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

Overview: Are Plants Computers? Romanesco grows according to a repetitive program The development of plants depends on the environment and is highly adaptive © 2011 Pearson Education, Inc.

Concept 35.1: Plants have a hierarchical organization consisting of organs, tissues, and cells Plants have organs composed of different tissues, which in turn are composed of different cell types A tissue is a group of cells consisting of one or more cell types that together perform a specialized function An organ consists of several types of tissues that together carry out particular functions © 2011 Pearson Education, Inc.

The Three Basic Plant Organs: Roots, Stems, and Leaves Basic morphology of vascular plants reflects their evolution as organisms that draw nutrients from below ground and above ground Plants take up water and minerals from below ground Plants take up CO2 and light from above ground © 2011 Pearson Education, Inc.

Three basic organs evolved: roots, stems, and leaves They are organized into a root system and a shoot system © 2011 Pearson Education, Inc.

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

Monocots and eudicots are the two major groups of angiosperms Roots rely on sugar produced by photosynthesis in the shoot system, and shoots rely on water and minerals absorbed by the root system Monocots and eudicots are the two major groups of angiosperms © 2011 Pearson Education, Inc.

Roots A root is an organ with important functions: Anchoring the plant Absorbing minerals and water Storing carbohydrates © 2011 Pearson Education, Inc.

Most monocots have a fibrous root system, which consists of: Most eudicots and gymnosperms have a taproot system, which consists of: A taproot, the main vertical root Lateral roots, or branch roots, that arise from the taproot Most monocots have a fibrous root system, which consists of: Adventitious roots that arise from stems or leaves Lateral roots that arise from the adventitious roots © 2011 Pearson Education, Inc.

In most plants, absorption of water and minerals occurs near the root hairs, where vast numbers of tiny root hairs increase the surface area © 2011 Pearson Education, Inc.

Figure 35.3 Figure 35.3 Root hairs of a radish seedling.

Many plants have root adaptations with specialized functions © 2011 Pearson Education, Inc.

Storage roots Prop roots Buttress roots Pneumatophores Figure 35.4 “Strangling” aerial roots Storage roots Prop roots Buttress roots Figure 35.4 Evolutionary adaptations of roots. Pneumatophores

Stems A stem is an organ consisting of An alternating system of nodes, the points at which leaves are attached Internodes, the stem segments between nodes © 2011 Pearson Education, Inc.

Apical dominance helps to maintain dormancy in most axillary buds An axillary bud is a structure that has the potential to form a lateral shoot, or branch An apical bud, or terminal bud, is located near the shoot tip and causes elongation of a young shoot Apical dominance helps to maintain dormancy in most axillary buds © 2011 Pearson Education, Inc.

Many plants have modified stems (e. g Many plants have modified stems (e.g., rhizomes, bulbs, stolons, tubers) © 2011 Pearson Education, Inc.

Rhizomes Rhizome Root Bulbs Storage leaves Stem Stolons Stolon Tubers Figure 35.5 Rhizomes Rhizome Root Bulbs Storage leaves Stem Stolons Stolon Figure 35.5 Evolutionary adaptations of stems. Tubers

Leaves The leaf is the main photosynthetic organ of most vascular plants Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem © 2011 Pearson Education, Inc.

Monocots and 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 © 2011 Pearson Education, Inc.

Simple leaf Axillary bud Petiole Compound leaf Doubly compound leaf Figure 35.6 Simple leaf Axillary bud Petiole Compound leaf Doubly compound leaf Leaflet Figure 35.6 Simple versus compound leaves. Petiole Axillary bud Axillary bud Petiole Leaflet

Some plant species have evolved modified leaves that serve various functions © 2011 Pearson Education, Inc.

Tendrils Spines Storage leaves Reproductive leaves Bracts Figure 35.7 Figure 35.7 Evolutionary adaptations of leaves. Bracts

Dermal, Vascular, and Ground Tissues Each plant organ has dermal, vascular, and ground tissues Each of these three categories forms a tissue system Each tissue system is continuous throughout the plant © 2011 Pearson Education, Inc.

Dermal tissue Ground tissue Vascular tissue Figure 35.8 Figure 35.8 The three tissue systems. Dermal tissue Ground tissue Vascular tissue

In nonwoody plants, 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 in older regions of stems and roots Trichomes are outgrowths of the shoot epidermis and can help with insect defense © 2011 Pearson Education, Inc.

Very hairy pod (10 trichomes/ mm2) Figure 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 Inquiry: Do soybean pod trichomes deter herbivores?

The two vascular tissues are xylem and phloem The vascular tissue system carries out long-distance transport of materials between roots and shoots The two vascular tissues are xylem and phloem Xylem conveys water and dissolved minerals upward from roots into the shoots Phloem transports organic nutrients from where they are made to where they are needed © 2011 Pearson Education, Inc.

The vascular tissue of a stem or root is collectively called the stele In angiosperms the stele of the root is a solid central vascular cylinder The stele of stems and leaves is divided into vascular bundles, strands of xylem and phloem © 2011 Pearson Education, Inc.

Tissues that are neither dermal nor vascular are the ground tissue system Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex Ground tissue includes cells specialized for storage, photosynthesis, and support © 2011 Pearson Education, Inc.

Common Types of Plant Cells Like any multicellular organism, a plant is characterized by cellular differentiation, the specialization of cells in structure and function © 2011 Pearson Education, Inc.

The major types of plant cells are: Parenchyma Collenchyma Sclerenchyma Water-conducting cells of the xylem Sugar-conducting cells of the phloem © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 m Figure 35.10a Figure 35.10 Exploring: Examples of Differentiated Plant Cells Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 m

Collenchyma Cells Collenchyma cells are grouped in strands and help support young parts of the plant shoot They have thicker and uneven cell walls They lack secondary walls These cells provide flexible support without restraining growth © 2011 Pearson Education, Inc.

Collenchyma cells (in Helianthus stem) (LM) 5 m Figure 35.10b Figure 35.10 Exploring: Examples of Differentiated Plant Cells Collenchyma cells (in Helianthus stem) (LM) 5 m

Sclerenchyma Cells Sclerenchyma cells are rigid because of thick secondary walls strengthened with lignin They are dead at functional maturity There are two types: Sclereids are short and irregular in shape and have thick lignified secondary walls Fibers are long and slender and arranged in threads © 2011 Pearson Education, Inc.

Sclereid cells in pear (LM) Figure 35.10c 5 m Sclereid cells in pear (LM) 25 m Cell wall Figure 35.10 Exploring: Examples of Differentiated Plant Cells Fiber cells (cross section from ash tree) (LM)

Water-Conducting Cells of the Xylem The two types of water-conducting cells, tracheids and vessel elements, are dead at maturity Tracheids are found in the xylem of all vascular plants © 2011 Pearson Education, Inc.

Vessel elements are common to most angiosperms and a few gymnosperms Vessel elements align end to end to form long micropipes called vessels © 2011 Pearson Education, Inc.

Tracheids and vessels (colorized SEM) Pits Figure 35.10d 100 m Vessel Tracheids Tracheids and vessels (colorized SEM) Pits Figure 35.10 Exploring: 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 Sieve plates are the porous end walls that allow fluid to flow between cells along the sieve tube Each sieve-tube element has a companion cell whose nucleus and ribosomes serve both cells © 2011 Pearson Education, Inc.

Sieve-tube elements: longitudinal view (LM) 3 m Figure 35.10e Sieve-tube elements: longitudinal view (LM) 3 m Sieve plate Sieve-tube element (left) and companion cell: cross section (TEM) Companion cells Sieve-tube elements Plasmodesma Figure 35.10 Exploring: Examples of Differentiated Plant Cells Sieve plate 30 m Nucleus of companion cell 15 m Sieve-tube elements: longitudinal view Sieve plate with pores (LM)

Concept 35.2: Meristems generate cells for primary and secondary growth 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 © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

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

Meristems give rise to: Initials, also called stem cells, which remain in the meristem Derivatives, which become specialized in mature tissues In woody plants, primary growth and secondary growth occur simultaneously but in different locations © 2011 Pearson Education, Inc.

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

Flowering plants can be categorized based on the length of their life cycle Annuals complete their life cycle in a year or less Biennials require two growing seasons Perennials live for many years © 2011 Pearson Education, Inc.

Concept 35.3: Primary growth lengthens roots and shoots Primary growth produces the parts of the root and shoot systems produced by apical meristems © 2011 Pearson Education, Inc.

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 differentiation, or maturation © 2011 Pearson Education, Inc.

Zone of differentiation Ground Root hair Vascular Figure 35.13 Cortex Vascular cylinder Key to labels Epidermis Dermal Zone of differentiation Ground Root hair Vascular Zone of elongation Figure 35.13 Primary growth of a root. Zone of cell division (including apical meristem) Mitotic cells 100 m Root cap

In angiosperm roots, the stele is a vascular cylinder The primary growth of roots produces the epidermis, ground tissue, and vascular tissue In angiosperm roots, the stele is a vascular cylinder In most eudicots, the xylem is starlike in appearance with phloem between the “arms” In many monocots, a core of parenchyma cells is surrounded by rings of xylem then phloem © 2011 Pearson Education, Inc.

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

The innermost layer of the cortex is called the endodermis The ground tissue, mostly parenchyma cells, fills the cortex, the region between the vascular cylinder and epidermis The innermost layer of the cortex is called the endodermis The endodermis regulates passage of substances from the soil into the vascular cylinder © 2011 Pearson Education, Inc.

Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder © 2011 Pearson Education, Inc.

100 m Epidermis Emerging lateral root Lateral root Cortex Figure 35.15-3 100 m Epidermis Emerging lateral root Lateral root Cortex Vascular cylinder Pericycle Figure 35.15 The formation of a lateral root. 1 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 © 2011 Pearson Education, Inc.

Developing vascular strand Figure 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 arranged in a ring © 2011 Pearson Education, Inc.

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

Tissue Organization of Leaves The epidermis in leaves is interrupted by stomata, which allow CO2 and O2 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 © 2011 Pearson Education, Inc.

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

Concept 35.4: Secondary growth increases the diameter of 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 Secondary growth is characteristic of gymnosperms and many eudicots, but not monocots © 2011 Pearson Education, Inc.

Figure 35.19 Primary and secondary growth of a woody stem. Primary and secondary growth in a two-year-old woody stem Epidermis Pith Cortex Primary xylem Primary phloem Vascular cambium Epidermis Primary phloem Cortex Vascular cambium Primary xylem Growth Vascular ray Pith Primary xylem Secondary xylem Vascular cambium Secondary phloem Primary phloem First cork cambium Cork Periderm (mainly cork cambia and cork) Growth Figure 35.19 Primary and secondary growth of a woody stem. Secondary phloem Bark Vascular cambium Primary phloem Secondary xylem Late wood Cork cambium Early wood Periderm Secondary phloem Cork Secondary xylem (two years of production) Vascular cambium 0.5 mm Secondary xylem Vascular cambium Bark Secondary phloem Primary xylem Vascular ray Most recent cork cambium Layers of periderm Growth ring Cork (b) Cross section of a three-year- old Tilia (linden) stem (LM) Pith 0.5 mm

The Vascular Cambium and Secondary Vascular Tissue The vascular cambium is a cylinder of meristematic cells one cell layer thick It develops from undifferentiated parenchyma cells © 2011 Pearson Education, Inc.

In cross section, the vascular cambium appears as a ring of initials (stem cells) The initials increase the vascular cambium’s circumference and add secondary xylem to the inside and secondary phloem to the outside © 2011 Pearson Education, Inc.

After one year of growth After two years of growth Figure 35.20 Vascular cambium Growth Vascular cambium Secondary phloem Secondary xylem Figure 35.20 Secondary growth produced by the vascular cambium. After one year of growth After two years of growth

Secondary xylem accumulates as wood and consists of tracheids, vessel elements (only in angiosperms), and fibers Early wood, formed in the spring, has thin cell walls to maximize water delivery Late wood, formed in late summer, has thick-walled cells and contributes more to stem support In temperate regions, the vascular cambium of perennials is inactive through the winter © 2011 Pearson Education, Inc.

Tree rings are visible where late and early wood meet, and can be used to estimate a tree’s age Dendrochronology is the analysis of tree ring growth patterns and can be used to study past climate change © 2011 Pearson Education, Inc.

RESULTS 2 1.5 Ring-width indexes 1 0.5 1600 1700 1800 1900 2000 Year Figure 35.21 RESULTS 2 1.5 Ring-width indexes 1 0.5 1600 1700 1800 1900 2000 Figure 35.21 Research Method: Using Dendrochronology to Study Climate Year

Older secondary phloem sloughs off and does not accumulate 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 Older secondary phloem sloughs off and does not accumulate © 2011 Pearson Education, Inc.

Growth ring Vascular ray Heartwood Secondary xylem Sapwood Figure 35.22 Growth ring Vascular ray Heartwood Secondary xylem Sapwood Figure 35.22 Anatomy of a tree trunk. Vascular cambium Secondary phloem Bark Layers of periderm

The Cork Cambium and the Production of Periderm Cork cambium gives rise to two tissues: Phelloderm is a thin layer of parenchyma cells that forms to the interior of the cork cambium Cork cells accumulate to the exterior of the cork cambium Cork cells deposit waxy suberin in their walls, then die Periderm consists of the cork cambium, phelloderm, and cork cells it produces © 2011 Pearson Education, Inc.

Lenticels in the periderm allow for gas exchange between living stem or root cells and the outside air Bark consists of all the tissues external to the vascular cambium, including secondary phloem and periderm © 2011 Pearson Education, Inc.