Plant hierarchy: • Cells • Tissue: group of similar cells with similar function: Dermal, Ground, Vascular • Organs: multiple kinds of tissue, very diverse function • Organ systems • Organism
35.1 Roots Roots • an organ that anchorsa vascular plant. • Absorbs water & inorganic nutrients • Storage of nutrients • Types of roots • Taproot Systems • Consist of one main vertical root • Gives rise to lateral roots (like branches) • Taproots store organic nutrients used in flowering and fruit production. • Fibrous Root System – a mat of roots that spread out below the soil • Root Hair – an extension of a root that gathers nutrients Root cap covers root tip (apical meristem): primary growth site epidermis, ground and vascular tissue. Mycorrhizae: mutualistic fungi and plant roots.
Roots Cont. http://belizebreeze.com/images/lamanai_tree_roots_rev_lowres.jpg http://quorumsensing.ifas.ufl.edu/HCS200/images/stems&roots/korni.jpg
Stems • an organ consisting of an altering system of: • nodes: point where leaves are attached • internodes: stem segments between nodes • Axillary bud – a structure that potentially forms a lateral shoot otherwise known as a branch • At the end of this branch is a terminal end which develops leaves. • Apical Dominance • A phenomenon where the proximity of the terminal bud inhibits the growth of an axillary bud • This is an evolutionary adaption where resources are concentrated toward elongation; it also increases the plant’s exposure to light. • If one is removed then the bud stimulates the growth of an axillary bud which produces more shoots. • That is why pinching back a plant makes it bushier.
Stems Cont. http://www.infovisual.info/01/015_en.html
Leaves • the main photosynthetic organ of vascular plants • Leaves usually consist of: • blade • petiole – Joins the leave to a node on the stem • veins – vascular tissues of the leaves • Veins are how monocots and dicots differ • Monocots have parallel veins • Endicots are multi branched • There are many different types of modified leaves • Spines, tendrils, storage, bracts (poinsettias), reproductive (succulents) http://photos.somd.com/data/500/LEAF.jpg
Three Types of Tissue: Dermal, Vascular, and Ground Tissue system – one or more tissues organized into a functional unit Dermal Tissue System • Outer protective covering (like skin) • Non woody plants – single layer of epidermis • Cuticle – A waxy coating on the leaves and the stems that helps prevent water loss. • Woody plants – periderm replaces epidermis Vascular Tissue System • Carries out long distance transport between root and shoot. • Two vascular tissues • Xylem – conveys water and dissolved mineral up to shoots • Phloem – transports organic nutrients to where they are needed. • Vascular tissue of a root = stele Ground Tissue System • Tissues that are neither dermal nor vascular
Tissue System http://www.emc.maricopa.edu/faculty/farabee/BIOBK/leafstru.gif
Plant Cells Type of cells found in plants: • Parenchyma Cells – a relatively unspecialized plant cell type that carries out most of the metabolism, synthesizes and stores organic products, and develops into a more differentiated cell type. • Guard cells • Sieve tube cells • Tracheoid cells • Palisade mesophyll: Photosynthesis • Spongy mesophyll: spaces allow the exchange of gases
35.2 - 35.4 Meristems generate cells for new organs • Apical meristems elongate shoots and roots through primary growth • With the process of primary growth it also allows roots to extend throughout the soil and for shoots to increase there exposure to light and CO2 • Lateral meristems add girth to woody plants through secondary growth. • Root cap: secretes a mucus that allows tip growth through soil
Primary Growth Roots • Primary growth produces the primary plant body. • ROOTS the root tip is covered by a thimble-like cap which protects the vulnerable apical meristem as the root pushed through the soil. • GROWTH occurs just behind the root tip, zone of cell division, elongation, and maturation. • The zone of cell division: produced in the apical meristem • The zone of elongation, root cells elongate and new cell are added allowing the root to dive further into the soil. • The zone of Maturation, cells complete their differentiation and become functionally mature.
Primary Growth of Shoots • The apical meristem of a shoot is a dome shaped mass which is located in the terminal bud, where it gives rise to a repetiton of internodes and leaf bearing nodes.
The Vascular Cambium and secondary Vascular tissue • The vascular cambium develops from parenchyma cells into a meristematic cylinder that produces secondary xylem to the inside and secondary phloem to the outside. • Older layers of secondary xylem (heartwood) eventually become inactive. • Younger layers (sapwood) still conduct water. • Only the youngest secondary phloem is active.
Cork Cambia and the Production of Periderm • The cork cambia is a lateral meristem: • Makes dermal tissue or periderm. • The bark on the other hand consists of all the tissues external to the vascular cambium which include secondary phloem and periderm.
35.5 Growth, Morphogenesis, and the Differentiation Produce the Plant Body • Morphogenesis: The development of body form and organization Each cell in the plant body contains the same set of genes, exact copies of the genome present in the fertilized egg. • Different patterns of gene expression among cells cause the cellular differentiation that creates a diversity of cell types. • The three developmental processes of growth, morphogenesis, and cellular differentiation act in concert to transform the fertilized egg into a plant.
Growth: Cell Division and Expansion • Cell division and self-expansion are primary factors for growth • Plant cells rarely expand in all directions, their greatest expansion occurs in the plants main axis. • Growing plant cells expand mainly through water uptake. In a growing cell, enzymes weaken cross–links in the cell wall, allowing it to expand as water diffuses into the vacuole by osmosis. • Orientation of the cytoskeleton also affects direction of cell elongation by controlling the orientation of cellulose micro fibrils.
Preprophase Band http://www.nature.com/nrm/journal/v2/n1/images/nrm0101_040a_f1.gif
Differentiation and Pattern Formation • Development of tissues and organs in specific locations (pattern formation) depends on cells ability to detect and respond to positional info. • Polarity-is the idea that a cell (egg) has diff. concentration of contents • Homeotic genes often control morphogenesis and also mediate many of the other events in an individual’s development, such an initiation of an organ. • Gene Expression and control of Cellular Differentiation • Cellular differentiation: selective gene expression • Cellular differentiation depends on a large extend on positional information, where a particular cell is located relative to other cells.
Gene Expression http://www.biosci.ohio-state.edu/~bdinglab/Research/Resear7.jpg
Shifts in Development: Phase Change • Internal or environmental cues may cause a plant to switch from one developmental phase to another. • From the development of juvenile leaves to the development of mature leaves, these are called phase changes.
Juvenile vs. Adult Leaves http://upload.wikimedia.org/wikipedia/en/c/ce/Pinus_pinea.jpg
Genetic Control of Flowering • Research on organ identity genes in developing flowers provides an important model of pattern formation. • The ABC modelof flower formation identifies how 3 classes of organ identity genes control the formation of sepals, petals stamens, and carpel’s. • The floral organs develop in four circles, or whorls: Sepals form the fourth (outermost) whorl; petals form the third; stamens form the second; and carpels form the first (innermost) whorl. Plant biologists have identified several organ identity genes that regulate the development of this characteristic floral pattern. Organ identity genes, also called plant homeotic genes, code for transcription factors. Positional information determines which organ identity genes are expressed in a particular floral organ. The result is development of an emerging leaf into a specific floral organ, such as a petal or a stamen.