The Plant Body • A. Consists mainly of three parts: • 1. Roots • 2. Stems • 3. Leaves • B. Comparison of monocots v. dicots
The basic morphology of a plant has two • systems: • 1. Root System: anchor the plant in the soil, • absorb minerals and water, and store food. • a. Monocots – fibrous • b. Dicots – taproot • c. Root hairs – • increase the • surface area of • roots to • maximize the • absorption.
Root hairs are made up of epidermal cells and are one-cell thick.
The Shoot System: Stems and Leaves • Stems: Alternating system of nodes and • internodes. • Axillary buds: • dormant, but • can become • a vegetative • branch. • 2.Terminal bud: • where growth • of a shoot • occurs. “Apical dominance”
Modified Stems: • a. Stolons: “Runners” • Ex. Strawberries • b. Rhizomes: • horizontal • underground • Ex. Ginger • c. Tubers: • swollen • rhizomes for • food storage • Ex. Potatoes • d. Bulbs: • vertical • underground • Ex. Onion
Stolons allow for asexual reproduction. Daughter plants are clones of the mother plant.
Leaves: Main photosynthetic organs of • most plants. • 1. Blade • 2. Petiole: • stalk that • joins the • leaf to the • node of the • stem.
Types of Leaves: Simple v. Compound: simple leaves have a single, undivided blade, while compound leaves have several leaflets attached to the petiole.
Modified Leaves: • a. Tendrils: • b. Spines of cacti: • c. Succulents: • d. Colored leaves: Cling to support Defense Storing water To attract pollinators
Plants are composed of three tissue systems: • 1. Dermal/Epidermis: • 2. Vascular: • 3. Ground: Covers and protects • Transports materials between • roots and shoots. • Xylem: water and minerals • Phloem: food/sugars “filler tissue”; neither dermal nor vascular; diverse functions such as photosynthesis, storage, and support. -Cortex: external to vascular tissue -Pith: internal to vascular tissue
The three tissue system in a plant body: -Dermal -Vascular -Ground
Vascular tissue structure: • Xylem: made up of two kinds of cells • -Tracheids and vessel elements • -Both types of cells are nonliving at functional • maturity; the secondary cell walls remain • behind and leave behind tubes through which • water can flow. • -Water flows from • tracheid to • tracheid and • vessel element • to vessel • element through • pits. Wider, short Thin, tapered
Phloem: Made up of two types of cells: • -Sieve-tube members and companion cells • -Sieve-tube members • have no nucleus, • ribosomes, a distinct • vacuole. • -Companion cells have • a nucleus and ribo- • somes and probably • assist sieve-tube cells. • -Companion cells also • help load sugars into • the sieve-tubes for • transport.
The Plant Cell Review Review: Vacuole Tonoplast Chloroplast Primary cell wall Secondary cell wall Nucleus Mitochondria Peroxisome (Protoplast: Plant cell minus the cell wall)
F. THREE TYPES OF PLANT CELLS: • Parenchyma cells: • -“typical” plant cell because they are the least • specialized; developing plant cells are • parenchyma cells before becoming specialized. -thin and flexible; most parenchyma cells lack a tough secondary cell wall. -most of the metabolic functions occur in these cells; photosynthesis takes place in the parenchyma cells of the leaf.
Collenchyma cells: • -thicker, uneven primary cell walls. -support young parts of the plant shoot. -lack secondary cell walls; allows for plant growth, while providing structural support.
Sclerenchyma cells: • -have secondary cell walls making them rigid • and supportive. -many are dead at functional maturity, but they produce the secondary walls before the protoplast dies; serves as a “skeleton” that supports the plant. -2 types of sclerenchyma cells: 1.Fibers: tough, long and slender; in groups 2.Sclereids: irregular shape; gritty texture in pears
Plant Growth and Development • How do plants develop their different cell • types and how do they mature? A.Most plants continue to grow: “indeterminate growth” B.Flowers and leaves undergo “determinate growth.” C.Life cycles of plants: 1.Annuals: Plants that complete their life cycle in a single year or less; food crop. 2.Biennials: life span 2 years, between germination, growth, and flowering. 3.Perennials: live many years; trees, shrubs, and some grasses.
D. Meristem: perpetual embryonic tissue; continual growth by cell division. 1. Apical meristem: shoots and roots Primary growth
2. Lateral meristems: Secondary growth • In contrast, secondary growth is the progressive thickening of roots and shoots in woody plants.
E. Primary growth in roots: 1. Root cap: protection of meristem 2. Zone of cell division: apical meristem 3. Zone of elongation: cells elongate; push root tip 4. Zone of maturation: differentiation of cells (3 tissue systems)
F. Primary tissues in the roots: 1. Stele: vascular bundle (xylem and phloem) 2. Pith: core; parenchyma cells 3. Cortex: region between stele and epidermis; innermost layer is called endodermis, which forms the boundary between cortex and stele.
4. Lateral roots: arise from the pericycle (outermost layer of stele). Pericycle cells become meristematic and start to divide, pushing through the cortex.
G. Primary tissue of stems: 1. Vascular bundles (xylem and phloem) surrounded by ground tissues, pith and cortex. 2. Mostly parenchyma; some collenchyma and sclerenchyma for support.
1. Epidermis: cuticle; protection and to prevent dessication 2. Stomata: tiny pores for gas exchange and transpiration. 3. Guard cells: specialized epidermal cells 4. Mesophyll cells: ground tissue (palisade and spongy parenchyma cells).
Secondary growth of Stems: • 1. Two lateral meristems: • -Vascular cambium secondary xylem • (wood) and secondary • phloem • -Cork cambium tough, thick covering Secondary growth is rare in monocots
How does the vascular cambrium produce • secondary xylem and phloem? -A cambrium cell divides into a cambrium cell and a derivative cell, which will differentiate into xylem or phloem. -As layers of xylem are added, stems increase in diameter.
Secondary xylem forms to the interior and secondary phloem to the exterior of the vascular cambium.
As secondary growth continues over the years, layer upon layer of secondary xylem accumulates, producing the tissue we call wood. Early wood Late wood These are the lines you count to estimate the age of trees.
How does cambrium cork produce a tough, • thick outer covering? • -Cork cambium produces cork cells which • contain a waxy, waterproof substance. • -The cork plus the cork cambium forms the • periderm, a protective layer that replaces • the epidermis.
-Lenticils are splits develop in the periderm because of higher local activity of the cork cambium.
-Bark refers to all tissues external to the vascular cambium, including secondary phloem, cork cambium, and cork.
-Only the youngest secondary phloem, internal to the cork cambium, functions in sugar transport. -Older phloem dies and sloughs off as bark later.
-After several years of growth, several zones are visible in the stem. a. Two zones of xylem: -Heartwood (dead; structural purpose) -Sapwood b. Vascular cambium c. Living phloem d. Cork cambium e. Cork
Mechanisms of Plant Growth and Development • Arabidopsis thaliana, a weed of the mustard • family was the first plant to have its entire • genome sequenced. • 1. 26,000 genes; many duplicates; 15,000 • different genes; • 45% unknown
Growth, morphogenesis, and differentiation • produce the plant body • 1. Morphogenesis: development of body • form and organization • 2. Differentiation: cellular diversity • Plant growth depends on the plane • (direction) of cell division.
Plant growth depends on the symmetry of • cell division. • Assymetrical cell division, in which one • cell receives more cytoplasm than the • other, is common in plants cells and • usually signals a key developmental event. • Guard cells
The plane of cell division is determined during • late interphase. -Microtubules concentrate into a ring called the preprophase band. -Actin micro- filaments direct the formation of cell plates.
Morphogenesis depends on pattern formation • Pattern formation: development of • specific structures in specific locations. • Pattern formation depends on positional • information - signals that indicate a cell’s • location. • Homeotic genes: genes that regulate • pattern formation. • Protein product ofKNOTTED-1 homeotic • gene is important • for the development • of compound leaves. • Over expression • of this gene • creates • “supercompound” leaves.