PowerLecture: Chapter 35 Plant Growth & Development

Success of the Angiosperms  The angiosperms are seed-bearing vascular plants  In terms of distribution and diversity, they are the most successful plants on Earth  The structure and function of this plant group help explain its success

Shoots and Roots  Shoots Produce food by photosynthesis Produce food by photosynthesis Carry out reproductive functions Carry out reproductive functions  Roots Anchor the plant Anchor the plant Penetrate the soil and absorb water and dissolved minerals Penetrate the soil and absorb water and dissolved minerals Store food Store food

Shoot Apical Meristem primary meristems active epidermis, ground tissues, primary vascular tissues forming primary meristems active Root Apical Meristem Fig. 29-3a, p.494

Protoderm Ground meristem Procambium epidermis ground tissues primary vascular tissues a The cellular descendants of apical meristems divide, grow, and differentiate. They form three primary meristems, the activity of which lengthens shoots and roots:

vascular cambium cork cambium Lateral Meristems thickening

Angiosperm Body Plan VASCULAR TISSUES GROUND TISSUES SHOOT SYSTEM ROOT SYSTEM EPIDERMIS  Ground tissue system  Vascular tissue system  Dermal tissue system Fig. 29-2, p.494

Simple Tissues Made up of only one type of cell ParenchymaCollenchymaSclerenchyma

Cutting Specimens transverse radial tangential

Parenchyma: A Simple Tissue  Most of a plant’s soft primary growth  Pliable, thin walled, many sided cells  Cells remain alive at maturity and retain capacity to divide  Mesophyll is a type that contains chloroplasts

stem epidermis simple and complex tissues inside the stem parenchyma vessel of xylem phloem fibers of sclerenchyma Fig. 29-6, p.496

Collenchyma: A Simple Tissue  Specialized for support for primary tissues  Makes stems strong but pliable  Cells are elongated  Walls thickened with pectin  Alive at maturity

Sclerenchyma: A Simple Tissue  Supports mature plant parts  Protects many seeds  Thick, lignified walls  Dead at maturity  Two types: Fibers: Long, tapered cells Fibers: Long, tapered cells Sclereids: Stubbier cells Sclereids: Stubbier cells

collenchymaparenchymalignified secondary wall Fig. 29-7, p.496

Complex Tissues Composed of a mix of cell types XylemPhloemEpidermis

Xylem Xylem  Conducts water and dissolved minerals  Conducting cells are dead and hollow at maturity vessel member tracheids

one cell’s wall pit in wall sieve plate of sieve tube cell companion cell ab c Fig. 29-8, p.497

Phloem: A Complex Vascular Tissue  Transports sugars  Main conducting cells are sieve- tube members  Companion cells assist in the loading of sugars sieve plate sieve-tube member companion cell

Epidermis: A Complex Plant Tissue  Covers and protects plant surfaces  Secretes a waxy, waterproof cuticle  In plants with secondary growth, periderm replaces epidermis

leaf surfacecuticleepidermal cell photosynthetic cell Fig. 29-9, p.497

Meristems  Regions where cell divisions produce plant growth  Apical meristems Lengthen stems and roots Lengthen stems and roots Responsible for primary growth Responsible for primary growth  Lateral meristems Increase width of stems Increase width of stems Responsible for secondary growth Responsible for secondary growth

Apical Meristems activity at meristems new cells elongate and start to differentiate into primary tissues activity at meristems new cells elongate and start to differentiate into primary tissues Root apical meristem Shoot apical meristem

immature leaf shoot apical meristem lateral bud forming vascular tissues pith cortex Fig a2, p.498

immature leaf shoot apical meristem descendant meristems (orange) b Sketch of the shoot tip, corresponding to (a) Fig b, p.498

Tissue Differentiation Protoderm Ground meristem Procambium Epidermis Ground tissue Primary vascular tissue

Lateral Meristems  Increase girth of older roots and stems  Cylindrical arrays of cells vascular cambium cork cambium thickening Figure a Page 504

Shoot Development immature leaf ground meristem primary phloem primary xylem pith procambium cortex procambium protoderm shoot apical meristem procambium epidermis Figure Page 498

immature leaf shoot apical meristem descendant meristems (orange) Stepped Art Fig b-d, p.498 primary phloem primary xylem pith cortex

Tissue Differentiation Vascular cambium Cork cambium Secondary vascular tissue Periderm

Internal Structure of a Dicot Stem  Outermost layer is epidermis  Cortex lies beneath epidermis  Ring of vascular bundles separates the cortex from the pith  The pith lies in the center of the stem Figure a Page 499

Internal Structure of a Monocot Stem The vascular bundles are distributed throughout the ground tissue No division of ground tissue into cortex and pith Figure b Page 499

cortex epidermis vascular bundle pith vessel in xylem meristem cell sieve tube in phloem companion cell in phloem Fig a, p.499

epidermis vascular bundle pith vessel in xylem collenchyma sheath sieve tube in phloem companion cell in phloem air space Fig b, p.499

Common Leaf Forms petiole blade axillary bud node blade sheath node DICOTMONOCOT Figure a,b Page 500

Adapted for Photosynthesis  Leaves are usually thin High surface area-to-volume ratio High surface area-to-volume ratio Promotes diffusion of carbon dioxide in, oxygen out Promotes diffusion of carbon dioxide in, oxygen out  Leaves are arranged to capture sunlight Are held perpendicular to rays of sun Are held perpendicular to rays of sun Arranged so they don’t shade one another Arranged so they don’t shade one another

POPLAR (Populus) OAK (Quercus) MAPLE (Acer) leaflet RED BUCKEYE (Aesculus) BLACK LOCUST (Robina) HONEY LOCUST (Gleditsia) Fig c,d, p.500

Leaf Structure UPPER EPIDERMIS PALISADE MESOPHYLL SPONGY MESOPHYLL LOWER EPIDERMIS one stoma cuticle O2O2 CO 2 xylem phloem Figure b Page 501

leaf blade leaf vein stem Leaf Vein (one vascular bundle) cuticle Upper Epidermis Lower Epidermis Palisade Mesophyll Spongy Mesophyll 50  m xylem phloem cuticle-coated cell of lower epidermis one stoma (opening across epidermia) Oxygen and water vapor diffuse out of leaf at stomata. Carbon dioxide in outside air enters leaf at stomata. Water, dissolved mineral ions from roots and stems move into leaf vein (blue arrow) Photosynthetic products (pink arrow) enter vein, will be transported throughout plant body Fig , p.501

Mesophyll: Photosynthetic Tissue  A type of parenchyma tissue  Cells have chloroplasts  Two layers in dicots Palisade mesophyll Palisade mesophyll Spongy mesophyll Spongy mesophyll

Leaf Veins: Vascular Bundles  Xylem and phloem; often strengthened with fibers  In dicots, veins are netlike  In monocots, they are parallel

Fig a, p.501 Leaf Veins

Fig b, p.501 Leaf Veins

Root Systems Taproot system of a California poppy Fibrous root system of a grass plant Figure Page 503

Root Structure  Root cap covers tip  Apical meristem produces the cap  Cell divisions at the apical meristem cause the root to lengthen  Farther up, cells differentiate and mature Figure a Page 502

Internal Structure of a Root  Outermost layer is epidermis  Root cortex is beneath the epidermis  Endodermis, then pericycle surround the vascular cylinder  In some plants, there is a central pith

primary xylem primary phloem epidermis VASCULAR CYLINDER cortex pith Fig , p.503

Fig , p.503 Formation of a lateral root - Originates in the pericycle and grows out through the cortex and epidermis

Fig a, p.503

Fig b, p.503

Fig c, p.503

Function of Endodermis  Ring of cells surrounds vascular cylinder  Cell walls are waterproof  Water can only enter vascular cylinder by moving through endodermal cells  Allows plant to control inward flow

Root Hairs and Lateral Roots  Both increase the surface area of a root system  Root hairs are tiny extensions of epidermal cells  Lateral roots arise from the pericycle and must push through the cortex and epidermis to reach the soil new lateral root

Fig , p.503

Fig a, p.503

Fig b, p.503

Secondary Growth  Occurs in all gymnosperms, some monocots, and many dicots  A ring of vascular cambium produces secondary xylem and phloem  Wood is the accumulation of these secondary tissues, especially xylem

What Happens at Vascular Cambium?  Fusiform initials give rise to secondary xylem and phloem  Ray initials give rise to horizontal rays of parenchyma

Fig , p.504

cork cambiumvascular cambium thickening Fig a, p.504

primary xylem primary phloem VASCULAR CAMBIUM secondary xylem secondary phloem stem surface Fig b, p.504

outer surface of stem root division One of the cells vascular cambium at the start of secondary growth. One of the two daughter cells differentiates into a xylem cell (coded blue), and the other remains meristatic. One of the two daughter cells differentiates into a phloem cell (coded pink), and the other remains meristatic. The same pattern of cell division and differentiation into xylem and phloem cells continues through the growing season. Fig c, p.504

Secondary Growth Figure c Page 504 Ongoing cell divisions enlarge the inner core of secondary xylem and displace vascular cambium toward the stem

Secondary growth Secondary Growth

Formation of Bark  All tissues outside vascular cambium  Periderm Cork Cork New parenchyma New parenchyma Cork cambium Cork cambium  Secondary phloem

Fig , p.506 A Coast Redwood

periderm (includes cork cambium, cork, new parenchyma) secondary phloem BARK vascular cambium HEARTWOODSAPWOOD Fig a, p.507

Annual Rings  Concentric rings of secondary xylem  Alternating bands of early and late wood  Early wood Xylem cells with large diameter, thin walls Xylem cells with large diameter, thin walls  Late wood Xylem cells with smaller diameter, thicker walls Xylem cells with smaller diameter, thicker walls

Fig a, p.507

year123 Fig b, p.507

1587– –1612 Fig c, p.509 Annual Rings  Narrow annual rings mark severe drought years

Types of Wood  Hardwood (oak, hickory) Dicot wood Dicot wood Xylem composed of vessels, tracheids, and fibers Xylem composed of vessels, tracheids, and fibers  Softwood (pine, redwood) Gymnosperm wood Gymnosperm wood Xylem composed mostly of tracheids Xylem composed mostly of tracheids Grows more quickly Grows more quickly