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Biology 202 Unit 2A Genetic Control and Genetic Engineering B. Krumhardt, Ph.D. ¥¥Rearrangement of genes - may\may not affect expression ¥¥Genetic Mutations - changes in DNA sequence in cells Genetic Control Regulatory Genes in Bacteria nonfunctional protein ¥¥encode for proteins that regulate the activity of structural genes ¥¥makes cells more efficient - they make only the RNA/proteins they need ––if new bases change codons different amino acid sequence maybe a ––Germinal mutation - in germ cell line - passed to offspring ––Somatic mutation - in cell line other than germ cell - not passed to offspring ––point mutation - only one DNA base wrong Cancer ¥¥e.g. - the enzyme for metabolism of the sugar galactose is not made if ¥¥uncontrolled growth that spreads throughout body ¥¥group of structural genes coding for a enzymes in a metabolic pathway tumors; lose contact inhibition more tumors and loss of normal functions galactose is not present Operon OPERON ¥¥DNA: transcription REGULATOR..........PROMOTOR-OPERATOR-STRUCTURAL GENES FOR ENZYMES RNA mRNA polymerase REPRESSOR binds binds - prevents REPRESSOR transcription ¥¥Operator ––on/off switch for transcription of structural genes ––located upstream of structural genes Operon examples ¥¥Inducible operon model ––metabolite binds repressor; this combo can't bind operator, transcription ensues ––metabolite = inducer (it builds up when enzymes coded are needed) ––e.g. lac operon LAC ¥¥Repressible operon model ––repressor binds only when corepressor metabolite attached ––product of the enzymes coded for by the structural genes ––E.g. trp operon TRP Organization of Eukaryotic DNA ¥¥Chromatin packing ––Only ÒunpackedÓ chromatin can be transcribed ––Only partially unpacked during interphase ––Coarse transcription control ¥¥Post-transcriptional processing ––Introns - non-coding (for protein) sequences in DNA ––allows for alternative processing of exons (transcribed and translated regions) ––processing in nucleus - splicing (post-transcriptional) ¥¥ introns removed, can be site of control ¥¥Repetitive Sequences ––sequences of repeated DNA ––Can be introns ––May be essential for cell division (sequences at centromeres and telomeres ––Perhaps allows reorganization of DNA without disruption of operons e.g.. cross-over Genetic Mutations ––in plants - callus mass of undifferentiated cells ––in animals, spreading = metastasis form unspecialized cell masses, ¥¥Oncogenes - cancer causing genes ––normal genes, but the regulation is changed due to a mutation - before loss of regulation - "proto-oncogenes" ––normal gene required for tissue\organ development - usually turned off in specialized cell ¥¥Mutagens - carcinogens - cause genetic mutations ––e.g. chemicals, viruses, x-rays ––e.g. - retroviruses ¥¥RNA not DNA is genetic material ¥¥Brings its own enzyme, reverse transcriptase, to make DNA from RNA to the infected cell; has no editor, mistakes occur ¥¥then DNA inserts into host DNA may cause cancer because of disruption of normal genetic control ¥¥Usually additional mutations are necessary for cancer to occur Control of Normal Cell Growth ¥¥growth factors - proteins made by cells –– bind cell membrane proteins of other cells –– they can either stimulate or inhibit cell cycling (mitosis) ––usually occurs between different types of cells ¥¥contact inhibition - cells touch inhibition of mitosis ¥¥hormones can work as growth factors Basics of Genetic Engineering Genetics technology advancing at the Òspeed of lightÓ Restriction Enzymes ¥¥enzymes made by bacteria that break DNA into discrete pieces ¥¥very specific ¥¥E.g. Double strand DNA cut by a restriction enzyme, EcoR1: C G|A A T T C T A C C G C T T A A|G A T G G ––Notation - G/AATTC ––After digest, Òsticky endsÓ are left ¥¥Enzyme looks for specific strand and always cuts it the same way ¥¥Several spots in the genome of an organism can be cut by the same restriction enzyme restriction fragments ¥¥Restriction digest ¥¥Electrophoresis - separates DNA by size, smaller pieces move further through the gel toward the positive electrode as current passes through a buffer ––Ethidium bromide makes bands (discrete pieces of DNA) fluoresce under UV light ––Electrophoresis Restriction Fragment Analysis e.g. Restriction digest of Viral DNA ¥¥Characteristic length pieces of DNA made when normal viral DNA is with a certain restriction enzyme ¥¥Mutant virus may have a restriction enzyme cutting site lost ¥¥"DNA Finger printingÓ or Restriction Fragment Length Polymorphisms (RFLP) ¥¥E.g. Viral DNA - Mutant viral DNA - - - ¥¥Same restriction enzymes used, same sticky ends on both plasmid and Ògene of choiceÓ ––Put together with DNA ligase gene of choice now in plasmid - called "recombinant DNAÒ ––Put recombinant plasmid in bacteria ––Bacteria multiply quickly possibilities ¥¥bacteria make the protein coded for by your gene of choice - isolate it ¥¥"cloning" = when plasmid has multiplied multiple exact copies of gene - "clones" ¥¥Can accumulate lots of the cloned gene of choice to use as research tools (cut it out of plasmid with same restriction enzyme) ––e.g. Heat plasmid -- DNA double strand will separate, use it as a probe of unknown DNA--it will anneal only with specific DNA sequence by basepairing--used to detect presence/absence of gene Other Vectors ––Disabled virus ¥¥some viruses insert into host DNA ¥¥Used to introduce new genes into plants ¥¥RFLP markers may indicate the site of alleles associated with genetic ¥¥Gene therapy with disabled and engineered viruses - take out disease- ¥¥Different restriction enzymes used to cut human DNA ¥¥each individual has a characteristic chromatogram a "fingerprint" ––Bacteriophages diseases Human DNA fingerprinting Polymerase Chain Reaction ¥¥amplifies small quantity of DNA, just need to know primer sequence ¥¥Process ––1. ––2. ––3. ––4. Melt DNA with heat Primers base-pair as tube cools High temperature stable DNA polymerase duplicates the DNA melt, prime, cool, duplicate.... ¥¥One copy produces billions in a few hours ¥¥PCR ÒCloningÓ ¥¥Using these techniques in a different way: causing genes & replace them with working human genes give to person who doesn't have the working gene - potential use in all genetically inherited diseases ¥¥Viruses of bacteria ¥¥Cut with DNA with restriction enzyme and cut other DNA with same enzyme ¥¥Ligate and infect the bacterium with the recombinant phage ¥¥Useful tool for production of a genomic library Human Genome Project ¥¥Linkage Mapping - ID location of 3000 genetic markers using RFLPÕs ¥¥Chromosome walking - order fragments made with different restriction enzymes ––use restriction enzyme to cut out Ògene of choiceÓ from donor DNA; ¥¥Sequence fragments common database ––Vectors used to transfer gene to a host cell that can express the gene ––Cloning a gene ¥¥Faster, alternative strategy - shotgun approach ¥¥plasmids ¥¥Analyze genomes of other species to develop techniques, strategies, and insert this into a ÒvectorÓ Vectors ––most commonly used vectors ––extra-chromosomal DNA in bacteria containing antibiotic resistance genes ¥¥in nature they can transfer antibiotic resistance from one bacterium to ––Cut DNA with several restriction enzymes, sequence all fragments, use computer to determine overlaps and overall sequence help with interpretation Determine gene expression ¥¥Using Microarrays - ties genes to physiology ¥¥Scientists working another ––Commercially-available plasmidÕs restriction sites & antibiotic resistance genes are mapped ––use same restriction enzyme to cut plasmid and cut out gene of choice ¥¥may cut out a ÒmarkerÓ gene BIOL 202 Unit 2B Photosynthesis and Leaves B. Krumhardt, Ph.D. Photosynthesis ¥ Light - captured (absorbed) by chlorophyll – 2 kinds of chlorophyll: a&b ¥ violet, blue, blue-green, orange, and red light are absorbed ¥ green, yellow, some orange are reflected so plants look green Chloroplasts ¥ Double membrane - inner membrane in flattened sacs - ÒthylakoidsÓ in stacks - ÒgranaÓ in fluid ÒstromaÓ – chlorophyll in thylakoid membranes – thylakoid compartment within ¥ many photosynthesis enzymes in stroma ¥ Overview of photosynthesis: CO2 + H2O ¬ Carbohydrate + O2 solar energy ¥ Chloroplasts are found mainly in mesophyll cells forming the tissues in the interior of the leaf ¥ O2 exits and CO2 enters the leaf through microscopic pores, stomata, in the leaf ¥ Veins deliver water from the roots and carry off sugar from mesophyll cells to other areas of the plant ¥ A typical mesophyll cell has 30-40 chloroplasts Light reactions ¥ occur on the thylakoid membrane ¥ two photosystems (Ps) – PsI - chlorophyll A (peak absorbance 700nm) – PsII - chlorophyll B (peak absorbance 680nm) – both contain other pigments, "light harvesting antennae", which harvest solar energy - light - and transfer it to the chlorophylls ¥ chlorophyll a and b have electrons which are energized by the solar energy ¬ transferred to acceptor molecules ¥ two electron pathways (of e- transfer) - both occur at once ¥ Noncyclic photophosphorylation – PsII (peak absorbance 680 nm) absorbs light ¬ e- energized – e- leaves chlorophyll b ¥ the hole left by the e- leaving is freed by H2O ¬ 2 H+ + 2e- + 1/2 O2 ¥ O2 diffuses off ¥ H+ into thylakoid space – e- transported in membrane via pigments--cytochromes ¬ p700PsI – H+ move to thylakoid compartment when e- pass through cytochromes – the increased H+ in thylakoid space provides proton-motive force of chemiosmotic phosphorylation ATP synthase (ADP + P ¬ ATP) – increased H+ in stroma (from H+ through ATP synthase and e- at p700) drives NADP+ reductase: ¥ NADP+ + 2e- + 2H+ ¬ NADPH ¥ NADPH used for synthesis of sugars, fatty acids, etc. later – non-cyclic photophosphorylation produces O2, NADPH & ATP ¥ Cyclic photophosphorylation – e- leave PsI without reaction with NADP, so – ¬ ¬ return to PsI (p700) ¬ more ATP made as light stimulates etransfer to e- acceptor and H+ moves to thylakoid compartment when epass through cytochromes ¬ more chemiosmotic phosphorylation Dark Reaction ¥ occurs in the stroma ¥ Dark reaction is really very light dependent – occurs in light most of the time because it uses the products of the light reaction – does occur in the dark too – (the light reactions only occur in light) ¥ a.k.a. Carbon Fixation ¥ Calvin Cycle - C3 Pathway: – first enzyme: RUBISCO--ribulose bisphosphate carboxylase, most abundant enzyme on Earth – 3 ATP + 3 NADPH + 3 Ribulose bisphosphates + 3 CO2) ¬ 3-6C sugars ¬ spontaneous ¬ 6-3C G3P's (glyceraldehyde 3-phosphate) – 5 of the G3P's are used with 3 ATP to re-synthesize the Ribulose bisphosphate to be used in the next round of cycle, leaving one extra G3P formed – extra G3P enzymatically converted to carbohydrates, fats, amino acids, nucleic acids, etc., using NADPH from light reaction ¥ this is the organic molecule gained due to the Calvin cycle ¥ C4 pathway – special mesophyll cells, bundle sheath cells, capture CO2 with special enzyme (PEPCO) – the C is then transferred to Calvin cycle (RUBISCO) – 1st molecule formed with CO2 fixation has 4C – found in tropical plants especially grasses ¥ e.g. corn ¥ CAM pathway – trap the CO2 at night - keep their stomata closed in day to conserve H2O – found in succulents, cactus Photorespiration ¥ O2 & CO2 compete for active site on RUBISCO; so if increased O2 & decreased CO2, RUBISCO is inhibited ¥ This causes photorespiration to occur: – Ribulose bisphosphate + O2 ¬ PGA + phosphoglycolic acid – The phosphoglycolic acid breaks to make two CO2 ¬ increasing the CO2 in cell ¬ stimulation of RUBISCO ¥ Photorespiraton is evolutionary baggage ¥ When RUBISCO first evolved, the atmosphere had far less O2 and more CO2 than today – Then, the inability of the active site of RUBISCO to exclude O2 would have made little difference ¥ Today it makes a significant difference – Photorespiration can drain away as much as 50% of the carbon fixed by the Calvin cycle on a hot, dry day ¥ C4 plant species have evolved alternate modes of carbon fixation to minimize photorespiration ¥ C4 plants - PEPCO unaffected by increased O2, so they are more efficient, do carbon fixation even when increased O2 ¥ Sugar made in the chloroplasts supplies the entire plant with chemical energy and carbon skeletons to synthesize all the major organic molecules of cells – About 50% of the organic material is consumed as fuel for cellular respiration in plant mitochondria – Carbohydrate in the form of the disaccharide sucrose travels via the veins to nonphotosynthetic cells. – There, it provides fuel for respiration and the raw materials for anabolic pathways including synthesis of proteins and lipids and building the extracellular polysaccharide cellulose ¥ Plants also store excess sugar by synthesizing starch – Some is stored as starch in chloroplasts or in storage cells in roots, tubers, seeds, and fruits ¥ Heterotrophs, including humans, may completely or partially consume plants for fuel and raw materials ¥ On a global scale, photosynthesis is the most important process to the welfare of life on Earth – Each year photosynthesis synthesizes 160 billion metric tons of carbohydrate per year Biology 202 Unit 2C Plant Form and Function B. Krumhardt, Ph.D. ¥ Plant morphology – study of external structures ¥ Plant anatomy – study of internal structures Angiosperms ¥ Most diverse and widespread ¥ 275,000 plant species extant ¥ Reproduction and seed dispersal adaptations – flowers and fruits Two Plant Groups ¥ Monocots – One cotyledon – Parallel venation – Vascular bundles complexly arranged – Fibrous root system – Floral parts in multiples of 3 ¥ – – – – – Dicots Two cotyledons Netlike venation Vascular bundles arranged in a ring Taproot system Floral parts in multiples of 4 or 5 Plant Organs ¥ Roots depend on shoots for sugars and other organic nutrients ¥ Shoots depend on roots for minerals, water, and support – Leaves on shoots provide photosynthesis – Flowers are shoots modified for reproduction Roots system ¥ Subterranean – roots anchor plants ¥ Roots absorb water and dissolved minerals from soil ¥ Sunlight cannot penetrate the soil – plants store food in roots ¥ – – – – – – – Tap roots One large vertical root (taproot) Many small secondary roots Firm anchorage Some are modified to store reserve food Penetrate soil more deeply Often store food for plant (e.g. carrot) Characteristic of dicots ¥ Fibrous roots – Fine threadlike roots – Extensive exposure to soil – Mostly shallow roots, anchoring the top of the soil ¥ Prevent erosion – Characteristic of most monocots and some dicots ¥ Root hairs – Extensions of epidermal cells on root surface ¥ NOT secondary roots – Increased surface area provides increased water and mineral absorption ¥ Enhanced by mycorrhizae ¥ Adventitious roots – Root in an atypical place ¥ Adventitious means a plant part in an atypical place – E.g. Prop roots of corn Shoots Shoot system ¥ Stems, leaves, and flowers ¥ Air is source of CO2 – Air is less than 1% CO2 ¥ Dry terrestrial environment provides challenges Stems ¥ Nodes – point of attachment for leaves ¥ Internodes – stem between nodes Buds ¥ Terminal – at the tip (apex, apical) of the shoot – Site of most growth in young shoots – Apical dominance – terminal bud produces hormones that inhibit the growth of axillary buds ¥ Axillary – in the angle of the leaf attachment – Dormant in young plants – Potentially can form a branch when apical dominance diminished Modified Stems ¥ Stolons – grow atop soil surface – reproduces asexually, forming small plants at each node ¥ Rhizomes – horizontal stems growing underground ¥ Tubers – swollen rhizomes specialized for food storage ¥ Bulbs – vertical underground stems with swollen underground leaves specialized for food storage Leaves ¥ Blade – main photosynthetic structure ¥ Petiole – attaches the blade to the stem at the node – Monocots generally lack petioles – instead the blade wraps the stem in a sheath Leaf Veins ¥ Monocots – major veins are parallel ¥ Dicots – major veins are multi-branched Leaf Division ¥ Simple leaves – consist of one undivided blade ¥ Compound – consist of divided leaflets ¥ Doubly compound – leaflets are divided ¥ Division minimizes loss due to damage Modified Leaves ¥ Tendrils – provide support ¥ Spines – provide protection from grazing ¥ Succulent leaves – modified to store water in dry environments ¥ Brightly colored modified leaves to attract pollinators to minimized flowers in some plants Plant Tissues ¥ Dermal tissue – epidermis – Single layer of tightly packed cells, form the skin of the plant – Root hairs are extensions of these cells – Cuticle – waxy coating secreted by stem and leaf epidermal cells ¥ Vascular tissues – Xylem conveys water and dissolved minerals to the shoots – Phloem conveys food from shoots to roots and other nonphotosynthetic parts ¥ Also from storage roots to actively growing shoots ¥ Ground tissue – All plant tissue that is not dermal or vascular – Functions in photosynthesis, storage and support Vascular tissue specialization ¥ Xylem – specialized for water transport – Gymnosperms ¥ Tracheids – function in both support and water transport – Angiosperms ¥ Tracheids of gymnosperms specialized into 2 cell types – Vessel elements – short tubular cells aligned to transport water – found only in angiosperms – Fiber cells – lignified cells provide support – found in some conifers and in angiosperms Xylem ¥ Tracheids and vessel elements – Conduct water in xylem – Dead at functional maturity – only thickened cell walls remain with pits at the ends of the cells ¥ Pits consist of only primary cell walls ¥ Tracheids – Long thin cells with tapered ends with pits to allow water flow – Secondary cell walls thickened with lignin – tracheids provide support too ¥ Vessel elements – Wider, shorter, and thinner-walled than tracheids – Aligned end to end with perforated ends to form xylem vessels ¥ Water flows freely through these ÒpipesÓ ¥ Both tracheids and vessel elements cells stop elongating when dead at maturity ¥ Wood in wood plants consists mostly of tracheids and vessel elements Phloem ¥ Sieve-tube member cells – Transport sucrose and other nutrients – Alive at functional maturity ¥ Lack nucleus, ribosomes, and vacuole – Sieve plates at the ends of these cells have pores for nutrient transport ¥ Companion cells – Connected sieve-tube members by plasmodesmata ¥ Pores in cell walls ¥ Connect the cytoplasm of one cell to another ¥ Allow functional elements of companion cells to serve the sieve-tube member – E.g. Endoplasmic reticulum is continuous through these pores Ground Tissue ¥ Dicots – Pith – internal to vascular tissue – Cortex – external to vascular tissue – Functions – photosynthesis, storage, and support ¥ Monocots – Vascular bundles are scattered throughout the ground tissue Plant Cells ¥ Protoplast surrounded by a cell wall – Contains cytoplasm and organelles ¥ Tonoplast encloses the vacuole containing cell sap ¥ – ¥ – ¥ ¥ – ¥ Plant cell walls Primary cell wall Present in all plant cells Secondary cell wall Present in some plant cells Forms later, closer to the protoplast, after the cell has stopped growing Middle lamella Adhesive layer – holds cells together ¥ Parenchyma cells – ÒTypicalÓ plant cells – relatively unspecialized – Most have only flexible primary cell walls – Characterized by a large central vacuole – Functions ¥ Metabolism – synthesizing and storing organic molecules – Photosynthesis – Starch storage ¥ All immature plants cells are parenchyma cells – they differentiate to other types as they mature ¥ Collenchyma cells – Found in growing plant tissue – Grouped in strands or cylinders – Thickened primary cell walls provide support ¥ Lignin is absent – cells are flexible and able to elongate to accommodate plant growth – Young stems and petioles have collenchyma cylinders just below their surface ¥ E.g. celery stalk ÒstringsÓ ¥ Sclerenchyma cells – Specialized cells for support ¥ Secondary cell walls hardened by lignin ¥ May be dead at functional maturity – Fiber cells ¥ Elongated cells ¥ Form the ÒfibersÓ of fibrous plant tissue – E.g. flax fibers used for linen – Sclereids ¥ Irregularly-shaped cells with very thick lignified cell walls – E.g. ÒgritÓ of pears and nutshells Plant Growth ¥ Most plants grow as long as they live – Indeterminate growth – In contrast, animals stop growing upon maturity – determinate growth Plant Life Cycles ¥ Annuals – Germinate, flower, and produce seeds in one year ¥ – – – Biennials Germinate and grow in one year Dormant through a cold period Flower and produce seed the second year ¥ Perennials – Live many years, often flowering many times throughout its life – Usually die from infections or environmental trauma, not old age Meristems ¥ Perpetually embryonic tissues – capable of mitosis and further growth ¥ Apical meristems – Located at tips of shoots and roots – Allow elongation – primary growth – found in youngest portion of the plant ¥ Lateral meristems – Provide secondary growth in woody plants ¥ Found in older portions of the plant – Thickens shoots and roots – Consists of two cylinders of dividing cells ¥ Outer cylinder replaces the epidermis with secondary dermal tissue – E.G. Bark ¥ Inner cylinder adds layers of vascular tissue – E.G. Wood = accumulated secondary xylem Winter Twigs ¥ Dormant terminal bud at tip – Enclosed by protective scales – Scales shed in spring as growth resumes ¥ Scars indicate the site of attachment of shed scales ¥ Growth produces nodes and internodes – Leaf scars indicate the site of attachment of shed leaves – Above leaf scars are axillary buds or branch twigs produced by axillary buds ¥ Each growing season, primary growth extends the shoot and secondary growth thickens older tissue Root Primary Growth ¥ Root cap – Protects the delicate root apical meristem – Secretes polysaccharide slime that lubricates the soil around the growing root tip ¥ Zone of cell division – primary meristem – Site of mitosis – Center of apical meristem contains slower growing cells – quiescent center cells – these cells can replace a damaged apical meristem – Three layers of mitotic cells ¥ Protoderm – produces dermal tissue ¥ Procambium – produces vascular tissue ¥ Ground meristem – produces ground tissues ¥ Zone of elongation – Cells elongate and push the root through the soil – Meristem continually produces new cells for the zone of elongation ¥ Zone of maturation – Cells differentiate and become functionally mature – Form the three primary tissue of roots Root Tissues ¥ Protoderm – Outer primary meristem – produces epidermis – Single layer of cells – Function in absorption of water and mineral nutrients from the soil – Root hairs aid absorption by increasing surface area ¥ Procambium – Produces stele – the vascular tissue of roots – Dicot roots ¥ Stele is a centrally-located cylinder of specialized vascular tissue ¥ Xylem cells radiate from the stele center in spokes ¥ Phloem cells fill the space between spokes – Monocot roots ¥ Central cells do not differentiate – they remain as unspecialized parenchymal cells calledÒpithÓ – Not the same as stem pith because these cells are part of the vascular tissue, not ground tissue ¥ – – ¥ ¥ ¥ Ground meristem Between the protoderm and procambium Produces the ground tissue Mostly parenchyma cells Fills the cortex, the region between the stele and epidermis Function in food storage (e.g. starch) and mineral uptake – Pericycle ¥ Outermost layer of the stele ¥ Can become meristematic and produce a lateral root ¥ Endodermis – Innermost layer of the cortex – Cylinder one cell layer thick – Form boundary between the cortex and the stele ¥ Forms selective boundary for passage of substances from the soil to the vascular tissue ¥ Lateral roots – Formed from pericycle – Stele of lateral root is continuous with the stele of the primary root Secondary Growth of Roots ¥ Vascular cambium forms within the stele – Produces secondary xylem to the inside and secondary phloem to the outside ¥ Cork cambium forms from the pericycle, making the periderm – Periderm is impermeable to water – Only young portions of roots absorb water – Older portions of roots anchor the plant and transport water and solutes Shoot Tissues ¥ Primary growth – Apical meristem produces primary meristems – protoderm, procambium, and ground meristem – Leaves arise as leaf primordia – Axillary buds develop in the axils of the leaves Stem Tissues ¥ Vascular tissues are in vascular bundles – cylinders running the length of the stem ¥ Dicots – vascular bundles are in a ring around the perimeter of the stem with pith in the center – Xylem – near the pith – Phloem – near the cortex – Ground tissue cells form rays that separate the bundles and connect to the pith ¥ Monocots – vascular bundles scattered throughout the ground tissue ¥ In both, the ground tissue is mostly parenchyma – Some stems are strengthened by colenchyma or schlerenchyma just beneath the epidermis ¥ Protoderm of terminal bud produces the continuous stem and leaf epidermis Secondary Growth of Stems ¥ Vascular cambium – Forms from parenchymal cells in a layer between the primary phloem and primary xylem – Makes a continuous cylinder of meristematic tissue around the primary xylem and the stem pith – Appears as a ring in cross section ¥ Fusiform initials of the vascular cambium form secondary xylem to inside and secondary phloem to the outside ¥ Ray initials form xylem and phloem rays ¥ Bark – all tissue from the vascular cambium out ¥ Periderm – Cork cambium and cork – Replaces the protective functions of the epidermis of the young plant – Lenticels – areas of the periderm that split open – allow cells within the trunk to exchange respiratory gases with the environment Tree Trunk ¥ Bark – Consists of living phloem and periderm (cork and cork cambium) – Only youngest phloem functions in phloem sap transport of sugar – Oldest phloem dies and help protect the stem until it is sloughed off ¥ Sapwood – Youngest xylem – Functions in xylem sap transport of water and minerals – Sapwood volume increases each year the growing circumference of the tree ¥ Heartwood – Older xylem – Vessel walls are lignified and clogged with resins – Provides support column for the tree and the resins inhibit pathogens and insects Leaf Tissues ¥ Epidermis – Waxy cuticle provides a continuous protective barrier water loss and environmental damagedue to physical forces or pathogens – Stomata ¥ Provide openings in the leaf epidermis for gas exchange with the environment ¥ Guard cells – specialized epidermal cells open and close the stomata ¥ Transpiration – evaporative water loss from stomata – occurs when stomata are open for gas exchange – this water must be replaced by that absorbed by the roots ¥ Mesophyll = ground tissue – Parenchymal cells with chloroplasts – Function – photosynthesis – Palisade parenchyma – columnar cells in upper leaf – Spongy parenchyma – irregular cells in the lower portion of the leaf with spaces filled with O2 and CO2 ¥ Air spaces are largest near stomata ¥ – – ¥ ¥ – Leaf vascular tissue – ÒVeinsÓ Continuous with vascular tissue of the stem Branching is significant within the leaf Monocots – parallel venation Dicots – netlike venation Provides a skeleton for the leaf, reinforcing its shape BIOL 202 Unit 2D Plant Transport and Nutrition B. Krumhardt, Ph.D. ¥ On land, internal transport of water and minerals from the soil, and gas exchange with the air, provided evolutionary pressure for development of structures to perform these functions Categories of Plant Transport ¥ Cellular – Uptake and loss of water and solutes by cells – E.g. absorption of water and minerals at the root cells ¥ Tissue – Short-distance transport cell to cell – E.g. photosynthetic cells of a leave to sieve tube cells of phloem ¥ Whole plant – Long-distance transport of sap in xylem and phloem ¥ Because secondary phloem cells and other cells external to the vascular cambium can not divide, cork cambium develops from parenchymal cells of the stem cortex ¥ ¥ Cork cambium makes cork cells, replacing stem epidermal cells ¥ In subsequent years, the vascular cambium adds to the secondary xylem and phloem and the cork cambium adds to the cork ¥ Water and minerals are transported from roots to shoots as xylem sap ¥ Transpiration, loss of water from leaves (mostly through stomata), creates a an upward force the pulls xylem sap Roots absorb water and dissolved minerals from the soil ¥ Leaves exchange CO2 and O2 through stomata – CO2 used for carbon fixation in photosynthesis – O2 used for cellular respiration ¥ Sugar is produced in the leaves by photosynthesis ¥ Sugar is transported in phloem sap to roots and other plant parts ¥ Roots exchange gases with air spaces in the soil – CO2 emitted and O2 absorbed for cellular respiration Proton Pumps ¥ Proton pumps pump H+ out of cells, producing a proton gradient and membrane potential – Cells are electronegative as compared to their environment – This provides potential energy for cellular work Cation Uptake ¥ Because cells are electronegative, they draw in electropositive cations ¥ Cation exchange – H+ production by root cellular respiration is exchanged for cations of soil Anion Uptake ¥ Cotransport of anions (e.g. NO3-) with H+ allows anion uptake – ATP used by the proton pump pays the energy price for this uptake Neutral Solute Uptake ¥ Neutral solutes are also cotransported with H+, with the proton pump again paying the energy price Mechanism of Water Movement ¥ Addition of solutes to the cell makes them hypertonic as compared to their environment ¥ This reduces water potential, promoting osmosis, drawing water into the cells – Aquaporins, water transport proteins, may speed water movement through plant membranes ¥ Water lost by transpiration at the leaves provides additional tension Water Tension in Plant Cells ¥ Flaccid cells have less water potential than their environment – Occurs most often when soil is dry ¥ Osmosis after watering allows the plant to regain turgor ¥ Plasmolysis - flaccid cells placed in hypertonic conditions will lose additional water to their environment ¥ Plasmolysis kills most plant cells ¥ Turgor pressure develops when a flaccid cell is placed in a hypotonic environment – Cell swells and presses against the elastic cell wall Cell Compartments ¥ Cell wall – Provides shape but does not regulate molecule flow ¥ Plasma membrane – Regulates molecule flow between the cell wall and the cytosol ¥ Tonoplast – Membrane surrounding the vacuole – Regulates molecule flow between the cytosol and the vacuole ¥ Plasmodesmata make the cytosol between cells continuous – Allowing certain molecules flow between cells by diffusion Tissue Compartments ¥ Symplast – Continuous cytosol through plasmodesmata allows tissue level transport ¥ Apoplast – The continuum of cell walls provides for a second means of tissue level transport Lateral Transport in Roots ¥ Root hairs – Increase surface area to allow more water and mineral absorption by roots ¥ Apoplastic flow – Soil solution of water and minerals flows into the hydrophilic cell walls of the epidermis – The soil solution then flows along the cell wall continuum to the endodermis ¥ Symplastic flow – Water and minerals that can cross the plasma membrane of root hairs enter the symplast and flow through the endodermis to xylem vessels in the stele – Because xylem vessel elements are dead cells, both their cell walls and their internal compartments are part of the apoplast ¥ Casparian strip – Endodermis cell encircled by waxy material that prevents flow between cells – Only substances that pass through the plasma membrane from the apoplast to the symplast can enter the stele ¥ Mycorrhizae, mycelia of symbiotic fungi, surround the roots and provide additional surface area for water and mineral absorption – Up to 3 m of hyphae can extend from each cm of root, reaching much more soil than the root hairs alone Xylem Sap Transport ¥ Transpiration – Stomata on leaves must open to allow gas exchange with the air in spaces between mesophyll cells to use for photosynthesis – Because air outside of these spaces is usually drier than inside, water is lost from the thin film coating mesophyll cells – Transpirational pull –this evaporated film of water is replaced by water pulled from the xylem ¥ Water is ÒpulledÓ upward ¥ Major force for upward xylem sap movement ¥ Root pressure – When transpiration is low (usually at night), root cells still expend energy to pump water and minerals into xylem – This creates a lower water potential in the stele and forces fluid up the xylem – Guttation – droplets of water may be seen in the morning on the leaves of some dicots that have accumulated excess water overnight Ascent of Xylem Sap ¥ Hydrogen bonding between water molecules and between water molecules and cell walls provides a continuous chain of water molecules from the roots through the shoot to the leaves where it is transpired ¥ If an air pocket disrupts this chain, root pressure can fill the gap in small plants, but in large plants the vessel will never function to transport water again – Other xylem vessel can provide an alternative route for the sap – In oaks and elms, only new xylem functions for xylem sap transport ¥ Old xylem continues to provide physical support for the tree Stomata ¥ Transpiration can cause leaves to loose more than their weight in water in one day ¥ Stomata must open to allow gas exchange for photosynthesis – C4 plants fix CO2 more efficiently than C3 plants – Water loss increases to allow more CO2 fixation, therefore, C4 lose more water as during photosynthesis than C3 plants ¥ Guard cells surround the stomata and control their opening and closing ¥ Guard cells are kidney-shaped in dicots and dumbbell-shaped in monocots ¥ When cells are turgid, radially-oriented microfibrils cause the turgid guard cells to increase in length only ¥ Because cell walls of guard cells are attached at the tips, the guard cells buckle, and stomata open ¥ When cells are flaccid, stomata close due to decreased buckling ¥ Guard cells control their turgor pressure by regulating their K+ content – Stomata open when guard cells accumulate K+ from neighboring epidermal cells because they become more turgid by osmosis ¥ This happens when proton pumps move H+ out of cells, making the cells more electronegative, drawing in K+ through K+ channels ¥ Studies using membrane ÒblistersÓ created by micropipettes indicate that blue light stimulates the process – Stomata close when guard cells lose K+ and water – Stomata are usually open during the day and closed at night when it is too dark for photosynthesis ¥ Circadian rhythms may also play a role ¥ Water stresses may cause stomata to close during the day Xerophytes ¥ Leaf modifications reduce transpiration in arid climates – Thickened cuticles – Stomata are concentrated on the lower, shady sides of leaves – Stomata are clustered in crypts and trichomes (ÒhairsÓ) break up the flow of air – Crassulacean acid (CAM) metabolism allows some succulents to accumulate CO2 into organic acids at night, reducing transpiration water losses – Some desert plants shed their leaves during the driest months ¥ Stem modifications may include fleshy stems that store water for dry seasons Translocation of Phloem Sap ¥ Sugar in phloem provides the osmotic force for flow – Other solutes are transported with the sugar ¥ Sugar sources – Photosynthesis – Breakdown of starch ¥ Sugar sinks – Growing plant tissue ¥ Mesophyll cells make most sugar, transferring it to sieve-tube member cells of phloem via transfer cells connected by plasmodesmata, that is, via the symplast – In some plants, apoplast transport allows sieve-tube members to accumulate sugar – In some plants, e.g. corn, sucrose accumulates in sieve-tube members ¥ Proton pumps pay the energy price for sucrose/H+ cotransport into the sieve-tube members Pressure Flow in Sieve Tubes ¥ Loading of sugar in sieve tubes draws in water by osmosis ¥ Absorbed water creates hydrostatic pressure in the tube, producing flow ¥ Unloading of sugar and water along the tube creates a pressure gradient, also producing flow ¥ In leaf-to-root translocation, xylem recycles the water back to the leaves 1. In the mature flower, the anthers undergo meiosis to produce microspores 2. Microspores undergo mitosis to make pollen grains consisting of 2 haploid cells 3. Pollen is transferred to the stigma by wind or animals 4. 5. ¥ ¥ ¥ 6. The pollen tube has now grown through the style to the ovule to deliver 2 sperm nuclei 7. Double fertilization: ¥ One unites with the egg, forming the diploid zygote ¥ The other unites with the large central cell with 2 haploid nuclei, forming the endosperm (3n) 8. ¥ ¥ ¥ ¥ ¥ ¥ Petals – Usually brightly colored to attract pollinators – Wind pollinated angiosperm – like grasses – have drab or green inconspicuous petals ¥ Stamen – Male reproductive part – Filament – stalk, places the anther most appropriately for pollination – Anther – site of pollen production ¥ – ¥ – ¥ – ¥ ¥ Carpel Stigma sticky end to which the pollen adheres Style stalk that the pollen tube must travel through to get to the ovule Ovary at the base of the carpel Site of seed production Angiosperm Life Cycle Zygotes become sporophyte seeds Embryo (2n) Rudimentary root Cotyledon - seed leaves Endosperm – food supply Seed coat (2n) – derived from integuments of parent sporophyte 9. When conditions are appropriate, seed germinates ¥ Seed coat ruptures ¥ Embryo emerges as a sporophyte seedling using food of endosperm and cotyledons Pollination ¥ Angiosperms have colorful flowers to attract pollinators ¥ Double fertilization prepares the embryo and the food for it at the same time Floral Diversity ¥ Complete flowers – Sepals, petals, stamens, and carpels are present – ÒPerfectÓ – Bisexual ¥ Incomplete – some floral parts lacking ¥ BIOL 202 Unit 2 E Plant Reproduction B. Krumhardt, PhD. Sexual Reproduction Flowers ¥ Composed of modified leaves – sepals, petals, stamens, and carpels ¥ Sepals – Usually green – Enclose flower before it opens Ovules produce megaspores in the embryo sac by meiosis Mitosis of one surviving megaspore produces 8 haploid nuclei in 7 cells One large central cell has 2 haploid nuclei Only 1 of the other cells is the egg Inflorescences - clusters of flowers ¥ Composite inflorescences - look like one big flower, but really composed of many complete flowers – Rays surrounding cluster are specialized incomplete flowers Unisexual Flowers ¥ Staminate or Carpellate – ÒimperfectÓ ¥ Monoecious - both staminate and carpellate flowers on one plant ¥ Dioecious - staminate and carpellate flowers on separate plants – Plants are male or female – Unisexual Prevention of Self-Fertilization ¥ Unisexual plants ¥ Structures vary within species - e.g. pin or thrum flowers of primrose ¥ Self incompatibility (most common mechanism) – Alleles of pollen grains must differ from the stigma alleles for pollen grains to grow Seeds ¥ Seed coat - protection ¥ Embryo connected to cotyledon(s) – Epicotyl above the connection - form shoots with plummule atop – Hypocotyl below the conncetion - forms the root with the radicle at the tip Dormancy and Germination ¥ Dormancy – Very slow metabolism – May accumulate over years before specific plant needs are met for germination - moisture, fire, freeze/thaw, etc ¥ Germination - nutrients mobilized from storage in seeds – In endosperm, starch is broken into glucose and the glucose is used by the embryo until photosynthesis can begin ¥ ¥ ¥ Inhibition - water absorbed, rupturing seed coat Nutrients mobilized Radicle emerges from the embryo ¥ Shoot emergence – Monocots - coleoptile sheaths the emerging shoot, the cotyledon and sotred endosperm remain beneath ground – Dicots - the hypocotyle elongates until light stimulate it to straighten, presenting the cotyledons and the shoot to light Asexual Reproduction ¥ Vegetative propagation - from cuttings – Grafting the best together ¥ Root from ÒstockÓ ¥ Shoot from ÒscionÓ ¥ Test tube cloning – A few parenchymal cells may be grown to produce a cllus on sterile media with appropriate nutrients and hormones ¥ Genetic engineering - DNA pellets introduce new genes into the plant, producing transgenic plants – Concerns exist about release of novel genes into the environment Biology 202 Unit 2F Plant Responses B. Krumhardt, Ph.D. Plant Signal Transduction ¥ All eukaryotic organisms respond by using second messenger to elicit a response inside cells Plant Hormones ¥ Like with animal hormones, plant hormones are made only by certain cells and they affect only certain cells Auxin ¥ Made in seeds, apical meristems of young buds on shoot, and in young leaves ¥ Controls cell growth and elongation – Stimulates elongation at low concentrations – Inhibits elongation at higher concentrations, probably but inducing ethylene production ¥ Mechanism of auxin stimulation of cell elongation – Transported from the apical meristem through specific transporters – Diffuses from the site of entry to be transported to the next cell – As auxin moves through the cell protons are pumped out of the cells and the lower pH softens the cell walls allowing the cells to elongate Cytokinins ¥ Synthesized by root cells and transported to the rest of the plant in xylem ¥ Affects are numerous: – Modifies root growth – Stimulates mitosis and cell growth – Stimulates germination – Delays aging ¥ Controls apical dominance with auxins and other factors; exactly how, is unknown Gibberellins ¥ Made by the apical buds and roots, also by young leaves and the embryonic plant ¥ Stimulates seed and bud germination – Germination can be stimulated with gibberellins, even when environmental factors are not optimal ¥ Stimulates stem elongation and leaf growth – Most dramatic effect is seen with rapid flower stem elongation – Genetically dwarfed plants grow to a normal height with gibberellin treatment ¥ Stimulates flowering and fruiting – Required for setting fruit – Stimulates production of large and plentiful fruit ¥ Also modifies root growth and differentiation Abscisic Acid ¥ Synthesized by leaves, stems, roots, and green fruit ¥ Generally inhibits growth and control abscission ¥ Closes stomata in water stress ¥ Counteracts breaking of dormancy Ethylene ¥ Made by ripening fruit, stem nodes, aging leaves, and flowers ¥ Promotes fruit ripening, modifies auxin effects – Effect seen if ripe apples are stored with potatoes; causes potato sprouting – Effect inhibited by flushing bins with CO2 ¥ Stimulates or inhibits development of roots, leaves and flowers depending upon the species – Promotes apoptosis, programmed cell death ¥ As cells die, macromolecules are hydrolyzed and recycled to be used elsewhere in the plant ¥ Allows leaf abscission Brassinosteroids ¥ Made by seeds, fruits, shoots, leaves, and flower buds ¥ Inhibits root growth ¥ Slows leaf abscission ¥ Promotes xylem differentiation Plant Response to Light Phytochrome in the Greening Response ¥ Phytochrome inside the cell is attached to a specific receptor ¥ When light hits the phytochrome, G-proteins make second messenger molecules that bring about the greening of the plant ¥ Phototropism is most effective with blue light ¥ Red light stimulates germination while far-red light inhibits it Biological Clocks of Plants ¥ Photoperiodism – the characteristic physiological response of plants to light ¥ Certain plants respond to long day lengths while other respond to short day lengths – Actually the night length brings about the effects ¥ Probably plant hormones bring about the effects Response to other environmental stimuli ¥ Gravity – Roots grow toward gravity – positive gravitropism ¥ Modified plastids, ÒstatolithsÓ, elicit response – Shoots grow away from gravity – negative gravitropism ¥ Mechanical stimulation – Response is thigmomorphogenesis – Cells elongate and grow due to rubbing – Tendrils demonstrate this effect ¥ Drought – promotes stomata closing to reduce transpiration ¥ Flooding – promotes apoptosis of some cells providing a ÒsnorkelÓ for root cellsÕ oxygen needs ¥ Salt stress- ion uptake is inhibited ¥ Heat stress- heat shock proteins are made; these may inhibit denaturation of other proteins Plant Defenses ¥ Certain plants respond to grazing and pathogens by producing chemicals that taste bad or inhibit pathogens ¥ Certain plants make thorns to inhibit grazing ¥ ¥ Some plants make chemicals that attract the predators of their pests Or vice versa
