Final Exam - Plant Development

Question 1

Arabidopsis thaliana

Answer 1

• a model for plant development
• common name: canola
• picked due to its genetics, small, easily grown in lab, short generation time (faster than mice)
• genome has been sequenced
• development relatively simple

Question 2

Root apical meristem

Answer 2

• Plants generate new tissue through stem cell populations called root and shoot apical meristems (SAM)
• Undifferentiated stem cell population
• Formed by the heart stage of development

Question 3

Shoot apical meristem (SAM)

Answer 3

• Plants generate new tissue through stem cell populations called root and shoot apical meristems (SAM)
• Undifferentiated stem cell population
• Formed by the heart stage of development

Question 4

Cambium

Answer 4

-a ring of meristem in the stems of plants that gives rise to new stem tissue, which increases the diameter of the stem

Question 5

Periclinal

Answer 5

-describes cell divisions in a plane parallel to the surface of the tissue

Question 6

Heart stage

Answer 6

• a stage in embryogenesis in dicotyledonous plants in which the cotelydons and embryonic root are starting to form, giving a heart-shaped embryo
• meristem regions have formed by this stage
• During maturation, following the heart stage, cells expand to allow for growth rather than divide
• Start to express genes that allow for accumulation of energy reserves such as starch
• root and shoot apical meristems are formed by this stage

Question 7

Torpedo stage

Answer 7

• Maturation of the embryo at the torpedo stage onward is largely due to cell expansion
• Plant cell wall breakdown and rebuilding

Question 8

Cambium

Answer 8

• stem radial growth
• distinct secondary stem cell population
• ring of stem cells
• a ring of meristem in the stems of plants that gives rise to new stem tissue, which increases the diameter of the stem
• is a secondary meristemic tissue and allows for radial growth (Most plant structures are generated by meristems with the deception of stem growth)

Question 9

FASS gene

Answer 9

• Mutation results in a disordered pattern of cell division in the embryo
• FASS mutants fail to produce microtubules pre-prophase which would predict the plane of cell division
• But in Fass mutants all cell types were still present in the embryo
• Suggests that precise cell division is not required for pattern formation in the embryo

Question 10

Cell division patterns

Answer 10

• precise cell division is not required for pattern formation
• Cells can divide in two directions
  a. Parallel to the radial axis (periclinal)
  b. Right angles (anticlinal)

Question 11

Periclinal

Answer 11

• parallel to the radial axis

- describes cell divisions in a plane parallel to the surface of the tissue

Question 12

Anticlinal

Answer 12

• right angles

- describes cell divisions in planes at right angles to the outer surface of a tissue

Question 13

Auxin

Answer 13

• Is a major plant hormone
• It’s trafficking within the embryo controls polarity and cell fate
• Accumulates in the embryo proper early in development
• The growth of lateral buds immediately below the apical shoot meristem are suppressed by auxin = apical dominance
• Auxin diffuses to inhibit the development of the lateral shoot meristem
• small organic molecule that is an important plant hormone in almost all aspects of plant development
• acts by regulating the expression of auxin-responsive genes by stimulating the degradation of Aux/IAA proteins and thus enabling gene expression

Question 14

Establishment of Cell polarity

Answer 14

• PIN1=auxin
• 16-cell embryo: PIN1 uniformly distributed relative to the longitudinal axis
• mid-globular stage embryo: PIN1 accumulates at basal end of specific cells
• heart-shaped embryo: PIN1 accumulates at the apex of epidermal cells in the cotyledons; PIN1 accumulates at the base of procambial cells

Question 15

PIN1

Answer 15

• A specific auxin efflux carrier (asymmetrical carrying auxin from one cell to the other)
• Loss of PIN 1 activity results in a pin-like bolt and the complete loss of lateral organs (leaves)
• Additional efflux carriers have since been found: PIN2, 3, 4 and 7 are required for regulated growth and development

Question 16

Hormone traffic

Answer 16

• genetic defects in hormone traffic or perception produce plants with altered body parts
• hormone traffic regulated by GNOM (gn)

Question 17

GNOM

Answer 17

• Encodes and ADP ribosylation GTP exchange factor (ARF GFFs)
• Regulates the hormone traffic of membrane vessicles
• Mutants in GNOM show a loss of apical basal polarity
• GNOM is required for PIN1 localization

Question 18

Embryonic shoot meristem

Answer 18

-becomes the shoot apical meristem, mainted after germination, gives rise to all stems, leaves and flowers

Question 19

Root meristem

Answer 19

gives rise to root structures

Question 20

Internode

Answer 20

• that portion of a plant stem between two nodes
• sites at which a leaf or leaves form
• Plants develop in models and consist of an internode (the cells produced by the meristem between leaf initiations)

Question 21

Meristems

Answer 21

• Meristems are undifferentiated stem cell populations that generate the stem, leaf and flower as well as root structure of the post-embryonic plant
• the meristem regions have formed by the heart stage of embryo development
• Most plant structures are generated by meristems with the deception of stem growth (cambium does this)

Question 22

Axillary bud

Answer 22

• forms the lateral shoot meristem

- a bud that grows from the axil of a leaf and may develop into a branch or flower cluster.

Question 23

Lateral shoot meristem

Answer 23

• meristem that arises from the apical shoot meristem and gives rise to lateral shoots
• Cell-cell interactions are a major determinant of cell fate, if the shoot apex is removed, the lateral shoot meristem becomes active to create a new shoot

Question 24

Apical dominance

Answer 24

• The growth of lateral buds immediately below the apical shoot meristem are suppressed
• This suppression requires the hormone auxin that is produced by the shoot apex
• Auxin diffuses to inhibit the development of the lateral shoot meristem
• the phenomenon in plants that buds in the axils of nodes behind the tip of a plant shoot will not form side stems when the tip is intact
• it is due to the production of the hormone auxin by the shoot tip which suppresses outgrowth of axillary buds

Question 25

Central zone

Answer 25

- zone of the shoot apical meristem - Central zone is a slowly dividing stem cell population that are self-renewing (12-20 cells that persist through the entire life of the plant)

Question 26

Rib zone

Answer 26

- zone of the shoot apical meristem - Rib zone gives rise to central tissues, some of these yellow cells are an organizing centre, underly the central zone and maintain a microenvironment that maintains the stem cell identity

Question 27

Peripheral zone

Answer 27

- zone of the shoot apical meristem - Peripheral zone are proliferating cells that are determined to differentiate into shoots, stems, or leaves (as well as flower organ with the right signal or cue)

Question 28

Organ initiation

Answer 28

-SAM maintenance is dependent on the coordination of two antagonistic processes: organ initiation and self-renewal of stem cell population

Question 29

Self-renewal of stem cell population

Answer 29

-SAM maintenance is dependent on the coordination of two antagonistic processes: organ initiation and self-renewal of stem cell population

Question 30

Shoot meristemless (STM)

Answer 30

- In STM mutants, the meristem is absent by the end of embryogenesis - Maintains stem cells population and prevents premature determination

Question 31

Wuschel (WUS)

Answer 31

- In wus mutants, the stem cells fail to establish in the embryo - Maintain the pool of stem cells

Question 32

Clavata (CLV) genes

Answer 32

- These inhibit the size of the meristem - Clavata mutants have enlarged meristems at the expense of organ formation - Required to promote organ formation/differentiation - CLV1: Receptor kinase protein - CLV2: Receptor protein - CLV3: Secreted peptide ligand - Interaction between WUS (Wuschel) and CLV genes establishes a negative feedback loop maintaining stem cells and the underlying organizing centre

Question 33

Over-expression of STM (shoot meristemless)

Answer 33

- increases meristematic activity in Arabidopsis - Increasing STM (shoot meristemless)= increase in size of SAM, increased production of flowers, therefore production of fruits and seeds

Question 34

Shoot apical meristem (SAM)

Answer 34

-Most apical node -Is central to plant development -Contains a few hundred undifferentiated cells that are capable of cell division -Most cell division in the plant occurs in this meristem or as cells leave the meristem -Cell growth outside the meristem is associated with cell enlargement and growth -The meristem is an organizing centre and is maintained by self-renewing stem cells 3 main zones: central zone, rib zone and peripheral zone -Central zone is a slowly dividing stem cell population that are self-renewing (12-20 cells that persist through the entire life of the plant) -Rib zone gives rise to central tissues, some of these yellow cells are an organizing centre, underly the central zone and maintain a microenvironment that maintains the stem cell identity -Peripheral zone are proliferating cells that are determined to differentiate into shoots, stems, or leaves (as well as flower organ with the right signal or cue) -SAM maintenance is dependent on the coordination of two antagonistic processes: organ initiation and self-renewal of stem cell population