Leaf Development And Evolution II: Polarity, Boundaries And Axes

Question 1

Phyllotactic patterns in angiosperms

Answer 1

1) alternate
2) opposite
3) whorled
4) spiral

Question 2

Spiral phyllotaxy in seed plants under SEM

Answer 2

• dome = S.A.
• protrusions = leaves
• pattern is shrinking

Question 3

Phytomers

Answer 3

1) leaf
2) axillary bud
3) internode
- iterative development
- specific arrangement

Question 4

Monocot phytomer

Answer 4

• leaf blade @ top
• different order

Question 5

S. kraussania

Answer 5

• dichotomous branching: specifically patterned major and minor branches
• ventral and dorsal leaf pairs w/ specific rhizophores

Question 6

S. kraussania shoot patterning

Answer 6

• how to generate 6/8 leaves?
• 2 cells on A surface act as stem cells
• meristem bifurcates
• 4x growth axes; DV, LR, 2x diagonal

Question 7

LR S. kraussania

Answer 7

How does meristem bifurcate?

Question 8

Fern shoot development

Answer 8

1) tetrahedral shoot initial
2) frond initial
3) pinna initial

Question 9

Older primordia specify leaf position

Answer 9

• anatomically distinguishable from S.A. flanks
• isolate I1 from apex by incision
• I3 develops closer to I2 than usual
• mechanical constraint? Biochemistry? Combinatorial?

Question 10

abphyll

Answer 10

2x P3 leaves

Question 11

NPA

Answer 11

• auxin analog
• binds to PATs and doesn’t detach

Question 12

Leaf initiation under NPA

Answer 12

• SAM becomes pin-shaped
• no leaf initiation from flanks

Question 13

pin1

Answer 13

• SAM becomes pin-shaped
• no leaf initiation from flanks
• auxin: rescue
• lanolin control

Question 14

Auxin:

Answer 14

• IAAH, IAA- (protonation states)
• cell wall/apoplast (5.5): IAAH
• diffuses through lipid bilayer to enter cytoplasm
• cytoplasm (7): IAA-
• stuck!

Question 15

PIN polarity creates

Answer 15

Auxin I1 maxima

Question 16

PIN polarity aligns w

Answer 16

• microtubule orientation
• stress, for support

Question 17

Ablating stressed cells with a laser

Answer 17

PIN moves away

Question 18

Leaf axes

Answer 18

1) proximo-distal
2) medio-lateral

Question 19

What determines axes in a leaf?

Answer 19

• when a leaf is developing, axes info comes from the shoot
• once a leaf is specified, it is all there

Question 20

Explant P1

Answer 20

• develops as a leaf

Question 21

Explant I1 and I2

Answer 21

Develop as shoots

Question 22

Remove all leaves

Answer 22

I1 develops as leaf

Question 23

Features of adaxial-abaxial leaf axis

Answer 23

• stomata (abaxial abundance)
• xylem (adaxial)
• phloem (abaxial)
• adaxial faces towards meristem
• abaxial faces away

Question 24

PHABULOSA and KANADI

Answer 24

2x important TFs for adaxial-abaxial specification

Question 25

recessive kanadi triple KO: kan1-2, 2-3, 3-1

Answer 25

- adaxialised

Question 26

recessive phabulosa triple KO: rev-9, phb-6, phv-5

Answer 26

- abaxialised - phloem encircles xylem -

Question 27

REVOLUTA, PHABULOSA, PHAVOLUTA

Answer 27

Class III HD-ZIP family

Question 28

dominant phabulosa

Answer 28

Adaxialised?

Question 29

PHB primordial expression by in situ hybridisation

Answer 29

- detect gene transcript thru colourimetric reaction - P2: ubiquitous - P6: adaxialised

Question 30

PHB regulation

Answer 30

- PHB mRNA: adaxial - miRNA165/166: abaxial - dominant phb mRNA: ubiquitous because miRNA can no longer bind

Question 31

KANADI

Answer 31

induce GARP TFs

Question 32

KANADI expression

Answer 32

- transverse and longitudinal sections of v young leaves - abaxialisation

Question 33

stm1

Answer 33

- no SAM - KNOX LOF

Question 34

cuc1, cuc2

Answer 34

- no SAM - fused cotyledons - NAC domain TFs

Question 35

STM and CUC2 expression

Answer 35

- STM repressed in cuc1, cuc2 - CUC2 similar expression to wt in stm

Question 36

STM and CUC feedback regulatory loop

Answer 36

- STM defines meristematic region - STM prevents CUC localisation - CUC defines borders of meristematic region - need both in a functioning meristem

Question 37

wox

Answer 37

- narrow leaf phenotype - lamina don’t expand @ base

Question 38

wox3

Answer 38

- thin blade - does not establish marginal region - no KNOX in SAM

Question 39

How is the margin defined?

Answer 39

Suppression of KNOX accumulation

Question 40

WOX

Answer 40

- WUS-like - expands leaf - defines middle of adaxial-abaxial axis

Question 41

WOX mechanism

Answer 41

- promotes auxin biosynthesis @ leaf margins ; growth agonist - increased expression at base; higher growth rate - decreased expression at tip; higher differ mention

Question 42

Structure

Answer 42

1. Phyllotaxis (S. kraussiana, PAT) 2. Leaf axes (adaxial-abaxial, medio-lateral)