Transcript Lecture 2
The Eudicot plant, morphology, meristems, cell types and tissues Objectives of the lecture: 1. To illustrate and name some essential parts of plants, 2. show how they are produced, 3. discuss how cell and tissue structure are integrated with morphology, 4. give examples of some variation in morphology between species. Text book pages: 472-473, 792-808, 800-812 Figure 36-19 Plant cells have cell walls, vacuoles, and chloroplasts. Adjacent plant cells are connected by plasmodesmata. Cell 2 Smooth ER Cell wall Plasma membrane Cell 1 Vacuole Chloroplast Plasmodesma Plasma membrane Cell wall Cell wall Plasma membrane Rough ER Smooth ER Mitochondria Golgi apparatus Communication between cells is through plasmodesmata Plant cell walls are flexible but have considerable tensile strength Figure 8-9 Secondary cell wall Primary cell walls Middle lamella Cell walls consist of 3 types of layers Middle lamella is formed during cell division. It makes up the outer wall of the cell and is shared by adjacent cells. It is composed of pectic compounds and protein. Primary wall: This is formed after the middle lamella and consists of a skeleton of cellulose microfibrils embedded in a gel-like matrix of pectic compounds, hemicellulose, and glycoproteins. Secondary wall: formed after cell enlargement is completed provides compression strength. It is made of cellulose, hemicellulose and lignin. The secondary wall is often layered. Figure 8-14 Plasmodesmata create gaps that connect plant cells. Cell walls Tubule of endoplasmic reticulum passing through plasmodesmata Membrane of cell 1 Smooth endoplasmic reticulum Cell wall Cell wall of cell 1 of cell 2 Membrane of cell 2 Plasmodesmata seen in Transverse Section: They are not simple openings as they have a complex internal structure. Tissues A tissue is a cooperative unit of many similar cells performing a specific function within a multicellular organism Tissues usually have cells that are specialized for particular functions The vascular tissue system conducts water and nutrients from roots to leaves through specialized cells and conducts the products of photosynthesis, sugars, from leaves in different but equally specialized cells. Plants comprises three main tissue types each with different functions. Dermal tissue – protection and interface with the environment Ground tissue – frequently the site of storage, sometimes support Vascular tissue – conduction of water and materials used in synthesis There is continuity of these individual tissue systems through the plant Meristematic tissue Cross sections: Leaf Dermal tissue system (brown) Ground tissue system (gray) Stem Root system Vascular tissue system (red) Dermal tissue system (brown) Root Meristematic tissue Figure 36-16 Ground tissue system (gray) Vascular tissue system (red) lateral (axillary) bud shoot tip (terminal bud) young leaf flower See Fig. 36.3 in your text book node internode node EPIDERMIS Dermal tissue leaf VASCULAR TISSUES seeds (inside fruit) GROUND TISSUES The angiosperm plant body withered cotyledon SHOOT SYSTEM ROOT SYSTEM A tomato plant primary root lateral root root hairs root tip root cap Figure 36-23 activity at meristems Shoot apical meristem Actively dividing cells near the dome-shaped tip new cells elongate and start to differentiate into primary tissues The apical meristem’s descendant cells divide, grow and differentiate to form: Protoderm Ground meristem Procambium new cells elongate and start to differentiate into primary tissues activity at meristems Root cap Root apical meristem Function of apical meristems Figure 36-15 Apical meristems and primary meristems in a root Apical meristem and primary meristems in a shoot Leaf primordia Apical meristem at tip of shoot Apical meristem in lateral bud Procambium Protoderm Ground meristem Apical meristem Root cap What does a meristem look like? Coleus Longitudinal section through the apical meristem Apical meristem Transverse section through the apical meristem and newly forming leaves Coleus Axilliary bud meristem The axilliary meristem may develop into a foliated branch. L4 S8 Immature leaf shoot apical meristem procambium protoderm procambium ground meristem Meristems-> Tissues Meristems Tissues Spiral thickening cortex procambium primary xylem pith primary pholem Figure 23-7 Mutants lacking hypocotyls and roots in Arabidopsis The MONOTERPOS gene encodes a transcription factor that regulates activity of target genes and the MONOTERPOS protein is manufactured in response to signals from auxin which is produced at the apex and occurs in a concentration gradient which provides positional information. Regulation of developmental pathways The expression of genes that encode transcription factors determines cell, tissue and organ identity The fate of a cell is determined by its position and not its clonal history Developmental pathways are controlled by networks of interacting genes Development is regulated by cell-to-cell signalling Ligand-induced signalling: cell wall component chemicals that communicate local positional information Hormonal signalling: auxin and others Signalling via regulatory proteins and/or mRNAs through plasmodesmata Plants of the day Celery Potato Carrot Brussels sprout Cabbage Simple tissues of parenchyma, collenchyma and sclerenchyma Important structural tissues of many angiosperms Transverse section epidermis collenchyma sclerenchyma xylem pholem Pages 804805 of your text book parenchyma Table 36-1 b x w z Sclerenchyma Figure 36-25 Fibers Sclereids Thick secondary cell walls Collenchyma Figure 36-24 Cross section of celery stalk Close-up of “string,” in cross section Collenchyma cells, in cross section Figure 36-22 In leaves, parenchyma cells function in photosynthesis and gas exchange. Chloroplasts Parenchyma In roots, parenchyma cells function in carbohydrate storage. Starch granules Figure 36-18 Cross section of a eudicot stem Cross section of a monocot stem Epidermis Cortex Pith Ground tissue Vascular bundles Lateral root Root hair Root meristem and structure Roots must ‘force’ their way through the soil Protection of the apical mersitem Vascular tissue Ground tissue Zone of Cellular Division Epidermal tissue Figure 36-17 Apical meristem Sloughed-off root cap cells Root cap Delayed initiation of lateral meristems Different requirements for support and water collection and distribution Zea mays root apex Zea mays root apex showing the junction between root apex and the root cap Lateral root development in Zea mays A meristem develops from parenchyma and the lateral root grows out through the cortex Things you need to know ... 1. The structure of cell walls and how communication between plant cells may take place. 2. Be able to define a tissue and give examples of cell types and functions within important tissues of the plant. 3. Define the structure of angiosperm plants. 4. Define the meristems of the angiosperm plant and describe how tissues develop from them