Transcript 植物結構、生長與發育

Chapter 35
Plant Structure, Growth,
and Development (植物結
構、生長與發育)
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Key Concepts(基本觀念)
• The plant body has a hierachy of organs,
tissues and cells.(器官、組織及細胞體系)
• Meristems generate cells for new organs.
(分生組織產生新器官的細胞)
• Primary growth lengthens roots and shoots.
(初級生長使根與枝條增長)
• Secondary growth adds girth to stems and
roots in woody plants. (次級生長使木本植物
莖與根擴增)
• Growth, morphogenesis, and differentiation
produce the plant body.(生長、形態發生與分
化產生植物體)
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Overview: No two Plants Are Exactly Alike (1)
• To some people
– The fanwort is an intrusive weed (入侵植物), but
to others it is an attractive aquarium plant (水
生植物).
• This plant exhibits development plasticity (展示發
育彈性)
– The ability to alter itself in response to its
environment.
Plants have to be exquisite
to survive because they
can’t run. Since the form of
any plant is controlled by
environmental as well as
genetic factors, no two
plants are exactly alike.
Figure 35.1
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surface leaf
(aid in flotation)
feathery leaf
(protection from stress
of moving water)
Overview: No two Plants Are Exactly Alike (2)
•In addition to plasticity (彈性)
– Entire plant species have by natural selection (天
擇) accumulated characteristics of morphology or
external form (形態特徵或外觀) that vary little
among plants within the species.
The reduction in leaf size, and thus
in surface area, results in reduced
water loss. These leaf adaptations
have enhanced survival and
reproductive success in the desert
environment.
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•Concept 35.1: The plant body has a hierarchy of
organs, tissues, and cells (器官、組織及細胞體系)
•Plants, like multicellular animals(植物如同多細胞動
物)
– Have organs composed of different tissues,
which are in turn composed of cells.
– Organs, tissues, cells.
– Organs in plant:
vegetative organs(營養器官)--root, stem, leaf
reproductive organs (繁殖器官)--flower, fruit,
seed
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The Three Basic Plant Organs: Roots, Stems, and Leaves
•The basic morphology of vascular plants(維管植
物的基本形態)
– Reflects their evolutionary history (演化歷史)
as terrestrial organisms (陸域生物)that draw
nutrients from two very different
environments: below-ground (地下部) and
above-ground (地上部).
below-ground
(地下部)
above-ground
(地上部).
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An overview of a flowering plant (開花植物)
• Three basic
organs evolved:
roots, stems,
and leaves.
• They are
organized into a
root system and
a shoot system.
• A plant’s root
and shoot
systems are
evolutionary
adaptations to
living on land.
繁殖枝條
花
Reproductive shoot (flower)
頂芽Terminal bud
莖節 Node
節間Internode
頂芽 Terminal
bud
營養枝條 Vegetative
shoot
葉
Leaf
腋芽
莖
Shoot
system
枝條系統
葉片
Blade
Petiole
葉柄
Axillary
bud
Stem
主(軸)根 Taproot
側根
CO2
light
Lateral roots
H 20
mineral
Root
system
根系統
Figure 35.2
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Functions of Roots (根)
• A root’s functions
– Is an organ(根是器官)
– Anchors the vascular plant in
the soil. (固定維管植物在土壤)
– Absorbs minerals and
water(吸收礦物質與水份)
– Often stores organic
nutrients(儲存有機養份)
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Root tips and Root hairs (根尖和根毛)
• In most plants
– The absorption of water and minerals
occurs near the root tips, where vast
numbers of tiny root hairs increase the
surface area of the root for the absorption
of water and minerals by the roots.
Root hairs are the extension of
root epidermal cell (protective
cell on a plant surface).
(根毛)Root hairs
(根尖)Root tips
Figure 35.3
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H 20
mineral
Many plants have modified roots(變態根，特化根)
Environmental
adaptations may result
in roots being modified
for a variety of
functions.
Many modified roots (a) Prop roots
are aerial roots (氣生根) 支持根與
氣生根
that are above the
ground during normal
development.
(b) Storage roots (c) “Strangling” aerial
儲藏根
roots
「窒息性」氣生根
O2
Figure 35.4a–e
(d) Buttress roots
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板根
(e) Pneumatophores
Mangrove air root (氣根)
Stems (莖)
Reproductive shoot (flower)
Terminal bud
• A stem is an organ
consisting of
Node
Internode
Terminal bud
– An alternating
system of
nodes(節), the
points at which
leaves are
attached
Vegetative
shoot
Shoot
system
Blade
Petiole
Axillary bud
Leaf
Stem
Taproot
– Internodes(節間),
the stem
segments
between nodes
Lateral roots
Figure 35.2
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Root
system
• An axillary bud(腋芽)
– Is a structure that has the potential to form a lateral
shoot, or branch.
• A terminal bud(頂芽)
– Is located near the shoot tip (apex) and causes
elongation of a young shoot with developing
leaves and compact nodes and internodes.
• Apical dominance(頂芽優勢)
– The proximity of the terminal bud is partly
responsible for inhibiting the growth of axillary
buds.
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Apical dominance (頂芽優勢)
The proximity of the terminal bud is partly
responsible for inhibiting the growth of axillary
buds.
頂芽
By concentrating resources Terminal bud
toward elongation, apical
dominance is an evolutionary Axillary bud
adaptation that increases the
腋芽
plant’s exposure to light.
Under some conditions, axillary
bud break dormancy(休眠), that
is, they start growing.
A growing axillary bud gives
rise to a lateral shoot.
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Many plants have modified stems(變態莖/特化莖)
Modified stems
with diverse
functions have
evolved in many
plants as
environmental
adaptations,
including:
stolons走莖
bulbs鱗莖
tubers塊莖
rhizomes根狀莖
走莖/匍匐莖
(a) Stolons. Shown here on a
strawberry plant, stolons
are horizontal stems that grow
along the surface. These “runners”
enable a plant to reproduce
asexually, as plantlets form at
nodes along each runner.
Storage leaves
儲藏葉
(d) Rhizomes. The edible base
of this ginger plant is an example
of a rhizome, a horizontal stem
that grows just below the surface
or emerges and grows along the
surface.
Stem
不定根 Root
(adventitious root)
(b) Bulbs. Bulbs are vertical,
underground shoots consisting (c)
Tubers. Tubers, such as these
mostly of the enlarged bases
red potatoes, are enlarged
of leaves that store food. You
ends of rhizomes specialized
can see the many layers of
for storing food. The “eyes”
modified leaves attached
arranged in a spiral pattern
to the short stem by slicing an
around a potato are clusters
onion bulb lengthwise.
of axillary buds that mark
the nodes.
鱗莖
Figure 35.5a–d
Node
塊
莖
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Rhizome
根狀莖
Root
Functions of Leaves(葉)
• The leaf
– Is the main photosynthetic organ of
most vascular plants
– Leaves generally consist of
A flattened blade and a stalk
The petiole(葉柄), which joins the
leaf to a node of the stem
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Leaf of monocots and dicots
• Monocots and dicots (單子葉與雙子葉植物)
– Differ in the arrangement of veins, the
vascular tissue of leaves.
• Most monocots
– Have parallel veins (平行脈)
• Most dicots
– Have a branching veins (multibranched
network of major veins). (網狀脈)
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•In identifying and classifying angiosperms(被子植物的鑑定與分類)
–
Taxonomists may use leaf morphology as a criterion.
–
Leaf morphology:
leaf shape
spatial arrangement
pattern of a leaf’s vein
margin
(a) Simple leaf. A simple leaf
is a single, undivided blade.
Some simple leaves are
deeply lobed, as in an
oak leaf.
單葉
(b) Compound leaf. In a
compound leaf, the
blade consists of
multiple leaflets.
Notice that a leaflet
has no axillary bud
at its base.
(羽狀)複葉
Banana leaf
(c) Doubly compound leaf.
In a doubly compound
leaf, each leaflet is
divided into smaller
leaflets.
雙重(羽狀)複葉
Figure 35.6a–c
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葉柄
Petiole
★
Axillary bud
Leaflet
小葉
Petiole
★
Axillary bud
Leaflet
Petiole ★
Axillary bud
Spatial arrangement on stem (葉在莖上的空間排列)
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Simple versus Compound leaf (單葉 vs 複葉)
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Leaf shape (葉形)
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Leaf margin (葉緣)
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Venation (葉脈)
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Modified leaves (變態葉，特化葉)
• Some plant species have evolved modified leaves
that serve various functions.
(a) Tendrils. The tendrils by which this
pea plant clings to a support are
modified leaves. After it has “lassoed”
a support, a tendril forms a coil that
brings the plant closer to the support.
Tendrils are typically modified leaves,
but some tendrils are modified stems,
as in grapevines.
捲
鬚
刺針
(b) Spines. The spines of cacti, such
as this prickly pear, are actually
leaves, and photosynthesis is
carried out mainly by the fleshy
green stems.
儲藏葉
(c) Storage leaves. Most succulents,
such as this ice plant, have leaves
modified for storing water.
繁殖葉
狗脊蕨
Figure 35.6a–e
(e) Reproductive leaves. The leaves
of some succulents, such as Kalanchoe
daigremontiana, produce adventitious
plantlets, which fall off the leaf and
take root in the soil.
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擬花葉
(d) Bracts. Red parts of the poinsettia
are often mistaken for petals but are
actually modified leaves called bracts
that surround a group of flowers.
Such brightly colored leaves attract
pollinators.
The Three Tissue Systems: Dermal, Vascular, and Ground
• Each plant organ has dermal, vascular, and
ground tissues (植物器官是由三種組織系統組成)
葉橫切面
莖橫切面
三種組織系統
Dermal tissue
表皮系統
Ground tissue
基本系統
Figure 35.8
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Vascular tissue
根橫切面
維管束系統
•The dermal tissue system (表皮組織系統)
– Consists of the epidermis (表皮) and
periderm (周皮)
葉橫切面
莖橫切面
根橫切面
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• The vascular tissue system (維管束組織系統)
– Carries out long-distance transport (長途運
輸) of materials between roots and shoots
– Consists of two tissues, xylem and phloem
• Xylem(木質部)
– Conveys water and dissolved minerals
upward from roots into the shoots
• Phloem(韌皮部)
– Transports organic nutrients from where
they are made to where they are needed
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• Ground tissue (基本組織系統) includes
various cells specialized for functions such
as
– storage (儲存)
– photosynthesis (光合作用)
– Support (支持)
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Common Types of Plant Cells
• Like any multicellular organism, a plant is
characterized by cellular differentiation, the
specialization of cells in structure and
function . Some of the major types of plant
cells include
– Parenchyma(薄壁細胞)
– Collenchyma(厚角細胞)
– Sclerenchyma(厚壁細胞)
– Water-conducting cells of the xylem (木質部
運輸水份細胞)
– Sugar-conducting cells of the phloem (韌皮
部運輸醣類細胞)
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Figure 35.9
Parenchyma, collenchyma, and sclerenchyma cells
薄壁細胞
PARENCHYMA CELLS
厚角細胞
厚壁細胞
石細胞
SCLERENCHYMA CELLS
COLLENCHYMA CELLS
5 m
80 m Cortical parenchyma cells
Sclereid cells
in pear
25 m
Cell wall
Parenchyma cells 60 m
相對未特化的細
胞，具薄及富彈
性的初級細胞壁
，執行大部份植
物生理功能。
Collenchyma cells
Fiber cells
具不均勻增厚的初
級細胞壁，在持續
增長的植物組織及
器官中，提供支撐
功能。
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纖維細胞
具次級細胞壁，且含
木質素強化其硬度，
具支撐功能。通常在
成熟時為死細胞。
• Water-conducting cells of the xylem (木質部)：
tracheids (假導管、管胞) and vessels (導管)
假導管呈紡錘形，有 假導管 Tracheids
100 m
紋孔，水可在細胞間
Vessel
流動。
導管
導管細胞頭尾相接成
長管狀的木質部導管
，相接面有無數小孔
，水份可通過小孔往
導管 Vessel
Vessel
上流動或紋孔側向流
細胞 element
elements
動。
一般所謂木材主要是
由假導管及導管所組
成。
Vessel elements with
partially perforated
end walls
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Pits 紋孔
水份輸
送方向
Tracheids 假導管
末端細胞部份
穿孔的導管
Figure. 35.9
Sieve-tube members: longitudinal view
• Sugar-conducting cells of the phloem (韌皮
部)：sieve tube and plate, company cell
SUGAR-CONDUCTING CELLS OF THE PHLOEM
伴細胞
Sieve-tube Companion cell
member
篩管細胞
篩管細胞頭尾相接處
具有多孔的篩板。
Sieve plate
篩板
Nucleus
Cytoplasm
Figure. 35.9
篩管細胞將富含糖類
養分的汁液從生產地的
葉片輸送到消耗區，如
生長中的根或枝。
Companion
cell
伴細胞
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30 m
15 m
每一篩板細胞旁都有
具細胞核的伴細胞。
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The Process of Plant Growth and
Development (植物生長與發育的過程)
Indeterminate growth(無限生長)—Most
plants
Determinate growth(有限生長)---Animals
and plant leaf and flower
Annual, Biennial, perennial
(一年、二年、多年生)
Meristems (embryonic tissues) cause
indeterminate growth of plants (分生組織導
致植物的無限生長)
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• Concept 35.2: Meristems generate cells for
new organs(分生組織產生新細胞以形成器官)
• Apical meristems (頂端分生組織)—all plants
– Are located at the tips of roots and in the
buds of shoots
– Elongate shoots and roots through primary
growth (初級生長)
• Lateral meristems (側端分生組織)— only
woody plants (木本植物)
– Add thickness to woody plants through
secondary growth (次級生長)
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初級生長與次級生長發生的位置
• An overview of primary and secondary growth
Shoot apical
meristems
(in buds)
頂端分生組織
In woody plants,
there are lateral
meristems that
add secondary
growth, increasing
the girth of
roots and stems.
Apical meristems
add primary growth,
or growth in length.
Primary growth in stems
Epidermis表皮
Cortex皮質
Primary phloem
維管束形成層
Vascular
cambium
Cork
cambium
Lateral
meristems
木栓形成層
初級韌皮部
側端分
生組織
根尖分生組織
Figure. 35.10
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Pith
髄
初級木質部
Secondary growth in stems
Pith
Primary
xylem
Root apical
meristems
Primary xylem
Secondary
xylem
周皮
Periderm
Cork cambium
The cork
cambium add
secondary
dermal tissue
Cortex
Primary
phloem
The vascular
cambium add
Secondary secondary
phloem
xylem and
phloem.
Vascular cambium
木本植物的初級生長與次級生長發生時間相同但位置不同
• In woody plants, primary and secondary
growth occur simultaneously but in different
locations
Terminal bud 頂芽
Bud scale 芽之苞葉
Axillary buds 側芽
Leaf scar
This year’s growth
(one year old)
Stem
Internode
Last year’s growth
(two years old)
Growth of two
years ago
(three years old)
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Node
One-year-old side
branch(側枝) formed
from axillary bud
near shoot apex
Leaf scar
Scars left by terminal
bud scales of previous
winters
Leaf scar
葉痕
Figure 35.11
• Concept 35.3: Primary growth lengthens
roots and shoots (初級生長使根與枝條增長)
• Primary growth produces the primary plant
body, the parts of the root and shoot
systems produced by apical meristems (頂
端分生組織)
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Primary Growth of Roots (根的初級生長)
• The root tip is covered by a root cap, which
protects the delicate apical meristem as the root
pushes through soil during primary growth
Cortex
Epidermis
Key
Dermal
Ground
Vascular
Root hair
Apical
meristem
Root cap
根冠
Figure 35.12
100 m
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Vascular cylinder
Zone of
maturation
成熟區
Zone of
elongation
延長區
Zone of cell
division 細胞分裂區
• The primary growth of roots produces
(根的初級生長)
the epidermis (表皮組織)
ground tissue (基本組織)
vascular tissue (維管組織)
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• Organization of primary tissues in young roots
Epidermis
Cortex
Vascular
Cylinder
(stele)
Endodermis
Pericycle
(a) Transverse section of a
typical root. In the roots of
typical gymnosperms and
eudicots, as well as some
monocots, the stele is a
vascular cylinder
consisting of a lobed core
of xylem with phloem
between the lobes.
中柱鞘
Core of
parenchyma
cells
Xylem
100 m
Phloem
Endodermis
Pericycle
中柱鞘
Xylem 木質部
Phloem 韌皮鞘
Figure 35.13a, b
50 m
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Key
Dermal
Ground
Vascular
100 m
(b) Transverse section of a root
with parenchyma in the center.
The stele of many monocot roots
is a vascular cylinder with a core
of parenchyma surrounded by a
ring of alternating xylem and
phloem.
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• Lateral roots (側根) arise from within the
pericycle(中柱鞘) , the outermost cell layer in the
vascular cylinder or stele(中柱)
100 m
Emerging
lateral
root
Cortex
Vascular
cylinder
1
2
Epidermis
Lateral root
3
4
Figure 35.14
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Primary Growth of Shoots
• A shoot apical meristem (枝條頂端分生組織)
– Is a dome-shaped mass (圓頂狀) of dividing
cells at the tip of the terminal bud
– Gives rise to a repetition of internodes and
leaf-bearing nodes
Apical meristem
Leaf primordia
Developing
Vascular strand
Axillary bud
meristems
Figure. 35.15
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0.25 mm
Tissue Organization of Stems
Figure 35.16a
• In gymnosperms and most eudicots (真雙子葉植物)
– The vascular tissue consists of vascular bundles
(維管束) arranged in a ring
Phloem
Xylem
Ground tissue connecting
pith to cortex
Sclerenchyma (fiber cells)
Pith
Key
Epidermis
Cortex
Vascular
bundle
Dermal
Ground
1 mm
Vascular
(a) A eudicot stem. A eudicot stem (sunflower), with vascular bundles
forming a ring. Ground tissue toward the inside is called pith, and ground
tissue toward theoutside is called cortex. (LM of transverse section)
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Figure 35.16b
• In most monocot stems (大部份單子葉植物的莖)
– The vascular bundles are scattered (分散)
throughout the ground tissue, rather than
forming a ring
Ground tissue
Epidermis
Vascular bundles
1 mm
(b) A monocot stem. A monocot stem (maize) with vascular bundles scattered
throughout the ground tissue. In such an arrangement, ground tissue is not partitioned
into
pith and cortex. (LM of transverse section)
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Tissue Organization of Leaves
• The epidermal barrier in leaves
– Is interrupted by stomata, which allow CO2
exchange between the surrounding air and
the photosynthetic cells within a leaf
• The ground tissue in a leaf
– Is sandwiched between the upper and
lower epidermis
• The vascular tissue of each leaf
– Is continuous with the vascular tissue of
the stem
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葉的解剖
Guard
cells
Key
to labels
• Leaf anatomy
Dermal
Ground
Stomatal pore
Vascular
Cuticle
Epidermal
cell
Sclerenchyma
fibers
50 µm
(b) Surface view of a spiderwort
(Tradescantia) leaf (LM)
Stoma
Upper
epidermis
Palisade
mesophyll
Bundlesheath
cell
Spongy
mesophyll
Lower
epidermis
Guard
cells
Cuticle
Vein
Xylem
Phloem
(a) Cutaway drawing of leaf tissues
Guard
cells
Figure 35.17a–c
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Vein Air spaces
Guard cells
(c) Transverse section of a lilac 100 µm
(Syringa) leaf (LM)
• Concept 35.4: Secondary growth adds girth
to stems and roots in woody plants
• Secondary growth
– Occurs in stems and roots of woody plants
but rarely in leaves
• The secondary plant body
– Consists of the tissues produced by the
vascular cambium and cork cambium
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The Vascular Cambium and Secondary Vascular Tissue
• The vascular cambium
– Is a cylinder of meristematic cells one cell thick
– Develops from parenchyma cells
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• Primary and secondary growth of a stem
(a) Primary and secondary growth
in a two-year-old stem
Epidermis
Cortex
Primary
phloem
Vascular
cambium
Primary
xylem
Pith
Periderm
(mainly cork
cambia
and cork)
1 In the youngest part of the stem, you can see the primary
plant body, as formed by the apical meristem during primary
growth. The vascular cambium is beginning to develop.
1
Pith
Primary xylem
Vascular cambium
Primary phloem
Cortex
2
Phloem ray
3
Xylem
ray
Primary
xylem
Secondary xylem
Vascular cambium
Secondary phloem
Primary phloem
4 First cork cambium
2 As primary growth continues to elongate the stem, the portion
of the stem formed earlier the same year has already started
its secondary growth. This portion increases in girth as fusiform
initials of the vascular cambium form secondary xylem to the
inside and secondary phloem to the outside.
Epidermis
3 The ray initials of the vascular cambium give rise to the xylem
and phloem rays.
4 As the diameter of the vascular cambium increases, the
secondary phloem and other tissues external to the cambium
cannot keep pace with the expansion because the cells no
longer divide. As a result, these tissues, including the
epidermis, rupture. A second lateral meristem, the cork
cambium, develops from parenchyma cells in the cortex. The
cork cambium produces cork cells, which replace the epidermis.
5 In year 2 of secondary growth, the vascular cambium adds to
the secondary xylem and phloem, and the cork cambium
produces cork.
Cork
6
6 As the diameter of the stem continues to increase, the
outermost tissues exterior to the cork cambium rupture and
slough off from the stem.
Primary
phloem
Secondary
phloem
Vascular
cambium
Secondary
xylem
Primary xylem
Pith
Figure 35.18a
Secondary
xylem (two
years of
production)
Vascular cambium
Secondary phloem
5 Most recent
cork cambium
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7 Cork cambium re-forms in progressively deeper layers of the
cortex. When none of the original cortex is left, the cork
cambium develops from parenchyma cells in the
secondary phloem.
8 Each cork cambium and the tissues it produces form a
layer of periderm.
9 Bark consists of all tissues exterior to the vascular
cambium.
8 Layers of
periderm
9 Bark
7 Cork
Secondary phloem
Vascular cambium
Cork
cambium
Cork
Secondary Late wood
Early wood
xylem
Periderm
(b) Transverse section
of a three-yearold stem (LM)
Xylem ray
Bark
0.5 mm
Figure 35.18b
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0.5 mm
• Viewed in transverse section, the vascular
cambium
– Appears as a ring, with interspersed regions of
dividing cells called fusiform initials and ray
initials
Vascular
cambium
(a) Types of cell division. An initial can divide
transversely to form two cambial initials (C)
or radially to form an initial and either a
xylem (X) or phloem (P) cell.
C
(b) Accumulation of secondary growth. Although shown here
Figure 35.19a, b
as alternately adding xylem and phloem, a cambial initial usually
produces much more xylem.
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• As a tree or woody shrub ages
– The older layers of secondary xylem, the
heartwood, no longer transport water and
minerals
• The outer layers, known as sapwood
– Still transport materials through the xylem
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Growth ring
Vascular
ray
Heartwood
Secondary
xylem
Sapwood
Vascular cambium
Secondary phloem
Bark
Layers of periderm
Figure 35.20
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Cork Cambia and the Production of Periderm
• The cork cambium
– Gives rise to the secondary plant body’s
protective covering, or periderm
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• Periderm
– Consists of the cork cambium plus the layers
of cork cells it produces
• Bark
– Consists of all the tissues external to the
vascular cambium, including secondary
phloem and periderm
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• Concept 35.5: Growth(生長), morphogenesis (形
態發生), and differentiation(分化) produce the
plant body
• The three developmental processes of growth,
morphogenesis, and cellular differentiation
– Act in concert to transform the fertilized egg
(受精卵) into a plant
• New techniques and model systems (模式系統)
– Are catalyzing explosive progress in our
understanding of plants (催化爆炸性的進步)
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Model plant (模式植物)
• Arabidopsis thaliana (阿拉伯芥) is the first
plant to have its entire genome sequenced
Cell organization and biogenesis (1.7%)
Unknown
(36.6%)
DNA metabolism (1.8%)
Carbohydrate metabolism (2.4%)
Signal transduction (2.6%)
Protein biosynthesis (2.7%)
Electron transport (3%)
Protein modification (3.7%)
Protein metabolism (5.7%)
Transcription (6.1%)
Other metabolism (6.6%)
Other biological
processes (18.6%)
Figure 35.21
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Transport (8.5%)
Growth: Cell Division and Cell Expansion
(生長：細胞分裂及細胞擴增)
• By increasing cell number (增加細胞數目)
– Cell division in meristems increases the
potential for growth
• Cell expansion (細胞擴增)
– Accounts for the actual increase in plant size
• The plane (direction) and symmetry of cell
division (細胞分裂的對稱性與方向)
– Are immensely important in determining plant
form
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• If the planes of division of cells are parallel (平
行) to the plane of the first division
– A single file of cells will be produced
Division in
same plane
Plane of cell division
Division in
three planes
Single file of cells forms
Cube forms
Nucleus
(a) Cell divisions in the same plane produce a single file of cells,
whereas cell divisions in three planes give rise to a cube.
Figure 35.22a
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保衛細胞經由不對稱細胞分裂而產生
• If the planes of division vary randomly
– Asymmetrical cell division occurs (不對稱分
裂)
Developing
guard cells
不對稱細胞分裂
Asymmetrical
cell division
Unspecialized
epidermal cell
Unspecialized
epidermal cell
未特化
表皮細胞
Guard cell
“mother cell”
Unspecialized
epidermal cell
保衛細胞
母細胞
(b) An asymmetrical cell division precedes the development of
epidermal guard cells, the cells that border stomata (see Figure
35.17).
Figure 35.22b
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• The plane in which a cell divides
– Is determined during late interphase (細胞分裂
間期的晚期)
• Microtubules (微管) in the cytoplasm
– Become concentrated (濃縮聚集) into a ring
called the preprophase band (早前期帶)
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早前期帶及細胞分裂平面
bands
微管的早前期帶 Preprophase
of microtubules
Nuclei
Cell plates
細胞板
Figure 35.23
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10 µm
Orientation of Cell Expansion (細胞擴增的定向)
• Plant cells
– Rarely expand equally in all directions
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• The orientation of the cytoskeleton (細胞骨架
的定向)
– Affects the direction of cell elongation by
controlling the orientation of cellulose
microfibrils (纖維素微纖素) within the cell wall
Cellulose
microfibrils
Nucleus
Vacuoles
5 µm
Figure 35.24
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Microtubules and Plant Growth (微管及植物生長)
• Studies of fass mutants of Arabidopsis have
confirmed the importance of cytoplasmic
microtubules in cell division and expansion
No asymmetric
cell division
Asymmetric
cell division
(b) fass seedling
Figure 35.25a–c
(a) Wild-type seedling (c) Mature fass mutant
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Morphogenesis and Pattern Formation
• Pattern formation
– Is the development of specific structures in
specific locations (特殊位置的特殊結構)
– Is determined by positional information (位
置訊息) in the form of signals that indicate
to each cell its location
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• Polarity (極性)
– Is one type of positional information
• In the gnom mutant of Arabidopsis
– The establishment of polarity is defective
Figure 35.26
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• Morphogenesis in plants, as in other
multicellular organisms is often under the
control of homeotic genes (同源基因)
Figure 35.27
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Gene Expression and Control of Cellular
Differentiation (基因表現與細胞分化的控制)
• In cellular differentiation (細胞分化)
– Cells of a developing organism synthesize
different proteins and diverge in structure
and function even though they have a
common genome
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• Cellular differentiation (細胞分化)
– To a large extent depends on positional
information (位置訊息)
– Is affected by homeotic genes (同源基因)
When epidermal cells border a single cortical
cell, the homeotic gene GLABRA-2 is selectively
expressed, and these cells will remain hairless.
(The blue color in this light micrograph indicates cells in which GLABRA-2 is expressed.)
Here an epidermal cell borders
two cortical cells. GLABRA-2
is not expressed, and the cell
will develop a root hair.
Cortical
cells
The ring of cells external to the epidermal layer is composed of root
cap cells that will be sloughed off as
the root hairs start to differentiate.
Figure 35.28
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20 µm
Location and a Cell’s Developmental Fate
• A cell’s position in a developing organ
– Determines its pathway of differentiation
(一個正發育中的器官，細胞的位置決定其分化的
途徑)
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Shifts in Development: Phase Changes (相變)
• Plants pass through developmental phases,
called phase changes
– Developing from a juvenile phase to an adult
vegetative phase to an adult reproductive
phase
(年幼階段成熟營養階段成熟生殖階段)
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• The most obvious morphological changes
(形態改變) typically occur in leaf size and
shape
Leaves produced
by adult phase (成熟期)
of apical meristem
Figure 35.29
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Leaves produced
by juvenile phase (幼年期)
of apical meristem
Genetic Control of Flowering (開花的遺傳調控)
• Flower formation (花的形成)
– Involves a phase change (相變) from
vegetative growth (營養生長) to
reproductive growth (生殖生長)
– Is triggered by a combination of
environmental cues and internal signals (由
外部環境與內在訊息所驅動)
• The transition from vegetative growth to
flowering
– Is associated with the switching-on (啟動)
of floral meristem identity genes (花分生組
織本體基因)
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• Plant biologists have identified several
organ identity genes (器官本體基因) that
regulate the development of floral pattern
(a) Normal Arabidopsis
flower. Arabidopsis
normally has four whorls
of flower parts: sepals (Se),
petals (Pe), stamens (St),
and carpels (Ca).
Sepal萼片
Petal花瓣
Stamen雄蕊
Carpel心皮/雌蕊
Figure 35.30a, b
Se
Pe
Se
(b) Abnormal Arabidopsis flower.
Reseachers have identified
several mutations of organ
identity genes that cause
abnormal flowers to develop. This
flower has an extra set of petals in
place of stamens and an internal
flower where normal
plants have carpels.
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Pe
Ca
St
Pe
Pe
Se
• The ABC model of flower formation
– Identifies how floral organ identity genes
direct the formation of the four types of floral
organs
Sepals
Petals
Stamens
A Carpels
B
C
Sepal萼片
Petal花瓣
Stamen雄蕊
Carpel心皮/雌蕊
A+B
gene B + C
activity gene
activity
C gene
activity
A gene
activity
Figure 35.31a
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(a) A schematic diagram of the ABC
hypothesis. Studies of plant mutations
reveal that three classes of organ identity
genes are responsible for the spatial
pattern of floral parts. These genes are
designated A, B, and C in this schematic
diagram of a floral meristem in transverse
view. These genes regulate expression of
other genes responsible for development
of sepals, petals, stamens, and carpels.
Sepals develop from the meristematic
region where only A genes are active.
Petals develop where both A and B genes
are expressed. Stamens arise where B
and C genes are active. Carpels arise
where only C genes are expressed.
• An understanding of mutants of the organ
identity genes (器官本體基因)
– Depicts how this model accounts for floral
phenotypes (花的表現型)
Active
BB B B
genes: AACCCCAA
Whorls:
Carpel
Stamen Petal
AA AA
ABBAABBA
BB
BB
CCCCCCCC
AACCCCA A
No sepal
No petal
No carpel
Mutant lacking B
Mutant lacking C
Sepal
Wild type
Mutant lacking A
(b) Side view of organ identity mutant flowers. Combining the model shown in part (a)
with the rule that if A gene or C gene activity is missing, the other activity spreads
through all four whorls, we can explain the phenotypes of mutants lacking a
functional A, B, or C organ identity gene.
Figure 35.31b
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