Applied physiology of horticultural crops

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<ul><li> 1. 1HORT 604APPLIED PHYSIOLOGY OFHORTICULTURAL CROPSDavid Wm. ReedDepartment of Horticultural SciencesTexas A&amp;M University Colegio de Postgraduados Campus MontecilloSummer 2007 David Wm. Reed, Texas A&amp;M University</li></ul><p> 2. 1Table of ContentsTopicsPagePlant Anatomy and Morphology2Hormones and Elicitor Molelules15The Genetic Basis of Life24Genetically Modified Organisms (GMOs) or Transgenic Crops30Seed Germination, Dormancy and Priming 33Growth Kinetics38Source Sink Relations44Senescence and Post Harvest Storage50David Wm. Reed, Texas A&amp;M University 3. 2 Plant Anatomy and MorphologyA horticulturist who does not know the basic anatomy of plants is like is like a nurse that doesnot know basic human anatomy. It could turn out to be down right uncomfortable where he/shesticks that thermometer! So we are going to take a tour of plant structure. A working knowledgeof plant anatomy is absolutely essential in:plant propagation: grafting, budding, division, cuttings, layering, tissue culturepruningmaking crosses in plant breedingdiagnosing plant disordersAnatomy is very simply. Anatomists simply look at the outside and inside of plants and whenthey see distinctive structures they give them a name. At the whole plant level, plants aredivided into four organs: The root, stem and leaf are vegetative organs, and the flower, andresultant fruit, is a reproductive organ.Plant OrgansrootstemleafflowerEach organ is composed of three tissue systems:Tissue Systems dermal tissue system vascular tissue system ground or fundamental tissue systemEach tissue system is composed of distinctive tissues (epidermis, periderm, xylem, phloem,cortex, pith and mesophyll), and tissues are in-turn composed of cells (parenchyma,collenchyma, sclerenchyma, and specialized cells such as trichomes, vessels, companion cells,laticifers, etc.).Plants produce all these structures by growing from discrete clusters of dividing cells calledmeristems. Herbaceous tissue is growth in length from: 1) apical meristems, which occur atthe end of every shoot and root, and 2) intercalary meristem at the base of grass leaves. Woodytissue is due to growth in diameter from: 1) vascular cambium, which produce secondaryxylem (wood) and phloem, and 2) phellogen, which produces the periderm (bark).Virtually all of the crops we grow in horticulture are monocots (linear leaves, ex. grasses, corn,dracaena, and palm), dicots (broad-leaved plants, ex. oak, lettuce, apple) or gymnosperms(leaves as needles and scales, ex. pine, juniper). The internal anatomy of monocots, dicots andgymnosperms are sometimes similar and sometimes different. Different types of plants are notlike animals - all the tissues and organs are not always in the same location. Thus, one mustknow the basic anatomical similarities and differences of each, or else you are not going to knowwhere to insert that thermometer - ouch! David Wm. Reed, Texas A&amp;M University 4. 3 ORGANS AND TISSUE SYSTEMSPlants are composed of 3 vegetative organs and 1 reproductive organ.Three tissue systems comprise each organ and are contiguous between each of the four organs. David Wm. Reed, Texas A&amp;M University 5. 4 HOW DO PLANTS GROW? Meristems and GrowthPrimary Growth - growth in length that gives rise to primary (herbaceous) tissues called the primary plant body. 2 -Types apical meristem or apex - the growing points located at the tips of stems and roots intercalary meristem -the growth region at the base of grass leaves which causes leaves to elongate.Secondary Growth - growth in width or diameter which gives rise to secondary (woody or corky) tissues called the secondary plant body. lateral meristem - meristematic regions along the sides of stems and roots. 2 Types vascular cambium or cambium - gives rise to secondary xylem (wood) on the inside and phloem on the outside. cork cambium or phellogen -gives rise to the periderm (bark). David Wm. Reed, Texas A&amp;M University 6. 5 STEM ANATOMYHerbaceous Dicot or Gymnosperm - Primary Growth(Fig. 16.1 from Esau 1960)David Wm. Reed, Texas A&amp;M University 7. 6STEM ANATOMYWoody Dicot or Gymnosperm - Secondary Growth (Plate 28 from Esau 1965)David Wm. Reed, Texas A&amp;M University 8. 7 STEM ANATOMYHerbaceous Monocot - Primary Growth(Plate 58 from Esau 1965, Fig. 17.8 from Esau 1960)David Wm. Reed, Texas A&amp;M University 9. 8 ROOT ANATOMYHerbaceous Dicot, Gymnosperm or Monocot - Primary Growth(Plate 84 &amp; 86 from Esau 1965)David Wm. Reed, Texas A&amp;M University 10. 9ROOT ANATOMY Woody Dicot or Gymnosperm - Secondary GrowthA woody dicot or gymnosperm root in secondary growth looks very similar to a stem insecondary growth. The tissue is more porous and less dense, and the periderm is thinner. Ringsof xylem growth may not be as distinctive as occurs in stems. This is because roots of temperateplants do not posses a distinctive rest or physiological dormancy period during the winter asdo buds and shoots. Root growth may occur whenever the soil moisture, fertility andtemperature are favorable. (Fig.15.4 from Esau 1960)David Wm. Reed, Texas A&amp;M University 11. 10 LEAF ANATOMY Dicot(Plate 73 from Esau 1965)Monocot(Similar to dicot, except no palisade, mesophyll is all spongy parenchyma) (Fig. 19.6 from Esau 1960) David Wm. Reed, Texas A&amp;M University 12. 11LEAF ANATOMYGymnosperm(Plate 78 from Esau 1965) David Wm. Reed, Texas A&amp;M University 13. 12 SUMMARY OF ANATOMY VEGETATIVE STRUCTURESMONOCOTDICOTGYMNOSPERMPRIMARY (herbaceous)GROWTHSTEM SECONDARYnone (woody)GROWTHPRIMARY (herbaceous)GROWTHROOT SECONDARY (woody)noneGROWTHPRIMARY (herbaceous)GROWTHLEAF SECONDARY (woody)none none noneGROWTH David Wm. Reed, Texas A&amp;M University 14. 13 FLOWER STRUCTURE FRUIT STRUCTUREExample of a dry fruit Example of a fleshy fruitSEED STRUCTUREDavid Wm. Reed, Texas A&amp;M University 15. 14 Anatomical Structure and Function"Structure and function" is a term used when the anatomy of a plant part explains how itfunctions. Structure and function brings anatomy to the real world, and it is what makes anatomyexciting. We are going to take a close look at one of the most important structure functionrelationships in plants - translocation. The tissues responsible for long distance translocation inplants are xylem and phloem.Xylem is composed dead, hollow cells with perforated walls. The xylem cells are called vesselelements or tracheids. . They are connected end to end and clustered side by side. They are likea cluster of leaky pipes with holes on all sides. If you took sewer drain field pipe and connectedthem end to end, and bundled many of them together side by side, you would have a perfectmodel of xylem. Xylem only flows up. All xylem is dead and the water is "passively" pulled upstems by transpiration of water from the leaves. It is like sucking water up a straw. In youngtissue, these bundles of xylem cells occur inside the vascular bundles, which are the stringytissue in herbaceous tissue (ex. veins in leaves). In woody plants, xylem is the wood. Thesapwood is functional because the hollow xylem cells are open and water easily flows up thetubes. All the water flows up the sapwood. The heartwood is old clogged xylem, and does nottranslocate water, and thus is not functional. The heartwood is clogged with resins and tanninsand this makes the heartwood both waterproof and prevents it from rotting.Phloem is composed of specialized cells that remain alive and "actively" translocate solutes(salts, sugars, metabolites, hormones, etc.) around plants. The phloem tissue is veryconcentrated in sugars, amino acids, and many nutrients. It is the phloem that sucking insect,such as aphids, puncture in order to feed on the sugar and nutrients... This is similar to amosquito piercing your veins and arteries as a food source.Phloem flows both up and down and all around. It is commonly stated that phloem flows down,but this is wrong. Phloem flows to where it is needed. Phloem flows from sources to sinks,which will be discussed next. David Wm. Reed, Texas A&amp;M University 16. 15HORMONES AND ELICITOR MOLECULESHormone - an endogenous or naturally-occurring compound that is produced orsynthesized in one part of the plant and causes a change in physiology,growth or development in another part of the plant; usually present in verysmall quantities.Elicitor Molecule - a compound which, when introduced in small concentrations to a livingcell system, initiates or improves the biosynthesis of specific compounds;a compound with hormone-like activity.Growth Substance - all naturally-occurring or synthetically produced compounds that affect the physiology, growth and development of plants.ReferencesMoore, T.C. 1979. Biochemistry and Physiology of Plant Hormones. Springer-Verlag, NY.Plant Hormones and Elicitor MoleculesClassically, plants have been known to contain five hormones, which are auxin, cytokinin,gibberellic acid, ethylene and abscisic acid. Recently, other endogenous compounds have beenshown to elicit hormone-like reactions, which are brassinosteroids, jasmonic acid, salicylic acidand polyamines. Some do not elevate these to the status of one of the five classical hormones, sooften they are called elicitor molecules.1) Auxin2) Cytokinin3) Gibberellic Acid4) Ethylene5) Abscisic Acid6) Brassinosteroid7) Jasmonic Acid8) Salicylic Acid9) PolyaminesDavid Wm. Reed, Texas A&amp;M University 17. 16AUXIN Naturally-SyntheticStructure Site of OccurringProduction indolebutyric acid (IBA) indoleacetic acidnaphthaleneacetic acidshoot tips, (IAA) (NAA) embryos2,4-dichlorophenoxy-aceticacid (2,4-D)SYNTHESIStryptophan indoleacetic acidTRANSPORT 3:1 basipetal transport primarily in phloem parenchymaEFFECTS1) Cell elongation - causes acid induced cell wall growth2) Cell division - stimulates3) Tropism - response of plants to environmental or physical stimuli. a) phototropism - response to light b) geotropism - response to gravity c) thigmotropism - response to touch4) Apical dominance - determined by correlative inhibition of apical bud, partly due to auxin produced5) Sprout Inhibitors retard basal branching.6) Branch angle - causes wide branch angles7) Fruit set - low concentrations stimulate8) Fruit or flower thinning - high concentrations cause9) Herbicides - 2,4-D at high concentrations10) Adventitious root formation - a) stem and leaf cuttingsb) tissue cultureDavid Wm. Reed, Texas A&amp;M University 18. 17CYTOKININNaturally-SyntheticStructureSite ofOccurring Production benzyladenine (BA)zeatin root tips,pyranylbenzyladeninekinetin (not in plants)embryos(PBA)SYNTHESISadenine zeatinTRANSPORTxylem transported, found in root exudatesprimarily acropetal, but not necessarily polarEFFECTS1) Cell division - stimulates cell division; named after cytokinesis2) Nutrient mobilization - nutrients transported towards high cytokinin concentration.3) Apical dominance - high cytokinin/low auxin may overcome apical dominance4) Chlorophyll breakdown - decreases chlorophyll breakdown5) Leaf Aging or abscission - may delay6) Seed germination - may overcome dormancy or stimulate germination7) Adventitious shoot formation - a) leaf and root cuttingsb) tissue culture8) Root growth - may be inhibitory to root growth David Wm. Reed, Texas A&amp;M University 19. 18 GIBBERELLIC ACID (GA) Naturally- Synthetic StructureSite of Occurring Productionshoot tips, over 50 root tips, (named bynone embryos consecutive numbers)SYNTHESIS (see next page) mevalonate farnesyl pyrophosphate geranylgeranyl pyrophosphate copalyl pyrophosphate kaurene GAgrowth retardants - chemicals that block synthesis of GA; most block the ring closure stepsbetween geranylgeranyl pryophosphate copalyl pyrophosphate kaurene.TRANSPORT no polarity in phloem or xylemEFFECTS1) Protein synthesis - triggers de novo synthesis of some proteins, ex. -amylase.2) Cell elongation - primary stimulus for cell elongation3) Rosette or dwarf plants - lack of endogenous GA often contributes to decreased height.4) Height control GA used to increase height growth retardants used to decrease height5) Flowering - may cause bolting in biennials6) Fruit size - increases size of seedless grapes7) Bud dormancy - may overcome and substitute for cold treatment8) Seed germination - may increase or speed up9) Sex expression - favors staminate flower formation on monoecious plantsDavid Wm. Reed, Texas A&amp;M University 20. 19Biosynthetic Pathway of Gibberellic Acid (from Moore, 1979)Mode of Action of Growth Retardants block ring closure between geranylgeranyl pyrophosphate and copalyl pyrophosphate block ring closure between copalyl pyrophosphate and kaureneDavid Wm. Reed, Texas A&amp;M University 21. 20 ETHYLENE Naturally- SyntheticStructureSite of OccurringProductionethephon or ripening fruits, ethylene ethrel aging flowers, (release ethylenegerminatinginside plant)seeds,wounded tissueSYNTHESISmethionine s-adenosylmethionine 1-aminocyclopropane-1-carboxylic acid ethylene(SAM)(ACC)ETHYLENE INHIBITORSethylene inhibitors - chemicals that inhibit the synthesis or action of ethyleneSynthesis Inhibitors (block synthesis of SAM ACC) AVG - aminoethoxyvinyl glycine MVG - methoxyvinyl glycine AOA - aminoacetic acidAction Blockers (ethylene block action) STS - silver thiosulfate CO2 - carbon dioxide Ni - nickel Co cobalt MCP 1-mehtylcyclopropane o it is a gas that can saturate the receptor sites, and block action for several days o EthylBloc commercial compoundTRANSPORT diffusion as a gas throughout plant (in and out)David Wm. Reed, Texas A&amp;M University 22. 21EFFECTS1) Auxin transport - alters basipetal transport2) Membrane permeability - increases3) Respiration - increases4) Cell elongation decreases5) Aerenchyma formation induces aerenchyma formation under anaerobic or hypoxic conditions (i.e. under low oxygen or flooded conditions)6) Fruit ripening - stimulates in many fruits, ex. banana7) Flowering - triggers flowering in some bromeliads, ex. pineapple8) Flower fading - increases9) Flower longevity - causes senescence (death) of cut flowers10) Fruit color - decreases green, increases other colors11) Seed germination - increases in some seeds12) Leaf abscission (leaf drop) - causes in some plants13) Leaf epinasty (curling and contortion or leaves) - causes in some plants14) Sex expression - favors pistillate flower formation on monoecious plantsDavid Wm. Reed, Texas A&amp;M University 23. 22 ABSCISIC ACID (ABA)Naturally-SyntheticStructureSite ofOccurring Productionabscisic acidnone plastids,especiallychloroplastHistorically also called:abscisin - because early investigators found caused leaf abscissiondormin - because early investigators found caused dormancySYNTHESISmevalonate farnesyl pyrophosphate ABAEFFECTS1) Dormancy - causes bud or seed dormancy2) Leaf abscission (leaf drop) - may cause in some plants3) Stoma - causes stomata to close (a response to drought stress) David Wm. Reed, Texas A&amp;M University 24. 23ELICITOR MOLECULESBrassinosteroid Effects: pollen tube growth stem elongation unrolling/bending...</p>


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