes; produces offspring that are genetically identical to their parents; mutations occasionally provide variability; vegetative propagation.

OTHER Reproduction

Reproduction involving the union of two gametes; in angiosperms and gymnosperms, results in the formation of seeds; gametes are produced and united to form a single cell called a zygote (first cell of a new individual).

Meiosis

Occurs during S.R.; halves the number of chromosomes in each resulting gamete (to prevent fatal/inconvenient extras/doubling); four cells are produced from two successive divisions (take place without pause); each daughter cell is genetically distinct.

Prophase I

Chromosomes coil;

becoming shorter and thicker and

aligned in homologous pairs;

nuclear membrane dissolves and

dissociates;

crossing over occurs (chiasmata are

visible).

Spindle fibers begin to form.

Metaphase I

Pairs of chromosomes become aligned

at the center of the cell.

The now-complete spindle

becomes more apparent;

homologous pairs line up at the

equator;

the chromatids are still

holding

on to each other.

Anaphase I

Each chromosome migrates to a pole.

Telophase I

Chromosomes may partially

revert back to their previous state;

if not,

proceed directly to Division Two.

Two new cells

have formed—

each with half the information.

Nucleoli typically reappear.

Division Two

All of the same steps repeated again; crossing over does not occur again (it’s a one-time deal); ‘tids are separated :(

Haploid

A cell that contains one set of chromosomes; gametes.

Diploid

A cell that contains two sets of chromosomes; zygotes.

Polyploidy—and Other Plant Chromosome Anomalies

Many plant species contain more than two sets of chromosomes and are said to be polyploid; some plants may be triploid (such as in seedless watermelons), hexaploid (bread wheat), octaploid (strawberries); aneuploid → plants containing one or more chromosome(s), or lacking one or more chromosome(s).

Alternation of Generations

Alternation between a haploid gametophyte phase and a diploid sporophyte phase in the life cycle of sexually-reproducing organisms.

Sporophyte

The diploid (2n), spore-producing phase of the life cycle of an organism exhibiting alternation of generations; develops from a zygote and eventually produces sporocytes—each of which undergoes meiosis, producing four spores; the spores undergo mitosis to produce haploid bodies called gametophytes; first cell = zygote; last cell = sporocyte; change from sporocyte to gametophyte occurs due to meiosis.

Gametophyte

The haploid (n), gamete-producing phase of the life cycle of an organism that exhibits alternation of generations; develops from spores; specialized cells within gametophytes function as gametes (pollen; eggs); always contains half as many chromosomes as the sporophyte generation; change from gametophyte to sporophyte occurs as a result of fertilization.l

Barbara McClintock

Published work introducing the concept of transposition (the movement of a piece of a chromosome to another chromosomal location); transposable genetic element (jumping gene) = a DNA fragment that can move to another location on the same chromosome or another chromosome; if it moves into an existing gene, the function of that gene is disrupted (can also move out of that gene); McClintock noticed patches of color in corn kernels and leaves where they did not belong; patches caused by transposable elements moving into and out of genes.

Won a Nobel Prize!!!

Transposons can be used to create mutations; often activated under genomic stress (chromosomal damage caused by radiation, creation of hybrids between divergent species, and attack by pathogens).

Molecular Genetics

Discovery of DNA structure in 1953 by Watson and Crick (boo) helped introduce this field of study; genes were recognized as sequences of nucleic acids that could be isolated and characterized; mutations became better understandable.

Cytogenetics

The study of chromosome behavior and structure from a genetic point of view (chromosome movement during meiosis and mitosis, chromosome pairing during meiosis, and chromosomal variation due to changes in chromosome structure and number).

Changes in Chromosome Structure

Inversion - a piece of a chromosome is broken and reinserted in the opposite orientation.

Translocation - a piece of a chromosome breaks off and becomes attached to another one.

Both can be important in speciation: plants carrying chromosomes from each of these events may become reproductively isolated from other plants and develop into a new species.

Changes in Chromosome Number

Mistakes during chromosome pairing and separation can result in gametes carrying extra or missing chromosomes.

Aneuploid - carries or is missing one or more extra chromosome.

Polyploid - has at least one complete extra set of chromosomes; polyploid plants are often larger or have higher yield (cotton, potato, peanuts, wheat, oats, strawberry, sugar cane).

Mendel, His Peas, and His Laws

Gregor Mendel was an Austrian monk who carried out a variety of experiments around 1860 (his work was not understood in his lifetime, but he was rediscovered and recognized as the father of genetics). He selected plants with different forms of the same trait (such as height: he crossed tall and short pea plants).

Law of unit characters - Factors (alleles), which always occur in pairs, control the inheritance of various characteristics; genes are always at the same position (locus) on homologous chromosomes.

Law of dominance - For any given pair of alleles, one (dominant) may mask the expression of the other (recessive).

Law of independent assortment - Factors (genes) controlling two or more traits segregate independently of each other (unless the genes are linked [on the same chromosome]).

Genotype

Genetic information responsible for contributing to phenotype.

Homozygous - both alleles are identical (AA).

Heterozygous - alleles are contrasting (Aa).

Phenotype

Organism’s physical appearance (as governed by its genotype).

Monohybrid Cross

Start with a cross between two true-breeding parents differing for a single trait (e.g., AA and aa).

Parental generation (P) - demonstrate parental phenotypes; the Parents (AA and aa).

First filial generation (F1) - offspring of parental generation; demonstrate dominant phenotype, but heterozygous genotype (Aa).

Second filial generation (F2) - offspring of F1 plants (intercrossed); demonstrate a phenotypic ratio of 3:1 and a genotypic ratio of 1:2:1 (1 AA, 2 Aa, 1 aa).

Dihybrid Cross

A cross involving two different pairs of genes; start with a cross between two true-breeding parents differing for two traits; cross the F1 (dihybrid; heterozygous generation); F2 generation will typically result in a ratio of 9:3:3:1.

Backcross

A cross between a hybrid and one of its parents; Mendel used this method to test his predictions; expect a phenotypic ratio of 1:1 in offspring

Testcross

Cross between a plant with a dominant phenotype and a homozygous recessive plant; will determine whether the plant expressing the dominant phenotype is homozygous or heterozygous.

Incomplete Dominance

A condition in which the heterozygous phenotype is intermediate between two homozygous phenotypes (as a result of one allele only partly masking another); e.g., a red flower x a white flower = a pink flower.

Interactions Among Genes

Genes are generally responsible for the production of proteins that are components of complex biochemical pathways; often necessary to consider the genotype of an individual at more than one locus before a prediction of a phenotype can be made.

In blue-eyed Mary plants, two genes control flower color in a biochemical pathway:

colorless → gene W → magenta → gene M → blue

If a plant contains at least one dominant W allele, then it can proceed through the first step of the pathway and produce either magenta or blue flowers; flowers will be magenta if the plant is homozygous recessive for the M gene, or blue if it has at least one dominant copy; flowers that are homozygous recessive for either the W gene or both genes will be colorless.

How Genotype Controls Phenotype

Dominant allele codes for protein that effectively catalyzes a reaction, producing a phenotype; recessive allele represents a mutant form (cannot catalyze reaction and therefore does not produce a functional product).

Quantitative Traits

Traits that are controlled by several genes and are influenced by the environment; typically measured on a continuous scale; exhibit a range of phenotypes; include traits like fruit yield and days to flowering; under identical environments, phenotypes differ due to genetic differences; genetically identical plants produce different phenotypes under different environments; molecular geneticists identify chromosomal fragments—quantitative trait loci (QTLs)—associated with quantitative traits; QTLs contain genes that influence traits and behave like Mendelian genes.

Extranuclear DNA

DNA in mitochondria and chloroplasts (supports the theory of endosymbiosis; mitochondria and chloroplasts were likely once free-living bacteria in evolutionary history); sperm rarely carry mitochondria and chloroplasts—thus passed to the next generation only by the female (maternal inheritance).

Linkage and Mapping

Linked genes - genes together on a chromosome; genes that are closer together are more likely to be inherited together.

Each gene has a specific location on a chromosome; crossing-over is more likely to occur between genes that are farther apart; frequency of crossing-over is used to construct a genetic map of chromosomes; DNA sequence information is used to explore gene function in other species.

Recombinant types - offspring in which crossing-over has occurred.

Bateson and Punnett → flower color and pollen shape.

The Hardy-Weinberg Law

Proportions of dominant alleles to recessive alleles in a large, random mating population will remain the same from generation to generation in the absence of forces that change those proportions.

Forces that be:

Small populations - random loss of alleles can occur if individuals do not mate as often.

Selection - most significant cause of exception to H-W.

The Structure of DNA

Chromosomes are composed of two types of large molecules: DNA and protein; DNA molecule organized into a chain of nucleotides composed of three parts: nitrogenous base, 5-carbon sugar, phosphate group; four types of DNA nucleotides exist—each with unique nitrogenous base: two purines (molecular structure of two linked rings; Adenine and Guanine) and two pyrimidines (molecular structure of a single ring; Thymine and Cytosine).

Nucleotides are bonded to each other in a ladder-like form that’s twisted into a double helix (sides are alternating sugar and phosphate groups); hydrogen bonds hold base on one side of the helix to the base on the other (ladder rungs).

DNA Functions

Storage of genetic information (resides in sequence of nucleotides); genes are segments of DNA that direct protein synthesis (protein used by cell as structural or storage material or may act as an enzyme that influences cell activities); genome = sum total of DNA in an organism’s chromosomes.

Replication (duplication) of information; occurs during S-phase of cell cycle; strands of double helix unzip; single strands are templates for the creation of new double strands; nucleotides are added by DNA polymerase in precise sequence; new DNA molecule consists of one strand from original molecule and another built using that parental template (semi-conservative replication).

Expression of information; different subsets of genetic information read in different cell types; cell’s environment can influence set of genes expressed; expression requires two processes: transcription (copy of gene message made from DNA template using RNA building blocks) and translation (RNA translated to produce proteins; occurs in the cytoplasm).

RNA

Three different types of RNA produced:

Messenger RNA (mRNA) - translated to produce proteins.

Transfer RNA (tRNA) - machinery for translation.

Ribosomal RNA (rRNA) - machinery for translation.

RNA synthesis - nucleotides added to single-stranded DNA molecule using RNA polymerase (complimentary base pairing); only portions of the genome transcribed; remainder is noncoding DNA.

Transcription

Promoter region at the beginning of every gene signals transcription enzymes to begin copying gene; terminator DNA sequence at end signals transcription enzymes to fall off; single-stranded RNA transcript produced; non-protein-coding DNA fundamental to control of gene expression.

Translation

Chromosomes contain genes for building tRNA; acts as translator during translation; one end binds to mRNA, the other binds to a specific amino acid; there is at least one tRNA for each amino acid; each form of tRNA has a specific anticodon loop (sequence of three amino acids that recognize and pair with codon on mRNA); genes for rRNA are also transcribed in the nucleus; used to construct ribosomes (which act as workbenches and assist with the assembly of proteins during translation).

Genetic Code

mRNA transcripts code for proteins; the genetic code is based on codons (sequences of three nucleotides); 64 possible combinations that code for 20 amino acids; order of nucleotides on mRNA determines sequence of amino acids during translation.

The genetic code is universal - in bacteria, protists, fungi, plants, and animals.

mRNA and tRNA

Anticodon of tRNA binds to mRNA codon; start of translation signaled by a ribosome in the cytoplasm binding to mRNA; the codon AUG sets the reading frame.

The Central Dogma

The flow of information is unidirectional—from DNA to RNA to protein.

Mutations

Changes in the DNA sequence.

Mutagens - agents that alter the DNA sequence; UV light, ionizing radiation, certain chemicals

DNA repair enzymes often find and correct the damage.

Somatic mutations - occur in body cells

Germ-line mutations - occur in tissues that will produce sex cells; passed on to future generations

All genetic variability exists due to mutations.

Origins of Agriculture

Domestication of crop plants is a recent event in our history (of the 80 billion humans that have lived on this earth, only 6% were farmers); not entirely known why most humans switched from hunter-gathererer to farmer lifestyles; people began to domesticate plants around 10,000 years ago; domesticated plants were developed 1,000 to 3,000 years later; farming probably began around 4,000 years ago; systematic breeding of crop plants has only been carried out in the last 200 years.

Evolution Under Domestication

First domesticated crops were cereal grains, then root crops and legumes (1,000 to 2,000 years later), then plants used for forage, decoration, and drugs (2,000 years ago); modern plant breeders devote more energy to improving existing crops, rather than creating new ones; seed dispersal mechanism was likely the first trait altered during domestication (humans gathered seeds from plants that retained—rather than dropped—their seeds); early domesticators likely also focused on plants with high seed numbers, large seed size, high seedling vigor, and fast germination (lack of dormancy).

Plant breeding

Accelerated evolution guided by humans (rather than nature); breeders replace natural selection with human selection in order to modify plants genetically to meet our needs; typically, the primary goal of plant breeding is to improve yield (with disease resistance, pest resistance, and stress tolerance contributing to yield).

Crop Germplasm

Sum of all genes in the crop and its relatives; sexually-compatible germplasm can contribute new genes through crosses to the crop.

Self-Pollinating Crops and Breeding

Pants that are capable of fertilizing themselves; tend to be highly homozygous; have undergone significant amounts of inbreeding; most primitive form of breeding is called pure-line selection (involves collecting seeds from each of several plants, planting seeds from each plant all in a row, and selecting the most desirable row); more advanced breeders can make crosses between self-pollinating plants; most breeders today create hybrid populations by crossing desirable inbred parents (offpsring are highly diverse and provide the basis for selecting pure-line varieties); Norman Borlaug; example crops: wheat, rice, oats, barley, peas, beans, tomatoes, peppers, apricots, nectarines, peaches, and citrus.

Cross-Pollinating Crops and Breeding

Plants that are incapable of fertilizing themselves; simplest form of selection is mass selection (many plants from a population are selected, and seeds from these plants are used to create the next generation); outcrossing (crossing between genetically different plants) often results in hybrid vigor (heterosis) → plants are large, vigorous, fertile, and high yielding.

Breeders must be wary of inbreeding depression → self-pollination of cross-pollinating plants; results in plants that are small with poor vigor, low fertility, and high proportions of abnormality.

Heirloom Varieties

Open-pollinated populations of plants; each variety is a mixture of genotypes, and all plants are allowed to pollinate each other during seed production; plants are not as uniform, but their genetic variability allows them to produce a crop under many different environments.

Gene Banks

Progress in plant breeding is absolutely dependent on genetic variability; in order to meet current and future needs for plant genetic diversity, gene banks have been established worldwide (collect and conserve crop plant germplasm); plant samples are collected, where they are catalogued, propagated, and screened for desirable traits; some seeds are put into long-term storage for future needs, while others are given to plant breeders for immediate use.

Protoplast Fusion

A method of breeding using sexually-incompatible germplasm; the process of combining in vitro two protoplasts (of distantly-related plant species) into one cell; cells of each species are grown in a liquid nutrient solution, then their cell walls are chemically stripped off to produce protoplasts; the protoplasts of the two species are mixed together and stimulated; selected hybrids (somatic hybrids) are grown in a series of tissue events to produce a whole plant.

Gene Splicing and Transgenic Plants

Genes from virtually any organism (from viruses to humans) can now be inserted into plants—creating transgenic plants; a desirable gene is discovered in an organism’s genome (e.g., a bacterium); the bacterial chromosome is cut on both sides of the gene using a restriction enzyme, but not within the DNA sequence; the bacterial DNA and a cloning vector (a piece of DNA that can copy itself in a living cell) are cut using the same restriction enzyme; their sticky ends join together and create recombinant DNA; E. coli can be stimulated to take up the plasmid via transformation; as the E. coli replicates, each of the offspring contain the recombinant plasmid; the plasmids can then be removed and inserted into plants through transformative methods (such as through the infection of plants with Agrobacterium tumefaciens, which inserts its DNA [T-DNA] into the plant’s chromosomes); the particle gun method is used in monocots (in which DNA-coated particles are shot into a plant).

Transgenic Plants

Commonly insect-resistant; golden rice is a famous example (which contains genes for beta-carotene); also used in ornamental plants; transgenic plants can allow farmers to use fewer and less noxious chemicals for crop production; there is concern that resistance genes will make their way into the weed population (via hybrids); human health issues are also a major concern.

Seed Propagation

Hybrid varieties are often grown from the seed produced by crosses between two inbred parents; growing inbred plants is pretty easy (just allow them to self-pollinate); commercial seeds usually come from fields planted solely for seed production; seed quality depends on the health of the plants that produce it (growing conditions are meticulously monitored).

Crown Division

A method of vegetative propagation in which a plant is separated into several pieces (each of which contains a portion of the crown and root system); commonly used for many ornamental perennial plants; can be used to perpetuate a genotype indefinitely; avoids genetic variability and unpredictability that result from seed propagation.

Cuttings

Propagations of plant parts such as leaves or stems (stems must be coaxed into producing adventitious roots); formation of adventitious structures requires plant cells near the wound to dedifferentiate and create a new meristematic region; cuttings must be kept in an environment that will allow wound healing and the development of new organs; most critical step is the prevention of water loss; rooting can be stimulated with auxin.

Layering

A modified form of cutting propagation that allows adventitious roots to develop before the new plant part is severed from the parent plant.

Tip Layering - involves burying the tip of a flexible stem in the soil to induce the formation of adventitious roots; the rooted portion is then cut from the parent plant and grown separately; blackberries, boysenberries.

Air Layering - aerial stems are induced to form roots; a branch or main stem is wounded with a sterile knife or through girdling (removal of a ring of bark around the stem); damp sphagnum moss is wrapped around the wound, and the area is covered with clear plastic and aluminum foil; when roots are visible, the layer is removed from the parent plant and transplanted.

Grafting

The process by which segments of different plants are connected and induced to grow together as one plant; top part of the graft = scion; bottom part = rootstock; top of rootstock is cut diagonally inches above the soil; scion is also cut diagonally; scion and rootstock must be aligned so that their vascular cambiums are making good contact; held together with tape or string and often wax.

Propagation of Specialized Stems and Roots

Herbaceous perennials regrow from underground storage structures; bulbs, corms, tuberous roots, rhizomes → contain buds that will sprout in the spring.

Micropropagation

The propagation of plants in vitro in a sterile medium (agar, inorganic salts containing macro- and micro-nutrients, sucrose, vitamins, and growth regulators—all of which are sterilized in an autoclave) under highly controlled environmental factors; relies on the totipotency (the capacity of a cell to give rise to any structure of a mature organism) of plant cells; an explant is carried through three steps:

Establishment in tissue culture

Induction of multiple shoots (microshoots can be separated and placed in a new medium through subculturing)

Root formation (sometimes requires a rooting medium)

After all of the above, the plant is transferred back to an outdoor environment; this is difficult: in vitro plants do not produce as much wax as outdoor plants, and their stomata do not close as readily in response to water stress; they must be acclimitized.

Angiosperms

Flowering plants; come from the word angion, meaning “vessel,” and sperma, meaning “seed;” the vessel is the carpel; all angiosperms are presently considered to be in the Phylum Magnoliophyta; most diverse land plants; most scientists agree that flowers evolved to take advantage of motile animals in the reproduction process; most contemporary botanists point to anatomical, chemical, and fossil evidence that indicate angiosperms evolved independently from pteridosperms; it’s hypothesized that a flower is a modified stem bearing modified leaves; many hypothesize that all flowers came from the same primitive stock.

Bee Pollination

20,000 species of bees are included among the pollinators of present-day flowering plants; flowers that bees visit are generally brightly colored and mostly blue or yellow (bees can’t see red); flowers often have lines or other distinctive markings that function as honey guides that lead bees to the nectar; bees can see U.V. light; some markings are only visible via U.V. light; many bee-pollinated flowers are sweet and fragrant.

Pollinator Attraction

Many beetle-pollinated flowers are dull or white (they don’t have keen eyesight), secreting stronger, yeasty, spicy, or fruity odors; they may also furnish insects with pollen or food in special storage cells (as opposed to nectar).

Some flowers smell like rotten meat (carrion flowers) to attracted short-tongued flies.

Moth- and butterfly-pollinated flowers often have sweet fragrances and are usually red, blue, yellow, or orange; night-flying moths tend to visit flowers that are white or yellow (they stand out against the dark of the night).

Birds tend to visit flowers that are bright red or yellow and have little odor; bird-pollinated flowers are often large and contain large amounts of nectar (pollinating is busy work).

Bat-pollinated flowers tend to be open only at night and are typically dull and either large or contain ball-like inflorescences that contain large numbers of small flowers that dust the visitor with pollen.

Orchid Pollination

Highly diverse pollinator ecology; pollen grains of most orchids are produced in little sacs called pollinia that typically have sticky pads at the bases; these get “glued” to the head of the pollinator; members of Ophrys have a modified petal that resembles a female bumblebee or wasp; this attracts males, who try to…copulate…with the flowers; as they do so, pollinia are deposited on their heads; when they visit other flowers, the polinia catch in sticky stigma cavities; they then receive a new one; pollinia of of orchids pollinated by moths and butterflies are attached to their long tongues; some bog orchids blind their pollinators by attaching pollen to their eyes; bucket orchids.

Herbaria

A library of dried, pressed (and/or liquid-preserved) plants, fungi, or algae, typically mounted on paper and provided with a label that gives collection information and an identification; properly prepared and maintained specimens should remain in excellent condition for 300 or more years.

Fungi, Algae, and Bryophyte Preservation

Typically dried and stored in small boxes or packets; larger algae tend to have unique properties that lend themselves to special preservation (spreading out specimens and allowing them to adhere to blotting paper).

Plant Press

A simple device that consists of two pieces of plywood (or other wood/metal plates) and a pair of webbing or leather straps to go around the boards; a number of sheets of heavy blotting paper are placed between the boards; a folded page of newspaper is placed between each pair; any soil clinging to the roots of a specimen is washed off, and the plant is laid out on one of the newspaper sheets, straightened out, and the newspaper is folded over top; the press is then left in the sun or near a heater for 3-4 days; used to reduce moisture content as quickly as possible

Without the Press

Flowers can be dried in a shoebox covered with sand, silica gel, or borax mixture