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(2) 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) • Concept 35.1: The plant body has a hierachy of organs, tissues and cells. (器官、組織及細胞體 系) • Concept 35.2: Meristems generate cells for new organs. (分生組織產生新器官的細胞) • Concept 35.3: Primary growth lengthens roots and shoots. (初級生長使根與枝條增長) • Concept 35.4: Secondary growth adds girth to stems and roots in woody plants. (次級生長擴增 木本植物的莖與根) • Concept 35.5: Growth, morphogenesis, and differentiation produce the plant body. (生長、 形態發生與分化產生植物體) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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). Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of a flowering plant (開花植物) 繁殖枝條 花 Reproductive shoot (flower) • Three basic organs evolved: roots, stems, and leaves. 頂芽Terminal bud 莖節 Node 節間Internode 頂芽 Terminal bud • They are organized into a root system 營養枝條 Vegetative shoot 葉片 and a shoot system. 葉 Leaf Blade Petiole CO2 light Shoot system 枝條系統 葉柄 • A plant’s root and shoot systems are evolutionary adaptations to living on land. Axillary bud Stem 腋芽 莖 主(軸)根 Taproot 側根 Lateral roots H 20 mineral Root system 根系統 Figure 35.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 不定根 (adventitious root) 鱗莖 (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 Root (b) 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. Figure 35.5a–d 走莖/匍匐莖 塊 莖 (c) 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 根狀莖 Node Rhizome 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •In identifying and classifying angiosperms(被子植物的鑑定與分類) – Taxonomists (分類學家) may use leaf morphology (葉子形態) as a criterion. (a) Simple leaf. A simple leaf – Leaf morphology: is a single, undivided blade. Some simple leaves are deeply lobed, as in an oak leaf. 單葉 leaf shape (葉形) spatial arrangement (b) Compound leaf. In a compound leaf, the blade consists of multiple leaflets. Notice that a leaflet has no axillary bud at its base. pattern of a leaf’s vein margin (葉緣) (羽狀)複葉 (c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets. 雙重(羽狀)複葉 Banana leaf Figure 35.6a–c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 葉柄 Petiole ★ Axillary bud Leaflet 小葉 Petiole ★ Axillary bud Leaflet Petiole ★ Axillary bud 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 (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. 刺 針 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 (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. Figure 35.6a–e Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. 報告完畢 敬請指教 !? !? !? !? !? !? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Leaf 莖橫切面 Stem 三種組織系統 Dermal tissue 表皮系統 Ground tissue Root 基本系統 根橫切面 Figure 35.8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vascular tissue 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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)---upward – Conveys water and dissolved minerals upward from roots into the shoots • Phloem(韌皮部)---downward – Transports organic nutrients from where they are made to where they are needed Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Ground tissue (基本組織系統) includes various cells specialized for functions such as: – 1. storage (儲存) – 2. photosynthesis (光合作用) – 3. support (支持) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Common Types of Plant Cells • Like any multicellular organism, a plant is characterized by cellular differentiation (細胞分 化), the specialization of cells in structure and function (細胞在結構與功能的特化) . Some of the major types of plant cells include: – 1. Parenchyma(薄壁細胞) – 2. Collenchyma(厚角細胞) – 3. Sclerenchyma(厚壁細胞) – 4. Water-conducting cells of the xylem (木質 部水份運輸細胞) – 5. Sugar-conducting cells of the phloem (韌 皮部醣類運輸細胞) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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。 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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): vessels (導管) and tracheids (假導管、管胞) 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。 假導管呈紡錘形,有 紋孔,水可在細胞間流 動。 一般所謂木材主要是 由假導管及導管所組成 。 假導管 Tracheids 100 m Vessel 導管 Pits 紋孔 水份輸 送方向 導管 Vessel Vessel 細胞 element elements Vessel elements with partially perforated end walls Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Companion Cytoplasm cell 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。 伴細胞 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 30 m 15 m 每一篩板細胞旁都有 具細胞核的伴細胞。 報告完畢 敬請指教 !? !? !? !? !? !? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Root apical meristems 根尖分生組織 Figure. 35.10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 初級韌皮部 側端分 生組織 Primary xylem Pith 髄 初級木質部 Secondary growth in stems 周皮 Periderm Cork cambium Pith The cork cambium adds secondary Primary dermal tissue. xylem Cortex Primary phloem Secondary The vascular xylem Secondary cambium adds secondary phloem xylem and Vascular cambium phloem. 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 (同步地) 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) 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Vascular cylinder Epidermis Zone of Root hair maturation 成熟區 Key Dermal Ground Vascular Zone of elongation Apical meristem Root cap 根冠 Figure 35.12 100 m Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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) 葉橫切面 – ground tissue (基本組織) – vascular tissue (維管組織) 莖橫切面 根橫切面 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX • Organization of primary tissues in young roots Epidermis Cortex Vascular Cylinder (stele)中柱 Endodermis (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. Pericycle 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 100 m (b) Transverse section of a root with parenchyma in the Key center. The stele of many Dermal monocot roots is a vascular Ground Vascular cylinder with a core of parenchyma surrounded by a ring of alternating xylem and phloem. • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 報告完畢 敬請指教 !? !? !? !? !? !? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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) Vascular bundle Pith Epidermis Cortex Vascular bundle 1 mm Key Dermal Ground 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Leaf anatomy (葉的解剖) Guard cells Key to labels 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 Xylem Phloem (a) Cutaway drawing of leaf tissues Vein Guard cells Figure 35.17a–c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 (維管束形成層) and cork cambium (木栓形成層) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 報告完畢 敬請指教 !? !? !? !? !? !? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Vascular Cambium and Secondary Vascular Tissue • The vascular cambium (維管束形成層) – Is a cylinder of meristematic cells one cell thick – Develops from parenchyma cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Primary and secondary growth of a stem (a) Primary and secondary growth in a two-year-old stem In the youngest part of the stem, you can see the primary plant 1 body, as formed by the apical meristem during primary growth. The vascular cambium is beginning to develop. 1 Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Primary xylem Vascular cambium Primary phloem Cortex 2 Epidermis Phloem ray 3 Xylem ray Pith Periderm (mainly cork cambia and cork) Primary xylem Secondary xylem Vascular cambium Secondary phloem Primary phloemCork 4 First cork cambium 6 Primary phloem Secondary phloem Vascular cambium Secondary xylem Primary xylem Secondary xylem (two years of production) Vascular cambium 9 Bark Secondary phloem 7 Cork 8 5 Most recent cork cambium As primary growth continues to elongate the stem, the portion 2 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. 3 The ray initials of the vascular cambium give rise to the xylem and phloem rays. As the diameter of the vascular cambium increases, the 4 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. 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. 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. Pith Layers of periderm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 35.18a Primary and secondary growth of a stem xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Secondary phloem Vascular cambium Secondary xylem Cork cambium Cork Late wood Early wood Periderm (b) Transverse section of a three-yearold stem (LM) Xylem ray Bark 0.5 mm 0.5 mm Figure 35.18b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx • 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 C (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. (B) Accumulation of secondary growth. Although shown here as alternately adding xylem and phloem, a cambial initial usually produces much more xylem. Figure 35.19a, b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Growth ring Vascular ray Heartwood Secondary xylem Sapwood Vascular cambium Secondary phloem Bark Layers of periderm Figure 35.20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 報告完畢 敬請指教 !? !? !? !? !? !? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Model plant (模式植物)----阿拉伯芥 • 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%) Unknown(36.6%) Electron transport (3%) Protein modification (3.7%) Arabidopsis thaliana Protein metabolism (5.7%) Transcription (6.1%) Other biological processes (18.6%) Figure 35.21 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other metabolism (6.6%) 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 (分生組織) 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 (植物的形式) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • If the planes of division of cells are parallel (平 行) to the plane of the first division (首次分裂) – A single file of cells will be produced Division in same plane Plane of cell division (細胞分裂面) 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 之母細胞 (b) An asymmetrical cell division precedes the development of epidermal guard cells, the cells that border stomata (see Figure 35.17). Figure 35.22b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 10 µm Orientation of Cell Expansion (細胞擴增的定向) • Plant cells – Rarely expand equally in all directions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Asymmetric cell division (不對稱細胞分裂) Figure 35.25a–c No asymmetric cell division (無不對稱細胞分裂) (b) fass seedling (a) Wild-type seedling (c) Mature fass mutant Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Polarity (極性) – Is one type of positional information • In the gnom mutant of Arabidopsis – The establishment of polarity is defective Wild type Figure 35.26 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings gnom mutant • Morphogenesis in plants, as in other multicellular organisms is often under the control of homeotic genes (同源基因) Figure 35.27 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pe Ca St Pe Pe Se • The ABC model of flower formation – Identifies how floral organ identity genes (花器 官本體基因) 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 報告完畢 敬請指教 !? !? !? !? !? !? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings