Kingdom Plantae Plant Structure & Growth. Plants have evolved two systems: subterranean root system aerial shoot system of stems and leaves. roots shoots

Kingdom Plantae

Plant Structure & Growth

Plants have evolved two systems:

• subterranean root system

• aerial shoot system of stems and leaves.

roots

shoots

Primary Function of Organs

Three organs in plants:• Stem• Leaves• Root

Shoot system

• Roots anchor the plant in the soil

• Store food

• Absorb minerals and water

• Most absorption of water and minerals in occurs near the root tips.

Roots

ProprootsProproots

Black Mangrove with Pneumatophore

http://www.botany.hawaii.edu/faculty/webb/bot311/bot311-00/roots/Mangroves/MangrovePneumatophorelenticela.jpg

Shoots consist of stems and leaves.

• Stem: Raises leaves and flowers above ground (safer from herbivores and allow leaves to better photosynthesize). Path by which water, minerals, and food are transported.

• Leaves: Site of photosynthesis, i.e. food production

Shoots System: stems and leaves

• Stems– May be vegetative (leaf bearing) or

reproductive (flower bearing).– Node- area of stem where leaf is born– Internodes- stem area between nodes – Buds: Stem elongation. Embryonic tissue of

leaves and stem (not flower bud)–Terminal bud-Located at tip of stems or

branches. –Axillary bud- Gives rise to branches

– Apical Dominance: Prevention of branch formation by terminal bud

Shoots System:

• Leaves:Photosynthesis

– Petiole: Stalk of leaf, joins leaf to node of stem– Blade: Flattened, expanded portion of leaf.

Site of photosynthesis

Shoot System

• Modified shoots:– Include stolons, rhizomes, tubers, and bulbs, are

often mistaken for roots. – Stolons: allow plants to colonize large area and

to reproduce asexually

Pohuehue

– Rhizomes: horizontal stems that grow underground.

– Tubers: are the swollen ends of rhizomes specialized for food storage.

– Bulbs: vertical, underground shoots consisting mostly of the swollen bases of leaves that store food.

rhizomestubers bulbs

Classification of LeavesClassification of LeavesClassification of LeavesClassification of Leaves

• Arrangement on the stemArrangement on the stem

• Simple vs. compoundSimple vs. compound

• Overall leaf shapeOverall leaf shape

• Leaf margin shapeLeaf margin shape

• Leaf venationLeaf venation

• Arrangement on the stemArrangement on the stem

• Simple vs. compoundSimple vs. compound

• Overall leaf shapeOverall leaf shape

• Leaf margin shapeLeaf margin shape

• Leaf venationLeaf venation

Leaf Taxonomy

Leaf Arrangement on the Stem

Opposite: 2 leaves at a node, on opposite sides of the stem

Spiral: 1 leaf per node, with the second leaf being above the first but attached on the opposite side of the stem

Whorled: 3 or more leaves at a node

Leaf ModificationsLeaf ModificationsLeaf ModificationsLeaf Modifications

• TendrilsTendrils• SpinesSpines• StorageStorage• Petal-likePetal-like• Insectivorous leavesInsectivorous leaves

• TendrilsTendrils• SpinesSpines• StorageStorage• Petal-likePetal-like• Insectivorous leavesInsectivorous leaves

Leaf ModificationsLeaf Modificationstendrilstendrils spinesspines

storagestorage petal-likepetal-like

1. Dermal tissue

2. Vascular tissue

3. Ground tissue

Plant organs are composed of three tissue systems:

• The dermal tissue, or epidermis, is generally a single layer of tightly packed cells that covers and protects all young parts of the plant.

• Other specialized characteristics :– Root hairs: increased absorption– Cuticle: waxy coating, prevents water loss

Dermal Tissue

Plant Cell StructurePlant Cell StructurePlant Cell StructurePlant Cell Structurecell wallcell wallcell wallcell wall

chloroplastchloroplastchloroplastchloroplast

nucleusnucleusnucleusnucleus

central vacuolecentral vacuolecentral vacuolecentral vacuole

Cell Wall StructureCell Wall StructureCell Wall StructureCell Wall Structure

middle lamellamiddle lamellamiddle lamellamiddle lamella

primary cell wallprimary cell wallprimary cell wallprimary cell wall

secondary cell wallsecondary cell wallsecondary cell wallsecondary cell wall

Cell Wall StructureCell Wall StructureCell Wall StructureCell Wall Structure

plasmodesmataplasmodesmataplasmodesmataplasmodesmata

Plant Cell TypesPlant Cell TypesPlant Cell TypesPlant Cell Types• XylemXylem

–TracheidsTracheids

–Vessel elementsVessel elements

• PhloemPhloem–Sieve-tube Sieve-tube

membersmembers

–Companion cellCompanion cell

• XylemXylem–TracheidsTracheids

–Vessel elementsVessel elements

• PhloemPhloem–Sieve-tube Sieve-tube

membersmembers

–Companion cellCompanion cell

Vascular tissue:

• runs continuous throughout the plant

• transports materials between roots and shoots.– Xylem transports water and dissolved minerals

upward from roots into the shoots. (water the xylem)

– Phloem transports food from the leaves to the roots and to non-photosynthetic parts of the shoot system. (feed the phloem)

Vascular Tissue

The water conducting elements of xylem are the tracheids and vessel elements.

Xylem

XylemXylemXylemXylem• TracheidsTracheids

– CharacteristicsCharacteristics• tapered elongated cellstapered elongated cells• connect to each other through pitsconnect to each other through pits• secondary cell walls strengthened with secondary cell walls strengthened with

ligninlignin• dead at functional maturitydead at functional maturity

– FunctionsFunctions• transport of water plus dissolved mineralstransport of water plus dissolved minerals• supportsupport

• TracheidsTracheids– CharacteristicsCharacteristics

• tapered elongated cellstapered elongated cells• connect to each other through pitsconnect to each other through pits• secondary cell walls strengthened with secondary cell walls strengthened with

ligninlignin• dead at functional maturitydead at functional maturity


XylemXylem• Vessel ElementsVessel Elements

– CharacteristicsCharacteristics• shorter and wider than tracheidsshorter and wider than tracheids• possess thinner cell walls than tracheidspossess thinner cell walls than tracheids• Aligned end-to-end to form long micropipesAligned end-to-end to form long micropipes• dead at functional maturitydead at functional maturity


• Vessel ElementsVessel Elements– CharacteristicsCharacteristics

• shorter and wider than tracheidsshorter and wider than tracheids• possess thinner cell walls than tracheidspossess thinner cell walls than tracheids• Aligned end-to-end to form long micropipesAligned end-to-end to form long micropipes• dead at functional maturitydead at functional maturity


Water conducting cells of the xylem

• Food and minerals move through tubes formed by chains of cells, sieve-tube members.–sieve plates

–companion cell

Phloem

PhloemPhloemPhloemPhloem• Sieve-tube MembersSieve-tube Members

– CharacteristicsCharacteristics• living cells arranged end-to-end to form food-living cells arranged end-to-end to form food-

conducting cells of the phloemconducting cells of the phloem• lack lignin in their cell wallslack lignin in their cell walls• mature cells lack nuclei and other cellular mature cells lack nuclei and other cellular

organellesorganelles• alive at functional maturityalive at functional maturity

– FunctionsFunctions• transport products of photosynthesistransport products of photosynthesis

• Sieve-tube MembersSieve-tube Members– CharacteristicsCharacteristics

• living cells arranged end-to-end to form food-living cells arranged end-to-end to form food-conducting cells of the phloemconducting cells of the phloem

• lack lignin in their cell wallslack lignin in their cell walls• mature cells lack nuclei and other cellular mature cells lack nuclei and other cellular

organellesorganelles• alive at functional maturityalive at functional maturity

– FunctionsFunctions• transport products of photosynthesistransport products of photosynthesis

PhloemPhloemPhloemPhloem• Companion CellsCompanion Cells

– CharacteristicsCharacteristics• living cells adjacent to sieve-tube membersliving cells adjacent to sieve-tube members• connected to sieve-tube members via connected to sieve-tube members via

plasmodesmataplasmodesmata

– FunctionsFunctions• support sieve-tube memberssupport sieve-tube members• may assist in sugar loading into sieve-tube may assist in sugar loading into sieve-tube

membersmembers

• Companion CellsCompanion Cells– CharacteristicsCharacteristics

• living cells adjacent to sieve-tube membersliving cells adjacent to sieve-tube members• connected to sieve-tube members via connected to sieve-tube members via

plasmodesmataplasmodesmata

– FunctionsFunctions• support sieve-tube memberssupport sieve-tube members• may assist in sugar loading into sieve-tube may assist in sugar loading into sieve-tube

membersmembers

Food conducting cells of the phloem

Ground tissue fills the interior of the plant. It contains three basic cell types:

– Parenchyma cells

– Collenchyma cells

– Sclerenchyma cells

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Ground Tissue

Dermal tissue

Vascular tissue

Ground tissue

ParenchymaParenchyma• CharacteristicsCharacteristics

– least specialized cell typeleast specialized cell type– only thin primary cell wall is presentonly thin primary cell wall is present– possess large central vacuolepossess large central vacuole– generally alive at functional maturitygenerally alive at functional maturity

• FunctionsFunctions– make up most of the ground tissues of the plantmake up most of the ground tissues of the plant– storagestorage– photosynthesisphotosynthesis– can help repair and replace damaged organs by can help repair and replace damaged organs by

proliferation and specialization into other cellsproliferation and specialization into other cells

• CharacteristicsCharacteristics– least specialized cell typeleast specialized cell type– only thin primary cell wall is presentonly thin primary cell wall is present– possess large central vacuolepossess large central vacuole– generally alive at functional maturitygenerally alive at functional maturity

• FunctionsFunctions– make up most of the ground tissues of the plantmake up most of the ground tissues of the plant– storagestorage– photosynthesisphotosynthesis– can help repair and replace damaged organs by can help repair and replace damaged organs by

proliferation and specialization into other cellsproliferation and specialization into other cells

ParenchymaParenchyma

CollenchymaCollenchymaCollenchymaCollenchyma

• CharacteristicsCharacteristics– possess thicker primary cell walls the that of possess thicker primary cell walls the that of

parenchymaparenchyma– no secondary cell wall presentno secondary cell wall present– generally alive at functional maturitygenerally alive at functional maturity

• FunctionsFunctions– provide support without restraining growthprovide support without restraining growth

• CharacteristicsCharacteristics– possess thicker primary cell walls the that of possess thicker primary cell walls the that of

parenchymaparenchyma– no secondary cell wall presentno secondary cell wall present– generally alive at functional maturitygenerally alive at functional maturity

• FunctionsFunctions– provide support without restraining growthprovide support without restraining growth

CollenchymaCollenchyma

SclerenchymaSclerenchymaSclerenchymaSclerenchyma

• CharacteristicsCharacteristics– have secondary cell walls strengthened by ligninhave secondary cell walls strengthened by lignin– often are dead at functional maturityoften are dead at functional maturity– two forms: two forms: fibers and sclereidsfibers and sclereids

• FunctionsFunctions– rigid cells providing support and strength to rigid cells providing support and strength to

tissuestissues

• CharacteristicsCharacteristics– have secondary cell walls strengthened by ligninhave secondary cell walls strengthened by lignin– often are dead at functional maturityoften are dead at functional maturity– two forms: two forms: fibers and sclereidsfibers and sclereids

• FunctionsFunctions– rigid cells providing support and strength to rigid cells providing support and strength to

tissuestissues

• Two other sclerenchyma cells, fibers and sclereids, are specialized entirely in support.– Fibers are long, slender and tapered, and

usually occur in groups.• Those from hemp fibers are used for making rope

and those from flax for weaving into linen.

– Sclereids, shorter than fibers and irregular in shape, impart the hardness to nutshells and seed coats and the gritty texture to pear fruits.

Fiber CellsFiber Cells

SclereidsSclereids

–Growth is the irreversible increase in mass that results from cell division and cell expansion.

–Development is the sum of all the changes that progressively elaborate an organism’s body.

Plant Growth & Development

• Most plants demonstrate indeterminate growth, growing as long as the plant lives.

• In contrast, most animals and certain plant organs, such as flowers and leaves, undergo determinate growth, ceasing to grow after they reach a certain size.– Indeterminate growth does not mean immortality.

Meristems generate cells for new organs throughout the lifetime of a plant: an overview of plant growth

• Annual- in a single year or less.– Many wildflowers and important food crops,

such as cereals and legumes, are annuals.

• Biennial- spans two years.– Often, there is an intervening cold period

between the vegetative growth season and the flowering season.

• Perennials- Plants that live many years, - Includes trees, shrubs, and some grasses.– These often die not from old age, but from an

infection or some environmental trauma.

Plant Lifecycle:Germination flowering seed production death

• Meristems– embryonic tissue.– These cells divide to generate additional cells. – Initials- generative cells that remain in the

meristem.– Derivatives- Those that are displaced from the

meristem,and continue to divide for some time until the cells they produce begin to specialize within developing tissues.

• The pattern of plant growth depends on the location of meristems.


Fig. 35.12

• Apical meristems: located at the tips of roots and in the buds of shoots, supply cells for the plant to grow in length.

–Primary growth• initial root and shoot growth

• produced by apical meristem

• elongation occurs

• restricted to youngest parts of the plant, i.e, tips of roots & shoots

Locations of Meristematic TissuesLocations of Meristematic TissuesLocations of Meristematic TissuesLocations of Meristematic Tissues

–Secondary growth: thickening of roots and shoots.• Produced by lateral meristems

• Develop in slightly older regions of roots and shoots

• Examples: vascular and cork cambium.

• Lateral meristems: allow the plant to increase in girth

Locations of Meristematic TissuesLocations of Meristematic Tissues

MeristemsMeristems

Types of Primary MeristemsTypes of Primary MeristemsTypes of Primary MeristemsTypes of Primary Meristems

• ProtodermProtoderm: : forms dermal tissue systemforms dermal tissue system

• ProcambiumProcambium: : forms vascular tissue systemforms vascular tissue system

• Ground MeristemGround Meristem: : forms ground tissue systemforms ground tissue system

• ProtodermProtoderm: : forms dermal tissue systemforms dermal tissue system

• ProcambiumProcambium: : forms vascular tissue systemforms vascular tissue system

• Ground MeristemGround Meristem: : forms ground tissue systemforms ground tissue system

• Root Cap: covers root tip & protects the meristem as the root pushes through the abrasive soil during primary growth.– The cap also secretes a lubricating slime.

• Growth in length is concentrated near the root’s tip, where three zones of cells at successive stages of primary growth are located.– zone of cell division– zone of elongation– zone of maturation


Primary Growth in Roots

Primary Growth of the Root

• The zone of cell division includes the apical meristem and its derivatives, primary meristems.

• Near the middle is the quiescent center, cells that divide more slowly than other meristematic cells.– These cells are relatively resistant to damage

from radiation and toxic chemicals.– They may act as a reserve that can restore the

meristem if it becomes damaged.


Fig. 35.14

• The zone of cell division blends into the zone of elongation where cells elongate, sometimes to more than ten times their original length.– It is this elongation of cells that is mainly

responsible for pushing the root tip, including the meristem, ahead.

– The meristem sustains growth by continuously adding cells to the youngest end of the zone of elongation.


• In the zone of maturation, cells begin to specialize in structure and function.– In this root region, the three tissue systems

produced by primary growth complete their differentiation, their cells becoming functionally mature.


• Three primary meristems give rise to the three primary tissues of roots.– The epidermis develops from the dermal

tissues.– The ground tissue produces the endodermis

and cortex.– The vascular tissue produces the stele, the

pericycle, pith, xylem, and phloem.


• The protoderm, the outermost primary meristem, produces the single cell layer of the epidermis.– Water and minerals absorbed by the plant

must enter through the epidermis.– Root hairs enhance absorption by greatly

increasing the surface area.


• The procambium gives rise to the stele, which in roots is a central cylinder of vascular tissue where both xylem and phloem develop.


Stele

• The ground tissue between the protoderm and procambium gives rise to the ground tissue system.– These are mostly parenchyma cells between

the stele and epidermis.– They store food and are active in the uptake of

minerals that enter the root with the soil solution.

• The innermost layer of the cortex, the endodermis, is a cylinder one cell thick that forms a boundary between the cortex and stele.


Fig. 35.15

Dicot Monocot

Monocot Root

Anatomy

Monocot Root

Anatomycortexcortex

epidermisepidermis

endodermisendodermis

pithpith

phloemphloemxylemxylem

pericyclepericyclecortexcortex

pithpith

stelestele

Dicot Root Anatomy

Dicot Root Anatomy

cortexcortex

epidermisepidermis

endodermisendodermis

phloemphloem

xylemxylem

pericyclepericycle

cortexcortex

stelestele

Each growing season, primary growth produces young extensions of roots and shoots, while secondary growth thickens and strengthens the older part of the plant.

Fig. 35.18

Organization of Primary Tissues in Young Stems

Primary Growth of the Shoot

Primary Growth of the Shoot

Monocot Stem

Anatomy

Monocot Stem

Anatomy

epidermisepidermis

vascular bundlesvascular bundles

ground tissueground tissue

xylemxylem

phloemphloem

Dicot Stem Anatomy

Dicot Stem Anatomy

vascularcambiumvascularcambium

xylemxylem

pithpith

cortexcortex

epidermisepidermis

vascular bundlevascular bundle

phloemphloem

• The meristematic bands make a continuous cylinder of dividing cells surrounding the primary xylem and pith of the stem.


Fig. 35.21

• This ring of vascular cambium consists of regions of ray initials and fusiform initials.

• Ray initials (xylem rays and phloem rays) that transfer water and nutrients laterally

• Fusiform initials form 2o xylem to the inside of the vascular cambium and 2o phloem to the outside.


Fig. 35.21

• As secondary growth continues over the years, layer upon layer of secondary xylem accumulates, producing the tissue we call wood.– Wood consists mainly of tracheids, vessel

elements (in angiosperms), and fibers.– These cells, dead at functional maturity, have

thick, lignified walls that give wood its hardness and strength.

Secondary Growth of a Stem

Production of Secondary Xylem and Phloem

Production of Secondary Xylem and Phloem

C=cambium cellX=2o xylemP=2o phloemD=derivative

– The accumulation of this tissue over the years accounts for most of the increase in diameter of a woody plant.

– Secondary xylem forms to the interior and secondary phloem to the exterior of the vascular cambium.

Anatomy of a Tree TrunkAnatomy of a Tree Trunk• After several years

of secondary growth, several zones are visible in a stem.

Primary and Secondary Growth in a Woody Stem

• The leaf epidermis is composed of cells tightly locked together like pieces of a puzzle.– It is the first line of defense against physical

damage and pathogenic organisms – The waxy cuticle prevents desiccation.

The Leaf

Leaf AnatomyLeaf Anatomy

Typical Dicot Leaf X-Section

Palisade Parenchyma

Spongy Parenchyma

Vascular bundles

Epidermis

Cuticle

Stoma

Guard Cells

Typical Monocot Leaf X-Section

Xylem

Phloem

Bulliform Cells Stoma

EpidermisMidvein Vein Bundle sheath cell

Leaf Stomata: Allow Gas Exchange

Stomata in Zebrina leaf epidermis

Guard cells with

chloroplasts

Stoma

Subsidiary cells

• Mesophyll- the ground tissue of the leaf, located between the upper and lower epidermis.– mainly of parenchyma cells equipped with

chloroplasts and specialized for photosynthesis.• CO2 and O2 circulate through the air spaces

• The air spaces are particularly large near stomata, where gas exchange with the outside air occurs.

• The vascular tissue of a leaf is continuous with the xylem and phloem of the stem.– Leaf traces, branches of vascular bundles in

the stem, pass through petioles and into leaves.

– Within a leaf, veins subdivide repeatedly and branch throughout the mesophyll.• xylem brings water and minerals • phloem carries sugars • the vascular infrastructure reinforces the shape of

the leaf.

• Plants have tremendous developmental plasticity.– Environmental factors can influence growth and

development, and reproductive output– A broad range of morphologies can result from

the same genotype as the plant undergoes three developmental processes: growth, morphogenesis, and differentiation.

Molecular Biology and Plants


Much plant research has focused on Arabidopsis thaliana, a small weed in the mustard family.

– Ideal research subject: • Cultivates quickly • Requires little lab space• Generation time 6 weeks

Molecular biology is revolutionizing the study of plants


Arabidopsis

• first plant genome sequenced, taking six years to complete.

• Arabidopsis has a total of about 26,000 genes, with fewer than 15,000 different types of genes.– The functions of only

about 45% of the Arabidopsis genes are unknown.


Fig. 35.25

• Now plant biologists work to identify the functions of every gene and track every chemical pathway to establish a blueprint for how plants are built.– One key task is to identify which cells are

manufacturing which gene products and at what stages in the plant’s life.

– Potential to develop a designer plant from a computer model.


Documents

Kingdom Plantae Plant Structure & Growth. Plants have evolved two systems: subterranean root system aerial shoot system of stems and leaves. roots shoots