Introduction to Modern Plant Biology

         Molecular biology is revolutionizing the study of plants
         Plant biology reflects the major themes in the study of life

    The Angiosperm Body

         A plant's root and shoot systems are evolutionary adaptations to living on
         land
         Structural adaptations of protoplasts and walls equip plant cells for their
         specialized functions
         The cells of a plant are organized into dermal, vascular, and ground tissue
         systems

    Plant Growth

         Meristems generate cells for new organs throughout the lifetime of a plant:
         an overview of plant growth
         Primary growth: Apical meristems extend roots and shoots by giving rise to
         the primary plant body
         Secondary growth: Lateral meristems add girth by producing secondary
         vascular tissue and periderm

Chapter  35
monocots (MON-oh-kot) - A subdivision of flowering plants whose members possess one embryonic seed leaf, or cotyledon.
dicots (DY-kot)- A subdivision of flowering plants whose members possess two embryonic seed leaves, or cotyledons.
root system- subterranean sytem
shoot system- The aerial portion of a plant body, consisting of stems, leaves, and  flowers.
xylem- (ZY-lum) The tube-shaped, nonliving portion of the vascular system in plants that carries water and minerals from the roots to the
            rest of the plant.
phleom- (FLOH-um) The portion of the vascular system in plants consisting of living cells arranged into elongated tubes that transport
            sugar and other organic nutrients throughout the plant.
taproot-system consisting of one large, vertical root (the taproot) that produces many smaller lateral roots
fibrous root-root systems consisting of a mat of threadlike roots that spread out below the soil surface; gives the plant extensive exposure to
            soil water and mineral and anchors it tenaciously to the ground.
root hairs- A tiny projection growing just behind the root tips of plants, increasing surface area for the absorption of water and minerals.
adventitious-(L. adventicius "not belonging to") a term that describes any plant part that growsin an unusual location.
stems-an alternating system of nodes
nodes- A point along the stem of a plant at which leaves are attached.
internodes- The segment of a plant stem between the points where leaves are attached.
axillary bud- (AKS-ill-air-ee) An embryonic shoot present in the angle formed by a leaf and stem.
terminal bud-at the apex (tip) of a young shoot
apical dominance- (AY-pik-ul) Concentration of growth at the tip of a plant shoot, where a terminal bud partially inhibits axillary bud growth.
leaves- The main site of photosynthesis in a plant; consists of a flattened blade and a stalk (petiole) that joins the leaf to the stem.
blade-flattened shape of most leaves
petiole- (PET-ee-ole) The stalk of a leaf, which joins the leaf to a node of the stem.
protoplast- The contents of a plant cell exclusive of the cell wall.
parenchyma cells (pur-EN-kim-uh) A relatively unspecialized plant cell type that carries most of the metabolism, synthesizes and stores organic
            products, and develops into more differentiated cell types.
collenchyma cells- (koal-EN-keh-muh) A flexible plant cell type that occurs in strands or cylinders that support young parts of the plant
            without restraining growth.
sclerenchyma- (skler-EN-kim-uh) A rigid,supportive plant cell type usually lacking protoplasts andpossessing thick secondary walls
            strengthened by lignin at maturity.
fibers-one form of sclerenchyma; A lignified cell type that reinforces the xylem of angiosperms and functions in mechanical support; a slender,
            tapered sclerenchyma cell that usually occurs in bundles.
sclereids-form of sclerenchyma cell; shorter than fibers and irregular in shape.
tracheids-elongated cell that is one type of water conducting element of xylem
vessel elements- A specialized short, wide cell in angiosperms; arranged end to end, they form continuous tubes for water transport.
pits-interupt tracheids and vessel elements that have secondary walls and are no longer elongating
seive-tube members- A chain of living cells that form sieve tubes in phloem.
sieve plates-the end walls between sieve-tube members
companion cell- A type of plant cell that is connected to a sieve-tube member by many plasmodesmata and whose nucleus and ribosomes may
            serve one or more adjacent sieve-tube members.
dermal tissue system (epidermis)-is generally a single layer of tightly packed cells that covers and protects all young parts of the plant
cuticle- (KYOO-teh-kul) (1) A waxy covering on the surface of stems and leaves that acts as an adaptation to prevent desiccation in terrestrial
                                                  plants.
                                            (2) The exoskeleton of an arthropod, consisting of layers of protein and chitin that are variously modified for different
                                                  functions.
annuals- A plant that completes its entire life cycle in a single year or growing season.
perennials- (pur-EN-ee-ul) A plant that lives for many years.
meristems- (MARE-eh-stem) Plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth.
apical meristems- (AY-pik-ul MARE-eh-stem) Embryonic plant tissue in the tips of roots and in the buds of shoots that supplies cells for the
            plant to grow in length.
primary growth-enables roots to ramify throughout the soil and shoots to increase their exposure to light and carbon dioxide
secondary growth- The increase in girth of the stems and roots of many plants, especially woody, perennial dicots.
lateral meristems- (MARE-eh-stem) The vascular and cork cambium, a cylinder of dividing cells that runs most of the length of stems and
            roots and is responsible for secondary growth.
primary plant body-is produced by primary growth and consists of three tissue systems, dermal, vascular, and ground tissues
root cap- A cone of cells at the tip of a plant root that protects the apical meristem.
zone of cell division-includes the apical meristem and its derivatives, called primary meristems
quiescent center- A region located within the zone of cell division in plant roots, containing meristematic cells that divide very slowly.
protoderm- (PRO-toh-durm) The outermost primary meristem, which gives rise to the epidermis of roots and shoots.
procambium- (pro-KAM-bee-um) A primary meristem of roots and shoots that forms the vascular tissue.
ground meristem- A primary meristem that gives rise to ground tissue in plants.
zone of elongation-here the cells elongate to more than ten times their length.
zone of maturation-the cells of the root begin to specialize in structure and function, and the three tissue systems produced by primary growth
            complete their differentiation.
stele- The central vascular cylinder in roots where xylem and phloem are located.
pith- The core of the central vascular cylinder of monocot roots, consisting of parenchyma cells, which are ringed by vascular tissue; ground
            tissue interior to vascular bundles in dicot stems.
cortex- The region of the root between the stele and epidermis filled with ground tissue.
endodermis- (EN-doh-DUR-mis) The innermost layer of the cortex in plant roots; a cylinder one cell thick that forms the boundary between the
            cortex and the stele.
lateral roots-Sprouted by an established root and arise from the outermost layer of the stele.
pericycle- (PAIR-eh-sy-kul) A layer of cells just inside the endodermis of a root that may become meristematic and begin dividing again.
vascular bundles-vascular tissue that runs through the length of the stem in several bundles.
stoma- (plural, stomata) A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between
            the environment and the interior of the plant.
guard cells- A specialized epidermal plant cell that forms the boundaries of the stomata.
transpiration- The evaporative loss of water from a plant.
mesophyll- (MEZ-oh-fil) The ground tissue of a leaf, sandwiched between the upper and lower epidermis and specialized for photosynthesis.
phase changes-when the apical meristem changes from one developmental phase to another during its history.
secondary plant body-the tissues produced in diameter during secondary growth.
vascular cambium-produces secondary xylem (wood) and phloem
cork cambium- (KAM-bee-um) A cylinder of meristematic tissue in plants that produces cork cells to replace the epidermis during secondary
            growth.
vascular tissue- Plant tissue consisting of cells joined into tubes that transport water and nutrients throughout the plant body.
ray initials-cambium cells that produce radial files of parenchyma cells known as xylem rays and phloem rays
fusiform initials-are the cambium cells within the vascular bundles.
periderm-(PAIR-eh-durm) The protective coat that replaces the epidermis in plants during secondary growth, formed of the cork and cork
            cambium.
bark- All tissues external to the vascular cambium in a plant growing in thickness, consisting of phloem, phelloderm, cork cambium, and cork.
lenticels-spongy regions in the bark that make it possible for living cells within the trunk to exhange gases with the outside air for cellular
            respiration.

    An Overview of Transport Mechanisms in Plants

         Transport at the cellular level depends on the selective permeability of
         membranes
         Proton pumps play a central role in transport across plant membranes
         Differences in water potential drive water transport in plant cells
         Vacuolated plant cells have three major compartments
         The symplast and apoplast both function in transport within tissues and
         organs
         Bulk flow functions in long-distance transport

    Absorption of Water and Minerals by Roots

         Root hairs, mycorrhizae, and a large surface area of cortical cells enhance
         water and mineral absorption
         The endodermis functions as a selective sentry between the root cortex and
         vascular tissue

    Transport of Xylem Sap

         The ascent of xylem sap depends mainly on transpiration and the physical
         properties of water
         Xylem sap ascends by solar-powered bulk flow: a review

    The Control of Transpiration

         Guard cells mediate the photosynthesis-transpiration compromise
         Xerophytes have adaptations that reduce transpiration

    Translocation of Phloem Sap

         Phloem translocates its sap from sugar sources to sugar sinks
         Pressure flow is the mechanism of translocation in angiosperms
 

Chapter  36
transport proteins-embedded in a membrane, allowing solutes to pass through more quickly.
selective channels-selective passageways across a membrane.
proton pump- (PRO-tahn) An active transport mechanism in cell membranes that consumes ATP to force hydrogen ions out of a cell and, in the
            process, generates a membrane potential.
cotransport- The coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration
            gradient.
chemiosmosis- (KEM-ee-oz-MOH-sis) The production of ATP using the energy of hydrogen-ion gradients across membranes to
            phosphorylate ADP; powers most ATP synthesis in cells.
osmosis- (oz-MOH-sis) The diffusion of water across a selectively permeable membrane.
water potential- The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure.
megapascals- (MPa) (MEG-uh-pass-KAL) A unit of pressure equivalent to 10 atmospheres of pressure.
tension-negative pressure.
plasmolyze-shrink and pull away form cell wall.
turgor pressure- The force directed against a cell wall after the influx of water and the swelling of a walled cell due to osmosis.
turgid- (TUR-jid) Firm; walled cells become turgid as a result of the entry of water from a hypotonic environment.
aquaporins- channel that are water specific transport proteins that don't actively transport water but facilitate water diffusion (osmosis).
tonoplast- A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the cell sap.
symplast- In plants, the continuum of cytoplasm connected by plasmodesmata between cells.
apoplast- (AP-oh-plast) In plants, the nonliving continuum formed by the extracellular pathway provided by the continuous matrix of cell walls.
bulk flow- The movement of water due to a difference in pressure between two locations.
mycorrhizae- (MY-koh-RY-zee) Mutualistic associations of plant roots and fungi.
endodermis- (EN-doh-DUR-mis) The innermost layer of the cortex in plant roots; a cylinder one cell thick that forms the boundary between the
            cortex and the stele.
Casparian strip- (kas-PAR-ee-un) A water-impermeable ring of wax around endodermal cells in plants that blocks the passive flow of water and
            solutes into the stele by way of cell walls.
transpiration-the loss of water vapor from leaves and other aerial parts of the plant.
root pressure-upward push of xylem sap.
guttation-the exudation of water droplets that can be seen in the moringin on tips of grass blades or the leaf margin of some small, herbaceous
            (non-woody) dicots.
transpiration pull-a combination of two forces acting on water in the plant: adhesion to the wall and surface tension.  These cause the water
            film to form a meniscus, and in a sense being pulled by the adhesive and cohesive forces.
cohesion- The binding together of like molecules, often by hydrogen bonds.
adhesion- The tendency of different kinds of molecules to stick together.
transpiration-to-photosynthesis ratio-the amount of water lonst per gram of CO2 assimilated into organic material by photosynthesis.
circadian rhythms- (sur-KAY-dee-un) A physiological cycle of about 24 hours, present in all eukaryotic organisms, that persists even in the
            absence of external cues.
translocation -(1) An aberration in chromosome structure resulting from an error in meiosis or from mutagens;attachment of a chromosomal
            fragment to a nonhomologous chromosome.
                          (2) During protein synthesis, the third stage in the elongation cycle when the RNA carrying the growing polypeptide moves
            from the A site to the P site on the ribosome.
                          (3) The transport via phloem of food in a plant.
sugar source-is a plant organ in which sugar is being produced by either photosynteesis or the breakdown of starch.
sugar sink-is an organ that consumes or stores sugar.
transfer cells-ingrowths on the walls of companion cells that increases the cells' surface area and enhances the transfer of solutes between
            apoplast and symplast.

    Nutritional Requirements of Plants

         The chemical composition of plants provides clues to nutritional
         requirements
         Plants require nine macronutrients and at least eight micronutrients
         The symptoms of a mineral deficiency depend on the function and mobility
         of the element

    The Role of Soil in Plant Nutrition

         Soil characteristics are key environmental factors in terrestrial ecosystems
         Soil conservation is one step toward sustainable agriculture

    The Special Case of Nitrogen as a Plant Nutrient

         The metabolism of soil bacteria makes nitrogen available to plants
         Improving the protein yield of crops is a major goal of agricultural research

    Nutritional Adaptations: Symbiosis of Plants and Soil Microbes

         Symbiotic nitrogen fixation results from intricate interactions between roots
         and bacteria
         Mycorrhizae are symbiotic associations of roots and fungi that enhance
         plant nutrition
         Mycorrhizae and root nodules may have an evolutionary relationship

    Nutritional Adaptations: Parasitism and Predation by Plants

         Parasitic plants extract nutrients from other plants
         Carnivorous plants supplement their mineral nutrition by digesting animals
 
 
 

Chapter  37
mineral nutrients- In nutrition, one of many chemical elements, other than carbon, hydrogen, oxygen, and nitrogen, that an organism requires
            for proper body functioning.
essential nutrient-a nutrient required for a plant to grow from a seed and complete the life cycle, producing another generation of seeds.
macronutrients-elements required by plants in relatively large amounts.
micronutrients- elements that plants need in very small amounts.
topsoil-a mixture of particles derived from rock, living organisms, and humus, a residue of partially decayed organic material.
horizons-topsoil and/or other distinct soil layers.
loams-usually the most fertile soilsmade up of roughtly equal amounts of sand, silt (particles of intermediate size), and clay.
humus-
cation exchange- A process in which positively charged minerals are made available to a plant when hydrogen ions in the soil mineral displace
                  ions from the clay particles.
sustainable agriculture-using a variety of farming methods that are environmentally safe and profitable.
nitrogen-fixing bacteria-restock nitrogenous minerals in the soil by converting N2 to NH3 (ammonia,.
nitrogen fixation-the process of converting nitrogen into ammonia.
nitrogenase- (nih-TRAH-juh-nayz) An enzyme, unique to certain prokaryotes, that reduces N2 to NH3.
nodules-swellings on roots of legumes that are composed of plant cells that contain nitrogen-fixing bacteria (genus Rhizobium "root living").
bacteroids-the form of Rhizobium inside the nodules
Mycorrhizae- (MY-koh-RY-zee) Mutualistic associations of plant roots and fungi.
ectomycorrhizae-one of the two major forms of modified roots formed from symbiosis of fungi and plants; the mycelium forms a dense sheath,
            or mantle, over the surface of the root.
 
 

    Sexual Reproduction

         Sporophyte and gametophyte generations alternate in the life cycles of
         plants: a review
         Male and female gametophytes develop within a flower's anthers and
         ovaries, respectively
         Pollination brings male and female gametophytes together
         Researchers are unraveling the molecular mechanisms of
         self-incompatibility
         Double fertilization gives rise to the zygote and endosperm
         The ovule develops into a seed containing an embryo and a supply of
         nutrients
         The ovary develops into a fruit adapted for seed dispersal
         Evolutionary adaptations of seed germination contribute to seedling survival

    Asexual Reproduction

         Many plants can clone themselves by asexual reproduction
         Vegetative propagation of plants is common in agriculture
         Sexual and asexual reproduction are complementary in the life histories of
         many plants: a review

    Cellular Mechanisms of Plant Development

         Growth, morphogenesis, and differentiation produce the plant body: an
         overview of plant development
         The cytoskeleton guides the geometry of cell division and expansion
         Cellular differentiation depends on the control of gene expression
         Pattern formation determines the location and tissue organization of plant
         organs
 

Chapter  38
alternation of generations- A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the
            gametophyte; characteristic of plants.
sporophyte- The multicellular diploid form in organisms undergoing alternation of generations that results from a union of gametes and that
            meiotically produces haploid spores that grow into the gametophyte generation.
gametophytes- (guh-MEE-toh-fite) The multicellular haploid form in organisms undergoing alternation of generations, which mitotically
            produces haploid gametes that unite and grow into the sporophyte generation.
sepals- (SEE-pul) A whorl of modified leaves in angiosperms that encloses and protects the flower bud before it opens.
petals-floral organ.
stamens- The pollen-producing male reproductive organ of a flower, consisting of an anther and filament.
carpels- (KAR-pel) The female reproductive organ of a flower, consisting of the stigma, style, and ovary.
ovules- (OV-yool) A structure that develops in the plant ovary and contains the female gametophyte.
complete flowers- A flower that has sepals, petals, stamens, and carpels.
incomplete flowers- A flower lacking sepals, petals, stamens, or carpels.
perfect flowers-a flower equipped with both stamens and carpels.
imperfect flowers-incomplete flowers missing either stamens or carpels.
monoecious- (mon-EE-shus) Referring to a plant species that has both staminate and carpellate flowers on the same individual.
dioecious- (dy-EE-shus) Referring to a plant species that has staminate and carpellate flowers on separate plants.
microspores-haploid cells resulting from microsporocyte meiosis.
megaspores-haploid cells resulting from megasporocyte meiosis.
embryo sac- The female gametophyte of angiosperms, formed from the growth and division of the megaspore into a multicellular structure with
            eight haploid nuclei.
pollination (POL-eh-NAY-shun) The placement of pollen onto the stigma of a carpel by wind or animal carriers, a prerequisite to fertilization.
self-incompatible-if a pollen grain from an anther happens to land on a stigma of a flower on the same plant, a biochemical block prevents the
            the pollen from completing its development and fertilizing an egg.
endosperm-a food storing tissue.
double fertilization- A mechanism of fertilization in angiosperms, in which two sperm cells unite with two cells in the embryo sac to form the
            zygote and endosperm.
seed coat-encloses an embryo and its food supply, fromed from the integuments of the ovule, the progenitor of the seed.
hypocotyl-the embryonic axis below the point at which the cotyledons are attached.
radicle- An embryonic root of a plant.
epicotyl-the portion of the embryonic axis abouve the cotyledons
scutellum-specialized type of cotyledon that is very thin with a large surface area pressed against the endosperm, where the scutellum absorbs
            nutrients during germination.
coleorhiza-substance that makes a sheath to cover the root.
coleoptile-cloaks the embryonic shoot.
fruit-A mature ovary of a flower that protects dormant seeds and aids in their dispersal.
pericarp-thickened wall of the fruit formed from the wall of the ovary.
simple fruit-fruit derived from a single ovary.
aggregate fruit-results from a single flower that has several carpels, like a blackberry.
multiple fruit-develops from an inflorescence, a group of flowers thightly clustered together, like a pineapple.
inhibition-the absorption of water due to the low water potential of the dry seed.
vegetative reproduction- Cloning of plants by asexual means.
fragmentation-the separation of a parent plant into parts that re-form whole plants. One of the most common modes of vegetative reproduction.
apomixis-asexual production of seeds.
callus-undifferentiated cells.
stock-the plant that provides the root system.
scion-the twig grafted onto the stock.
protoplast fusion-is a technique, being coupled with tissue culture methods to actually invent new plant varities that can be cloned.
monoculture- Cultivation of large land areas with a single plant variety.
development-the sum of all changes that progressively elaborate an organism's body.
growth-an irreversible increase in size resulting from cell division and cell enlargement.
morphogenesis-accompanies growth, and is the development of form.
cellular differentiation- The structural and functional divergence of cells as they become specialized during a multicellular organism's
            development; dependent on the control of gene expression.
preprophase band- The ordering of cells into specific three-dimensional structures, an essential part of shaping an organism and its individual
            parts during development.
positional information- Signals, to which genes regulating development respond, indicating a cell's location relative to other cells in an
            embryonic structure.
meristem identity genes-the transition from vegetative growth to flowering is associated with the swithing of these floral genes.
organ-identity genes- A plant gene in which a mutation causes a floral organ to develop in the wrong location.
 
 

    Plant Hormones

         Research on how plants grow toward light led to the discovery of plant
         hormones: science as a process
         Plant hormones help coordinate growth, development, and responses to
         environmental stimuli
         Analysis of mutant plants is extending the list of hormones and their
         functions
         Signal-transduction pathways link cellular responses to plant hormonal
         signals and environmental stimuli

    Plant Movements as Models for Studying Control Systems

         Tropisms orient the growth of plant organs toward or away from stimuli
         Turgor movements are relatively rapid, reversible plant responses

    Control of Daily and Seasonal Responses

         Biological clocks control circadian rhythms in plants and other eukaryotes
         Photoperiodism synchronizes many plant responses to changes of season

    Phytochromes

         Phytochromes function as photoreceptors in many plant responses to light
         and photoperiod
         Phytochromes may entrain the biological clock

    Plant Responses to Environmental Stress

         Plants cope with environmental stress through a combination of
         developmental and physiological responses

    Defense Against Pathogens

         Resistance to disease depends on a gene-for-gene recognition between
         plant and pathogen
         The hypersensitive response (HR) contains an infection
         Systemic acquired resistance (SAR) helps prevent infection throughout the
         plant

Chapter  39
hormones-chemical signals that coordinate the parts of the organism.
phototrophism-the growth of a shoot towards light.
auxins- (AWK-sins) A class of plant hormones, including indoleacetic acid (IAA), having a variety of effects, such as phototropic response
            through the stimulation of cell elongation, stimulation of secondary growth, and the development of leaf traces and fruit.
cytokinins- (SY-toh-KY-nin) A class of related plant hormones that retard aging and act in concert with auxins to stimulate cell division,
            influence the pathway of differentiation, and control apical dominance.
apical dominance- (AY-pik-ul) Concentration of growth at the tip of a plant shoot, where a terminal bud partially inhibits axillary bud growth.
gibberellin- (JIB-ur-EL-ins) A class of related plant hormones that stimulate growth in the stem and leaves, trigger the germination of seeds
            and breaking of bud dormancy, and stimulate fruit development with auxin.
abscisic acid- (ABA) (ab-SIS-ik) A plant hormone that generally acts to inhibit growth, promote dormancy, and help the plant tolerate stressful
            conditions.
ethylene- (ETH-ul-een) The only gaseous plant hormone, responsible for fruit ripening, growth inhibition, leaf abscission, and aging.
senescence-progression of irreversible change that eventually leads to death.
Oligosaccharins-short chains of sugars released from cell walls by the hydrolytic action of enzymes on cellulose and pectin.
Brassinosteroids-steroids chemically similar to cholesterol and the sex hormones of animals that are named for their struture.
tropisms- A growth response that results in the curvature of whole plant organs toward or away from stimuli due to differential rates of cell
            elongation.
gravitropism- (GRAV-eh-TROH-piz-um) A response of a plant or animal in relation to gravity.
statoliths-specialized plastids containing dense starch grains.
thigmotropism- (THIG-moh-TROH-piz-um) The directional growth of a plant in relation to touch.
thigmomorphogenesis- A response in plants to chronic mechanical stimulation, resulting from increased ethylene production; an example is
            thickening stems in response to strong winds.
action potentials- A rapid change in the membrane potential of an excitable cell, caused by stimulus-triggered, selective opening and closing of
            voltage-sensitive gates in sodium and potassium ion channels.
sleep movements-lowered leaves in the evening and raised leaves in the morning, are powered by daily changes in the turgor pressure.
circadian rhythm-a physiological cycle witha frequency af about 24 hours
photoperiodism- (FOH-toh-PEER-ee-od-iz-um) A physiological response to day length, such as flowering in plants.
short-day plant- A plant that flowers, usually in late summer, fall, or winter, only when the light period is shorter than a critical length.
long-day plants- A plant that flowers, usually in late spring or early summer, only when the light period is longer than a critical length.
day-neutral plants- A plant whose flowering is notaffected by photoperiod.
phytochromes- (FY-tuh-krome) A pigment involved in many responses of plants to light.
heat-shock proteins- A protein that helps protect other proteins during heat stress, found in plants, animals, and microorganisms.
gene-for-gene recognition-scientific resistance to disease, which requires precise match-pu between an allele in the plant and an allele in the
            pathogen.
phytoalexins-antimicrobial compounds.
PR proteins-are produced by genes that are activated by infections.
hypersensitive response- (HR)
systemic aquired resisance- (SAR) (SAR) A defensive response in infected plants that helps protect healthy tissue from pathogenic invasion.