4 B. Forces for Change 1. Genetics 2. Environment – two time scales: a. Long-term: accumulation of adaptations thatenhanced survival & reproduction (evolution bynatural selection)b. Short-term: plasticity = wide range ofphenotypes for each genotype. Allows plants toadjust to changing environment (ex. Shorter plant indry year so that it can still reproduce)
6 II. Plant Organs: Roots, Stems, Leaves A. Roots1. Functionsa. Collect water & minerals from soilb. Anchor plantc. Store food (carb’s from photosynthesis) tobe used for flowering & fruitingd. Covered with root hairs – increases surfacearea for absorption
13 4. BudsApical dominance = the presence of an apical bud inhibits the growth of axillary buds.- remove or depress apical bud, axillary buds begin to grow.a. Terminal bud – contains a shoot apicalmeristem; shoot growth is concentrated hereb. Axillary buds – in angle (axil) between leaf &branch, contain meristem with potential to become avegetative shoot. Mostly dormant.
21 A. Dermal or Epidermis 1. Characteristics a. single layer of tightly packed cells coveringthe young parts of the plant.b. Functions in protectionc. Root hairs are specialized epidermalextensionsd. Secretes waxy cuticle of the leaf
23 a. Fills the space between dermal and vascular tissue systems. B. Ground1. Characteristicsa. Fills the space between dermal andvascular tissue systems.b . Diverse functions:Photosynthesis, storage, & supportpithIn eudicots stems:cortex
24 C. Vascular 1. Characteristics a. function in transport between roots & shoots,and structural support of plant2. Typesa. Xylem: H2O & minerals transported up toshoot systemb. Phloem: Food transported to roots & non-photosynthetic parts such as the flowers
26 A. Generalized Same as animals, except: 1. No lysozomes (digestive organelle)2. Cell walls: maintains shape, structural support,protects from damage. Made of cellulose, protein, &sometimes lignin3. Chloroplasts4. Vacuole – storage, waste breakdown, growth!5. Plasmodesmata – holes in cell wall, createschannels to connect cytoplasm of adjacent cells
27 B. Plant Cell Categories 1. Parenchyma4. Water-conducting cells of the xylem3. Sclerenchyma5. Sugar-conducting cells of the phloem2. Collenchyma
28 1. Parenchyma a. Characteristics i. Least specialized cell. Can differentiate intoother cell typesii. Primary cell walls only - thin and flexibleiii. Lack secondary plant cell wallsiv. Most metabolically active – lots of chloroplastsfor PSN (PhotoSyNthesis)v. Starch, carbohydrate production & storage instems
29 2. Collenchyma a. Characteristics i. Primary walls are unevenly thickenedii. Usually lack secondary walls.iii. Usually grouped in strands to support youngparts of plants without restraining growthiv. Flexible, elongate with growing shoots
30 3. Sclerenchyma a. Characteristics i. Function in mechanical support ii. Have rigid and thick secondary wallsstrengthened with lignin.iii. May be dead at functional maturityiv. Cell walls left behind as skeleton
35 4. Water/Mineral conducting cells of the xylem: a. 2 types: tracheids & vessel elements
36 i. Tracheidsare long, thin tapered cells having lignin-hardenedsecondary walls with pits.Dead at maturityWater flows from cell to cell (laterally) through pitsin cell wall (1o wall only)Support functionii. Vessel Elementsare wider, shorterArranged end-to-end to form tubesEnd walls are perforated for free flow of waterMore efficient as water conductors than tracheids
38 5. Sugar-conducting cells of the phloem a. 2 typesi. Sieve-tube members:Chains of cells arranged end-to-end, Alive at functionalmaturity, Lack a nucleus, ribosomes, & vacuole, andCells separated by perforated sieve plates – allow sugarmovement.ii. Companion cells:Load sugars into the sieve tube member, Nucleus andribosomes also serve the sieve-tube member.
41 A. Definitions1. Development is the sum of all the changes2. Cell Division3. Morphogenesis
42 B. Processes of plant cellular development: 1. Cell Growtha. Cell division (Mitosis) in itself does not mean anincrease in growth.b. Cell division yields no expansion of size.c. Cell elongation increases growth.
44 2. Cell elongation a. due to water uptake b. Direction of expansion = perpendicular toalignment of cellulose microfibrils in cell wallc. Enzymes weaken cross-link between microfibrils,allowing cell to expand.
47 3. Morphogenesisa. The coordinated arrangement of cells into tissues & organsb. Pattern formation – development of specific structures inspecific places (e.g. Flowers born on the terminus of branches asopposed to leaf axils.c. Depends on:i. Positional information – chemical signals from surroundingcells indicate the cell’s position on plantii. Polarity of the plant, asymmetrical cell divisionsiii. Both affect the transcription of homeotic genes
48 4. Cellular Differentiation a. Transformation of genetically identical cells into cells withdiverse biochemical and structural features. How?i. Selective transcription of appropriate genesii. How? Chapters 18 & 39iii. Flow of Info
49 The Flow of Information TranscriptionReplicationTranslationModificationRNAPolypeptideFunctional ProteinDNAEnergyAmino AcidsAdditional Materials
50 b. Regulation i. at transcriptional level ii. Regulation at translational leveliii. Regulation at post translational leveliv. Hormonal controlsv. Regulation at substrate levelvi. Regulation by environmental signals: light,gravity,…..
51 c. Processesi. Meristem identity genes – cause a vegetative shoot to become afloral shootii. Positional information (derived from chemical messengers)selectively turn on or off organ–identity genes.iii. Organ – identity genes - code for transcriptions factors thatregulate expression of genes controlling the development of specificorgans.
52 By “turning off” organ identity genes, we can give a rose more petals FigBy “turning off” organ identity genes, we can give a rose more petals
53 C. Plant growth vs. Animal growth 1. Comparison:a. Embryonic, developing, and mature organs exist togetherat the same time on one plant.b. Grow until they die, called indeterminate growth. Somedeterminate parts: leaves, flowers.
54 D. Plant life cycles:1. Annual – complete life cycle (germination throughfruiting) in one year or less. Examples: grasses, crops,wildflowers2. Biennial – complete life cycle in two years (first year= vegetative, second year = reproductive). Some need acold winter period to initiate flowering from vegetativestate. Ex. carrots3. Perennial – live year after year, do not die afterreproduction. Examples: trees, shrubs, some grasses.Causes of death = fire, disease
55 E. Plant Growth Sites Meristems Meristems are regions of the plant with continuous celldivision (i.e. perpetually embryonic tissue)1. Types of meristems:a. Apical meristem – located at the root and shoot tips,responsible for growth in length (called primary growth)b. Lateral meristems – extend lengthwise along the axis of thestem & roots. Responsible for growth in girth in older parts ofthe plant (called secondary growth). Exist only in perennialsHow is indeterminate growth possible?????
57 2. Primary Growth of Roots a. Descriptioni. Occurs at root tip (Root Apical Meristem)ii. Root cap – layer of cells that protect the RAM as it pushesthrough the soil
58 b. Zones i. Zone of cell division – contains the RAM ii. Zone of cell elongation – cells elongate, thereby pushingthe root tip through the soiliii. Zone of maturation – cells differentiate and becomefunctionally mature (i.e. become part of one of the 3 tissuesystems)
60 3. Shoots a. Leaves arise on sides of the Shoot Apical Meristem (SAM) b. Axillary buds arise from areas of meristematiccells left behind at the bases of the leaf primordia.c. Bud = cluster of leaf primordia created by meristem.No internodesd. Lateral branches arise from axillary buds
62 F. Secondary Growth in Shoots 1. Descriptiona. Shoots of perennials only, not in leavesb. Occurs in oldest parts of plant2. Layers (two lateral meristems):a. Vascular cambium – produces secondary xylem (= wood)& phloem
63 i. Vascular cambium – layer of cells between primary xylem & primary phloem. Puts on successive layers of secondary phloemto outside & secondary xylem to inside =====> stem widensii. Dormant in winter, leaves scar when activity resumes ==>annual ringiii. Wood = accumulation of secondary xylem. Dead at maturity,contains lignin
64 b. Cork cambium – replaces the epidermis with cork: tough, thick cover for stems, roots.i. Located in the cortexii. Produces cork cells to replace epidermisiii. Periderm = cork + cork cambiumiv. Lenticels = cracks in the periderm that allow gasexchange for living cells in the interiorv. “bark” = all cells external to the vascularcambium (secondary phloem & periderm)vi. Cork continually sloughs offvii. Growing secondary phloem becomes new corkcambium (thus no build up of secondary phloem)
69 G. Secondary growth in roots 1. Descriptiona. Vascular cambium forms within stele, produces secondaryxylem & phloemb. Cortex & epidermis shedc. Cork cambium arises from pericycle & produces theperidermd. Periderm – impermeable to water! Thus only young rootsabsorb from soil, old roots function = anchor & transport
70 VI. Tissue Arrangement in Plant Parts A. Roots1. Epidermis – water, minerals absorbed throughroot hairs2. Stele – central cylinder of vascular tissue(monocots have slightly different arrangement).3. Pericycle = outermost layer of stele. Lateralroots arise from this in order to remain continuouswith vascular system.
71 4. Ground tissue – mostly parenchyma cells of the cortex – area between the stele & epidermis; stores food& takes up minerals.5. Endodermis – single cell layer between cortex &stele. Selective barrier for uptake of soil solutioncontents into vascular system.
77 C. Leaves Ex. of how structure reflects function – designed for maximum photosynthetic efficiency1. Layers:a. Upper & lower epidermis – tightly interlocked cells,secrete waxy cuticle. Contains stomata flanked by guard cellsb. Vascular tissue – leaf veins, branch throughoutmesophyll
78 c. Mesophyll – ground tissue between upper & lower epidermis i. 2 kinds of parenchyma cells:Palisade – columnar, at top of leafSpongy – smaller, below palisade, gas-filled spacesbetween cells