1Plant Growth & Development•Plant body is unable to move.•To survive and grow, plants must be able to alter its growth, development and physiology.•Plants are able to produce complex, yet variable forms that are best suited to their local environment.•[Free Movies!]Questions: 1. What are the changes in form & function?2. What are the molecular and biochemical bases of the changes?Development1. What is development?Changes during the life history of an organism. E.g. How? zygote Æ embryoembryoÆ seedlingCells differentiate. e.g. root hair, epidermis, guard cellTissues form a specific pattern.2. What mechanisms control development?- Genes, hormones, environment- Cellular changesDifferences in the Developmental Mechanisms of Plants and Animals 1. Post-embryonic vs embryonic developmentzygote--> embryoAnimals- most of the organs are formed at this stagePlants- organs are formed after germination.2. Cell commitment for differentiationAnimal cell is irreversibly committed to a particular fatePlant cell commitment is rarely irreversible.3. Fate of plant cell is determined by its position in the organism.Cells do not move, so its position is determined by the plane of division. Positional information comes from chemical signals via cell-cell communication.Growth Stages1. Embryogenesis [part of seed development]zygote --> embryo2. Vegetative development includesa. Seed germinationFrom a heterotrophic to a photosynthetically-competent seedlingb. Development of the Vegetative plantIndeterminate growth regulated by environmental factors3. Reproductive developmentfloweringpollinationfertilization Æ zygoteBoyes et al 2001 Plant CellLife cycleGrowth stages of Arabidopsis, a model plant.1. Germination: seed to seedling2. Development of the vegetative plant3. Development of the reproductive plantfloweringpollinationfertilization4. Development of the seed (protected embryo)zygote -> embryoembryogenesis2Flowering and reproduction16-1. Arabidopsis thaliana•Flowering depends on• Photoperiod: Long, Short, neutral•Temperature: cold•Nutrients: sucrose•Hormones: GA, CytokininShoot apical meristem –ÆFloral apical meristemFour developmental pathways for floweringShoot Apical meristem4 organs of a flower: sepal, petal, stamen (male), --> pollen (sperm)pistil (female) ---> ovule (egg)Anther cells ÆPMC –> meiosis ->microspore ÆpollenDavid Twell’s Pollen website http://www.le.ac.uk/biology/research/pollen/pollen.htmlDevelopment of the male gametophyteGrowing pollen tubeDevelopment of the female gametophyteBuchanan, chap. 19-3Pollination & fertilization.Zygote develops into an embryoBuchanan. Ch 19-36Embryo development (embryogenesis)and formation of a seedEmbryogenesisEmbryo in a seed.Establish a shoot-root polarity.a. Shoot meristemb. Root meristemSeed dehydrates.DormantPostembryonic development derive from the root and shoot apical meristemsShoot apicalmeristem produce -stem, leaves, flower -tissues-Cell typesRoot apical meristem-root-tissues-cell typesDevelopment of seedling depends on environmental signalsShaping of each new structure depends on the oriented cell division and expansion4Cell signaling maintains the meristemQ? How does the apical meristem maintain itself?Cells divide but meristem remains constant at ~100 cells. Long-range hormonal signals coordinate development in separate parts of the plant.e.g. separate parts of plant experience different environments, but they must communicate with one another in order to function as one body.Homeotic genes specify the parts of a flowerCells acquire tissue identity as a result of specific gene expressione.g. Floral meristem-identity genesABC modelHomeotic genesencode proteins that bind to DNA and enable protein to regulate transcription. They act as developmental switches.Growth, Development and AdaptationI. What is development? Development is the sum of all changes that an organism goes through in its life cycle.Development = growth + differentiation•Growth is an irreversible increase in size or volume.•Differentiation occurs when cells take on a special form and function.•Pattern formation is determined by the plane of cell divisionII. What controls development? The orderly development of the plant depends on coordination and are subject to control at 3 distinct levels:1. Genetic control: developmental program 2. Environmental stimuli [or extrinsic factors]3. Hormones (or intrinsic factors) communicate signals long distance.III. How is gene expression regulated? Changes in gene expression is a principal factor in regulating development.A. Transcription B. RNA processingC. Translation D. Protein Modification or post-translationMost if not all environmental and hormonal stimuli act in part on modifying gene expression.16-5 Taiz. Development of an embryo from a zygote 18-4 Buchanan. Light-regulated seedling development is controlled by genes5Environmental & hormonal signals affect growth & development.18-2 BuchananReview of gene expression.Information flows from DNA ÆRNA ÆproteinQ: Do root hair cells contain the gene for rubisco?How is gene expression controlled?Regulation of gene expression in eukaryotes by cis-acting elements Cis-acting control elements: regions of DNA that bind to protein transcription factors and the binding activates or represses transcription. Two typesa. Upstream of structural gene or promoterb. Enhancer: upstream, downstream or within introns[e.g. guard-cell specific promoter- will control expression of protein in GC only]14-5 TaizMany levels of control of gene expression614-7 Taiz. Regulation of TranscriptionRegulatory DNA defines the program of development.Complexes of gene regulatory proteins bind to promoter and enhancer DNA to switch on [or off] gene expression14-7 TaizGene Regulatory proteins are also called transcription factorsExample of Spatial and temporal regulation of gene expression by Transcription Factors (trans-acting factors)Power of mutantsStudies of mutants have identified genes that control development.e.g. Cop mutants are not responsive to lightdet mutants are deetiolated in the dark.Hormone receptor identified from a mutant insensitive to a hormone.16-1. Arabidopsis thaliana- a model plant-completes life cycle in 6 weeks-self-fertilize-has one of the smallest genome: 28,000 genes; completely sequenced-is easily transformed by Agrobacterium to introduce new gene-many mutants availablePrinciples of plant development. 1. Expression of genes