Lecture 18 and 19 - Plant Tissues and Development Flashcards
What are the types of plant cells/tissues
Dermal
Ground (Cortex)
Vascular
Features of a plant cell
Features of cells common to all eukaryotic cells: (in black):
Crucial physiological, biochemical and molecular functions e.g., plasma membrane (PM), nucleus, endomembrane system including cisternae for protein folding, ribosomes, mitochondria, cytoskeleton, other organelles e.g., peroxisomes.
Cytoplasm of these cells is not static. Cytoskeleton components mediate directed organelle movement particularly during cell growth. The ER mediates organelle tethering. pp. 32-35
Characteristics unique to plant cells: (in red):
Plasma membranes: different composition of macromolecules e.g., lower concentration of cholesterol (for control of fluidity control of the PM) but higher concentration of more complex sterols for acclimation to changes in temperature in the environment.
Rigid cell wall for structural support and protection. Two wall types possible: all plants have primary cell walls, but only woody plants have secondary cell walls in certain tissues for added support and protection. Be aware: fungi (also eukaryotic do have cell walls but the components that make up these walls are different).
Presence of a vacuole for appropriate cell turgor. Contains water and important solutes for cellular function. Contains pigments in certain cell types. Makes up 95% of volume in many mature plant cells.
Intermediate filaments not present in plant cells. pp. 32-35
More extensive range of plastids and microbodies.
What are features of nuclei common to most eukaryotic cells?
One nucleus, contains most of the cell’s DNA. Be aware: many fungal species are multinucleate.
Double membrane of nuclear envelope is part of ER.
Nucleolus: site of nuclear ribosome synthesis: different types of RNA made. The rRNA subunits (60S and 40S) come together to make up 80S ribosomes in all eukaryotes. Be aware: size of ribosomes is different in plastids.
Heterochromatin: 10%: multi-coiled, usually found at periphery.
Similar cell cycle components and regulation stages. pp. 36-40.
Nuclear pore complexes (NPC): high order quaternary protein complex aggregates. Supramolecular sieves that control export and import. Proteins require nuclear localization signals in N-terminal sequences to gain entry.
What are the features of cell plasma membrane common to all living cells including prokaryotes
Fluid-mosaic model holds: bilayer made up of an inner and outer leaflet where hydrophobic regions face each other. Leaflets have different composition of peripheral and anchored proteins but share integral protein complexes.
Feature of plant cells:
Higher proportion of many types of sterols present in the plasma membrane. Lower concentration of cholesterol. Same point made on slide 5.
Contain galactolipids in chloroplast membranes so that phosphates can be used for other essential cellular processes. More efficient process evolved in ancestral prokaryotes.
What are features of vesicle transport common to eukaryotic cells
Plasma membrane of living cells is never static, e.g., receptor cycling changes signalling sensitivity.
Secretory pathways mediated by COPII-coated vesicles.
Endocytotic pathways mediated by clathrin-coated and COPI-coated vesicles.
Characteristics unique to plants and fungi:
More transport of sterols to PM and glycoproteins e.g. pectic polysaccharides (slides 15-16) processed in plant-specific enzymatic reactions. Sterols make up a high proportion of the PM, particularly in leaf epidermal cells and seed coat cells. 250 derivatives (many more than types of derivatives seen in animal cells). See image of root cap cell which have 20 times the amount of vesicle pits on a membrane surface than a normal plant cell on p. 22. pp. 19-23
What are the features of the endomembrane system in eukaryotes
Forms close associations with different organelles.
Certain proteins are specific to each type of association.
Rough (coated with ribosomes) and smooth ER.
Produce microbodies such as peroxisomes and oil bodies. Microbodies are small, specialized organelles (0.2-1.5 μm) with no DNA or ribosomes. They have simple PM leaflets. They carry out specific and specialized enzymatic reactions. They are known as being semi-autonomous because they are able to grow, divide or fuse. See the budding of oil body on next slide.
Key characteristics unique to plant cells:
ER shared between cells.
Transvacuolar strands.
Predominantly polygonal network structure in elongated plant cell types.
Cisternae: more flattened and very prevalent in young plant cells.
Unique protein-PM associations.
What are the features of micro bodies in eukaryotic cell
Have a single leaflet membrane. Carry out specialized functions of intermediate metabolites. Contain no DNA or ribosomes.
Characteristic features of microbodies in plant cells:
Much greater quantities in certain cell types:
Oil bodies: store triglycerides in seeds.
Peroxisomes: contain catalase to quickly degrade hydrogen peroxide which can be generated as a by-product of inefficient photosynthetic processes in leaves.
Glyoxysomes: specialized peroxisomes particularly found in large quantities in storage plant cells. They process fatty acids to make acetyl coenzyme A and sugars which are needed for metabolic processes in mitochondria.
What are plastids and what are their features common to living cells
Plastids are highly specialized organelles. Have two leaflets. Have their own DNA (different genes to nuclear DNA. Maternally inherited.) and ribosomes (70S - different to cytosolic ribosomes). Have complex double membranes primarily made up of galactolipids inherited from prokaryotic endosymbiotic ancestors. Like microbodies, plastids are semi-autonomous, because they can grow, divide (independently of cell division), fuse, be degraded. Unlike microbodies, they have DNA.
Moved around the cytosol via actin microfilaments.
Mitochondria: energy-producing (mainly ATP). Highly dynamic; readily undergo fission (see slide 9) or fusion.
Feature predominantly characteristic of plants:
Chloroplasts: energy-producing (mainly sugars) in certain cells, tissues and organs. Have a third set of membranes called thylakoids which are highly specialized to promote efficient photosynthesis.
More types of plastids possible in different plant cell types.
What are proplastids
Plastids with membrane is rudimentary and internal grana are missing.
What are Etioplasts
Internal lattice of rudimentary membranes which will develop into grana
What do leucoplasts not have
Pigments
What are some examples of peptidoglycan cell walls
Bacterial cell walls and protein coats in viruses
What are the plant primary cell walls composed of
Middle lamella
Primary cell wall
Plasma membrane
Hemicellulose
Cellulose microfibrils
Pectin
What is pectin
Inter-connecting gel-like polysaccharide galacturonans for variable rigidity
What are cellulose microfibrils
Long, provide core strength in protective matrix
What is Hemicellulose
Mesh-like polysaccharide glycoproteins
What are the features of a secondary plant cell wall
Middle lamella
Primary cell wall
Secondary cell wall
Plasma membrane
Lignin
Hemicellulose
Cellulose microfibrils
What is lignin
Water-impermeable polyphenolic molecules laid down in specialized cells which will then die. Provide greater rigidity and support.
Where are plant cell secondary walls primarily found
Present in vascular tissue of many plant groups e.g. ferns, and in woody plants e.g. certain shrubs, trees
Other polyphenolic compounds (waxy) that are also water-impermeable are laid down in other cell types, e.g., cell walls in bark contain suberin.
What is the cellulose-pectin equivalent for fungi
Chitin
Why do animal cells have junctions
Adhesion and communication
What are the types of junction in an animal cell
Tight junctions
Desmosomes
Gap junctions
What is the only type of plant junction and why is its key features
Have partially permeable primary cell walls stuck together with a gel-like middle lamella for organism flexibility
Specialized tissues have additional impermeable secondary cell walls for organism rigidity
What are plasmodesmata
Desmotubules link to ER and contribute to biomechanical sensing and signalling.
Can have a complex architecture (branched) to maintain cell wall integrity
Important for symplastic movement of water through cells.
What are the two types of plant growth
Primary growth
Secondary growth
What is primary growth
Elongation growth at RAMs and SAMs
Primary body plan e.g., phyllotaxy
Cell division, cell elongation, cell differentiation
Assymetrical cell division in embryos
What effects does leaf development have
Determine growth
Asymmetrical cell division in guard cells
What are the process of growth and differentiation that shape the body plan
Growth: irreversible increase in organism size (cell division and cell elongation)
Cell differentiation: cells with the same genes become structurally and biochemically different from each other
Morphogenesis: organized spatial distribution of cell or tissue types to form organs
What is meristematic tissue
key source of undifferentiated cells for growth and differentiation
What is developmental plasticity
the effect of environment on autonomous development
How can the cabomba plant adapt to their environment
If meristem tissue is submerged, feathery leaf growth is favoured.
If meristem tissue is above the water surface, surface leaves form.
Heterophylly: hetero (Gr: different), phyll (Gr: leaf)
What are the two phases to a plant life cycle
Vegetative phase - Dominant form is the sporophyte (2n) in most plant species
Reproductive phase: Generation of gametophytes (1n)
Made up of very small tissue within the protective sporophyte plant.
What are the types of vegetative growth
Indeterminate: allows for continual growth
Determinate: stop growing after reaching a certain size: gradual loss of meristematic tissue:
Leaves, thorns, trichomes
Reproductive:
Determinate: Flowers
No growth:
Dormant periods e.g., winter
Severe, prolonged stress e.g., unfavourable, environmental conditions
Where are meristematic tissues located
Apical (tips of roots and stems)
Roots: RAMs
Stems: SAMs
Axillary (in axils [angled joins] of petioles and stems)
For the morphogenesis of new stems/leaves:
Lateral meristems: (circular/tubular)
Pericycle of roots: lateral root formation
Cambiums: secondary growth (girth increase
What is morphogenesis
Development of vegetative organs or reproductive organs
What are adapted life cycles to avoid stress
Annuals: grow, produce reproductive organs, go to seed, die in one season/year
e.g., some wildflowers, legumes, cereal crops
Biennials: need two years to complete life cycle
e.g., turnips, teasels
Perennials: grow year on year, reproductive phase may vary but usually happens once a year
e.g., trees, shrubs
Less complex tissues and organ arrangement
Sessile (non-motile)
Ability to respond flexibly to environmental cues
Less resources: growth in plants is slowed
Example of annual life cycle
Wheat
Example of biennial life cycle
Teasel
Human development mitigators
Limited plasticity (can’t grow new limbs), only new cells (bone marrow)
Cancer cells (more plasticity): deregulated gene control and signaling. Tissues lack uniformity in shape and packing.
What is pluripotency
stem cells or meristematic cells that can develop into several cell types
What is totipotency
stem cells or meristematic cells that can develop into any other cell type (usually develops a pluripotent stem tissue intermediate).
How can mammal cells be reverted to toti or pluripotent
Cell culture:
Media, chemicals
Usually only get another cell type
From pigs: organs, ethical ‘meat’
How can plant cells be reverted to toti or pluripotent
Much easier to grow a whole new plant with all organs.
Why? Many more developmental genes:
Transcription factors
Small RNAs: e.g., microRNAs
SLIDE 11
What are SAMs
Shoot apical meristem
dome-shaped mass of dividing totipotent cells at the shoot tip
What do SAMs give rise to
Protoderm
Ground meristem
Procambium
Leaves develop from leaf primordia along the sides of the apical meristem
How does gradient signalling in SAMs occur
Like a see saw (how it tips, depends on dosage and positioning)
Vegetative phase:
Mediate primary growth and morphogenesis: maintains balance
Mitosis, differentiation, elongation
Usually indeterminate: SAM is maintained
Multiple signals control patterning
Reproductive phase transition:
Triggered by specific cues
Multiple, contributory
Redundant
Some inhibitory
Some cause activation
Control floral patterning
Sepals, petals, stamens, carpel
What are the signalling profiles away from the SAM
Determine fate of cells and to produce an ordered body plan of tissues which make up organs.
Important to maintain apical dominance (position of OC -red) for continued primary growth
Brought about by auxin-cytokinin interaction which affects expression of specific genes (transcription factors, small RNA molecules) transcribed in the OC, initials, elongating cells, fully differentiated cells.
Gives rise to primary growth and new vegetative cells and tissues.
Development of conserved shoot architecture for a plant species: e.g., opposite, alternate, whorled, etc
What are the repetitive pattern of tissues created by phyllotaxis and the SAM
Genetically determined by the autonomous developmental programme of each species
Most common: stem, leaf, bud
Will respond flexibly to environmental cues: i.e., can change the number and arrangement of branches and leaves
e.g., may grow branches on the sunnier side
What is fractal patterning
each bud resembles the overall shape and structure
What is angling determined by
by exact nature of gradient (overlap) signaling of molecules and transcription factors
