Topic 4 - Specific organelles of the plant cell Flashcards
Plant specifications
- Cell wall
- Non-living cells are part of the body
- Tiny connections between cells (plasmodesmata) - all cells interconnected
- Plastids
- Vacuoles
- Inclusions
Cell size
Micrometer (bacteria) ↓ Millimeter (nettle hair) ↓ centimeter (hemp fibers)
Cellular compartments
Surrounded with a double phospholipid membrane, differences in function, interaction
Cell membranes
Function: separation and transport
Double phospholipid layer
Unit membrane hypothesis → fluid mosaic membrane
Plasma membrane (plasmalemma), tonoplast (vacuoles)
Function of membrane proteins
Receptor proteins Channel proteins Carrier protein Transport proteins Filaments of cytoskeleton pH regulation (vacuoles) Excretion (dictyosome)
The cytoplasm
Cytosol and cytoskeleton
Cytosol
o Soluble proteins o RNA o Water o Ions o Caarbohydrates o Fatty acids
Cytoskeleton
Spiral protein filaments
Mechanical resistance, migration of cell organelles
Play role in cell
Plant specific organelles
The vacuole system Plastids The cell wall Incrustations Adcrustations Plasmodesmata
The vacuole system
A Chamber bounded with tonoplast membrane storing solid or fluid compounds and gases
Minor importance in animal cells
Provacuole
Vesicles or ER and dictyosomes
Central vacuole
Three provacuoles fused into a larger one
Major functions of the vacuole system
Storage (isolating materials) Cell lysis Maintaining hydrostatic pressure (tugor) and pH Dispersal Protection
Types of vacuoles
Lysosomes
Vegetative (storage) vacuoles
Inclusions
Crystals
Lysosomes (vacuole)
Thick membrane
Hyrdolytic enzymes in the middle - autophage
Vegetative (storage) vacuoles
Diluted water solution, mildly acidic pH 5-6
Ions (e.g. high salt habitats)
By-products (important products for plant life: essenctial oils, paints, flavours)
Waste products (e.g.: glycosides, alkaloids)
Nutrient storage (protein, carbohydrates)
Inclusions
o Non constant, but not essential substances
o No metabolic activity, no membranes
o Protein inclusions: in pulse grains or aleurone layer, globoid or chrystalloid forms homogeneous/heterogeneous
o Carbohydrate inclusions: mainly starch
o Oil inclusions: small droplets of oil in the cytoplasm
Crystals
o Accumulation of inorganic compounds
o Oxalates, carbonates, silicates
o Digestion problems, irritation
Plastids
Assimilation, synthesizing metabolic processes, storage functions
Double phospholipid layer, chloroplast DNA
Coloured plastids: chloro- and chromoplastids
Colourless plastids: leucoplastids
Originated from prokaryotes
Development of plastids
Plastid initial (meristematic cell) → proplastid
Etioplastid: in cotyledons and plants have not been exposed to sunlight
Light → chloroplastid, synthesis of membrane proteins and pigments
Types of plastids
Leucoplastid
Chromoplastids
Chloroplastids
Leucoplastid
Colourless plastids in organs not exposed to sunlight
Storage function
The plant uses stored nutrients and plastids can turn into green ones (potato)
Globular or fusiform shape
Types of leucoplastids
Amiloplastids - starch
Elaioplastids - oil, fatty acids
Proteinoplastids - protein
Amiloplastids
Starch
In ground tissues, roots, modified stems, endosperm of seeds Chrystalline center (hilum) → amorphous and crystalline regions Simple and compound starch
Elaioplastids
Oil, fatty acids
Stored nutrients in different organs
Essential for germination
Drying (linseed, poppy), semi-drying (sunflower) and non-drying (castor bean) oils
Proteinoplastids
Protein
Simple or compound
In modified stems, seeds
Chromoplastids
Originated from proplastids or amiloplastids or chloroplastids (ripening, ageing leaves)
Less developed inner membranes
Carotenoid pigments: carotene, xanthophylls
Globular, fibrillary or crystalline forms
In flowers, fruits, leaves, roots
Pollination, dispersal
Chloroplastids
Thylakodis
Stroma
Structure and function of thylakodis
Outer membrane similar to cell membrane
Photosystems: integral proteins and pigments
Electron transport chain: proteins
ATP and NADPH production photosynthesis (light dependent reactions)
Compounds and functions of stroma
RuBisCO enzyme (protein complex)
Photosynthesis (light independent reaction) – production of glucose and intermediate products
Plastids of C3 and C4 plants
For C4 plants mesophyll cells has a granum structure, but it’s absent form the bundle-sheath cells
the cell wall
Similar in fungi cell but with different composition
Importance in everyday life
Woods
Fibers
Cooking quality
Nutrients
Cell wall proteins - hay fever
Major functions of the cell wall
Protection (environmental stress, pathogens, water loss)
Gives a definite shape
Enables transport information to the exterior
Helps in osmotic-regulation, prevents water loss
Transport processes
Ion exchange, mineral uptake (root hairs)
Skeletal substances in the cell wall
Cellulose
1,4 linked ß-D-glucose chain
Synthesised by the rosette enzyme of the plasma membrane
Primary cell wall
Web of microfibrils + auxin → loosened structure, formation of new fibrils → increasing cell wall surface
Secondary cell wall
New transverse layers of cellulose fibrils (increased strength)
Cellulase enzymes → decomposition of cell wall (secretory ducts, transport vessels)
Matrix substances
Pectins (soluble fiber) – linear chain of galacturonic acid polymers: high proportion in fruits and storage organs
Hemicellulose (glucose chain + oligosaccharides): cross-link between pectins and cellulose (e.g. arabinoxylan)
Proteins
Soluble (hydrolitic enzymes, peroxidases)
Insoluble (= extensins) – web-like structure
Incrustations
Lignin (wood)
Suberin (cork)
Pigments
Mucilage - storage of water, gelling effect
Inorganic compounds - in plant hairs → irritation
Lignin
Phenolic polymers consists of
Coumaryl alcohol
Coniferyl alcohol
Sinapyl alcohol
Mainly in the secondary wall (lignification)
Increase rigidity
Decrease digestibility
Suberin
Polymers of aromatic and aliphatic compounds
Waterproof layer, decreasing evaporation
Decreasing digestibility
Adcrustations
On cell wall surface
Wax, cutie
Water insulators, decreasing evaporation
Plasmodesmata
Channels traverse the cell walls - smooth ER tubes and protein filaments
Direct transport between cells
Large number in young cells, later decreasing abundance
The secondary wall
After the end of cell growth
Generally in mature cells with no cytoplasm (e.g.: fibers)
Increasing amount of incrustations decreasing digestibility
Outer (centrifugal) thickening
In case of spores and pollens
Spikes, grains, appendages
Inner (centripetal) thickening
Strengthening, protection (e.g.: transport tissues)
Total – complete cell wall (sclerenchyma)
Local – some part of a cell wall (e.g.: tracheids)
Partial – some of the cell wall (collenchyma)
General – whole cell wall except plasmodesmata
