Ground tissue of roots, consisting mostly of parenchyma cells, fills the cortexThe innermost layer of the cortex is called the endodermis – a cylinder 1 cell thick that forms the boundary with the vascular system (selective barier).Pericycle – outermost cell layer in vascular cylinder adjacent to & just inside endodermis – from which lateral roots ariseLateral roots cannot originate near the roots surface because its vascular system must be continuous with the vascular cylinder at the center of the established root.Casparian strip – waxy material impervious to water & dissolved minerals
Ground tissue consists mostly of parenchyma butcollenchyma just beneath the epidermis provides strength for stems.Sclerenchyma cells, especially fiber cells, also provide support in those parts of the stems that are no longer elongating.Vascular cambium (lateral meristem) – cylinder of dividing cells for growth in thickness – adds layers of vascular tissue called secondary xylem and secondary phloem
Ground tissue of a leaf, a region called the mesophyll is sandwiched between the upper and lower epidermal layers.Mesophyll consists mainly of parenchyma specialised for photosynthesis, including pallisade and spongy mesophyll.
Vascular cambium and cork cambium = lateral meristems for secondary growth (thickness)Vascular cambium adds layers of vascular tissue: secondary xylem (wood) & secondary phloemCork cambium (adds secondary dermal tissue)replaces the epidermis with the thicker, tougher periderm.
Primary growth from activity of apical meristem nears completion – vascular cambium forms.Secondary growth begins – stem thickens as vascular cambium forms secondary xylem to the inside and secondary phloem to the outside.Some initials give rise to vascular rays – connect the secondary xylem with the secondary phloem, move water and nutrients, store carbohydrates and aid in wound repair.Secondary phloem can’t keep pace as cells no longer divide – as a result these tissues & epidermis will ruptureCork cambium develops – produces cork cells which replace epidermis
Cytosol - the semi-fluid portion of the cytoplasm
UNIT 5: SUPPORT AND TRANSPORTSYSTEMS IN PLANTS(CAMPBELL & REECE (2010) CHAPTER 35 &36)
1. ANATOMY OFDICOTYLEDONOUS PLANTS• Plants, like multicellular animals, haveorgans composed of different tissues,which in turn are composed of cells• Three basic organs evolved: roots, stems,and leaves• They are organized into a root system anda shoot system
Dermal tissue• In nonwoody plants, the dermal tissuesystem consists of the epidermis• A waxy coating called the cuticle helpsprevent water loss from the epidermis• In woody plants, protective tissues calledperiderm replace the epidermis in olderregions of stems and roots• Trichomes are outgrowths of the shootepidermis and can help with insect defence.
Vascular Tissues• The vascular tissue system carries outlong-distance transport of materialsbetween roots and shoots• The two vascular tissues are xylem andphloem• Xylem conveys water and dissolvedminerals upward from roots into the shoots• Phloem transports organic nutrients fromwhere they are made to where they areneeded
Ground Tissues• Tissues that are neither dermal norvascular are the ground tissue system• Ground tissue internal to the vasculartissue is pith; ground tissue external to thevascular tissue is cortex• Ground tissue includes cells specialized forstorage, photosynthesis, and support
2. SECONDARY GROWTH(Chapter 35 p.751-754)• Secondary growth occurs instems and roots of woody plantsbut rarely in leaves• The secondary plant bodyconsists of the tissues producedby the vascular cambium andcork cambium
a. The Vascular Cambium andSecondary Vascular Tissue• The vascular cambium is a cylinder of meristematiccells one cell layer thick• It develops from undifferentiated parenchyma cells• Secondary xylem accumulates as wood, andconsists of tracheids, vessel elements and fibers.• Early wood, formed in the spring, has thin cell wallsto maximize water delivery.• Late wood, formed in late summer, has thick-walled cells and contributes more to stem support.
a. The Vascular Cambium andSecondary Vascular Tissue• Tree rings are visible where late and early woodmeet, and can be used to estimate a tree’s age• Dendrochronology is the analysis of tree ringgrowth patterns, and can be used to study pastclimate change.• As a tree or woody shrub ages, the older layers ofsecondary xylem, the heartwood, no longertransport water and minerals.• The outer layers, known as sapwood, stilltransport materials through the xylem.
a. The Vascular Cambium andSecondary Vascular Tissue
3. UPTAKE OF WATER ANDMINERALS INTO THE ROOTS• The plasma membrane directly controls thetraffic of molecules into and out of the cell.• In most plant tissues, the cell wall and cytosol arecontinuous from cell to cell.• The cytoplasmic continuum is called thesymplast.• The cytoplasm of neighboring cells is connectedby channels called plasmodesmata.• The apoplast is the continuum of cell walls andextracellular spaces.
Water and minerals can travel througha plant by three routes:Transmembrane route: out of onecell, across a cell wall, and intoanother cell.Symplastic route: via the continuumof cytosol.Apoplastic route: via the cell wallsand extracellular spaces.
Water and minerals can travel througha plant by three routes:
Pathway 1: Transmembrane routeWater and minerals move from the soil (highWP) through the cell wall, plasmamembraneand into the cytoplasm of the roothair.Through the cell wall, plasma membraneand into the cytoplasm of the cortex cells.Through the cell wall, plasma membraneand into the cytoplasm of the endodermisThrough the cell wall, plasma membraneand into the cytoplasm of the pericycle.Through the cell wall, plasma membraneand into the xylem of the plant.
Pathway 2: symplastic route Water and minerals flow from the highWP in the soil, through the cell wall,plasma membrane and into thecytoplasm of the roothair. Through the plasmodesmata linking thecytoplasm of the cells into the cytoplasmof the cortex cells. Flowing through the plasmodesmatainto the cytoplasma of the endodermiscells and pericycle and into the xylem.
Pathway 3: Apoplastic route During the Apoplastic route the water andminerals travel along the cell walls of theroothairs, cortical cells, and endodermis, butthe endodermis has Casparian strips thatprevent further movement of water, thereforewater enter the cytoplasm of the endodermalcells and then take the symplastic route(through cytoplasm and plasmodesmata thatlink cytoplasm of cells) into the xylem of theroot. D:Chapter_36A_PowerPoint_Lectures36_Lecture_Presentation36_12TransportInRoots_A.html
Transport of minerals across anendodermal plasma membrane Minerals follow the same routes as water when it movesthrough the roothair and cortex cells. But when it moves through the endodermal plasmamembrane it does it in the following way: An ATP driven pump removes hydrogen ions from thecell. This establishes an electrochemical gradient thatallows potassium ions and other positively chargedions to cross the membrane via a channel protein. Negatively charged mineral ions can cross themembrane by way of a carrier when they “hitch aride” with hydrogen ions, which are diffusing downtheir concentration gradient.
Transport of minerals across anendodermal plasma membrane
3. TRANSPORT OF WATER ANDMINERALS TO THE LEAVESWhat makes the upward movement of waterin the xylem of the stems and leaves possible? Root pressure Cohesion-adhesion-tension Transpiration
• Water entering root cells creates a positivepressure called root pressure.• It occurs at night and tends to push xylemsap upwards.I) Root pressure
Upward movement of water requiring noenergy. Cohesion- Tendency of watermolecules tocling together and form a continuous watercolumn. Adhesion- Tendency of water molecules tocling to the sides of the container (xylem)they are in. It gives the water column extrastrength and prevents it from slipping backII) Cohesion-adhesion-tensionmodel
Transpiration is the loss of water vapour throughthe stomata of the leaf. The water molecules that evaporate from the cellsinto the intercellular airspaces are replaced byother water molecules from the leaf xylem. Because the water molecules are cohesive,transpiration exerts a pulling force, or tension, thatdraws the water column through the xylem toreplace the water lost by the stomata. This is also a mechanism by which minerals aretransported throughout the plant body. D:Chapter_36A_PowerPoint_Lectures36_Lecture_Presentation36_15Transpiration_A.htmlIII) Transpiration
High temperature – faster transpirationHigh light intensity – faster transpirationWindy – faster transpirationHigh humidity – slower transpirationD:Chapter_36A_PowerPoint_Lectures36_Lecture_Presentation36_15WaterTransportPlants_A.htmlEnvironmental factors that influencethe speed of transpiration
Environmental factors that influencethe speed of transpiration
What is guttation and what causes it? Root pressure is responsible for guttation. Guttation is when drops of water areforced out of the vein endings along theedges of leaves called hydathodes.
4. TRANSLOCATION OF SUBSTANCES FROMTHE LEAVES TO THE REST OF THE PLANT(Chapter 36 p. 779-780) The products of photosynthesis aretransported through phloem by theprocess of translocation. Phloem sap is an aqueous solution that ishigh in sucrose. It travels from a sugar source to a sugarsink
A sugar source is an organ that is a netproducer of sugar, such as mature leaves A sugar sink is an organ that is a net consumeror storer of sugar Sugar must be loaded into sieve-tube elementsof the phloem. Sugar then moves by symplastic or bothsymplastic and apoplastic pathways. At the sink, sugar molecules diffuse from thephloem to sink tissues and are followed bywater. D:Chapter_36A_PowerPoint_Lectures36_Lecture_Presentation36_20PhloemTranslocSpring_A.html D:Chapter_36A_PowerPoint_Lectures36_Lecture_Presentation36_20PhloemTranslocSummer_A.html
TRANSLOCATION OF SUBSTANCES FROM THELEAVES TO THE REST OF THE PLANT