lec 31- roots part 1

Question 1

what does the root apical meristem produces?

Answer 1

cells that make up the root

Question 2

what do the cells produced from the root meristem differentiate into?

Answer 2

vascular tissues, root hairs, and lateral roots

Question 3

do the root hairs and lateral roots arise from cells displaced from the apical meristem?

Answer 3

yes

Question 4

what are the parts of the root?

Answer 4

-root apical meristem is located at the tip of the root
-behind the meristem is the zone of cell divisions, cells expand mainly in longitudinal directions
-behind the zone of elongation is the cells that differentiate into root hairs
-lateral roots are the farthest away from the root meristem

Question 5

what does cell divisions in the meristem produce?

Answer 5

cells that make up the root and the root cap

Question 6

what do the root cap cells do?

Answer 6

root cap cells have sensory roles, they detect environmental cues and redirect root growth accordingly

Question 7

what is in the center of the root?

Answer 7

-the future vascular tissue, the protoxylem and proto phloem
-they are surrounded by other tissue layers

Question 8

each initial cell in the meristem undergoes:

Answer 8

a stereotypical pattern of cell divisions that give rise to the columns or files of cells in the root

Question 9

how does the direction of cell expansion and division determine root morphology?

Answer 9

cell division: can either be perpendicular and add more cells to each file, or parallel to the long axis and add more cell files to the root
cell expansion: occurs mainly parallel with the long axis of the root

cell expansion drives most of the growth that occurs in the root

Question 10

how does auxin move through the roots?

Answer 10

-auxin flow is directed down through the central cylinder, from site of synthesis to the quiescent center and root cap
-auxin is also synthesized at the tip of the root, causing high levels of auxin to accumulate in and around the quiescent center
-auxin moves laterally, when it reaches the outer cell layers it moves back towards the shoot through the outer cell layers
-the end result is high levels of auxin at the tip of the root and a gradient of auxin in the outer cell layers where it goes to the shoot and is then sent back to the root
-auxin gradients can affect cell fate by controlling distribution of gene products like transcription factors

Question 11

where do root hairs emerge from?

Answer 11

epidermal cells

Question 12

how is non-hair and hair cell fate specified?

Answer 12

by cell to cell communications between epidermal and cortical cells

Question 13

explain the model for root hair specification:

Answer 13

-the wathway is controlled by WEREWOLF (WER) and CAPRICE (CPC)
-werewolf is more abundant in non hair cells and CAPRICE is more abundant in hair cells
-they both interact with TTG and bHLH transcription factors
-in non-hair cell types, werewolf forms a complex that activates transcription of GL2 which inhibits transcription of genes that promote root hair developemnt
-werewolf also activates caprice in non hair cells, they are active and move to adjacent cells (hair cells)
-hair cells accumulate more caprice then werewolf, complexes that contain caprice do not activate GL2 which allows the transcriptional genes to promote root hair formation

Question 14

what are the 5 evidences that support WER and CPC pathway?

Answer 14

1. GL2 is expressed only in non hair cells, GL2 is in the right place and time to have a role in specifying hair cells
2. expression of GL2 is reduced in wer mutants, meaning wer must promote GL2 expression
3. in wer or GL2 mutants, extra root hairs form as no inhibition occurs
4. CPC mutants produce fewer roots hairs than wild type, meaning CPC must promote root hair formation
5. in CPC and GL2 mutants, root hairs form on both hair and non hair cells, meaning CPC must inhibit GL2, which inhibits root hair formation