Plant Form and Function

Tissue

• A group of cells consisting of one or more cell types that together perform a specialized function

  • xylem, phloem, ground, dermal

Organ

• Consists of several types of tissues that together carry out particular functions

  • Root and shoot system

Apical Meristems

• Plant sustains growth

• Primary growth

• Populations of pluripotent stem cells

• Cell division to produce new tissues

• Localized regions of cell growth

• Root Apical Meristem (RAM)

• Shoot Apical Meristem (SAM)

Arabidopsis growth

• Emerge one at a time in a spiral

  • Maximizes sunlight absorption

  • Photosynthesis

Lateral Meristems

• Add thickness to woody plants, a process called secondary growth

  • Vascular Cambium, Cork Cambium

Vascular Cambium

• Lateral meristem

• Adds layers of vascular tissue

  • Secondary xylem (wood)

  • Secondary phloem (inner bark)

• Secondary tissues

Cork Cambium

• Replaces the epidermis with periderm

  • Thicker and rougher

  • Produces cork like wine bottle or cork board

  • Cork cells

  • Outer bark

Shoot Apical Meristem (SAM)

• Primary growth

• Axial growth

• Primary tissues: ground, vascular, dermal

Root Apical Meristems (RAM)

• Primary growth

• Axial growth

• Primary tissues: ground vascular, dermal

• Produces cells in two directions — pushes cells up or down root cap communication

• Produces a cap of tissue called the root cap and covers the distal tip of the root

  • Protects the root tip as it grows through the soil

  • Cell are sloughed off

• Ram produces cells proximally that contribute to the root proper growth

• Produce no lateral appendages

Plant Tissue System

• Dermal tissue

• Ground tissue

• Vascular tissue

• Continuous throughout plant

Dermal Tissue

• Non-woody plants

• Consists of the epidermis — able to secrete

• A waxy coating called the cuticle helps prevent water loss from the epidermis

• Woody plants

  • Protective tissues called periderm replace the epidermis in older regions of stems and roots

Trichomes

• Outgrowths of the shoot epidermis that help reduce water loss and with insect defense

• Hair-like

• Glandular accumulate specialized metabolites for plant defense

• Other trichomes help to prevent the plant from drying out and can increase the relative humidity closer to the leaf or stem surface

Do roots form a cuticle?

• No because it wants to absorb nutrients and water

Vascular tissue system

• Facilitates long-distance transport of materials between roots and shoots and provides mechanical support

• Xylem

  • Conducts water and dissolve minerals upward from roots into shoots

• Phloem

  • Transports organic nutrients from where they are made to where they needed

Stele

• Vascular tissue of a stem or root

  • Deep within the root

• In angiosperms a solid central vascular cylinder

• Stems and leave sis divided into vascular bundles, strands of xylem and phloem

Ground Tissue system

• Internal to vascular tissue — pith

• External to vascular tissue — cortex

• Include cell specialized in:

  • Storage, macromolecules, starch

  • Photosynthesis

  • Support

  • Transport

Mature Parenchyma Cells

• Have thin and flexible primary walls — metabolically active

  • Cellulose, other sugars, and proteins

• Lack secondary walls

  • Primary walls + lignin

• Are the least specialized

• Performs metabolic functions

• Retains the ability to divide and differentiate

Collenchyma Cells

• Are grouped in strands and help support young parts of the plant shoot

• Have thicker and uneven cell walls

• Provide flexible support without restraining growth

• Alive

• Crunchy celery

Sclerenchyma cells

• Thick secondary walls strengthened with lignin

• Dead at maturity

  • Tough

  • Rigid

  • No movement of nutrients

• Are short and irregular in shape with thick lignified secondary walls

• Fibers are long and slender and arranged in threads

Embryo

• (2N)

• Primary dermal, ground and vascular tissue

• SAM, RAM established in the embryo

• Cotyledons

Endosperm

• (3N)

• Stores starch, proteins, and lipids

Seed coat

• Parent 2N tissues

• Thickened cell walls of seed coat help to protect the seed

Seed Dormancy

• Increases the chances that germination will occur at a time and place most advantageous to the seedling

• Breaking this requires environmental cues, such as moisture, temperature, or light changes

Germination

• Depends on imbibition, the uptake of water due to low water potential of a dry seed

• The radicle (embryonic root) emerges first; developing the root system anchoring the plant

• Next shoot tip breaks through the soil surface

Roots

• Function of a root

  • Anchoring plant

  • Absorbing mineral and water

  • Storing carbohydrates

• Primary root first to emerge

• Lateral roots branch from primary root

• Root hairs

• Mycorhizas (soil fungi)

  • Form a mutualistic associaation

Primary Growth on Roots

• Growth occurs just behind root tip, in three zones of cells

  • Zone of cell division

  • Zone of elongation

  • Zone of differentiation or maturation

• RAM

• Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder

• Are in line with xylem to facilitate transport

Root Cap

• Covers the root tip

• Protects the apical meristem as the root pushes through the soil

• Secrets polysaccharide slime

• Continually sloughs off

• Produces signals to attract beneficial microbes

• Senses gravity to grow down into the soil

In which region would you expect the majority of water and nutrient uptake to occur?

• Zone of differentiation

  • Most surface area therefore more intake

Dicot root c.s.

• Xylem is starlike in appearance with phloem between the “arms”

• 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

• Endodermis regulates passage of substances from soil into the vascular cylinder

Monocot c.s.

• In many monocots, the core parenchyma cells are surrounded by rings of xylem then phloem

Tap root system

• Tall plants

• Large shoot masses

  • Eudicots, gymnosperm

Fibrous root system

• Adventitious roots that come from stem

• Lateral roots

  • Monocots (grasses)

Root Adaptations

• Many plants have root adaptations with specialized functions

• Help hold

• Photosynthesis in orchid

• Allow roots to obtain air

• Support

Shoot function

• Photosynthesis

• Transpiration

  • Loss of water through open stomata

• Transport

  • Xylem and Phloem

• Reproduction

Node

• Where leaves attach on a stem

Internodes

• Between leaves of a stem

Axillary Bud

• Potential to form a lateral shoot, or branch

• Dormant meristem

Apical Bud

• Elongation of young shoot

Apical Dominance

• Helps to maintain dormancy in most axillary buds

• (To grow taller)

Rhizome

• A horizontal shoot that grows just below the surface

Stolons

• Horizontal shoots that grow along the surface

• AKA “Runners”

• enable a plant to reproduce asexually, as plant-lets form at nodes along each runner

Tubers

• Enlarged ends of rhizomes or stolons specialized for storing food

Dicot vs. Monocot stem architecture

• Dicot vascular tissue consists of vascular bundles arranged in a ring

• Monocot stems, vascular bundles are scattered throughout the ground tissue, rather than forming a ring. Surrounded by a sheath

Tracheids

• Found in the xylem of all vascular plants

  • Capillar yaction

  • H2O becomes easy to move

  • Small wall to wall

Vessel elements

• Common to most angiosperms and a few gymnosperms

• Align end to end to form long micro pipes called vessels

• Dead at maturity

Sieve tube Elements

• Are alive and functional at maturity, though they lack organelles

• Plates are porous end walls that allow fluid to flow between cells along the sieve tube

• Has a companion cell whose nucleus and ribosomes serve both cells

Primary Growth of the shoot

• SAM initiates new stem tissue and new leaves

• Primary growth is concentrated at the shoot tip

• Primary growth is continuous and increases stem length

  • Internode elongation

  • Stimulated by auxin and gibberelic acid (plant hormones)

• Leaf development is mostly determinant

  • If differentiated, cells are mature and growth stops

Leaves

• Initiated by the activity of the SAM

• Main photosynthetic structures of the plant

• Intercept light, exchange gas, dissipate heat, defend plant from herbivores, and pathogens

• Generally consist of flattened blade and a stalk called the petiole which joins the leaf to a node of the stem

Simple leaf

• Blade not divided into leaflets

Compound leaaf

• Blade is divided into leaflets

  • Pinnate leaf

    • Leaflets attached to long petiole

  • Palmate leaf

    • All leaflets connect to a central location

Modified Leaves

• Some plant species have evolved these to serve various functions

  • Protection

  • Grasp

  • Reproductive

  • Storage

Epidermis in leaves

• Interrupted by stomata — pores

  • Allow for exchange of CO2 and O2 between air and photosynthetic cells in a leaf

  • Major avenues for evaporative water loss

• Each stomatal pore is flanked by two guard cells, which regulate opening and closing

Stomata

• Occur in pairs in the epidermis of the leaf or stem

  • Guard cells

  • Stomata

• Functions:

  • Gas exchange

  • Changes in potassium ions and plant hormones like cytokinin and abscisic acid

  • Open during day — closed at night K+ goes out H2O follows

Mesophyll

• Ground tissue in a leaf — sandwiched between the upper and lower epidermis

• Palisade

• Spongy

Palisade Mesophyll

• Upper part of the leaf

• Majority of Photosynthesis

Spongy Mesophyll

• Lower part of the leaf

• Gas exchange

• Loose arrangement with ample air spaces

Vascular Tissue of Leaves

• Veins are the leafs vascular bundles and function as the leaf’s skeleton

• Each vein in a leaf is enclosed by a protective bundle sheath

Monocot vs. Dicot leaf

• Monocots have parallel veins

• Eudicots have branching veins