lec 28- meristems Flashcards
where are most of the plant adult structures derived from?
the shoot and root apical meristem
when do the meristems form?
during embryogenesis, remain inactive until the seed germinates
what do the meristems give rise to?
shoot meristem- stems, leaves, and flowers
root meristem- roots
are shoot meristems small in size?
yes
what is the first stage of future organs called?
primordia
what does each primordium consist of?
small number of founder cells that produce the new structure by cell division and expansion followed by differentiation
what is the shoot meristem composed of?
3 layers: L1, L2, and L3
explain the 3 layers of the shoot meristem:
-L1 and L2 are one cell thick, cell division is almost always anticlinal, meaning new cells are always added to the same layer
-Cells in L3 divide in any plane
what is the central zone?
a group of 20 undifferentiated cells in the center of the meristem known as initials
what is the peripheral zone?
a zone that contains proliferating cells that will give rise to leaves and side shoots
what is the rib zone?
a zone that underlies the central zone and forms the organizing center that gives the meristem cells their identity
do cells slowly become displaced outside the meristem as the meristem divides more and more?
yes, allowing for them to form organs like leaves, side shoots, and flowers
what is the fate of L, L2, and L3 cells?
L1 = epidermal cells
L2 = leaves and flowers
L3 = stem
if the shoot meristem is removed and if it is cut in half, can it still function normally?
yes, it will still do its normal job meaning it doesn’t need external signals
are the fates of the cells in each layer determined?
no because if one cell in one layer enters the other, it will take on the fate of the layer they are in despite originally being from another
how do cells in the meristem signal to one another?
-WUS is secreted from the organizing center and it enters cells in the central zone, WUS promotes stem cells fate and prevents differentiation and it helps with the release of CLV3
-CLV3 diffuses away from the central zone and triggers CLV1/CLV2 receptors that repress the expression of WUS in cells outside of the organizing center
what evidence is there of the CLV-WUS loop?
- expression: CLV3 is found in L1 and L2 layers, WUS in the organizing center and CLV receptors around it
- analyses of mutant phenotypes: mutations in CLV3 or the CLV1/CLV2 receptors caused WUS to not be controlled and as such the mutants meristems were larger than normal
what happens to mutants that lack WUS?
a small meristem forms but shortly terminates after forming a few leaf primordia
can the CVS-WUS loop fix abberations?
yes, an increase in CLV3 cells that release a lot of CVS3 signals can result in less WUS expression to decrease cell proliferation and the cells being produced
