Cells & Tissues

Apical Meristems Tips of roots and shoots Tips of roots and shoots Extension of plant body Extension of plant body Initials Initials  One cell remains as initial – maintaining meristem  Other cell is derivative – new body cell 2

Primary Meristems Multiple divisions before differentiation Multiple divisions before differentiation  Partly differentiated tissue Primary growth Primary growth  Extension of the plant body Secondary growth Secondary growth  Thickening of the plant body Indeterminate growth Indeterminate growth  Formation of new organs during their entire life 3

Growth, Morphogenesis & Differentiation Development – sum total of events that form an organisms body Development – sum total of events that form an organisms body  Driven by genetics  In response to environment: day length, light quality/quantity, temperature, gravity Development – 3 processes Development – 3 processes  Growth  Morphogenesis  Differentiation 4

Growth Combination of cell division and elongation Combination of cell division and elongation  Cell division alone only increases number!  Most growth – elongation & enlargement 5

Morphogenesis Primary event – expansion of tissue Primary event – expansion of tissue Subdivided by cell division Subdivided by cell division Cell/tissue differentiation follow morphogenesis Cell/tissue differentiation follow morphogenesis 6

Differentiation Often begins while cell is still enlarging Often begins while cell is still enlarging Depends on gene expression Depends on gene expression Ultimate fate positional Ultimate fate positional  Not dependant on cell lineage Determination Determination  Commitment to specific course of development Competency Competency  Ability of cell to develop in response to specific signal 7

Differentiation

Internal Organization Cells  tissues  tissue systems Cells  tissues  tissue systems Tissue Systems Tissue Systems  Ground  Vascular  Dermal 9

Tissue Systems Ground Ground  Parenchyma  Collenchyma  Sclerenchyma Vascular Vascular  Xylem  Phloem Dermal Dermal  Epidermis  periderm 10

Tissue Systems Characteristic Distribution Patterns Characteristic Distribution Patterns  Primary difference – vascular/ground tissue 11

Fig 12.1

ROOT STEM Dicot vs Monocot

Tissues Functionally/ structurally distinct cells Functionally/ structurally distinct cells Simple tissues – one type of cell Simple tissues – one type of cell  Ground tissues Complex tissues – more than 1 type of cell Complex tissues – more than 1 type of cell  Vascular tissues  Dermal tissues 14

Ground Tissues -- Parenchyma Living at maturity Living at maturity Capable of cell division Capable of cell division Some have 2º cell walls Some have 2º cell walls Adventitious roots Adventitious roots Photosynthesis, storage & secretion Photosynthesis, storage & secretion  “chlorenchyma” Movement of water and food Movement of water and food 15

Parenchyma – Transfer Cells Increased surface area Increased surface area  Facilitates movement of solutes over short distances  Intensive solute transfer Common Common Associated with xylem/phloem of minor veins Associated with xylem/phloem of minor veins  Cotyledons  Leaves in herbaceous Eudicots  Leaf traces Reproductive tissues – placentae, endosperm … Reproductive tissues – placentae, endosperm … Glandular structures – nectaries, salt glands … Glandular structures – nectaries, salt glands … 16

Ground Tissues -- Collenchyma Living at maturity Living at maturity Discrete strands of elongated cells Discrete strands of elongated cells  Continuous cylinders in stems and petioles  Borders veins in Eudicot leaves Unevenly thickened, nonlignified cell walls Unevenly thickened, nonlignified cell walls Supports young growing organs Supports young growing organs 17

Ground Tissues -- Sclerenchyma Continuous masses or small groups Continuous masses or small groups Hard, lignified cell walls Hard, lignified cell walls Strengthening and supporting plant parts Strengthening and supporting plant parts Fibers Fibers  Long, slender cells o strands or bundles  Bast fibers Sclerids Sclerids  Variable in shape  Seed coats, nut shells, endocarp 18

Vascular Tissue Xylem and Phloem Xylem and Phloem  Conducts water and nutrients 19

Vascular Tissues -- Xylem Conducts water Conducts water  Also conducts minerals  Support  Food storage 1º growth – procambium 1º growth – procambium 2º growth – vascular cambium 2º growth – vascular cambium Dead at maturity Dead at maturity 20

Vascular Tissues -- Xylem Trachery elements Trachery elements  Tracheids  Vessel elements May have wall pits May have wall pits 21 A-C – vessel elements D – tracheid E-F -- fibers

Xylem – Vessel Elements Vessel elements – perforation plate Vessel elements – perforation plate End rims End rims 22

Xylem -- Tracheids Less specialized Less specialized No perforations No perforations Seedless vascular plants & Gymnosperms Seedless vascular plants & Gymnosperms  Only water conducting cells Less efficient because of lack of perforations Less efficient because of lack of perforations Safer because of pit membranes Safer because of pit membranes  Stop air bubbles 23

Xylem -- Tracheids Variety of 2º wall thickenings Variety of 2º wall thickenings  During elongation – spiral or annular  Allow for extension after differentiation Programmed cell death Programmed cell death  Only cell walls retained 24

Xylem – Miscellany Parenchyma – stores stuff Parenchyma – stores stuff  Vertical strands  In rays -- 2º xylem Fibers Fibers  Storage and support  May be living Sclerids Sclerids 25

Vascular Tissue -- Phloem Principal food-conducting tissue Principal food-conducting tissue  Not just sugars!  Long distance signaling molecules 1º or 2º growth 1º or 2º growth Sieve elements – principal conducting cells Sieve elements – principal conducting cells  Sieve areas connecting adjacent sieve elements  Sieve cells – only phloem tissue in gymnosperms  Sieve-tube elements – only angiosperms 26

Phloem Sieve Cells Sieve Cells  Narrow pores  Uniform sieve areas Sieve-tube elements Sieve-tube elements  Sieve Plate o Some areas  larger pores 27

Phloem Sieve Cells Narrow pores Narrow pores Uniform sieve areas Uniform sieve areas Sieve Tube Elements 28

Sieve Elements Living at maturity Living at maturity Differentiation Differentiation  Trachery elements – complete breakdown  Sieve elements – partial breakdown o Breakdown of nucleus, loss of ribosomes, Golgi & cytoskeleton o Remainder distributed along wall → plasma membrane, SER, some plastids & mitochondria P-protein – except in some monocots P-protein – except in some monocots 29

Sieve Tube Elements 30 Arrows show P-protein bodies

Sieve-tube Elements Companion Cells – specialized parenchyma Companion Cells – specialized parenchyma Same mother cell Same mother cell Deliver stuff to sieve-tube elements Deliver stuff to sieve-tube elements  Hormones, proteins, ATP, etc. Life support system for STE Life support system for STE Companion cell dies when sieve element cell dies Companion cell dies when sieve element cell dies 31

Sieve-Tube Element Differentiation

Gymnosperm Sieve Cells Associated with albuminous cells Associated with albuminous cells  Have nucleus, etc.  Similar function to companion cells  Also dies when sieve element cell dies 33

Dermal Tissue Epidermis – outermost layer Epidermis – outermost layer  Variable functionally & structurally Unspecialized or specialized! Unspecialized or specialized!  Guard cells  Trichomes Protects plant Protects plant  cuticle 34

Epidermis – Guard Cells Contain chloroplasts Contain chloroplasts Regulate stomatal opening Regulate stomatal opening 35

Epidermis -- Trichomes Root hairs Root hairs Increased reflection of radiation Increased reflection of radiation  lower temps  Lower water loss Absorption of water and minerals Absorption of water and minerals Secretory functions Secretory functions Protection against herbivory Protection against herbivory Carniverous plants Carniverous plants 36

Trichomes

Carnivorous Plants NepenthesDroseraDionaea

Periderm 2º protective tissue 2º protective tissue  Replaces epidermis in 2º growth Cork (phellem) → nonliving Cork (phellem) → nonliving Cork cambium (phellogen) Cork cambium (phellogen)  Cork – outer surface  Phelloderm -- inner Phelloderm – living parenchyma tissue Phelloderm – living parenchyma tissue 39

Periderm -- Lenticels Loosely arranged Loosely arranged Gas exchange across the cork Gas exchange across the cork 40