Plant Tissues Chapter 28 Part 1

Impacts, Issues Drought Versus Civilization Without plants, we would die – prolonged drought can destroy crops and civilizations

28.1 Components of the Plant Body The unique organization of tissues in flowering plants is part of the reason why they are the dominant group of the plant kingdom

The Basic Body Plan Shoots Roots Aboveground plant parts such as stems, leaves, and flowers Roots Structures that absorb water and dissolved minerals, store food, and support the plant Usually grow down and outward in the soil

Plant Tissue Systems Ground tissue system Vascular tissue system Photosynthesis, storage, and structural support of other tissues Vascular tissue system Distributes absorbed water and mineral ions and products of photosynthesis Dermal tissue system Covers and protects exposed plant surfaces

Body Plan: Tomato Plant

shoot tip (terminal bud) lateral (axillary) bud young leaf flower node internode dermal tissue node vascular tissues leaf seeds in fruit withered seed leaf (cotyledon) ground tissues stem Figure 28.2 Body plan of a tomato plant (Lycopersicon esculentum). Its vascular tissues (purple) conduct water, dissolved minerals, and organic substances. They thread through ground tissues that make up most of the plant. Epidermis, a type of dermal tissue, covers root and shoot surfaces. SHOOTS ROOTS primary root lateral root root hairs root tip root cap Fig. 28-2, p. 476

Animation: Tissue systems of a tomato plant

Eudicots and Monocots Flowering plants are divided into two classes with tissues organized into different patterns Eudicots have two cotyledons (seed leaves) Monocots have one cotyledon

Eudicots and Monocots

In seeds, two cotyledons (seed leaves of embryo) Flower parts in fours or fives (or multiples of four or five) Leaf veins usually forming a netlike array Pollen grains with three pores or furrows Vascular bundles organized in a ring in ground tissue B Figure 28.3 Comparison of eudicots and monocots. In seeds, one cotyledon (seed leaf of embryo) Flower parts in threes (or multiples of three) Leaf veins usually running parallel with one another Pollen grains with one pore or furrow Vascular bundles throughout ground tissue Fig. 28-3, p. 477

Animation: Eudicots and monocots

Introducing Meristems All plants tissues arise at meristems (regions of rapidly dividing, undifferentiated cells) Growth in apical meristems at tips of shoots and roots (primary growth) increases length In some plants, growth in lateral meristems (secondary growth) thickens roots and shoots

Apical and Lateral Meristems

Figure 28.4 Locations of apical and lateral meristems. Fig. 28-4a, p. 477

shoot apical meristem (new cells forming) cells dividing, differentiating three tissue systems developing three tissue systems developing cells dividing, differentiating root apical meristem (new cells forming) Figure 28.4 Locations of apical and lateral meristems. a Many cellular descendants of apical meristems are the start of lineages of differentiated cells that grow, divide, and lengthen shoots and roots. Fig. 28-4a, p. 477

Figure 28.4 Locations of apical and lateral meristems. Fig. 28-4b, p. 477

vascular cambium cork cambium thickening Figure 28.4 Locations of apical and lateral meristems. b In woody plants, the activity of two lateral meristems—vascular cambium and cork cambium—result in secondary growth that thickens older stems and roots. Fig. 28-4b, p. 477

28.2 Components of Plant Tissues Different plant tissues form just behind shoot and root tips, and on older stem and root parts Tissue systems are organized as simple tissues (one cell type) or complex tissues (two or more cell types)

Simple Tissues Parenchyma makes up most primary growth Functions in secretion, storage, photosynthesis (mesophyll), and tissue repair Collenchyma supports growing plant parts Pectin provides flexibility Sclerenchyma contains lignin for support Cells (fibers, sclereids) are dead at maturity

Simple Tissues

collenchyma parenchyma Figure 28.7 Simple tissues. (a) Collenchyma and parenchyma from a supporting strand inside of a celery stem, transverse section. Sclerenchyma: (b) Fibers from a strong flax stem, tangential view. (c) Stone cells, a type of sclereid in pears, transverse section. Fig. 28-7a, p. 479

lignified secondary wall Figure 28.7 Simple tissues. (a) Collenchyma and parenchyma from a supporting strand inside of a celery stem, transverse section. Sclerenchyma: (b) Fibers from a strong flax stem, tangential view. (c) Stone cells, a type of sclereid in pears, transverse section. Fig. 28-7c, p. 479

Complex Tissues: Vascular Tissues Xylem carries water and ions through the plant Consists of two types of cells that are dead at maturity: tracheids and vessel members Lignin-filled secondary walls Phloem conducts sugars, other organic solutes Sieve tubes connect end to end at sieve plates Companion cells load sugars into sieve tubes

Vascular Tissues

sieve plate of sieve-tube cell one cell’s wall sieve plate of sieve-tube cell pit in wall companion cell a b c Figure 28.8 Simple and complex tissues in a stem. In xylem, (a) part of a column of vessel members, and (b) a tracheid. (c) One of the living cells that interconnect as sieve tubes in phloem. parenchyma vessel of xylem phloem fibers of sclerenchyma Fig. 28-8, p. 479

Complex Tissues: Dermal Tissues Epidermis Usually a single outer layer of cells that secrete a waxy, protective cuticle May contain specialized cells that form stomata for gas exchange Periderm Replaces epidermis in woody stems and roots

Plant Cuticle

leaf surface cuticle epidermal cell photosynthetic cell Figure 28.9 A typical plant cuticle, with many epidermal cells and photosynthetic cells under it. Fig. 28-9, p. 479

Flowering Plant Tissues

Studying Plant Parts: Tissue Specimens Tissue specimens are cut along standard planes

radial: tangential: transverse: Figure 28.6 Terms that identify how tissue specimens are cut from a plant. Longitudinal cuts along a stem or root radius give radial sections. Cuts at right angles to the radius give tangential sections. Cuts perpendicular to the long axis of a stem or root give transverse sections—that is, cross-sections. Fig. 28-6, p. 478

Tissues in a Buttercup Stem

sclerenchyma (fibers) parenchyma epidermis Figure 28.5 Some tissues in a buttercup stem (Ranunculus). xylem phloem Fig. 28-5, p. 478

28.1-28.2 Key Concepts Overview of Plant Tissues Seed-bearing vascular plants have a shoot system, which includes stems, leaves, and reproductive parts; most also have a root system Such plants have ground, vascular, and dermal tissues Plants lengthen or thicken only at active meristems

28.3 Primary Structure of Shoots Inside the soft, young stems and leaves of both eudicots and monocots, the ground, vascular, and dermal tissue systems are organized in predictable patterns

Behind the Apical Meristem Terminal buds Main zones of primary growth in shoots Naked or encased in modified leaves (bud scales) Form leaves at nodes Lateral buds (axillary buds) Dormant shoots in leaf axils Form side branches, leaves, or flowers

Apical Meristem and Primary Growth

Figure 28.10 Stem of Coleus, a eudicot. (a–c) Successive stages of the stem’s primary growth, starting with the shoot apical meristem. (d) The light micrograph shows a longitudinal cut through the stem’s center. The tiers of leaves in the photograph below it formed in this linear pattern of development. Figure It Out: What is the transparent layer of cells on the outer surface of b and c? Answer: Epidermis Fig. 28-10 (a-c), p. 480

immature leaf shoot apical meristem a Sketch of the shoot tip in the micrograph at right, tangential cut. The descendant meristematic cells are color-coded orange . b Same tissue region later on, after the shoot tip lengthened above it Figure 28.10 Stem of Coleus, a eudicot. (a–c) Successive stages of the stem’s primary growth, starting with the shoot apical meristem. (d) The light micrograph shows a longitudinal cut through the stem’s center. The tiers of leaves in the photograph below it formed in this linear pattern of development. Figure It Out: What is the transparent layer of cells on the outer surface of b and c? Answer: Epidermis primary phloem primary xylem cortex pith c Same tissue region later still, with lineages of cells lengthening and differentiating Fig. 28-10 (a-c), p. 480

Figure 28.10 Stem of Coleus, a eudicot. (a–c) Successive stages of the stem’s primary growth, starting with the shoot apical meristem. (d) The light micrograph shows a longitudinal cut through the stem’s center. The tiers of leaves in the photograph below it formed in this linear pattern of development. Figure It Out: What is the transparent layer of cells on the outer surface of b and c? Answer: Epidermis Fig. 28-10d (1), p. 480

youngest immature leaf apical meristem epidermis forming lateral bud forming Figure 28.10 Stem of Coleus, a eudicot. (a–c) Successive stages of the stem’s primary growth, starting with the shoot apical meristem. (d) The light micrograph shows a longitudinal cut through the stem’s center. The tiers of leaves in the photograph below it formed in this linear pattern of development. Figure It Out: What is the transparent layer of cells on the outer surface of b and c? Answer: Epidermis vascular tissues forming pith Fig. 28-10d (1), p. 480

Figure 28.10 Stem of Coleus, a eudicot. (a–c) Successive stages of the stem’s primary growth, starting with the shoot apical meristem. (d) The light micrograph shows a longitudinal cut through the stem’s center. The tiers of leaves in the photograph below it formed in this linear pattern of development. Figure It Out: What is the transparent layer of cells on the outer surface of b and c? Answer: Epidermis Fig. 28-10d (2), p. 480

Inside the Stem Vascular bundles Multistranded cords of vascular tissues threaded lengthwise through ground tissues of all shoots Two distinct patterns of vascular bundles Eudicot stems: Cylinders run parallel with stem, divide ground tissue into cortex and pith Monocot stems: Bundles distributed throughout ground tissue

Eudicot and Monocot Stems

Figure 28.11 Zooming in on a eudicot and a monocot stem. Fig. 28-11a, p. 481

companion cell in phloem vessel in xylem meristem cell epidermis cortex vascular bundle pith Figure 28.11 Zooming in on a eudicot and a monocot stem. sieve tube in phloem companion cell in phloem A Stem fine structure for alfalfa (Medicago), a eudicot Fig. 28-11a, p. 481

Figure 28.11 Zooming in on a eudicot and a monocot stem. Fig. 28-11b, p. 481

collenchyma sheath cell companion cell in phloem air space vessel in xylem epidermis vascular bundle pith Figure 28.11 Zooming in on a eudicot and a monocot stem. sieve tube in phloem companion cell in phloem B Stem fine structure for corn (Zea mays), a monocot Fig. 28-11b, p. 481

Animation: Stem organization

Animation: Apical meristems

Animation: Cutting tissue specimens

Animation: Ground tissues

Animation: Vascular tissues