Evolutionary Biology 6: Comparative Development 1

Question 1

Key stages in early plant development

Answer 1

Plants: Mostly postembryonic development from Meristems
-> give rise to all major organ systems, roots, stems, leaves, flowers

• morphogenesis cannot be achieved through cell migration (no cell migration)
• anticlinal divisions, cell plate perpendicular to surface, results in expansion of surface layer
• periclinal divisions, cell plate parallel to surface, results in formation of new layers/protrusions

Question 2

Important characteristics of Arabidopsis thaliana that make it a good plant model organism?

Answer 2

1) Easy cultivation in small place
2) Rapid development (6-8 weeks)
3) Self fertile, easy crossing
4) Simple diploid - recessive mutations visible
5) Low chromosome number (n=5, 2n=10)
6) Smallest genome in angiosperms
7) Low content of repetitive DNA (~15%)
8) Complete genome sequenced
9) Gene transfer easy - floral dipping
10) Easy mutagenesis and genetic mapping

Question 3

What are zebra fish and why are they a good model organism (animal)?

Answer 3

Small freshwater fish native to Northern india / Bangladesh

• mice too complex, microorganisms too simple

1) small, cheap, easy to maintain
2) External development
3) Large numbers of offspring
4) Rapid development
5) Short generation time
6) Genome sequenced
7) Optically transparent
8) Vertebrate

Question 4

Can cell migration occur in plants? Why?

Answer 4

No

‘Cells in boxes’, rigid cell wall

> Morphogenesis cannot be achieved by movement and folding of cell sheets

( no gastrulation etc.)

Question 5

Explain 2 types of cell division in plant morphogenesis

Answer 5

Anticlinal divisions

• cell plate perpendicular to surface
• results in expansion of cell layer

Periclinal divisions

• cell plate parallel to surface
• results in formation of new layers/protrusions

Question 6

Where does all postembryonic development originate from?

Answer 6

Meristems

- localised regions of cell division

Question 7

Difference between stem cell niches in plants and animals?

Answer 7

Plants
- Meristem acts as long term maintenance environment of stem cells
- Almost entire above-ground tissue of plant derived from Shoot-apical meristem (SAM)
(General development)

Animals
- Individual stem cell niches only supply a defined organ system in adult development
(Specific development)

Question 8

Describe meristem transformation during developmental stages of a plant

Answer 8

Root apical meristem fairly constant (RAM)

1) Vegetative meristem -> Leaf primordia
2) Influorescence meristem -> Flower primordia
3) Floral meristem -> Flower organ primordia

Question 9

How are plant cells often directly connected and what is the function?

Answer 9

Plasmodesmata

• cytoplasmic bridges and channel proteins
• Analogous to animal cell gap junctions

Mediates cell signalling

Transcription factors can move though plasmodesmata -> key feature of plant development

Question 10

What are symplasts and how were they discovered?

Answer 10

Multiple cells (within SAM etc.) that are cytoplasmically connected

• Defined by dye movement, dye moves freely within symplast