Plant Body Fig. 35 - Waterford Mott Biologymottbiology.weebly.com/uploads/1/3/6/8/13688163/chapter... · 2018-10-11 · •Organ that anchors the vascular plant •Absorbs minerals

Chapters 35: Plant Structure, Growth and Development AP Biology 2013

Plant Body

• Has a hierarchy of organs, tissues, and cells

• Basic morphology of vascular plants reflects evolutionary history as terrestrial organisms that draw nutrients from below and above ground

• Three basic types of organs: roots, stems, and leaves

• Organized into two organ systems: a root system and a shoot system

Fig. 35.2Reproductive shoot (flower)

Apical bud

Node

Internode

Apical bud

Vegetative shoot

Leaf Blade Petiole

Stem

Taproot

Lateral (branch) roots

Shoot system

Root system

Axillary bud

Roots• Organ that anchors the vascular plant

• Absorbs minerals and water

• Occurs near the root tips where tiny root hairs increase the surface area of the root

• Often stores organic nutrients/carbohydrates

• Taproot - main vertical root

• Lateral roots - arise from taproot

• Root hairs - increase surface area

Figs. 35.3 & 35.4

Prop roots

Storage roots

“Strangling” aerial roots

Buttress roots

Pneumatophores

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2

3

Stems• Organ consisting of an alternating

system of nodes (points at which the leaves are attached) and internodes (stem segments between nodes)

• Axillary bud - structure that has the potential to form a lateral shoot or branch

• Apical bud (terminal bud) - located near the shoot tip and causes elongation of a young shoot

• Apical dominance - maintains dormancy in most axillary buds

Fig. 35.5

Rhizomes

Rhizome

Bulbs

Storage leaves

Stem Stolons

Tubers

Root

Stolon

Leaves• Main photosynthetic organ of most

vascular plants

• Consist of a flattened blade and a stalk

• Petiole - joins the leave to a node of the stem

• Classification of angiosperms is often related to leaf morphology

• Modified leaves: tendrils (lassoes neighboring plant and forms a coil for support), spines, storage (ex. storage of water), bracts (brightly colored leaves that surround a group of flowers), reproductive

Monocots - parallel veins

Eudicots - branching veins

Simple leaf

Axillary bud Petiole

Compound leaf Leaflet

Axillary bud Petiole

Doubly compound leaf

Axillary bud

Petiole

Leaflet

Figs. 35.6 & 35.7

Tendrils

Spines

Storage leaves

Reproductive leaves

Bracts

Tissues• Dermal - consists of epidermis and periderm

• cuticle waxy coating that helps prevent water loss (replaced by periderm in woody plants)

• Vascular - carries out long-distance transport of materials between roots and shoots

• Xylem - carries water and dissolved minerals upward (roots to shoots)

• Phloem - transports organic nutrients from where they are made to where they are needed

• Ground - cells specialized fro storage, photosynthesis, and support

Fig. 35.8

Dermal tissue

Ground tissue

Vascular tissue

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5

6

Major Cell Types

• Parenchyma - thin walled cells that make up most of the non-woody structure

• Collenchyma - thick walled

• Sclerenchyma - lignified cell walls that lose their protoplasm at maturity

• Water conducting (xylem)

• Sugar conducting (phloem)Fig. 35.10

Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 µm Collenchyma cells

(in Helianthus stem) (LM) 5 µm

Cell wall

Sclereid cells in pear (LM)

Fiber cells (cross section from ash tree) (LM)

25 µm

5 µm

Vessel Tracheids 100 µm

Tracheids and vessels (colorized SEM)

Perforation plate

Vessel element

Vessel elements, with perforated end walls

Pits

Tracheids

Sieve-tube element (left) and companion cell: cross section (TEM)

Sieve-tube elements: longitudinal view

Sieve plate

3 µm

Companion cells

Sieve-tube elements

Plasmodesma

Sieve plate

Nucleus of companion cell

Sieve-tube elements: longitudinal view (LM)

30 µm

15 µm

Sieve plate with pores (LM)

Meristems• Meristems - perpetually

embryonic tissue that generates cells for new organs

• Apical meristems - located at the tips of roots and buds of shoots, elongate roots and shoots through primary growth

• Lateral meristems - add thickness to woody plants through secondary growth

• Primary and secondary growth occurs simultaneously but in different locations in woody plants

Figs. 35.11 & 35.12

Shoot tip (shoot apical meristem and young leaves)

Axillary bud meristem

Root apical meristems

Vascular cambium Cork cambium

Lateral meristems

Primary growth in stems

Epidermis Cortex Primary phloem

Primary xylem Pith

Secondary growth in stems

Cork cambium

Cortex

Primary phloem

Secondary phloem

Vascular cambium

Secondary xylem

Primary xylem

Pith

Periderm

Apical bud

This year’s growth (one year old)

Last year’s growth (two year old)

Growth of two years ago (three years old)

One-year-old side branch formed from axillary bud near shoot tip

Bud scale Axillary buds

Leaf scar

Bud scar

Node

Internode

Leaf scar Stem

Bud scar

Leaf scar

Primary Growth

Figs. 35.13 - 35.15

Epidermis

Cortex

Root hair

Vascular cylinder

Zone of differentiation

Zone of elongation

Zone of cell division (including apical meristem)

Key to labels

Root cap

Dermal Ground Vascular

Mitotic cells

100 µm

Emerging lateral root

Cortex

Vascular cylinder

Pericycle

100 µm Epidermis

Lateral root

3 2 1

Endodermis

Pericycle

Xylem

Phloem

Dermal Ground

Vascular

Key to labels

50 µm

• Apical meristem produces the primary plants body (produces epidermis, ground tissue, and vascular tissue)

• Root tips are covered by a root cap to protect the apical meristem as the root pushes through the soil

• Lateral roots arise form the pericycle (outermost layer of vascular tissue)

• Shoot apical meristem is dome shaped

7

8

9

Organization of Shoots• In gymnosperms and most eudicots the vascular tissue consists of vascular bundles

arranged in a ring

• In most monocot stems the vascular bundles are scattered throughout the ground tissue

Fig. 35.16 - 35.17

Shoot apical meristem Leaf primordia

Young leaf

Developing vascular strand

Axillary bud meristems

0.25 mm

Sclerenchyma (fiber cells)

Phloem Xylem

Ground tissue connecting pith to cortex

Pith

Cortex Vascular bundle

Epidermis

1 mm 1 mm

Vascular bundles

Epidermis

Ground tissue

Dermal Ground Vascular

Key to labels

(a) (b) Cross section of stem with vascular bundles forming a ring (typical of eudicots)

Cross section of stem with scattered vascular bundles (typical of monocots)

Organization of Leaves• Epidermal barrier is

interrupted by stomata

• Each stomatal pore is flanked by two guard cells which regulate opening and closing

• Mesophyll - ground tissue is between the upper and lower epidermis

• Vascular tissue in a leaf is continuous with vascular tissue of the stem

Fig 35.18

Key to labels

Dermal Ground

Vascular

Cuticle

Bundle- sheath cell

Xylem

Phloem

Sclerenchyma fibers

Stoma

Upper epidermis Palisade mesophyll

Spongy mesophyll Lower epidermis

Cuticle Vein Guard cells

(a) Cutaway drawing of leaf tissues

(b)

(c) Cross section of a lilac (Syringa) leaf (LM)

Surface view of a spiderwort (Tradescantia) leaf (LM)

Guard cells

Stomatal pore

Epidermal cell

Vein Air spaces Guard cells

50 µ

m

100 µ

m

(b) Surface view of a spiderwort (Tradescantia) leaf (LM)

Guard cells

Stomatal pore

Epidermal cell 50

µm

Primary and Secondary Growth

Vascular cambium Pith Primary xylem

Secondary xylem Vascular cambium

Secondary phloem

Primary phloem

Periderm (mainly cork cambia and cork)

Pith Primary xylem

Vascular cambium Primary phloem

Cortex Epidermis

Vascular cambium 4 First cork cambium

Secondary xylem (two years of production)

Pith Primary xylem

Vascular cambium Primary xylem

Epidermis Cortex

2

1

6

Growth

Primary xylem

Secondary xylem

Secondary phloem

Primary phloem Cork

Phloem ray 3 Xylem

ray

Growth

9 Bark

8 Layers of periderm

7 Cork

5 Most recent cork cambium

(a) Primary and secondary growth in a two-year-old stem

Secondary phloem

Fig. 35.19

10

11

12

Secondary Growth• Adds girth to stems and roots (rarely occurs in

leaves)

• Secondary tissue consists of tissues produced by vascular cambium and cork cambium

• vascular cambium - cylinder of meristematic cells one cell thick that develops from undifferentiated parenchyma cells

• Appears as a ring with interspersed regions of dividing cells called fusiform initials and ray initials

• The older layers of secondary xylem (heartwood) no longer transports water and minerals as the plant ages

• The outer layers (sapwood) still transports materials through the xylem

Figs. 35.19 - 35.20

Secondary xylem

0.5 mm

Secondary phloem Vascular cambium Late wood Early wood

Vascular ray Growth ring

Bark

Cork cambium

Cork

Periderm

(b) Cross section of a three-year- old Tilia (linden) stem (LM)

0.5

mm

Vascular cambium Growth

Secondary xylem

Secondary phloem

Vascular cambium

After one year of growth

After two years of growth

Growth ring

Vascular ray

Secondary xylem

Heartwood

Sapwood

Vascular cambium

Bark Secondary phloem

Layers of periderm

Year

Rin

g-w

idth

inde

xes

1600 1700 1800 1900 2000

2

1.5

0.5

1

0

RESULTS

Figs. 35.21-35.22

Secondary Growth

• Cork cambium - gives rise to the secondary plant body’s protective covering (periderm)

• Periderm - consists of the cork cambium and layers of cork cells it produces

• Bark - all tissues external to the vascular cambium including secondary phloem and periderm

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14

15

Morphogenesis and Pattern Formation• Development of specific structures in

specific locations

• Determined by positional information from signals that indicate to each cell its location

• Polarity - knowing which end the cell is located

• Morphogenesis is controlled by homeotic genes

• Most obvious morphological changes happen with leaf size and shape

• Flower growth is caused by a change from vegetative growth to reproductive growth because of environmental and internal signals.

• Floral meristem identity genes

Figs. 35.28, 35.32,

& 35.33

Leaves produced by adult phase of apical meristem

Leaves produced by juvenile phase of apical meristem

(a) Normal Arabidopsis flower

Abnormal Arabidopsis flower

(b)

Ca

Pe

St

Se

Se

Se

Pe

Pe

Pe

ABC Hypothesis for Flower FormationSepals

Petals

Stamens

Carpels A B

C

A schematic diagram of the ABC hypothesis

(a)

(b) Side view of flowers with organ identity mutations

Carpel

Petal

Stamen

Sepal

A + B gene

activity

B + C gene

activity

C gene activity

A gene activity

Active genes:

Whorls:

Stamen Carpel

Petal

Sepal Wild type Mutant lacking A Mutant lacking B Mutant lacking C

A A A A C C C C B B B B

C C C C C C C C B B B B

A A A A C C C C A B B A B A A B A A A A

Fig. 35.34

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