ch. 31 – plant structure, growth and differentiation
TRANSCRIPT
Plant Body
• Root system– Underground– Anchor and absorb
• Shoot system– Vertical stem, leaves (flowers, fruits w/seeds)– photosynthesis
Fig. 35-2Reproductive shoot (flower)
Apical bud
Node
Internode
Apicalbud
Shootsystem
Vegetativeshoot
LeafBlade
Petiole
Axillarybud
Stem
Taproot
Lateralbranchroots
Rootsystem
Plant Cells and Tissues
• Ground tissue system – majority– Photosynthesis, storage, support
• Vascular tissue system– Conduction, strength, support
• Dermal tissue system– Covering, protection
All 3 are Interconnected throughout the plant
Ground Tissue System
• Parenchyma, collenchyma, sclerenchyma tissue
• Primary cell wall – secreted by growing cell; stretches and expands as cell grows
• Secondary cell wall – secreted when cell stops growing; thick and strong (inside primary)
Parenchyma• Living, metabolizing• Most common• Soft parts• Function
– Photosynthesis – green chloroplasts– Storage – starch, oil, water, salt– Secretion – resins, tannins, hormones, enzymes, nectar
• Can differentiate if plant injured (i.e. xylem cells)
Collenchyma
• Flexible, structural support (nonwoody parts)• Elongated cells• Alive at maturity• Primary CW – unevenly thick, thicker in
corners• Near stem surface, leaf veins
Sclerenchyma
• Structural support• Primary and secondary CW (strong and hard,
extreme thickening, so can’t stretch, elongate)• Cells dead at maturity• 2 types:
– Sclereids – variable shape, nut shells, pits of stone fruits, pears gritty (clusters of sclereids)
– Fibers – long, tapered – patches, clumps; wood, inner bark, leaf veins
Fig. 35-10c
5 µm
25 µm
Sclereid cells in pear (LM)
Fiber cells (cross section from ash tree) (LM)
Cell wall
Xylem
• Conducts water, dissolved nutrient minerals roots stems, leaves
• Support• Angiosperms –
– tracheids, vessel elements - conduct– parenchyma cells - storage– fibers - support
Tracheids and vessel elements
• Dead at maturity hollow, CW remain• Tracheids – long, tapering, patches/clumps;
water passes from 1 tracheid to another by pits (thin areas where sec. wall did not form)
• Vessel elements – larger in diameter than tracheid; end walls have perforations; stacked water goes between; stack = vessel; pits in side walls for lateral water transport
Fig. 35-10d
Perforationplate
Vesselelement
Vessel elements, withperforated end walls Tracheids
Pits
Tracheids and vessels(colorized SEM)
Vessel Tracheids 100 µm
Phloem
• Conducts food• Support• Angiosperms
– Sieve tube members, companion cells – conduct– Fibers – support– Parenchyma cells
Sieve tube members
• Conduct food in solution• Joined end-to-end long tubes• CW ends = sieve plates; cytoplasm extends
between cells• Living at maturity – many organelles
shrink/disintegrate• Can function w/o nuclei
Companion cells
• Adjacent to each sieve tube member (stm)• Assists stm• Living w/ nucleus – directs activities of both
cells• Plasmodesmata between stm and companion• Helps move sugar into stm
Fig. 35-10e
Sieve-tube element (left)and companion cell:cross section (TEM)
3 µmSieve-tube elements:longitudinal view (LM)
Sieve plate
Companioncells
Sieve-tubeelements
Plasmodesma
Sieveplate
Nucleus ofcompanioncells
Sieve-tube elements:longitudinal view Sieve plate with pores (SEM)
10 µm
30 µm
Dermal tissue system
• Epidermis and periderm• Protective covering• Herbaceous – single layer = epidermis• Woody – epidermis splits w/ growth
– Periderm – layers thick, under epidermis; replaces epidermis in stems, roots, composing outer bark
Epidermis
• Unspecialized dermal cells• Special guard cells + trichomes• Single layer, flat cells• Usually no chloroplasts transparent
– Allow light through
Fig. 35-18a
Keyto labels
Dermal
Ground
VascularCuticle Sclerenchyma
fibersStoma
Bundle-sheathcell
Xylem
Phloem
(a) Cutaway drawing of leaf tissuesGuardcells
Vein
Cuticle
Lowerepidermis
Spongymesophyll
Palisademesophyll
Upperepidermis
Fig. 35-18b
Guardcells
Stomatapore
Surface view of a spiderwort(Tradescantia) leaf (LM)
Epidermalcell
(b)
50 µ
m
Fig. 35-18c
Upperepidermis
Palisademesophyll
Keyto labels
Dermal
Ground
Vascular
Spongymesophyll
Lowerepidermis
Vein Air spaces Guard cells
Cross section of a lilac(Syringa) leaf (LM)
(c)
100
µm
Cuticle
• Aerial parts• Secreted by epidermal cells• Waxy – water loss• Slows diffusion of CO2 – stomata help• Stomata
– Open – day – photosynthesis, evaporative cooling– Closed – night– Closed in day if drought
Trichomes
• Outgrowths or hairs• Many shape, sizes, functions• Ex:
– Roots hairs – increase SA– Salty env. – remove excess salt– Aerial parts – increase light reflection, cooler– Protections – stinging nettles
Growth at Meristems
• Cell division– Increase # cells
• Cell elongation– Vacuole fills, increase pressure on CW, expands
• Cell differentiation– Specialize into cell types
• Meristems = where plant cells divide, mitosis– No differentiation
2 kinds of Growth
• Primary growth– Increase stem, root length– All plants, soft tissues
• Secondary growth– Increase width– Gymnosperms, woody dicots– Wood + bark
Fig. 35-11
Shoot tip (shootapical meristemand young leaves)
Lateral meristems:
Axillary budmeristem
Vascular cambiumCork cambium
Root apicalmeristems
Primary growth in stems
Epidermis
Cortex
Primary phloem
Primary xylem
Pith
Secondary growth in stems
Periderm
Corkcambium
Cortex
Primaryphloem
Secondaryphloem
Pith
Primaryxylem
Secondaryxylem
Vascular cambium
Primary growth• Increase in length• Apical meristem – tips of roots + shoots (buds)• Buds = dormant embryonic shoot (develop into
branches next spring• Root tip
– Root cap – protective layer of cells, covers root tip– Root apical meristem – directly behind root cap– Cell elongation – behind meristem, push tip ahead,
some differentiation
Fig. 35-13
Ground
Dermal
Keyto labels
Vascular
Root hair
Epidermis
Cortex Vascular cylinder
Zone ofdifferentiation
Zone ofelongation
Zone of celldivision
Apicalmeristem
Root cap
100 µm
Fig. 35-14a1
Root with xylem and phloem in the center(typical of eudicots)
(a)
100 µm
Epidermis
Cortex
Endodermis
Vascularcylinder
Pericycle
Xylem
Phloem
Dermal
Ground
Vascular
Keyto labels
Fig. 35-14a2
Vascular
Ground
Dermal
Keyto labels
Root with xylem and phloem in the center(typical of eudicots)
(a)
Endodermis
Pericycle
Xylem
Phloem
50 µm
Fig. 35-14b
Epidermis
Cortex
Endodermis
Vascularcylinder
Pericycle
Core ofparenchymacells
Keyto labels
Dermal
Ground
Vascular
Xylem
Phloem
Root with parenchyma in the center (typical ofmonocots)
(b)
100 µm
Fig. 35-16
Shoot apical meristem Leaf primordia
Youngleaf
Developingvascularstrand
Axillary budmeristems
0.25 mm
Fig. 35-17a
Sclerenchyma(fiber cells)
Phloem Xylem
Ground tissueconnectingpith to cortex
Pith
CortexEpidermisVascularbundle
1 mm
Cross section of stem with vascular bundles forminga ring (typical of eudicots)
(a)
Dermal
Ground
Vascular
Keyto labels
Fig. 35-17b
Groundtissue
Epidermis
Keyto labels
Cross section of stem with scattered vascular bundles(typical of monocots)
Dermal
Ground
Vascular
(b)
Vascularbundles
1 mm
Secondary Growth
• Increase in width• Make secondary tissues: sec. xylem, sec.
phloem, periderm• Lateral meristem – cells divide, not elongate• 2 types:
– Vascular cambium • Between wood and bark• Make sec. xylem (wood) + sec. phloem (inner bark)
Fig. 35-20
Vascular cambium Growth
Secondaryxylem
After one yearof growth
After two yearsof growth
Secondaryphloem
VascularcambiumX X
X X
X
X
P P
P
P
C
C
C
C
C
C
C C C
C C
CC
Fig. 35-22
Growthring
Vascularray
Secondaryxylem
Heartwood
Sapwood
Bark
Vascular cambium
Secondary phloem
Layers of periderm
– Cork cambium• In outer bark• Form cork to outside +parenchyma (storage)• Periderm = cork, parenchyma, cork cambium
• Bark – outermost covering of woody stems– Everything outside of vascular cambium– 2 regions:
• Living inner bark of secondary phloem• Mostly dead outer bark of periderm
Fig. 35-19a3
Epidermis
Cortex
Primary phloem
Vascular cambium
Primary xylem
Pith
Primary and secondary growthin a two-year-old stem
(a)
Periderm (mainlycork cambiaand cork)
Secondary phloem
Secondaryxylem
Epidermis
Cortex
Primary phloem
Vascular cambiumPrimary xylem
Pith
Vascular ray
Secondary xylem
Secondary phloem
First cork cambium
Cork
Growth
Cork
Bark
Most recent corkcambium
Layers ofperiderm
Fig. 35-19b
Secondary phloemVascular cambium
Secondary xylem
Bark
Early woodLate wood Cork
cambium
Cork
Periderm
0.5
mm
Vascular ray Growth ring
Cross section of a three-year-old Tilia (linden) stem (LM)
(b)
0.5 mm
You should now be able to:
1. Compare the following structures or cells:– Dermal, vascular, and ground tissues – Parenchyma, collenchyma, sclerenchyma, water-
conducting cells of the xylem, and sugar-conducting cells of the phloem
– Sieve-tube element and companion cell2. Describe in detail the primary and secondary growth
of the tissues of roots and shoots3. Describe the composition of wood and bark