Plant Structure, Growth, and Development (植物結構、生長與發育)

Plant Structure, Growth, and Development (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)

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)

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 feathery leaf (protection from stress of moving water) surface leaf (aid in flotation)

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.

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

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).

An overview of a flowering plant (開花植物)
Figure 35.2 Reproductive shoot (flower) Terminal bud Node Internode Terminal bud Vegetative shoot Blade Petiole Stem Leaf Taproot Lateral roots Root system Shoot Axillary CO2 light H20 mineral 主(軸)根側根莖節節間葉莖腋芽營養枝條繁殖枝條枝條系統根系統頂芽葉片葉柄花 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.

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)

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. Figure 35.3 Root hairs are the extension of root epidermal cell (protective cell on a plant surface). (根毛)Root hairs (根尖)Root tips H20 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 are aerial roots (氣生根) that are above the ground during normal development. (a) Prop roots (b) Storage roots (c) “Strangling” aerial roots (d) Buttress roots (e) Pneumatophores 支持根與氣生根儲藏根板根「窒息性」氣生根 Mangrove air root (氣根) O2 Figure 35.4a–e

Reproductive shoot (flower)
Stems (莖) Reproductive shoot (flower) Terminal bud A stem is an organ consisting of An alternating system of nodes(節), the points at which leaves are attached Internodes(節間), the stem segments between nodes Node Internode Terminal bud Shoot system Vegetative shoot Leaf Blade Petiole Axillary bud Stem Taproot Root system Lateral roots Figure 35.2

Apical dominance(頂芽優勢)
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.

Apical dominance (頂芽優勢)
The proximity of the terminal bud is partly responsible for inhibiting the growth of axillary buds. Terminal bud 頂芽腋芽 By concentrating resources toward elongation, apical dominance is an evolutionary adaptation that increases the 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. Axillary bud

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 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. (d) Tubers. Tubers, such as these red potatoes, are enlarged ends of rhizomes specialized for storing food. The “eyes” arranged in a spiral pattern around a potato are clusters of axillary buds that mark the nodes. (c) Bulbs. Bulbs are vertical, underground shoots consisting mostly of the enlarged bases of leaves that store food. You can see the many layers of modified leaves attached to the short stem by slicing an onion bulb lengthwise. (b) 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. (a) Storage leaves Stem Root Node Rhizome 走莖/匍匐莖根狀莖塊莖不定根 (adventitious root) 儲藏葉鱗莖 Figure 35.5a–d

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

Leaf of monocots and dicots
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)

葉柄單葉小葉 (羽狀)複葉 Banana leaf 雙重(羽狀)複葉
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. 葉柄單葉 Petiole (b) Compound leaf. In a compound leaf, the blade consists of multiple leaflets. Notice that a leaflet has no axillary bud at its base. ★ Axillary bud Leaflet 小葉 (羽狀)複葉 Petiole ★ Axillary bud (c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets. Banana leaf 雙重(羽狀)複葉 Leaflet Petiole ★ Figure 35.6a–c Axillary bud

Spatial arrangement on stem (葉在莖上的空間排列)

Simple versus Compound leaf (單葉 vs 複葉)

Leaf shape (葉形)

Leaf margin (葉緣)

Venation (葉脈)

Modified leaves (變態葉，特化葉)
Some plant species have evolved modified leaves that serve various functions. Figure 35.6a–e (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. (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. (c) Storage leaves. Most succulents, such as this ice plant, have leaves modified for storing water. (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. (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. 捲鬚刺針儲藏葉擬花葉繁殖葉狗脊蕨

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) 葉橫切面三種組織系統莖橫切面 Dermal tissue 表皮系統 Ground tissue 基本系統 Vascular tissue Figure 35.8 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

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

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)

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)

Cortical parenchyma cells
Figure 35.9 Parenchyma, collenchyma, and sclerenchyma cells Parenchyma cells 60 m PARENCHYMA CELLS 80 m Cortical parenchyma cells COLLENCHYMA CELLS Collenchyma cells SCLERENCHYMA CELLS Cell wall Sclereid cells in pear 25 m Fiber cells 5 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。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。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。石細胞纖維細胞薄壁細胞厚角細胞厚壁細胞

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，有紋孔，水可在細胞間流動。 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，水份可通過小孔往上流動或紋孔側向流動。 一般所謂木材主要是由假導管及導管所組成。 Tracheids Vessel 100 m 導管 Pits 紋孔水份輸送方向導管細胞 Vessel element Vessel elements Vessel elements with partially perforated end walls 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 Companion cell Sieve-tube member Sieve plate Nucleus Cytoplasm Companion cell 30 m 15 m 伴細胞篩管細胞篩板 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。 篩管細胞頭尾相接處具有多孔的篩板。 每一篩板細胞旁都有具細胞核的伴細胞。 Figure. 35.9

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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)

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)

Primary growth in stems Secondary growth in stems
初級生長與次級生長發生的位置 An overview of primary and secondary growth Figure 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. Vascular cambium Cork Lateral meristems Root apical Primary growth in stems Epidermis Cortex Primary phloem Primary xylem Pith Secondary growth in stems Periderm Cork cambium Primary phloem Secondary Vascular cambium xylem Shoot apical (in buds) The cork cambium adds secondary dermal tissue. The vascular xylem and phloem. 維管束形成層木栓形成層初級木質部初級韌皮部皮質表皮髄周皮根尖分生組織頂端分生組織側端分生組織

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 Figure 35.11 This year’s growth (one year old) Last year’s growth (two years old) Growth of two years ago (three years old) One-year-old side branch(側枝) formed from axillary bud near shoot apex Scars left by terminal bud scales of previous winters Leaf scar Stem Bud scale Axillary buds Internode Node Terminal bud 側芽芽之苞葉頂芽葉痕

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)

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 Figure 35.12 Dermal Ground Vascular Key Cortex Vascular cylinder Epidermis Root hair Zone of maturation elongation Zone of cell division Apical meristem Root cap 100 m 根冠成熟區延長區細胞分裂區

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)

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 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. Endodermis Key Dermal Pericycle Ground 中柱鞘 Vascular Xylem 木質部 Phloem 韌皮鞘 Figure 35.13a, b 50 m

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

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 0.25 mm Figure

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 Xylem Phloem Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Pith Epidermis Vascular bundle Cortex Key Dermal Ground Vascular 1 mm (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)

In most monocot stems (大部份單子葉植物的莖)
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)

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

Cutaway drawing of leaf tissues
葉的解剖 Key to labels Dermal Ground Vascular Guard cells Stomatal pore Epidermal cell 50 µm Surface view of a spiderwort (Tradescantia) leaf (LM) (b) Cuticle Sclerenchyma fibers Stoma Upper epidermis Palisade mesophyll Spongy Lower Vein Xylem Phloem Bundle- sheath Cutaway drawing of leaf tissues (a) Air spaces Guard cells 100 µm Transverse section of a lilac (Syringa) leaf (LM) (c) Figure 35.17a–c Leaf anatomy

The secondary plant body
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

The Vascular Cambium and Secondary Vascular Tissue
Is a cylinder of meristematic cells one cell thick Develops from parenchyma cells

Primary and secondary growth of a stem
Vascular cambium Pith Primary xylem Secondary xylem Vascular cambium Secondary phloem Primary phloem Periderm (mainly cork cambia and cork) Primary xylem Cortex Epidermis 4 First cork cambium Secondary xylem (two years of production) Primary phloem 2 1 6 Growth Secondary xylem Secondary phloem Cork Phloem ray 3 Xylem ray Bark 8 Layers of periderm 7 5 Most recent cork cambium 9 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. 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. The ray initials of the vascular cambium give rise to the xylem and phloem rays. 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. In year 2 of secondary growth, the vascular cambium adds to the secondary xylem and phloem, and the cork cambium produces cork. As the diameter of the stem continues to increase, the outermost tissues exterior to the cork cambium rupture and slough off from the stem. 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. Each cork cambium and the tissues it produces form a layer of periderm. Bark consists of all tissues exterior to the vascular cambium. (a) Primary and secondary growth in a two-year-old stem Figure 35.18a

Secondary phloem Vascular cambium Late wood Early wood Secondary xylem Cork cambium Periderm (b) Transverse section of a three-year- old stem (LM) Xylem ray Bark 0.5 mm Figure 35.18b

Viewed in transverse section, the vascular cambium
Appears as a ring, with interspersed regions of dividing cells called fusiform initials and ray initials Figure 35.19a, b Vascular cambium C X P 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. (a) Accumulation of secondary growth. Although shown here as alternately adding xylem and phloem, a cambial initial usually produces much more xylem. (b)

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

Growth ring Vascular ray Heartwood Sapwood Vascular cambium Secondary phloem Layers of periderm Secondary xylem Bark Figure 35.20

Cork Cambia and the Production of Periderm
The cork cambium Gives rise to the secondary plant body’s protective covering, or periderm

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

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)

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%) 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%) Transport (8.5%) Other biological processes (18.6%) Unknown (36.6%) Figure 35.21

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

Single file of cells forms
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 Figure 35.22a Division in same plane Plane of cell division Single file of cells forms Cube forms Nucleus Cell divisions in the same plane produce a single file of cells, whereas cell divisions in three planes give rise to a cube. (a) three planes

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 Guard cell “mother cell” Unspecialized epidermal cell 未特化表皮細胞保衛細胞母細胞 (b) An asymmetrical cell division precedes the development of epidermal guard cells, the cells that border stomata (see Figure 35.17). Figure 35.22b

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)

早前期帶及細胞分裂平面微管的早前期帶細胞板 Figure 35.23 Preprophase bands of microtubules
Nuclei Cell plates 10 µm Figure 35.23 微管的早前期帶細胞板

Orientation of Cell Expansion (細胞擴增的定向)
Plant cells Rarely expand equally in all directions

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 Figure 35.24 Vacuoles Nucleus 5 µm Cellulose microfibrils

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 (a) Wild-type seedling (c) Mature fass mutant Figure 35.25a–c

Morphogenesis and 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

In the gnom mutant of Arabidopsis
Polarity (極性) Is one type of positional information In the gnom mutant of Arabidopsis The establishment of polarity is defective Figure 35.26

Morphogenesis in plants, as in other multicellular organisms is often under the control of homeotic genes (同源基因) Figure 35.27

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

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) Figure 35.28 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 indi- cates 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. 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. Cortical cells 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)

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)

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 Leaves produced by juvenile phase (幼年期) of apical meristem Figure 35.29

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)

Plant biologists have identified several organ identity genes (器官本體基因) that regulate the development of floral pattern Figure 35.30a, b (a) Normal Arabidopsis flower. Arabidopsis normally has four whorls of flower parts: sepals (Se), petals (Pe), stamens (St), and carpels (Ca). (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. Ca St Pe Se Sepal萼片 Petal花瓣 Stamen雄蕊 Carpel心皮/雌蕊

The ABC model of flower formation
Identifies how floral organ identity genes direct the formation of the four types of floral organs Petals Stamens Carpels A B Sepals C C gene activity B + C gene A + B A gene (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. Figure 35.31a Sepal萼片 Petal花瓣 Stamen雄蕊 Carpel心皮/雌蕊

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) Stamen Carpel Petal Sepal Wild type Mutant lacking A Mutant lacking B Mutant lacking C Active genes: Whorls: A C B No sepal No petal No carpel (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

Plant Structure, Growth, and Development (植物結構、生長與發育)

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Plant Structure, Growth, and Development (植物結構、生長與發育)

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Presentation on theme: "Plant Structure, Growth, and Development (植物結構、生長與發育)"— Presentation transcript:

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