lec 12- plant vegetative growth and organogenesis Flashcards
what does the SAM do?
provides cells for leaf and stem development
what appears at the flanks of the SAM and what does it do?
the leaf primordia appears at the flanks and the cells there divide and expand to give rise to a mature leaf, the cells around the leaf primordia divide and differentiate to give rise to the stem
does all cell division take place in the meristem?
no, it starts there then moves away
in what pattern are leaves formed?
spiral pattern
what is formed at the base of leaf primordia and what does it result in?
buds are formed at the base of leaf primordia and it will later give rise to branches producing leaves, flowers or both
what is the position where a leaf and a bud both exist called?
a node
what is the space between two nodes called?
internode
how do buds act in perennial plants?
buds are dormant in the first year, the leaf falls off in the fall, and the buds start growing the following year, producing a branch with its own SAM and lateral organs
what happens to buds when the shoot is cut off?
it results in the dormant buds being activated to initiate growth after loss of apex from grazing animals or freezing damage
what does the apex do?
exerts apical dominance on buds, so when apex is destroyed, so is the dominance (mechanism involves auxin and polar auxin transport)
how is the leaf primordia different in monocot grass?
it extends almost around the meristem
what is a petiole?
the stalk that attaches the leaf to the stem
what do monocot grasses have instead of the petiole?
they have long leaf sheaths that form a stem like structure
what else do monocot grasses have different in their structure?
-their internodes are short and the SAM remains close to ground
-leaf blades expand well above SAM (so leaf blades can be eaten and SAM is safe)
-upon flowering in grasses, intercalary meristems in the internodes between forming leaves are activated, forming more cells, when cell elongates, a stem shoots up which turns into an inflorescence producing flower instead of leaves at the flanks of the SAM
-in monocots, intercalary meristems and internal lateral meristems are always active forming a proper stem from the beginning
is the meristem layered?
Yes
what type of division does the L1 and L2 layer cells undergo in the SAM, and what does each layer turn into?
anticlinal, L1 cells turn into leaf epidermis, L2 cells turn into leaf mesophyll
what do L3 cells do?
divide in various planes and give rise to the internal part of the stem and most internal part of the leaves
where are the three layers located and what do they form?
L1 is the outside then L2 in the middle (tunica) with L3 inside (corpus), L1 forms epidermis while L2 and L3 produce cells for leaves and stems
how does chimeric plants show that fate is determined by lineage?
L1 cells dont have chloroplasts while L2 albinos do, when L1 is pushed into L2 area, L1 take on the fate of L2 and gain chloroplasts
can L2 albinos also help differentiate between the layers of leaves?
yes
what causes leaf and flower formation?
polar auxin transport that establishes auxin maxima at the shoot apical meristem
what do auxin efflux inhibitors (like NPA) do?
inhibit auxin maxima formation resulting in leafless stems
paradigm shift steps:
- polar auxin transport mechanism generates auxin maxima causing leaf formation
- at same time, auxin transport drains the vicinity auxin, preventing leaf formation
- growth generates new areas that are not subject to drainage, allow formation of new maxima and new leaf primordia
- removal of an activator suppresses leaf formation close to existing leaf primordia
- results in spiral pattern in leaves
