lec 11- plant embryogenesis

Question 1

what is plant embryogenesis?

Answer 1

The process that occurs after fertilization to make a fully developed plant embryo

Question 2

what is the best studied plant species when it comes to embryogenesis?

Answer 2

arabidopsis

Question 3

what are the advantages and disadvantages of arabidopsis species when it comes to studying embryogenesis?

Answer 3

advantages- short life cycle, produces many seeds, self fertilizing, small genome and easy to introduce modified genes using agrobacterium
disadvantages- not a crop species so requires funding that is hard to get

Question 4

what are the 4 parts of the body plan established in a plant during embryogenesis?

Answer 4

1. plant axis
2. shoot-root polarity of plant axis
3. radial pattern of tissue meristems
4. apical meristems (root and shoot apical meristems)

Question 5

steps to embryogenesis:

Answer 5

1. primary axis is formed
2. polarity are established before first cell division
3. radial pattern of tissue meristems are established in the globular embryo (protoderm –> epidermis, ground meristem –> cortex, procambium –> vascular tissues)
4. apical growth zones, meristems are established in the heart shaped embryo, shoot apical meristem (SAM) and root apical meristem (RAM)
5. first lateral organs are formed (embryonic leaves, cotyledons)
6. pattern refinement and differentiation of cells
7. accumulation of nutrients
8. seed desiccation
9. seed rest

Question 6

how is cell fate determined?

Answer 6

by position, not by lineage

Question 7

what does the ablation experiment in the root tip prove?

Answer 7

when an undifferentiated cell is moved to a new position, it takes on the cell fate of the new position

Question 8

what is cell ablation?

Answer 8

the killing of individual cells with a laser

Question 9

what plant hormone is produced in young leaves and moves from shoot to root?

Answer 9

auxin (indole acetic acid (IAA))

Question 10

what is the movement of the hormone from shoot to root called?

Answer 10

polar auxin transport (PAT)

Question 11

what are the steps of PAT?

Answer 11

1. IAA enters the cell either passively or by secondary active transport
2. the cell wall is maintained at an acidic pH by the activity of the plasma membrane H+-ATPase
3. in the cytosol, which has a neutral pH, the anionic form (IAA-) predominates
4. the anions exit the cell via auxin anion efflux carriers that are concentrated at the basal ends of each cell in the longitudinal pathway

Question 12

what defects do mutants defective in body axis patterns have?

Answer 12

defects in auxin perception (gene activation) and auxin transport

Question 13

what do mp (monopteros) mutants lack and what occurs?

Answer 13

hypocotyl and root, mutant fails to establish auxin maximum in the base of the globular embryo, fails to activate expression of genes needed to form hypocotyl, fails to activate expression of genes defining RAM

Question 14

what are gnom mutants defective in and what occurs?

Answer 14

defective in shoot-root axis formation and polarity, form weak auxin maximum (high auxin concentration) which causes weak shoot-root axis in seedlings

Question 15

what are cotyledons?

Answer 15

embryonic leaves

Question 16

what is a hypocotyl?

Answer 16

embryonic stem

Question 17

where is the primary root grown from?

Answer 17

grown from RAM

Question 18

what do mutants defective in auxin signalling (ARFs) and transport (PINs) fail to form and what does it result in?

Answer 18

one or both cotyledons causing weak or absent auxin maximum

Question 19

what is auxin maximum required for?

Answer 19

-root-shoot axis
-apical portion of embryo
-basal portion of embryo
-root apical meristem (RAM)
- cotyledons (later leaves and flowers)
- formation of side roots (later)