lec 27- plant development Flashcards
what are the similarities in plants with other eukaryotes?
-same way to regulate gene expression
-same use of asymmetric cell divisions
-same use of positional signals
what are the differences in plants from other eukaryotes?
-lack of large scale cell movement
-develop organs and body parts after embryogenesis
-plant development is synchronized with environmental conditions
-cells can re-differentiate throughout the plants lifetime
what are the model organisms to study plants?
corn, rice, and arabidopsis
what does plant embryogenesis refer too?
development that occurs within the seed
what do the meristems produce?
roots, leaves, and flowers
what are the two axes of plants?
apical-basal axis and radial axis
what is the meristem?
undifferentiated cells that produce structures after germination has occured
what happens first in plant embryogenesis?
-the zygote undergoes asymmetric cell division and produces an apical cell and a basal cell, apical cell contributes to most of the embryo while the basal cell forms the suspensor
what does the suspensor do?
it attaches the embryo to the maternal cells in the ovule and supplies nutrients to the developing embryo
what happens second in embryogenesis?
-the triangle shaped embryo elongates, forming two groups of cells that will become meristems located at each end of the embryo (between cotyledons and at the base)
-the region in between will become the hypocotyl (embryonic stem)
what happens after embryogenesis?
the embryo enlarges and then enters dormacy
what is the fate of each part of the embryo?
-upper tier forms cotyledons and shoot meristem
-middle tier forms hypocotyl
-bottom tier with the uppermost suspensor cell forms the root
how does radial patterning occur?
-occurs during 16 cell stage when central and peripheral cylinders appear
-periclinal divisions occur parallel with the surface and add cylindrical layers to forming stem
-anticlinal divisions occur perpendicular to the surface and add additional cells to each layer
can isolation and transplantation experiments be done on plants?
no, because the embryos are in seeds and held together by cell walls
how is specification and determination studied in plants?
by looking at mutants
how do plant cells determine their fate?
by the position they are in
why is auxin important in plants?
it specifies the apical basal axis, it regulates gene expression, influences cell division, cell expansion, and cell differentiation
what is the normal form of auxin?
IAA
how does auxin regulate gene expression?
when no auxin: AUX/IAA proteins bind to transcription factors known as auxin response factors or ARFs and prevent activity
when auxin present: auxin binds to the SCF TIR1 complex and the complex binds to AUX/IAA proteins for degredation, preventing their interaction with ARFs and allowing for gene expression
how are auxin levels controlled in pants?
- regulation of genes encoding auxin biosynthetic enzymes
- plants control the directional, cell to cell transport of auxin
- can be converted to inactive forms like IAA esters, IAA amino acids, and IAA sugars
how is auxin transported cell to cell?
-IAA can diffuse through the cell and once in the cytoplasm it dissociates into IAA-
-IAA- can also enter the cell by auxin important proteins
-once the IAA- is in the cell, it can move to the next cell via auxin efflux proteins/transporters
this allows for the regulation of auxin
how is the apcical basal axis specified?
auxin from the basal cell moves out of it into the apical membrane via auin export proteins
-the auxin accumulates in the apical making it specified
-the auxin then moves out of the apical into the basal via auxin export proteins letting it becomes specified
what is the role of the WOX genes?
-they encode the DNA binding domain and the expression of auxin exporters needed to move auxin
-WOX2 is expressed in the apical and WOX8 and WOX9 are expressed in the basal
-WOX8 expression in the basal is required for WOX2 expression and normal development
what does Topless do in plants?
topless forms a complex with AUX/IAA and is needed to repress activity
-it works in the top half of the embryo and prevents root formation in the top
