lec 12- plant vegetative growth and organogenesis

Question 1

what does the SAM do?

Answer 1

provides cells for leaf and stem development

Question 2

what appears at the flanks of the SAM and what does it do?

Answer 2

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

Question 3

does all cell division take place in the meristem?

Answer 3

no, it starts there then moves away

Question 4

in what pattern are leaves formed?

Answer 4

spiral pattern

Question 5

what is formed at the base of leaf primordia and what does it result in?

Answer 5

buds are formed at the base of leaf primordia and it will later give rise to branches producing leaves, flowers or both

Question 6

what is the position where a leaf and a bud both exist called?

Answer 6

a node

Question 7

what is the space between two nodes called?

Answer 7

internode

Question 8

how do buds act in perennial plants?

Answer 8

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

Question 9

what happens to buds when the shoot is cut off?

Answer 9

it results in the dormant buds being activated to initiate growth after loss of apex from grazing animals or freezing damage

Question 10

what does the apex do?

Answer 10

exerts apical dominance on buds, so when apex is destroyed, so is the dominance (mechanism involves auxin and polar auxin transport)

Question 11

how is the leaf primordia different in monocot grass?

Answer 11

it extends almost around the meristem

Question 12

what is a petiole?

Answer 12

the stalk that attaches the leaf to the stem

Question 13

what do monocot grasses have instead of the petiole?

Answer 13

they have long leaf sheaths that form a stem like structure

Question 14

what else do monocot grasses have different in their structure?

Answer 14

-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

Question 15

is the meristem layered?

Answer 15

Yes

Question 16

what type of division does the L1 and L2 layer cells undergo in the SAM, and what does each layer turn into?

Answer 16

anticlinal, L1 cells turn into leaf epidermis, L2 cells turn into leaf mesophyll

Question 17

what do L3 cells do?

Answer 17

divide in various planes and give rise to the internal part of the stem and most internal part of the leaves

Question 18

where are the three layers located and what do they form?

Answer 18

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

Question 19

how does chimeric plants show that fate is determined by lineage?

Answer 19

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

Question 20

can L2 albinos also help differentiate between the layers of leaves?

Answer 20

yes

Question 21

what causes leaf and flower formation?

Answer 21

polar auxin transport that establishes auxin maxima at the shoot apical meristem

Question 22

what do auxin efflux inhibitors (like NPA) do?

Answer 22

inhibit auxin maxima formation resulting in leafless stems

Question 23

paradigm shift steps:

Answer 23

1. polar auxin transport mechanism generates auxin maxima causing leaf formation
2. at same time, auxin transport drains the vicinity auxin, preventing leaf formation
3. growth generates new areas that are not subject to drainage, allow formation of new maxima and new leaf primordia
4. removal of an activator suppresses leaf formation close to existing leaf primordia
5. results in spiral pattern in leaves