PLANT STRUCTURE AND FUNCTION

THE PHYLOGENY OF PLANTS… Charophytes (green algae) Bryophytes (non vascular) Trachoephytes (seedless, vascular) Gymnosperms (“naked seeds”,vascular) Angiosperms (contained seeds, vascular) Monocots / Dicots

Double Fertilization

Plant Structure, Growth and Differentiation Flowering Plant Reproduction Review *sporophyte*style*carpel *seed*stigma*ovule *endosperm*ovary*pollen grain *pollen sac*petal*gametophyte *anther*sepal*megaspore *filament*carolla*microspore *stamen*calyx*pollen tube *pollination*double fertilization * seed dispersal

The Seed

Seed structure Cotyledon Plumule Radicle Micropyle Seed coat or testa © 2008 Paul Billiet ODWSODWS

The Seed  Fertilization  zygote  seed (embryo)  Seed parts: –Epicotyl : becomes shoot tip –Plumule: young leaves –Hypocotyl: food source for cotyledons. becomes shoot –Radicle: becomes root –Coleoptile: protects epicotyl (esp. monocots)

Seed Parts –Epicotyl –Plumule –Hypocotyl – Radicle –Coleoptile  Becomes shoot tip  Young leaves  Food source for cotyledons. Becomes shoot.  Becomes root  Protects epicotyl (esp. monocots)

Seed viability  Viability: When a seed is capable of germinating after all the necessary environmental conditions are met.  Average life span of a seed 10 to 15 years.  Conditions are very important for longevity  Cold, dry, anaerobic conditions

Germination of Seeds Dormant Mature seeds internal / external factors Increased metabolism Material synthesis / degredation

Germination: The breaking of dormancy The growth of the embryo and its penetration of the seed coat Break down of barriers Abrasion of seed coat (soil particles) Decomposition of seed coat (soil microbes, gut enzymes) Cracking of seed coat (fire) Change in physical state - rehydration Destruction and dilution of inhibitors Light, temperature, water Production of growth promoters

External Factors Influencing Germination  Water : Imbibition initiates enzymatic activity  Oxygen : Necessary for Aerobic Respiration  Temperature: optimal temp = germination  Light:necessary for PS  Seed coat damage

Internal Factors Affecting Germination  Presence / absence of chemical inhibitors  Stage of embryonic development

What is the 1 st part of the plant to emerge during germination? THE RADICLE !!

After Germination…  Growth occurs in Meristematic Regions!  Growth involves 3 processes: –Cell Division –Cell Elongation –Cell Differentiation

Stages leading to cell division Mitchondria reconstituted Soluble sugars Respiration Initially anaerobic Later aerobic ATP RNA activated Protein synthesis (0.5h) Enzymes (proteins) Mitosis (70h) DNA replication (45h)

Cell Division  Increase in NUMBER of cells  Indeterminate Growth: Stems and Roots Division continues throughout life of plant!  Determinate Growth: Leaves and Flowers Division ceases upon reaching certain size!

Cell Elongation  Increase in the SIZE of cells

Cell Differentiation  Specialization of cells  Allows for developmental differences in structure and function which in turn allows for distinct plant activities!

Two Types of Plant Growth PRIMARY GROWTH: –Increase in length of plant –Occurs in ALL plants

SECONDARY GROWTH increase in width/girth of stems and roots Occurs in woody plants only!

Primary Growth  Occurs in apical meristems of plant –(found at tips of stems and roots)

GROWTH IN ROOTS FOUR AREAS OF ROOT:  ROOT TIP (ROOT CAP): protects apical meristem! secretes lubricating polysaccharide that aids with progression of root through soil!

ZONE OF CELL DIVISION (APICAL MERISTEM REGION): located closest to root tip contains actively dividing cells!

ZONE OF ELONGATION superior to apical meristem! composed of cells no longer dividing, but enlarging!

ZONE OF MATURATION superior to Zone of Elongation Cells here are completely differentiated and are fully mature! Growth of Stems: no root cap

Secondary Growth  Occurs at lateral meristems (on sides of roots and stems)  Two types of Meristematic Cells: 1.VASCULAR CAMBIUM 2.CORK CAMBIUM

Vascular Cambium  Thin layers of cells  Form rings around the stem and root trunk  Wood forms toward the inside;  Bark forms toward the outside!

Cork Cambium  Patches of cells  Located in outer bark region of plant  Divides to form tissues of outer bark

SecondarySecondary GROWTHGROWTH

In General… Plants with secondary growth are P E R R E N I A L S Plants with primary growth only are A N N U A L S or H E R B A C E O U S

PLANT TISSUES 3 types: 1. GROUND TISSUE 2. DERMAL TISSUE 3. VASCULAR TISSUE

GROUND TISSUE “FILLER TISSUE” 3 types of GT cells – differing in cell wall structure 1. Parenchyma 2. Collenchyma 3. Sclerenchyma

Parenchyma cells:  Very thin, flexible cell walls!  Located throughout plant body  Function in PS (mesophyll), storage, secretion of products  Living at maturity w/ ability to divide after injury

Collenchyma Cells  Thick, flexible cell walls!  Provide structural support in stems/leaves!  Living at maturity

Sclerenchyma  Thicker 2 cell walls than collenchyma  Cell wall filled with LIGNIN!  Provide strength and rigidity to plant  Dead at maturity!  2 types of sclerenchyma cells:  Sclerids: short/ irregularly shaped  Fibers: long, slender, tapered

Parenchyma SclerenchymaCollenchyma

DERMAL TISSUE  Provides protective covering over plant  2 layers: –Epidermis –Periderm

Epidermis  Outermost layer on herbaceous plants  Secretes cuticle to: –Prevent water loss (TRANSPIRATION)

PROBLEM! IF THE CUTICLE BLOCKS WATER, WHAT ELSE IS PREVENTED FROM ENTERING/EXITING THE PLANT? C O 2 !!

Solution?  STOMATA! –Tiny pores in epidermis surrounded by two guard cells! –Open during the day! Why?  PS occurs during the day  Transpiration necessary for cooling

Periderm  Outermost layer of cells on woody plants  Replacement of epidermis for plants with secondary growth  Continually formed by Cork Cambium

VASCULAR TISSUE  2 MAJOR TYPES: –XYLEM TISSUE –PHLOEM TISSUE –Found together in VASCULAR BUNDLES –Arise primarily from apical meristem –Arise secondarily from vascular cambium

XYLEM TISSUE  CONDUCTS WATER  PROVIDES MECHANICAL SUPPORT  2 TYPES OF XYLEM CELLS: –TRACHEIDS: –VESSEL ELEMENTS:

 TRACHEIDS –LONG, TAPERED CELLS –Dead at maturity –CONDUCT WATER FROM ONE TRACHEID TO ANOTHER VIA PITS (NO 2 CELL WALL, ONLY THIN 1)

 VESSEL MEMBERS/ELEMENTS shorter/wider than tracheids dead at maturity water passes between vessel members through perforations (no cell walls at all at perforations!)

PHLOEM TISSUE  CONDUCTS SUGARS  COMPOSED OF TWO CELL TYPES: –SIEVE-TUBE MEMBERS –COMPANION CELLS

Sieve tube members  Form sieve tubes to conduct sugars throughout plant  Lack nuclei, ribosomes, vacuoles, etc. Vascular bundle

 Pores:at ends of sieve tube members form sieve plates btwn adjacent cells

Companion Cells  Parenchymal cells  Connect to sieve tube members via plasmodesmata  Support nuclei-lacking STM’s  Aid in loading sugar into STM’s!

xylem

ROOTS  Taproots –Dicots –Single Primary Root

 Fibrous Roots –Monocots –Several roots of same size w/ branching

 Roots can be adapted for storage of nutrients: –Example: Carrot (Taproot) Sweet Potato (Fibrous Root)