Plant structure and growth Flashcards
secondary growth in woody plants
occurs in stems and roots but rarely in leaves
Secondary plant body consists of tissues produced by the vascular cambium and cork cambium
Secondary growth characteristic of
gymnosperms and many eudicots, not monocots
Process of secondary growth in woody stem
primary growth from apical meristem nears completion, vascular cambium forms.
Secondary xylem and phloem thicken stem, vascular rays form. Cells external to the cambium can’t divide, so rupture, incl the epidermis. Cork cambium develops from the parenchyma cells
vascular rays
radial files of parenchyma connecting secondary xylem & phloem for nutrient & water movement & repair
developmental plasticity describes
effect of environment on development (influences expression of genes eg in different parts of the plant)
growth
irreversible incr in size
morphogenesis
development of body form and organisation
what accounts for the incr in plant size during growth
cell expansion not cell division (only incr cell number and potential for growth)
New CWs form in what plane
plane perpendicular to main axis of cell expansion
When is the plane in which a cell divides determined
late interphase
What predicts future plane of cell division
mcrotubules become conc into a ring called preprophase band- predicts future plane
leaf growth consists of what 2 types of cell division
tranverse and longitudinal
Plane of cell division determines what
leaf form, but leaf shape does not depend solely on precise spatial control of cell division
what determine cell fate
symmetry of cell division
distribution of cytoplasm between daughter cells
Formation of guard cells
involves asymmetric cell division- key event in development
and change in plane of cell division
what do asymmetric cell divisions play a role in establishing
polarity- critical step in plant morphogenesis
Polarity
having structural or chemical differences at opposite ends of an organism
First division of a plant zygote
asymmetrical and initiates polarisation into the shoot and root
how is expansion of plant cells different from animal cells
animal cells mainly grow by synthesising protein rich cytoplasm- metabolically expensive
Plant cells grow rapidly and at lower energy cost by intake and storage of water in vacuoles
Only 10% of plant cell expansion is in cytoplasm
Plant cells expand primarily along the plant’s main axis - shoot and root
What causes restricting direction (along main axis) of cell elongation in plants
orientation of cellulose microfibrilis
don’t stretch so cell expands perpendicular to their orientation
role of enzymes in cell expansion
weaken cw cross links allowing expansion
What is made to maintain expanding CW
more wall microfibrils
lineage based hypothesis to explain fate of plant cells
cell fate determined early in development and passed on to progeny cells
position based hypothesis
cell fate determined by final position in an emerging organ
which is correct
experiments suggest plant cell fate is established late in development and depends on signalling from neighbouring cell
cell fate in animals
lineage dependent mostly
How can positional info be conveyed
cell to cell communication eg arabidopsis root epidermis forms root hairs or hairless cells depending on number of cortical cells it is touching
phase changes
developmental phases plants pass through going from juvenile phase to adult vegetative phase to adult reproductive, phase,
phase changes in animals
affect morphology of organism
phase changes in plants
occur only in shoot apical meristem
most obvious morphological changes are in leaf size and shape
flower formation
involves phase change from vegetative to reproductive growth
flowering triggered by combo of
environmental cues eg day length and internal signals eg hormones
transition from vegetative growth to flowering associated with
switching on of floral meristem identity genes
difference between vegetative and floral growth
floral growth determinate
MADS box genes
organ identity genes that regulate development of floral pattern
abnormal floral development
mutation in plant organ identity gene
3 classes of floral organ identity genes encoding MADS box transcription factors
A, B and C genes
regulate expression of other genes responsible for development of se, pe, sta, ca
sepals
A
Pe
A and B
STa
B and C
CA
C
