Plant Tissues

Angiosperms – flowering plants The angiosperms are seed-bearing vascular plants In terms of distribution and diversity, they are the most successful plants on Earth The structure and function of this plant group help explain its success

Monocots and Dicots – same tissues, different features 1 cotyledon 2 cotyledons 4 or 5 floral parts 3 floral parts Netlike veins Parallel veins 3 pores 1 pore Vascular bundles dispersed Vascular bundles in ring

Flowering Plant Life Cycle Diploid Double fertilization Meiosis Meiosis Haploid Mitosis without cytoplasmic division microspores pollination Two sperms enter ovule Female gametophyte

Plant Life Histories Annuals complete life cycle in one growing season Biennials live for two seasons; flowers form in second season Perennials grow and produce seeds year after year

Meristems – Where Tissues Originate Regions where cell divisions produce plant growth Apical meristems Responsible for primary growth (length) Lateral meristems Responsible for secondary growth (width)

Apical Meristems Lengthen shoots and roots: StemAM and RootAM activity at meristems Cells that form at apical meristems: new cells elongate and start to differentiate into primary tissues protoderm  epidermis ground meristem  ground tissues procambium  primary vascular tissues

Lateral Meristems Increases girth of older roots and stems Cylindrical arrays of cells vascular cambium  secondary vascular tissues periderm  cork cambium thickening

Plant Tissue Systems Ground tissue system Vascular tissue system Dermal tissue system EPIDERMIS VASCULAR TISSUES GROUND TISSUES SHOOT SYSTEM ROOT SYSTEM

Ground Tissue fills space b/t dermis & vascular  Parenchyma: Primary metabolic function (photosynthesis) Found in roots, stems & leaves Least specialized, thin flexible walls, don’t divide unless specializing, respire, store food & water Schlerenchyma: support w/ thick 2o wall strengthened by lignin Found in stems & leaves generally lack protoplasts Very rigid cell wall, dead at maturity, cannot lengthen scaffolding “fibers” & “Sclereids” Collenchyma: child support Found in stems and leaves Grow and elongate with stems and leaves they support, flexible in young parts of plant

Morphology of three simple tissue types parenchyma collenchyma sclerenchyma

Simple Tissues Complex Tissues Composed of a mix of cell types Xylem Phloem Epidermis Made up of only one type of cell Parenchyma Collenchyma Sclerenchyma

Vascular Tissue   Phloem: Phood conduction, carries products of photosynthesis to non-photo cells Found in roots, stems, leaves Sieve cells, albuminous cells, companion cells, parenchyma Gymnospersm: sieve, angiosperms, sieve-tube members, connected vertically by sieve plates Alive at maturity Xylem: provides water & ion transport from roots to leaves Vessel elements, tracheids, fibers, wood parenchymal tracheids & vessel members, thick w/ secondary wall with lignin Dead at maturity Seedless vascular & gymnosperms have tracheids w/ tapered ends Angiospersm have both tracheids and vessel members wh are continuous

Xylem Conducts water and dissolved minerals Conducting cells are dead and hollow at maturity vessel member tracheids

Phloem: A Complex Vascular Tissue sieve plate Transports sugars Main conducting cells are sieve-tube members Companion cells assist in the loading of sugars sieve-tube member companion cell

Epidermis: A Complex Plant Tissue - Covers and protects plant surfaces Secretes a waxy, waterproof cuticle In plants with secondary growth, periderm replaces epidermis protection, increase absorption area in roots, reduces H2O loss in stem & leaves, Regulates gas exchange in leaves Signaling between Plants and Pathogens

Shoot and Root Systems: Not independent Shoot system produces sugars by photosynthesis carries out reproduction water & minerals sugar SHOOT SYSTEM Root system anchors the plant penetrates the soil and absorbs water and minerals stores food ROOT SYSTEM

Shoot Development shoot apical meristem protoderm procambrium ground meristem cortex procambrium pith primary xylem primary phloem

Roots also have meristems

Leaf Gross Structure-Adapted for Photosynthesis Leaves are usually thin High surface area-to-volume ratio Promotes diffusion of carbon dioxide in, oxygen out Leaves are arranged to capture sunlight Are held perpendicular to rays of sun Arrange so they don’t shade one another petiole blade axillary bud node sheath DICOT MONOCOT

Leaf Structure UPPER EPIDERMIS cuticle PALISADE MESOPHYLL xylem SPONGY phloem LOWER EPIDERMIS CO2 one stoma O2

Mesophyll: Photosynthetic Tissue A type of parenchyma tissue Cells have chloroplasts Two layers in dicots Palisade mesophyll Spongy mesophyll Parenchyma Collenchyma

Leaf Veins: Vascular Bundles Xylem and phloem – often strengthened with fibers In dicots, veins are netlike In monocots, they are parallel

Internal Structure of a Dicot Stem - Outermost layer is epidermis - Cortex lies beneath epidermis - Ring of vascular bundles separates the cortex from the pith - The pith lies in the center of the stem

Internal Structure of a Monocot Stem The vascular bundles are distributed throughout the ground tissue No division of ground tissue into cortex and pith

Dicots Monocots Ground tissue system Dermal tissue system Vascular tissue system Dicots and Monocots have different stem and root anatomies

Stems Monocot stems differ from dicot stems in that they lack secondary growth No vascular cambium nor cork cambium Stems usually uniform in diameter Scattered vascular bundles (not in a ring like dicot stems)

The Translocation of Phloem the process of moving photosynthetic product through the phloem In angiosperms, the specialized cells that transport food in the plant are called sieve-tube members, arranged end to end to form large sieve tubes Phloem sap is very different from xylem sap sugar (sucrose) can be concentrated up to 30% by weight Phloem transport is bidirectional Phloem moves from a sugar source (a place where sugar is produce by photosynthesis or by the breakdown of sugars) to a sugar sink (an organ which consumes or stores sugar) What are some organs which would be sugar sinks? Transport in Plants: The Pressure Flow Model , 2

Root Systems

Root Structure Root cap covers tip Apical meristem produces the cap pericycle phloem xylem root hair endodermis epidermis cortex Root cap covers tip Apical meristem produces the cap Cell divisions and elongation at the apical meristem cause the root to lengthen Farther up, cells differentiate and mature root apical meristem root cap

Primary Root Growth Root Cap Secretes polysaccharide slime that lubricates the soil Constantly sloughed off and replaced Apical Meristem Region of rapid cell division of undifferentiated cells Most cell division is directed away from the root cap Quiescent Center Populations of cells in apical meristem which reproduce much more slowly than other meristematic cells Resistant to radiation and chemical damage Possibly a reserve which can be called into action if the apical meristem becomes damaged The Zone of Cell Division - Primary Meristems Three areas just above the apical meristem that continue to divide for some time Protoderm Ground meristem Procambium The Zone of Elongation Cells elongate up to ten times their original length This growth pushes the root further downward into the soil The Zone of Maturation Region of the root where completely functional cells are found

Internal Structure of a Root Outermost layer is epidermis Root cortex is beneath the epidermis Endodermis, then pericycle surround the vascular cylinder In some plants, there is a central pith

Root Anatomy - Dicot Roots Epidermis Dermal tissue Protection of the root Cortex Ground tissue Storage of photosynthetic products Active in the uptake of water and minerals Endodermis cylinder once cell thick that forms a boundary between the cortex and the stele contains the casparian strip, Pericycle found just inside of the endodermis may become meristematic responsible for the formation of lateral roots Vascular Tissue Xylem and Phloem Root Anatomy - Monocot Roots cylinder once cell thick that forms a boundary between the cortex and the stele even more distinct than dicot counterpart contains the casparian strip, monocot roots rarely branch, but can, and this branch will originate from the pericycle Forms a ring near center of plant Pith Center most region of root

Root Hairs and Lateral Roots Both increase the surface area of a root system Root hairs are tiny extensions of epidermal cells Lateral roots arise from the pericycle and must push through the cortex and epidermis to reach the soil Root of a single rye plant (fibrous system) measure and counted 6400 roots w/ 12.5 million root hairs = 250 km, dist from Memphis, TN to Atlanta, GA new lateral root

Symplastic Movement Movement of water and solutes through the continuous connection of cytoplasm (though plasmodesmata) No crossing of the plasma membrane (once it is in the symplast) Apoplastic Movement Movement of water and solutes through the cell walls and the intercellular spaces No crossing of the plasma membrane More rapid - less resistance to the flow of water

Net flow in whole plants Fig. 36.1 overview of transport in plants Animation 36.1.4 Transpiration Pull (animation ~ 5)

Fig. 39.12b

Ascent of xylem sap transpirational pull flow from greater to lower water concentration relies on cohesion & adhesion of water cavitation breaks chain of water molecules corresponding overheads: Fig. 36.10 roles of cohesion & adhesion in ascent of xylem sap Fig. 36.11 control of stomatal opening & closing

Fig. 39.11

The availability of soil water and minerals Animation 37.1. (animation~4) Mineral uptake in roots Long-distance transport of water from roots to leaves

Net flow in whole plants Key Concepts: Diffusion: movement of molecules from high to low concentration. Osmosis: diffusion of water across a semi-permeable membrane. Mass or bulk flow: movement of fluid due to pressure or gravity differences. Fig. 36.1 overview of transport in plants Animation 36.1.4 Transpiration Pull (animation ~ 5)

Long-distance movement of water Plants mostly obtain water & minerals from soil. Water moves up the xylem by bulk flow. Movement of water depends on transpiration pull, cohesion & adhesion of water molecules, capillary forces, and strong cell walls. Other mechanisms of water transport not as important: Diffusion (note mosses, etc.) Capillary forces (cohesions & adhesion) Osmotic pressure (guttation)

Water – pushed or pulled? Fig. 39.11 Water – pushed or pulled? Pushing of the xylem sap occurs via root pressure – root cells expend energy to pump mineral into the xylem. Minerals accumulate in the xylem sap lowering water potential there. Thus water flows into the xylem, generating a positive pressure that pushes fluid up the xylem. Guttation – from root pressure

The availability of soil water and minerals But root pressure can only push sap up a few meters and many plants generate no root pressure at all. How does water reach leaves of 100 m tall trees? Xylem sap is pulled up the plant via transpirational pull. Leaves actually generate the negative pressure necessary to bring water to them. The availability of soil water and minerals Animation 37.1. (animation~4) Mineral uptake in roots Long-distance transport of water from roots to leaves

Translocation The transport of food throughout a plant is known as translocation. Sugar from mesophyll cells in the leaves and other sources must be loaded before it can be moved. Often sieve tube members accumulate very high sucrose concentrations – 2 to 3 times higher than concentrations in the mesophyll – so phloem requires active transport using proton pumps At the sink end of a sieve tube, the phloem unloads its sugar. Phloem unloading is a highly variable process; its mechanism depends upon the plant species and the type of organ. In any case, the concentration of sugar in the sink cells is lower than in the phloem because the sugar is either consumed or converted into insoluble polymers like starch. Phloem moves at up to 1 m/hour – too fast to be by diffusion. So phloem also moves via bulk flow – pressure drives it.

Secondary Growth Occurs in perennials A ring of vascular cambium produces secondary xylem and phloem Wood is the accumulation of these secondary tissues, especially xylem The Plant Body: Secondary Growth: The Vascular Cambium

Woody Stem periderm (consists of cork, cork cambium, and secondary cortex) secondary phloem HEARTWOOD SAPWOOD BARK vascular cambium

Annual Rings Concentric rings of secondary xylem Alternating bands of early and late wood Early wood Xylem cells with large diameter, thin walls Late wood Xylem cells with smaller diameter, thicker walls

Types of Wood Hardwood (oak, hickory) Softwood (pine, redwood) Dicot wood Xylem composed of vessels, tracheids, and fibers Softwood (pine, redwood) Gymnosperm wood Xylem composed mostly of tracheids Grows more quickly

Resources Plants in Motion: Movement of Water in Plants Transport in Plants Root Pressure Water Transport in 3 Parts