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FT1043 LECTURE 1

INTRODUCTION:

PLANTS AND PLANT

CELLS

THE SCOPE OF PLANT PHYSIOLOGYTHE PLANT CELL

BIOLOGICAL MEMBRANES

CELLULAR ORGANELLES

CYTOSKELETON

THE EXTRACELLULAR MATRIX

PLASMODESMATA

CELL AND TISSUESPLANT ORGANS

Phloem of Douglas fir (Pseudotsuga menziesii) from Stern, 2006.

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THE SCOPE OF PLANT

PHYSIOLOGY

The termphysiologyis constructed from the

Greek words

Physis meaning nature

Logos meaning discourse

Plant physiology is a discourse about the

nature of plants

Plants are viewed as biochemical machines

Is about how plants function

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THE PLANT CELL

Cell is the basic functional unit of plants and all living

organisms

The architecture of a plant reflects the number,

morphology and arrangement of its individual cells A cell is an solution of chemicals called protoplasm

surrounded by a plasma membrane

The membrane and the protoplasm it contains are

collectively referred to as a protoplast

The plasma membrane is selectively permeable

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The protoplast contain a variety of subcellular

structures called organelles

Nucleus: contains genetic information and is the

control center of the cell

Cytoplasm: contains other organelles excluding

the nucleus

Different organelles is the cytoplasm are thesite of cellular respiration, photosynthesis,

protein synthesis, secretion and so forth

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Plant Cells, showing the major organelles. (a) Diagram of a mature leaf cell.

From Rost, Barbour, Stocking and Murphy, 2006.

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From: Rost, Barbour, Stocking and Murphy, 2006.

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Source: Stern, 2006.

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Source: Stern, 2006.

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BIOLOGICAL MEMBRANES

Biological membranes are composed

primarily of lipids and proteins, with smaller

amounts of carbohydrate

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The Membrane Bilayer

Phospholipids are the most abundant lipids in cell

membranes

Phospholipids have 2 hydrophobic (water-fearing)

non-polar hydrocarbon tails and a hydrophilic(water loving) polar head group

They are highly fluid and impermeable to most polar

molecules

The membrane bilayer is also impermeable to most

polar or charged solutes. Exceptions to water,

carbon dioxide, and oxygen

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Membrane Protein

Most membranes contains as much as 50%

protein by weight

May be categorized as either integral protein

or peripheral protein

Integral: may consist of a single protein or large

complexes made up of several proteins with

additional nonprotein components Peripheral: a predominantly hydrophilic and bind

loosely with the polar phospholipid heads

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Membrane proteins are responsible for all

metabolic activities associated with

membranes

Some function as enzymes, others assist in

the selective transport of solute molecules

across the membrane, and others participate

in energy transduction The functions of different membranes in the

cell are very diverse

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Source: Stern, 2006.

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Source: Rost, Barbour, Stocking and Murphy, 2006.

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THE EXTRACELLULAR

MATRIX

Cells wall contains predominantly

carbohydrate and protein

2 types of cell walls:

Primary walls: surround young, actively growing

cells

Secondary walls: laid down as the cells mature

and are no longer growing

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The Primary Cell Wall

Thin, few micrometers in thickness, consists of

randomly arranged threadlike polymers of glucose,

called cellulose

A single molecule of cellulose may contain as manyas 3,000 or more glucose units

In the cell wall, the celulose molecules are grouped

together in long parallel arrays called microfibrils

The orientation of microfibrils in the primary wall is

random

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The Secondary Cell Wall

Laid down on the inside of the primary wall

Secondary walls are thicker and more rigidthan primary walls

Often consists of 2 zones, depending on theorientation of the microfibrils

They contain up to 45% cellulose, up to 35%

lignin Lignin has a stronger than cellulose

microfibrils strength

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Source: Stern, 2006.

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Plasmodesmata

Membrane-lined channels as the cellulose is laid

down and the wall increases in thickness

Plasmodesma are small (60 nm in diameter) but

often in large numbers, permits the diffusion of smallsolute molecules

The connection of neighboring protoplasts through

plasmodesmata creates a continous cytoplasmic

network reffered to as the symplast

Apoplast is comprised of interconnected cell walls,

intercellular spaces, and non-living vascular tissues

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CELLULAR ORGANELLES

Vocuole

In a mature cell, the vacuole may occupy as much as 80-

90% of the cell volume

Surrounded by a membrane called the vacuolar membraneor tonoplast

Contains a variety of inorganic ions, organic acids, sugars,

enzymes, secondary metabolic products

Important in water uptake for cell enlargement

Smaller vocuoles combine to form single large vocuoles

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Nucleus

Is the information of the cell

Contains cells genetic material deoxyribonucleic

acid (DNA)

Genes in DNA encode information for the

synthesis of ribonucleic acid (RNA)

RNA is exported to the cytoplasm where it directsthe synthesis of specific proteins

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Source: Stern, 2006.

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Endoplasmic Reticulum and GolgiComplex The Endoplasmic Reticulum (ER)

and the Golgi Complex togetherform an elaborate system ofmembranes involved in lipid andprotein biosynthesis and

secretion Protein synthesized on rough ER

(associated with ribosomes) arepassed through the membrane intothe lumen, move into region ofsmooth ER

The protein in ER modified andsugars are added to formglycoproteins

Glycoproteins are then packed inspherical transport vesicles thatbud off the smooth ER

Source: Stern, 2006.

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The golgi complex is astack of flattened,

membranous sacs called

cisterna

Serves to assemble and

process carbohydratechains of glycoproteins

Here the sugar chains are

modified and enlarged and

other sugars are added

The modified glycoproteinsleave the Golgi in secretory

vesicles, which deliver their

contents to sites inside the

cell for protein storageSource: Stern, 2006.

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Mitochondria The mitochondria and

chloroplasts are the twoenergy-transducingorganelles in plants cells

Mitochondria are the site ofcellular respiration, theprocess in which the energyof sugar oxidation is used todrive the synthesis ofadenosine triphosphate(ATP)

The ATP is then exported toother regions of the cell forvarious cellular activities

Source: Stern, 2006.

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Plastids

Plastics are a family of double membrane-boundorganelles common to plant cells

Chloroplasts contain the photosynthetic pigments,carry out photosynthesis and responsible forthe prominent green colour of leaves

Chromoplasts contain pigments other than

chlorophylls Colourless plastids are called leucoplasts,

leucoplasts that accumulate starch calledamyloplasts

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Source: Stern, 2006.

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Source: Rost, Barbour, Stocking and Murphy, 2006.

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Source: Rost, Barbour, Stocking and Murphy, 2006.

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Microbodies

Small organelles and bound by a singlemembrane

Specialized roles in specific metabolic pathwaysand are usually characterized by a particularenzymes or enzymes

Ribosomes

The site of protein synthesis Ribosomes are complex aggregated of RNA and

protein, which appear as small granules

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CYTOSKELETON

The cytoskeleton plays vital roles in determining theorganization of cytoplasm and cell shape, and in celldivision, growth and differentiation

Composed of 2 different elements: microtubules andmicrofilaments

Microtubules are constantly being assembled,disassembled, and rearranged as the cell divides,enlarges, and differentiates

Microfilaments control the direction of cytoplasmicparticles and organelles around the periphery of thecell

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CELLS AND TISSUES

Cell is the basic unit of life and the fundamental

morphological unit of the plant body

Tissue is a group of cells whose structure or

function, or both are distinct from others A plant begins as a fertilized egg (zygote), in the

ovary of a flower

Zygote undergoes cell division and differentiation,

giving rise to an embryo

Embryo has root (radicle) and shoot (plumule)

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Regions of continued cell division called

meristems

Apical meristems located at the apex of the shoot

and the root; responsible for adding to the lengthof the shoot and root axis (primary growth)

Lateral meristems located in the vascular

cambium; responsible in increase in girth or

thickening of the stems and roots (secondary

growth)

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Epidermis

Is a superficial tissue that forms a continuouslayer over the surface of the primary plant

body Epidermis cells are usually regular in shape,

are appressed very tightly together, and theirouter walls are covered with a waxy cuticle

Some cells are specialized as hairs(trichomes); guard cells in leaves; cork

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Parenchyma

Cells found throughout the plant body in the

cortical regions of stems and roots and in the

mesophyll (meso, middle; phyll, leaf) of

leaves, and are scattered throughout the

vascular tissues

Parenchyma cells serve primarily inphotosynthesis (sometimes called

chlorenchyma), storage, and wound healing

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Supporting tissues

Two supporting tissues are collenchyma and

sclerenchyma

Collenchyma: parenchyma cells that are specialized forsupport in young tissues; found in the cortex of stems and

petioles or along the veins in leaves

Schlerenchyma: Sclerids (polyhedral or branched) and

Fibers (very long and slender)

Both sclerids and fibers have thick secondary walls that

may be heavily lignified

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Vascular Tissues

Concerned primarily with the distribution of

nutrients, water, and photosynthesis products

Two types: xylem and phloem

Xylem: water conduction, storage and support

Phloem: distribution of primarily organic

molecules between photosynthesis/storagetissues and regions of active growth

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PLANT ORGANS

The principal organs of a plant are roots,stems, leaves, flower, and fruits

Roots: consists of stele (xylem, phloem,

pericycle and endodermis), cortex andepidermis; functions of root are anchorage,storage, water/nutrient absorption

Stem: the vascular tissues are arranged inbundles & scattered (monocotyledonous) andconcentric rings enclosing a central pith indicotyledonous

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Leaves: composed of an upper and lower

epidermis, enclose mesophyll (photosynthetic

parenchyma);

Two types of mesophyll: palisade mesophyll

(tightly packed, elongated cells toward the

upper leaf surface) and spongy mesophyll

(loosely packed, irregular cells with anextensive network of air spaces)