Plant tissues
May 20, 2015
Plant tissues
Plant OrganizationRoot system- growth toward gravity;
generally below ground; consists of rootsRoot – epidermis; cortex; stele (vascular
tissue); pith
Shoot systemGrowth away from gravity along the axisGenerally above the groundConsists of the stem and the leavesFlowers are modified shoot system
Plant TissuesMeristemsSurface or dermal tissuesVascular tissuesGround or fundamental tissues
Meristems Responsible for increase in number of cellsMeristems do not specializePlant tissues are derived from the meristemsThree types:
ApicalLateralIntercalary
MeristemsIntercalary Meristem- plants without vascular
cambium (grasses)Growth regions that occur at the base of nodes
Growth Primary growth
Inc in length of plants (apical meristem)Secondary growth
Inc in plant girth (lateral meristem)Select plants only (woody plants such as dicot
and gymnosperms)Product: wood and cork
Plant growth patterns and regionsPrimary growth- growth in length; primary
meristemsSecondary growth- growth which increases
the girth or circumference of the plantVascular cambium- bet wood and barkCork cambium-found in the outer bark
Primary meristemsAt tipsShoot tip meristems (shoot system)
Stem meristem; leaf primordia; bud primordiaRoot tip meristems
Primary meristems are permanent and self perpetuating
Derivative meristemsProduced when meristem cells divide; forms
the tissue systems of the plant Protoderm- develops into surface or dermal tissues Procambium- develops into vascular tissue Ground meristem- fundamental /ground tissues Secondary meristems Vascular cambium- produces wood (strength);
produces part of bark (protection) Cork cambium- produces protective layer of bark
called cork
Plant GrowthPrimary Growth
(roots and shoots)
Secondary Growth (roots and shoots)
Meristems from Cell DedifferentiationDedifferentiate-any plant cell has the ability
to dedifferentiate
Lateral root formation Adventitious growth Wound healing Secondary cork cambium
Primary Growth of RootsRoot cap
protects the delicate meristems as the root elongates through the abrasive soil
secretes mucous that lubricates the soil
3 Zones of cells at successive station Zone of cell division Zone of cell elongation Zone of cell differentiation
Simple Tissues
Ground or fundamental tissues
Fibers- for supportPhotosynthetic cellsStorage cellsFill in the spaces cells
Ground or Fundamental Tissues
Parenchyma basic tissue type
Collenchymasupports young plants
Sclerenchymasupports for mature plants
ParenchymaDefinition: a simple tissue composed of
spherical-shaped cells; most common type of tissue
Have thin primary wallsLiving, metabolizing tissueE.g. Chlorenchyma, AerenchymaFunctions:
Photosynthesis & RespirationStorage (starch, oil droplets, air, water, and
salts)Wound healing & regeneration
CollenchymaDefinition: a simple tissue found beneath
the epidermis in young stems and in large veins of leaves (“strings” in celery).
Provides a flexible support system (like our skeletal system).
Found uniformly throughout the plant.Elongated cells that have unevenly
thickened cell walls (especially in the corners)
Alive at maturity
SclerenchymaDefinition: a simple
tissue specialized for structural support; occurs in many areas
Two types:Fibers Sclereids
Have both primary and secondary cell walls.
At functional maturity cells are often dead
FibersLong, tapered cells
that often occur in groups or clumps (abundant in the wood and bark of flowering plants)
Found in leaves & stems.
Primary function is support
SclereidsShort, cuboidal
cells common in shells of nuts and pits of fruits (peaches, cherries)
Found in all plant parts, usually clustered.
Primary function is for protection
Complex tissuesVascular Tissue System
Vascular tissuesFunctions: conduct water and solutes support and strength of the
plantTypes of vascular tissues
Xylem- conducts water and mineralsPhloem- conducts solutes/foodContinues throughout the plant
XylemConduction of H2O from roots to leavesMade up the woodComposed of:
Vessel Elements- elongated cells with secondary walls Dead at functional maturity; perforated Large diameter
Tracheids – elongated, narrow cells with secondary walls; dead at functional maturity; pitted Xylem fibers Xylem parenchyma Xylem rays
Parenchyma cells and Fibers
TracheidsTracheids are
typically found in gymnosperms and seedless vascular plants and aid in transporting water.
Movement of water is only longitudinal
Vessel ElementsVessel elements are
typically found in angiosperms and aid in transporting water.
Movement of water can be transverse or longitudinal
Phloem Moves solutes (especially carbs)Composed of:
Sieve tube cells Elongated cells forming tubes End walls have pores forming sieve plates Alive at functional maturity Carry food
Companion cells Connected to the sieve tube through plasmodesmata Parenchyma cells adjoining the sieve tube cells Phloem fibers Phloem parenchyma(Sclerenchyma fibers and parenchyma cells)
Sieve tube membersSieve tube members
can secrete a protein called callose to plug sieve plates to stop the flow of food if the phloem is damaged
Complex tissuesDermal Tissues
Surface or dermal tissuesProtectionPrevents dessication
Dermal (surface) tissueEpidermis (herbaceous plants)
Cuticle (protective waxy layer)- prevents dessication (cuticle) and invasion of pathogens , absorption of water, control of gas exchange
Periderm or cork layer (woody plants) Produced from cork cambium Secondary epidermis or periderm of woody plants
DermisEpidermis: Two
typesParenchyma cellsGuard cells
NO Chloroplasts
CuticleA waxy layer
secreted by epidermal cells of stems and leaves
Prevents water loss and diffusion of gases
Cuticle Parenchyma cells
Guard cellsGuard cells form the tiny opening called the
stomata
PeridermisWoody plants initially produce an
epidermis that splits as the plant grows. These plants also have periderm, which
is several cells thick and forms under the epidermis.
Periderm composes the outer barkComposed of two types of cells
Cork cells- secrete suberinCork parenchyma
Dermal (surface) tissueEpidermal modifications
Hairs of trichomes Root hairs: absorption of water Guard cells: form stomata for gas exchange Glands: modified cells containing oils or other substances for secretion
Transport in PlantsCellular level transportLateral transportLong-distance transport
Plant NutritionChemical composition of plants
80%-85% of herbaceous plants is H2OPlants grow mainly by accumulating water in
the central vacuoles of their cellsCarbon, hydrogen, oxygen are the most
abundant elements in the dry weight of a plant
Essential NutrientsHydroponic structure- used to determine
which of the mineral elements are actually essential nutrients
Macronutrients- elements required by plants in relatively large amounts
Micronutrients- elements needed by plants in small amounts