Plant Structure, Growth, and Development Chapter 35 Plant Structure, Growth, and Development

Overview: Plastic Plants? To some people, the fanwort is an intrusive weed, but to others it is an attractive aquarium plant This plant exhibits developmental plasticity, the ability to alter itself in response to its environment

Fig. 35-1 Figure 35.1 Why does this plant have two types of leaves?

Developmental plasticity: Is more marked in plants than in animals In addition to plasticity, plant species have by natural selection accumulated characteristics of morphology that vary little within the species

The plant body has a hierarchy of organs, tissues, and cells Plants, like multicellular animals, have: Organs Organs are composed of: Different tissues Tissues are composed of: Similar cells

The Three Basic Plant Organs: Roots, Stems, and Leaves Basic morphology of vascular plants reflects: Their evolution as organisms able to draw nutrients from below ground and above ground

Three basic organs evolved: They are organized into: Roots, stems, and leaves They are organized into: A root system, and A shoot system Roots rely on: Sugar produced by photosynthesis in the shoot system Shoots rely on: water and minerals absorbed by the root system

Reproductive shoot (flower) Fig. 35-2 Reproductive shoot (flower) Apical bud Node Internode Apical bud Shoot system Vegetative shoot Blade Leaf Petiole Axillary bud Stem Figure 35.2 An overview of a flowering plant Taproot Lateral branch roots Root system

Roots are multicellular organs with important functions: Anchoring the plant Absorbing minerals and water Storing organic nutrients

A taproot system consists of: One main vertical root that gives rise to lateral roots, or branch roots Adventitious roots arise from: Stems or leaves Seedless vascular plants & monocots: Have a fibrous root system characterized by: Thin lateral roots with no main root

In most plants, Absorption of water & minerals occurs near the tips of roots Vast numbers of tiny root hairs at root tips increase the surface area

Fig. 35-3 Figure 35.3 Root hairs of a radish seedling

Many plants have modified roots

Prop roots “Strangling” aerial roots Storage roots Buttress roots Fig. 35-4 Prop roots “Strangling” aerial roots Storage roots Buttress roots Figure 35.4 Modified roots Pneumatophores

Fig. 35-4a Figure 35.4 Modified roots Prop roots

Fig. 35-4b Figure 35.4 Modified roots Storage roots

“Strangling” aerial roots Fig. 35-4c Figure 35.4 Modified roots “Strangling” aerial roots

Fig. 35-4d Figure 35.4 Modified roots Pneumatophores

Fig. 35-4e Figure 35.4 Modified roots Buttress roots

A stem is an organ consisting of: Stems A stem is an organ consisting of: An alternating system of nodes (the points of attachment of leaves) Internodes, the stem segments between nodes

An axillary bud: Is a structure that has the potential to form a lateral shoot, or branch An apical (terminal) bud: Is located near the shoot tip and causes elongation of a young shoot Apical dominance: Inhibition of axillary buds by an apical bud helps maintains dormancy in nonapical buds

Many plants have modified stems

Rhizomes Bulbs Storage leaves Stem Stolons Stolon Tubers Fig. 35-5 Figure 35.5 Modified stems Tubers

Fig. 35-5a Figure 35.5 Modified stems Rhizomes

Fig. 35-5b Storage leaves Figure 35.5 Modified stems Stem Bulb

Fig. 35-5c Stolon Figure 35.5 Modified stems Stolons

Fig. 35-5d Figure 35.5 Modified stems Tubers

Leaves Leaves are: The main photosynthetic organs of most vascular plants Generally consist of: A flattened blade A stalk called the petiole, which joins the leaf to a node of the stem

In classifying angiosperms, taxonomists may: Monocots & eudicots differ in the arrangement of veins (the vascular tissue of leaves): Most monocots have parallel veins Most eudicots have branching veins In classifying angiosperms, taxonomists may: Use leaf morphology as a criterion

(a) Simple leaf Petiole Axillary bud Leaflet (b) Compound leaf Petiole Fig. 35-6 (a) Simple leaf Petiole Axillary bud Leaflet (b) Compound leaf Petiole Axillary bud Figure 35.6 Simple versus compound leaves (c) Doubly compound leaf Leaflet Petiole Axillary bud

(a) Simple leaf Petiole Axillary bud Fig. 35-6a Figure 35.6 Simple versus compound leaves Axillary bud

Leaflet (b) Compound leaf Petiole Axillary bud Fig. 35-6b Figure 35.6 Simple versus compound leaves Axillary bud

(c) Doubly compound leaf Leaflet Petiole Axillary bud Fig. 35-6c Figure 35.6 Simple versus compound leaves Axillary bud

Some plant species have: Evolved modified leaves Such leaves serve various functions

Tendrils Spines Storage leaves Reproductive leaves Bracts Fig. 35-7 Figure 35.7 Modified leaves Bracts

Fig. 35-7a Figure 35.7 Modified leaves Tendrils

Fig. 35-7b Figure 35.7 Modified leaves Spines

Fig. 35-7c Figure 35.7 Modified leaves Storage leaves

Fig. 35-7d Figure 35.7 Modified leaves Reproductive leaves

Fig. 35-7e Figure 35.7 Modified leaves Bracts

Dermal, Vascular, and Ground Tissues Each plant organ has the following tissues: Dermal Ground Vascular Each of these three categories forms: A tissue system

Dermal tissue Ground tissue Vascular tissue Fig. 35-8 Figure 35.8 The three tissue systems Dermal tissue Ground tissue Vascular tissue

In nonwoody plants: In woody plants: Trichomes: The dermal tissue system consists of the epidermis A waxy coating called the cuticle helps prevent water loss from the epidermis In woody plants: Protective tissues called periderm replace the epidermis This occurs in older regions of stems & roots Trichomes: Are outgrowths of the shoot epidermis Can help with insect defense

EXPERIMENT Very hairy pod (10 trichomes/ mm2) Slightly hairy pod Fig. 35-9 EXPERIMENT Very hairy pod (10 trichomes/ mm2) Slightly hairy pod (2 trichomes/ mm2) Bald pod (no trichomes) RESULTS Very hairy pod: 10% damage Slightly hairy pod: 25% damage Bald pod: 40% damage Figure 35.9 Do soybean pod trichomes deter herbivores?

The vascular tissue system: Transports materials between roots & shoots Consists of two vascular tissues: The xylem: Conveys water & dissolved minerals from roots into the shoots The Phloem: Transports organic nutrients from where they are made to where they are needed

The vascular tissue of a stem or root is collectively called the stele The stele arrangement varies depending on species & organ In angiosperms: The root stele is a solid central vascular cylinder of xylem & phloem The stele of stems & leaves consists of vascular bundles, separate strands of xylem & phloem

Ground tissue system: Tissues that are neither dermal nor vascular The tissue includes cells specialized for: Storage Photosynthesis Support Pith: Ground tissue internal to the vascular tissue Cortex: Ground tissue external to the vascular tissue

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 major types of plant cells: Parenchyma Collenchyma Sclerenchyma Water-conducting cells of the xylem Sugar-conducting cells of the phloem

BioFlix: Tour of a Plant Cell Parenchyma Cells Mature parenchyma cells: Have thin and flexible primary walls Lack secondary walls Are the least specialized Perform the most metabolic functions Retain the ability to divide and differentiate BioFlix: Tour of a Plant Cell

Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 µm Fig. 35-10a Figure 35.10 Examples of differentiated plant cells Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 µm

Collenchyma Cells: Grouped in strands Help support young parts of the plant shoot Have thicker and uneven cell walls Lack secondary walls Provide flexible support without restraining growth

Collenchyma cells (in Helianthus stem) (LM) Fig. 35-10b 5 µm Figure 35.10 Examples of differentiated plant cells Collenchyma cells (in Helianthus stem) (LM)

Are rigid because of thick secondary walls strengthened with lignin Sclerenchyma Cells Are rigid because of thick secondary walls strengthened with lignin Dead at functional maturity There are two types: Sclereids: Short & irregular in shape Have thick lignified secondary walls Fibers: Long & slender and Arranged in threads

Sclereid cells in pear (LM) Fig. 35-10c 5 µm Sclereid cells in pear (LM) 25 µm Cell wall Figure 35.10 Examples of differentiated plant cells Fiber cells (cross section from ash tree) (LM)

Water-Conducting Cells of the Xylem Two types of water-conducting cells (dead at maturity): Tracheids: Found in the xylem of all vascular plants Vessel elements: Common to most angiosperms and a few gymnosperms Align end to end to form long micropipes called vessels

Vessel Tracheids Pits Tracheids and vessels (colorized SEM) Fig. 35-10d Vessel Tracheids 100 µm Pits Tracheids and vessels (colorized SEM) Figure 35.10 Examples of differentiated plant cells Perforation plate Vessel element Vessel elements, with perforated end walls Tracheids

100 µm Vessel Tracheids Tracheids and vessels (colorized SEM) Fig. 35-10d1 100 µm Vessel Tracheids Figure 35.10 Examples of differentiated plant cells Tracheids and vessels (colorized SEM)

Pits Perforation plate Vessel element Vessel elements, with Fig. 35-10d2 Pits Figure 35.10 Examples of differentiated plant cells Perforation plate Vessel element Vessel elements, with perforated end walls Tracheids

Sugar-Conducting Cells of the Phloem Sieve-tube elements: Are alive at functional maturity, though they lack organelles Each element has a companion cell whose nucleus and ribosomes serve both cells Sieve plates: Are the porous end walls allowing fluid to flow between cells along the sieve tube

longitudinal view (LM) 3 µm Fig. 35-10e Sieve-tube elements: longitudinal view (LM) 3 µm Sieve plate Sieve-tube element (left) and companion cell: cross section (TEM) Companion cells Sieve-tube elements Plasmodesma Sieve plate Figure 35.10 Examples of differentiated plant cells 30 µm 10 µm Nucleus of companion cells Sieve-tube elements: longitudinal view Sieve plate with pores (SEM)

Sieve-tube element (left) and companion cell: cross section (TEM) Fig. 35-10e1 3 µm Figure 35.10 Examples of differentiated plant cells Sieve-tube element (left) and companion cell: cross section (TEM)

longitudinal view (LM) Fig. 35-10e2 Sieve-tube elements: longitudinal view (LM) Sieve plate Companion cells Sieve-tube elements Figure 35.10 Examples of differentiated plant cells 30 µm

Sieve plate with pores (SEM) Fig. 35-10e3 Sieve-tube element Plasmodesma Sieve plate 10 µm Nucleus of companion cells Figure 35.10 Examples of differentiated plant cells Sieve-tube elements: longitudinal view Sieve plate with pores (SEM)

Break Slide Resume editing from here Sunday, July 21, 2013

Concept 35.2: Meristems generate cells for new organs A plant can grow throughout its life; this is called indeterminate growth Some plant organs cease to grow at a certain size; this is called determinate growth Annuals complete their life cycle in a year or less Biennials require two growing seasons Perennials live for many years

Meristems are perpetually embryonic tissue and allow for indeterminate growth Apical meristems are located at the tips of roots and shoots and at the axillary buds of shoots Apical meristems elongate shoots and roots, a process called primary growth

Lateral meristems add thickness to woody plants, a process called secondary growth There are two lateral meristems: the vascular cambium and the cork cambium The vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem The cork cambium replaces the epidermis with periderm, which is thicker and tougher

Primary growth in stems Fig. 35-11 Primary growth in stems Epidermis Cortex Shoot tip (shoot apical meristem and young leaves) Primary phloem Primary xylem Pith Lateral meristems: Vascular cambium Secondary growth in stems Cork cambium Axillary bud meristem Periderm Cork cambium Cortex Figure 35.11 An overview of primary and secondary growth Pith Primary phloem Primary xylem Root apical meristems Secondary phloem Secondary xylem Vascular cambium

Meristems give rise to initials, which remain in the meristem, and derivatives, which become specialized in developing tissues In woody plants, primary and secondary growth occur simultaneously but in different locations

Apical bud Bud scale Axillary buds This year’s growth (one year old) Fig. 35-12 Apical bud Bud scale Axillary buds This year’s growth (one year old) Leaf scar Bud scar Node One-year-old side branch formed from axillary bud near shoot tip Internode Last year’s growth (two years old) Leaf scar Figure 35.12 Three years’ growth in a winter twig Stem Bud scar left by apical bud scales of previous winters Growth of two years ago (three years old) Leaf scar

Concept 35.3: Primary growth lengthens roots and shoots Primary growth produces the primary plant body, the parts of the root and shoot systems produced by apical meristems

Primary Growth of Roots The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil Growth occurs just behind the root tip, in three zones of cells: Zone of cell division Zone of elongation Zone of maturation Video: Root Growth in a Radish Seed (Time Lapse)

Cortex Vascular cylinder Epidermis Key to labels Zone of Fig. 35-13 Cortex Vascular cylinder Epidermis Key to labels Zone of differentiation Root hair Dermal Ground Vascular Zone of elongation Figure 35.13 Primary growth of a root Apical meristem Zone of cell division Root cap 100 µm

The primary growth of roots produces the epidermis, ground tissue, and vascular tissue In most roots, the stele is a vascular cylinder The ground tissue fills the cortex, the region between the vascular cylinder and epidermis The innermost layer of the cortex is called the endodermis

Figure 35.14 Organization of primary tissues in young roots Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Xylem 100 µm Phloem (a) Root with xylem and phloem in the center (typical of eudicots) 100 µm (b) Root with parenchyma in the center (typical of monocots) Endodermis Key to labels Figure 35.14 Organization of primary tissues in young roots Pericycle Dermal Ground Vascular Xylem Phloem 50 µm

Root with xylem and phloem in the center (typical of eudicots) Fig. 35-14a1 Epidermis Key to labels Cortex Dermal Endodermis Ground Vascular Vascular cylinder Pericycle Figure 35.14 Organization of primary tissues in young roots Xylem 100 µm Phloem (a) Root with xylem and phloem in the center (typical of eudicots)

Root with xylem and phloem in the center (typical of eudicots) Fig. 35-14a2 (a) Root with xylem and phloem in the center (typical of eudicots) Endodermis Key to labels Pericycle Dermal Ground Vascular Xylem Phloem Figure 35.14 Organization of primary tissues in young roots 50 µm

Root with parenchyma in the center (typical of monocots) Fig. 35-14b Epidermis Cortex Endodermis Vascular cylinder Key to labels Pericycle Dermal Core of parenchyma cells Ground Vascular Figure 35.14 Organization of primary tissues in young roots Xylem Phloem 100 µm (b) Root with parenchyma in the center (typical of monocots)

Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder

Emerging lateral root Cortex Vascular cylinder 100 µm 1 Fig. 35-15-1 Figure 35.15 The formation of a lateral root 1 Vascular cylinder

Epidermis Emerging lateral Lateral root root Cortex Vascular cylinder Fig. 35-15-2 100 µm Epidermis Emerging lateral root Lateral root Cortex Figure 35.15 The formation of a lateral root 1 Vascular cylinder 2

Epidermis Emerging lateral Lateral root root Cortex Vascular cylinder Fig. 35-15-3 100 µm Epidermis Emerging lateral root Lateral root Cortex Figure 35.15 The formation of a lateral root 1 Vascular cylinder 2 3

Primary Growth of Shoots A shoot apical meristem is a dome-shaped mass of dividing cells at the shoot tip Leaves develop from leaf primordia along the sides of the apical meristem Axillary buds develop from meristematic cells left at the bases of leaf primordia

Shoot apical meristem Leaf primordia Young leaf Developing vascular Fig. 35-16 Shoot apical meristem Leaf primordia Young leaf Developing vascular strand Figure 35.16 The shoot tip Axillary bud meristems 0.25 mm

Tissue Organization of Stems Lateral shoots develop from axillary buds on the stem’s surface In most eudicots, the vascular tissue consists of vascular bundles that are arranged in a ring

Figure 35.17 Organization of primary tissues in young stems Phloem Xylem Sclerenchyma (fiber cells) Ground tissue Ground tissue connecting pith to cortex Pith Epidermis Key to labels Figure 35.17 Organization of primary tissues in young stems Epidermis Cortex Vascular bundles Dermal Vascular bundle Ground 1 mm Vascular 1 mm (a) Cross section of stem with vascular bundles forming a ring (typical of eudicots) (b) Cross section of stem with scattered vascular bundles (typical of monocots)

Cross section of stem with vascular bundles forming Fig. 35-17a Phloem Xylem Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Pith Figure 35.17 Organization of primary tissues in young stems Key to labels Epidermis Cortex Dermal Vascular bundle Ground 1 mm Vascular (a) Cross section of stem with vascular bundles forming a ring (typical of eudicots)

Cross section of stem with scattered vascular bundles Fig. 35-17b Ground tissue Epidermis Key to labels Figure 35.17 Organization of primary tissues in young stems Vascular bundles Dermal Ground Vascular 1 mm (b) Cross section of stem with scattered vascular bundles (typical of monocots)

In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring

Tissue Organization of Leaves The epidermis in leaves is interrupted by stomata, which allow CO2 exchange between the air and the photosynthetic cells in a leaf Each stomatal pore is flanked by two guard cells, which regulate its opening and closing The ground tissue in a leaf, called mesophyll, is sandwiched between the upper and lower epidermis

Below the palisade mesophyll in the upper part of the leaf is loosely arranged spongy mesophyll, where gas exchange occurs The vascular tissue of each leaf is continuous with the vascular tissue of the stem Veins are the leaf’s vascular bundles and function as the leaf’s skeleton Each vein in a leaf is enclosed by a protective bundle sheath

Fig. 35-18 Figure 35.18 Leaf anatomy Guard cells Key to labels Stomatal pore 50 µm Dermal Epidermal cell Ground Cuticle Sclerenchyma fibers Vascular Stoma (b) Surface view of a spiderwort (Tradescantia) leaf (LM) Upper epidermis Palisade mesophyll Bundle- sheath cell Spongy mesophyll Figure 35.18 Leaf anatomy Lower epidermis 100 µm Cuticle Xylem Phloem Vein Guard cells Vein Air spaces Guard cells (a) Cutaway drawing of leaf tissues (c) Cross section of a lilac (Syringa)) leaf (LM)

(a) Cutaway drawing of leaf tissues Fig. 35-18a Key to labels Dermal Ground Cuticle Sclerenchyma fibers Vascular Stoma Upper epidermis Palisade mesophyll Bundle- sheath cell Spongy mesophyll Figure 35.18 Leaf anatomy Lower epidermis Cuticle Xylem Phloem Vein Guard cells (a) Cutaway drawing of leaf tissues

Surface view of a spiderwort (Tradescantia) leaf (LM) Fig. 35-18b Guard cells Stomatal pore 50 µm Epidermal cell Figure 35.18 Leaf anatomy (b) Surface view of a spiderwort (Tradescantia) leaf (LM)

Cross section of a lilac (Syringa) leaf (LM) Fig. 35-18c Upper epidermis Key to labels Palisade mesophyll Dermal Ground Vascular Spongy mesophyll Lower epidermis 100 µm Figure 35.18 Leaf anatomy Vein Air spaces Guard cells (c) Cross section of a lilac (Syringa) leaf (LM)