Plant Structure, Growth and Development: Organs, Tissues and Cells

Plant Structure, Growth, and Development ,[object Object],[object Object],[object Object]

The Three Basic Plant Organs: Roots, Stems, and Leaves ,[object Object],[object Object],Figure 35.2 Reproductive shoot (flower) Terminal bud Node Internode Terminal bud Vegetative shoot Blade Petiole Stem Leaf Taproot Lateral roots Root system Shoot system Axillary bud

Roots ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],Figure 35.4a–e (a) Prop roots (b) Storage roots (c) “Strangling” aerial roots (d) Buttress roots (e) Pneumatophores

Stems ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],Figure 35.5a–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. (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 Root

Leaves ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],Figure 35.6a–c Petiole (a) Simple leaf. A simple leaf is a single, undivided blade. Some simple leaves are deeply lobed, as in an oak leaf. (b) Compound leaf. In a compound leaf, the blade consists of multiple leaflets. Notice that a leaflet has no axillary bud at its base. (c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets. Axillary bud Leaflet Petiole Axillary bud Axillary bud Leaflet Petiole

[object Object],[object Object],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.

The Three Tissue Systems: Dermal, Vascular, and Ground ,[object Object],[object Object],Figure 35.8 Dermal tissue Ground tissue Vascular tissue

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object]

[object Object],Figure 35.9 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

[object Object],Figure. 35.9 WATER-CONDUCTING CELLS OF THE XYLEM Vessel Tracheids 100 m Tracheids and vessels Vessel element Vessel elements with partially perforated end walls Pits Tracheids SUGAR-CONDUCTING CELLS OF THE PHLOEM Companion cell Sieve-tube member Sieve-tube members: longitudinal view Sieve plate Nucleus Cytoplasm Companion cell 30 m 15 m

[object Object],Figure. 35.10 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 cambium Lateral meristems Root apical meristems Primary growth in stems Epidermis Cortex Primary phloem Primary xylem Pith Secondary growth in stems Periderm Cork cambium Cortex Primary phloem Secondary phloem Vascular cambium Secondary xylem Primary xylem Pith Shoot apical meristems (in buds) The cork cambium adds secondary dermal tissue. The vascular cambium adds secondary xylem and phloem.

[object Object],[object Object],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 formed from axillary bud near shoot apex Scars left by terminal bud scales of previous winters Leaf scar Leaf scar Stem Leaf scar Bud scale Axillary buds Internode Node Terminal bud

[object Object],[object Object],[object Object]

Primary Growth of Roots Figure 35.12 Dermal Ground Vascular Key Cortex Vascular cylinder Epidermis Root hair Zone of maturation Zone of elongation Zone of cell division Apical meristem Root cap 100 m

[object Object],[object Object]

[object Object],Figure 35.13a, b Cortex Vascular cylinder Endodermis Pericycle Core of parenchyma cells Xylem 50 m Endodermis Pericycle Xylem Phloem Key 100 m Vascular Ground Dermal Phloem 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. (b) 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. (a) 100 m Epidermis

[object Object],[object Object],Figure 35.14 Cortex Vascular cylinder Epidermis Lateral root 100 m 1 2 3 4 Emerging lateral root

Primary Growth of Shoots ,[object Object],[object Object],[object Object],Figure. 35.15 Apical meristem Leaf primordia Developing vascular strand Axillary bud meristems 0.25 mm

Tissue Organization of Stems ,[object Object],[object Object],Figure 35.16a 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 the outside is called cortex. (LM of transverse section)

[object Object],[object Object],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) Figure 35.16b

Tissue Organization of Leaves ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],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 mesophyll Lower epidermis Cuticle Vein Guard cells Xylem Phloem Guard cells Bundle- sheath cell Cutaway drawing of leaf tissues (a) Vein Air spaces Guard cells 100 µm Transverse section of a lilac ( Syringa ) leaf (LM) (c) Figure 35.17a–c

[object Object],[object Object],[object Object],[object Object],[object Object]

The Vascular Cambium and Secondary Vascular Tissue ,[object Object],[object Object],[object Object],[object Object]

[object Object],Figure 35.18a Vascular cambium Pith Primary xylem Secondary xylem Vascular cambium Secondary phloem Primary phloem Periderm (mainly cork cambia and cork) Pith Primary xylem Vascular cambium Primary phloem Cortex Epidermis Vascular cambium 4 First cork cambium Secondary xylem (two years of production) Pith Primary xylem Vascular cambium Primary phloem 2 1 6 Growth Primary xylem Secondary xylem Secondary phloem Primary phloem Cork Phloem ray 3 Xylem ray Growth Bark 8 Layers of periderm 7 Cork 5 Most recent cork cambium Cortex Epidermis 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. 1 2 3 4 5 6 7 8 9 Secondary phloem (a) Primary and secondary growth in a two-year-old stem

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

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

Cork Cambia and the Production of Periderm ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Morphogenesis and Pattern Formation ,[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],Figure 35.26

[object Object],[object Object],Figure 35.27

Gene Expression and Control of Cellular Differentiation ,[object Object],[object Object]

[object Object],[object Object],[object Object],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 ,[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],Leaves produced by adult phase of apical meristem Leaves produced by juvenile phase of apical meristem Figure 35.29

Genetic Control of Flowering ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],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 Pe Pe Se Pe Se

Transport in Vascular Plants ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],Minerals H 2 O CO 2 O 2 CO 2 O 2 H 2 O Sugar Light Sugars are transported as phloem sap to roots and other parts of the plant. Figure 36.2 Sugars are produced by photosynthesis in the leaves. 5 6 Through stomata, leaves take in CO 2 and expel O 2 . The CO 2 provides carbon for photosynthesis. Some O 2 produced by photosynthesis is used in cellular respiration. 4 Transpiration, the loss of water from leaves (mostly through stomata), creates a force within leaves that pulls xylem sap upward. 3 Water and minerals are transported upward from roots to shoots as xylem sap. 2 Roots absorb water and dissolved minerals from the soil. 1 Roots exchange gases with the air spaces of soil, taking in O 2 and discharging CO 2 . In cellular respiration, O 2 supports the breakdown of sugars. 7

Selective Permeability of Membranes: A Review ,[object Object],[object Object],[object Object],[object Object]

The Central Role of Proton Pumps ,[object Object],[object Object],[object Object],Figure 36.3 CYTOPLASM EXTRACELLULAR FLUID ATP H + H + H + H + H + H + H + H + Proton pump generates membrane potential and H + gradient. – – – – – + + + + +

[object Object],[object Object],Figure 36.4a + CYTOPLASM EXTRACELLULAR FLUID Cations ( , for example) are driven into the cell by the membrane potential. Transport protein K + K + K + K + K + K + K + K + – – – + + (a) Membrane potential and cation uptake – – + +

[object Object],[object Object],Figure 36.4b H + H + H + H + H + H + H + H + H + H + H + H + NO 3 – NO 3 – NO 3 – NO 3 – NO 3 – NO 3 – – – – + + + – – – + + + NO 3 – (b) Cotransport of anions H + of through a cotransporter. Cell accumulates anions ( , for example) by coupling their transport to the inward diffusion

[object Object],[object Object],H + H + H + H + H + H + H + H + H + H + S S S S S Plant cells can also accumulate a neutral solute, such as sucrose ( ), by cotransporting down the steep proton gradient. S H + – – – + + + – – + + – Figure 36.4c H + H + S + – (c) Contransport of a neutral solute

Effects of Differences in Water Potential ,[object Object],[object Object],[object Object],[object Object],[object Object]

Quantitative Analysis of Water Potential ,[object Object],[object Object],Figure 36.5a 0.1 M solution H 2 O Pure water  P = 0  S = 0.23  = 0.23 MPa  = 0 MPa (a)

[object Object],[object Object],Figure 36.5b, c H 2 O  P = 0.23  S = 0.23  = 0 MPa  = 0 MPa (b) H 2 O  P = 0.30  S = 0.23  = 0.07 MPa  = 0 MPa (c)

[object Object],[object Object],Figure 36.5d H 2 O  P = 0  S = 0.23  = 0.23 MPa (d)  P = 0.30  S = 0  = 0.30 MPa

[object Object],[object Object],[object Object],[object Object],Figure 36.6a 0.4 M sucrose solution: Initial flaccid cell: Plasmolyzed cell at osmotic equilibrium with its surroundings  P = 0  S = 0.7  P = 0  S = 0.9  P = 0  S = 0.9  =  0.9 MPa  = 0.7 MPa  =  0.9 MPa

[object Object],[object Object],Distilled water: Initial flaccid cell: Turgid cell at osmotic equilibrium with its surroundings  P = 0  S = 0.7  P = 0  S = 0  P = 0.7  S = 0.7 Figure 36.6b  = 0.7 MPa  = 0 MPa  = 0 MPa

[object Object],[object Object],Figure 36.7

Aquaporin Proteins and Water Transport ,[object Object],[object Object],[object Object]

Bulk Flow in Long-Distance Transport ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],Figure 36.9 1 2 3 Uptake of soil solution by the hydrophilic walls of root hairs provides access to the apoplast. Water and minerals can then soak into the cortex along this matrix of walls. Minerals and water that cross the plasma membranes of root hairs enter the symplast. As soil solution moves along the apoplast, some water and minerals are transported into the protoplasts of cells of the epidermis and cortex and then move inward via the symplast. Within the transverse and radial walls of each endodermal cell is the Casparian strip, a belt of waxy material (purple band) that blocks the passage of water and dissolved minerals. Only minerals already in the symplast or entering that pathway by crossing the plasma membrane of an endodermal cell can detour around the Casparian strip and pass into the vascular cylinder. Endodermal cells and also parenchyma cells within the vascular cylinder discharge water and minerals into their walls (apoplast). The xylem vessels transport the water and minerals upward into the shoot system. Casparian strip Pathway along apoplast Pathway through symplast Plasma membrane Apoplastic route Symplastic route Root hair Epidermis Cortex Endodermis Vascular cylinder Vessels (xylem) Casparian strip Endodermal cell 4 5 2 1

The Roles of Root Hairs, Mycorrhizae, and Cortical Cells ,[object Object],[object Object]

[object Object],[object Object],Figure 36.10 2.5 mm

The Endodermis: A Selective Sentry ,[object Object],[object Object],[object Object]

Factors Affecting the Ascent of Xylem Sap ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Pulling Xylem Sap: The Transpiration-Cohesion-Tension Mechanism ,[object Object],[object Object],[object Object]

[object Object],[object Object],Evaporation causes the air-water interface to retreat farther into the cell wall and become more curved as the rate of transpiration increases. As the interface becomes more curved, the water film’s pressure becomes more negative. This negative pressure, or tension, pulls water from the xylem, where the pressure is greater. Cuticle Upper epidermis Mesophyll Lower epidermis Cuticle Water vapor CO 2 O 2 Xylem CO 2 O 2 Water vapor Stoma Evaporation At first, the water vapor lost by transpiration is replaced by evaporation from the water film that coats mesophyll cells. In transpiration, water vapor (shown as blue dots) diffuses from the moist air spaces of the leaf to the drier air outside via stomata. Airspace Cytoplasm Cell wall Vacuole Evaporation Water film Low rate of transpiration High rate of transpiration Air-water interface Cell wall Airspace  = –0.15 MPa  = –10.00 MPa 3 1 2 Figure 36.12 Air- space

Cohesion and Adhesion in the Ascent of Xylem Sap ,[object Object],[object Object],[object Object]

[object Object],Xylem sap Outside air  = –100.0 MPa Leaf  (air spaces) = –7.0 MPa Leaf  (cell walls) = –1.0 MPa Trunk xylem  = – 0.8 MPa Water potential gradient Root xylem  = – 0.6 MPa Soil  = – 0.3 MPa Mesophyll cells Stoma Water molecule Atmosphere Transpiration Xylem cells Adhesion Cell wall Cohesion, by hydrogen bonding Water molecule Root hair Soil particle Water Cohesion and adhesion in the xylem Water uptake from soil Figure 36.13

Xylem Sap Ascent by Bulk Flow: A Review ,[object Object],[object Object]

[object Object],[object Object],[object Object],20 µm Figure 36.14

Effects of Transpiration on Wilting and Leaf Temperature ,[object Object],[object Object],[object Object]

[object Object],[object Object],Cells flaccid/Stoma closed Cells turgid/Stoma open Radially oriented cellulose microfibrils Cell wall Vacuole Guard cell Changes in guard cell shape and stomatal opening and closing (surface view). Guard cells of a typical angiosperm are illustrated in their turgid (stoma open) and flaccid (stoma closed) states. The pair of guard cells buckle outward when turgid. Cellulose microfibrils in the walls resist stretching and compression in the direction parallel to the microfibrils. Thus, the radial orientation of the microfibrils causes the cells to increase in length more than width when turgor increases. The two guard cells are attached at their tips, so the increase in length causes buckling. (a) Figure 36.15a

[object Object],[object Object],H 2 O H 2 O H 2 O H 2 O H 2 O K + Role of potassium in stomatal opening and closing. The transport of K + (potassium ions, symbolized here as red dots) across the plasma membrane and vacuolar membrane causes the turgor changes of guard cells. (b) H 2 O H 2 O H 2 O H 2 O H 2 O Figure 36.15b

Xerophyte Adaptations That Reduce Transpiration ,[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],Lower epidermal tissue Trichomes (“hairs”) Cuticle Upper epidermal tissue Stomata 100  m Figure 36.16

Movement from Sugar Sources to Sugar Sinks ,[object Object],[object Object],[object Object]

[object Object],[object Object],Figure 36.17a Mesophyll cell Cell walls (apoplast) Plasma membrane Plasmodesmata Companion (transfer) cell Sieve-tube member Mesophyll cell Phloem parenchyma cell Bundle- sheath cell Sucrose manufactured in mesophyll cells can travel via the symplast (blue arrows) to sieve-tube members. In some species, sucrose exits the symplast (red arrow) near sieve tubes and is actively accumulated from the apoplast by sieve-tube members and their companion cells. (a)

[object Object],[object Object],[object Object],[object Object],A chemiosmotic mechanism is responsible for the active transport of sucrose into companion cells and sieve-tube members. Proton pumps generate an H + gradient, which drives sucrose accumulation with the help of a cotransport protein that couples sucrose transport to the diffusion of H + back into the cell. (b) High H + concentration Cotransporter Proton pump ATP Key Sucrose Apoplast Symplast H + H + Low H + concentration H + S S Figure 36.17b

Pressure Flow: The Mechanism of Translocation in Angiosperms ,[object Object],[object Object],Vessel (xylem) H 2 O H 2 O Sieve tube (phloem) Source cell (leaf) Sucrose H 2 O Sink cell (storage root) 1 Sucrose Loading of sugar (green dots) into the sieve tube at the source reduces water potential inside the sieve-tube members. This causes the tube to take up water by osmosis. 2 4 3 1 2 This uptake of water generates a positive pressure that forces the sap to flow along the tube. The pressure is relieved by the unloading of sugar and the consequent loss of water from the tube at the sink. 3 4 In the case of leaf-to-root translocation, xylem recycles water from sink to source. Transpiration stream Pressure flow Figure 36.18

[object Object],[object Object],Aphid feeding Stylet in sieve-tube member Severed stylet exuding sap Sieve- Tube member EXPERIMENT RESULTS CONCLUSION Sap droplet Stylet Sap droplet 25 m Sieve- tube member To test the pressure flow hypothesis,researchers used aphids that feed on phloem sap. An aphid probes with a hypodermic- like mouthpart called a stylet that penetrates a sieve-tube member. As sieve-tube pressure force-feeds aphids, they can be severed from their stylets, which serve as taps exuding sap for hours. Researchers measured the flow and sugar concentration of sap from stylets at different points between a source and sink. The closer the stylet was to a sugar source, the faster the sap flowed and the higher was its sugar concentration. The results of such experiments support the pressure flow hypothesis. Figure 36.19

Plant Structure, Growth and Development: Organs, Tissues and Cells

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Plant Structure, Growth and Development: Organs, Tissues and Cells