Plant structure & growth 2 Flashcards
What is the general role of meristems?
Generating cells for primary + secondary growth
What type of tissue are meristems?
What are the 2 types of meristems?
Embryonic tissue
Apical & lateral
What does secondary growth cause?
Increase in diameter of stems + roots in woody plants
Where in a woody plant does secondary growth occur?
Stems & roots
- rarely leaves
What does the secondary plant body consist of?
The tissues produced by the vascular cambium + cork cambium
What type of plant is secondary growth a characteristic of?
Gymnosperms & many eudicots
- NOT monocots
What happens when primary growth from apical meristems nears completion?
Vascular cambium forms
What happens during 1st year of secondary growth in the vascular cambium?
> Secondary xylem & phloem thicken the stem
Vascular rays form
Cork cambium develops from parenchyma cells + produces cork
What happens to cells external to the cambium during secondary growth?
Cells (including epidermis) cannot divide so rupture
What are vascular rays?
Radial files of parenchyma
- connects secondary xylem + phloem for nutrient + water movement and repair
What happens in the 2nd year of secondary growth?
Secondary growth in secondary xylem, phloem & cork
What is bark?
All tissue exterior to vascular cambium
What does developmental plasticity describe?
Give an example
The effect of environment on development
Cabomba caroliniana forms diff leaves depending on whether or not apical meristem is submerged
- feathery leaves underwater reduces resistance to moving water
- pads on surface to aid flotation
What does development consist of?
Define the components
> Growth = irreversible increase in size
Morphogenesis = development of body form & organisation
Cell differentiation = process by which cells w/ same genes become diff from each other
What are the 2 components of growth?
Cell division
Cell expansion
What does cell division in meristems do?
What is cell expansion accountable for
Increases cell no. + the potential for growth
Actual increase in plant size
In what plane do new cell walls form?
Perpendicular to main axis of cell expansion
When is the plane in which a cell divides determined?
How is it predicted?
During late interphase
Microtubules become concentrated into a ring (=preprophase band) that predicts the future of cell division
Leaf growth results fro m a combination of what?
Transverse + longitudinal cell divisions
It has long been thought that leaf form is determined by what?
Plane of cell division
What does a mutation in the tangled-1 gene in maize do?
Affects longitudinal divisions BUT doesn’t affect leaf shape
Mutant leaves grow slower
What determines cell fate?
The symmetry of cell division
= distribution of cytoplasm between daughter cells
Give an example of asymmetrical cell division
Asymmetrical cell division and change in plane of cell division in the formation of guard cells
What do asymmetrical cell division play a role in?
Establishing polarity
- critical step in plant morphogenesis
What is polarity?
The condition of having structural or chemical differences at opposite ends of an org
e.g. plants have roots + shoots
Describe the 1st division of a plant zygote
> Asymmetrical
>Initiates polarisation into root + shoot
How are gnom mutants of Aridopsis different to normal plants?
> Result from a symmetrical 1st division
Have no leaves or roots
Defect traced to an inability to transport auxin in a polar manner
How is the expansion of plant cells different to animal cells?
Animals: synthesise protein-rich cytoplasm (metabolically expensive)
Plants: grow rapidly at lower energy cost by storage of water in vacuoles
- only 10% is by synthesis of cytoplasm
In what plane do plant cells expand primarily?
Along plant’s main axis
- shoot + root
What does the orientation of cellulose microfibrils in the cell wall cause?
How?
Restricts direction of cell elongation
- microfibrils don’t stretch so cell expands perpendicular to their orientation
- enzymes weaken cross-links allowing more expansion
What is pattern formation?
Development of specific structures in precise locations
What are the 2 hypotheses to explain the fate of plant cells?
Lineage-based
= cell fate is determined early in development + is passed on to progeny cells
Position-based
= cell fate is determined by final position in an emerging organ
What do laser ablation experiments suggest about plant cell fate?
How does this compare to animal cells?
Cell fate is established late in development + depends on signalling from neighbouring cells
Cells are largely lineage-dependent
Describe how positional info is conveyed by cell-to-cell communication in Arabidopsis root epidermis.
What does this result in?
Epidermal cell boarding single cortical cell expresses GLABRA-2
= hairless
Epidermal cell boarding 2 cortical cells doesn’t express GLABRA-2
= develops a root hair
What does flower formation involve?
A phase change from vegetative growth to reproductive growth
- associated w/ switching on of floral meristem identity genes
What is flower formation triggered by?
Combination of enviro cues (e.g. day length) + internal signals (e.g. hormones)
What are the organ identity gens that regulate the development of floral pattern known as?
MADS-box genes
Which organ develops where only A genes are expressed?
What about A + B genes?
What about B + C genes?
What about only C genes?
Sepals
Petals
Stamens
Carpels
