Flowers, Fruits, and Seeds Flashcards
(48 cards)
how can floral meristems be distinguished from vegetative meristems?
by their large size
what is the transition to reproductive development marked by?
an increase in the frequency of cell divisions in the central zone of the shoot apical meristem
primary inflorescence meristem
- when reproduction is initiated, the vegetative meristem is transformed in the primary inflorescence meristem
- bears cauline leaves and flowers
secondary inflorescence meristems
- the axillary buds of the cauline leaves
inflorescence meristem vs flowers
- inflorescence meristem has indeterminate growth
- flowers have determinate growth
what are the four different types of organs in floral meristems?
- sepals
- petals
- stamen
- carpels in concentric rings called whorls
initiation of carpels
The initiation of the carpels consumes all of the meristematic cells in the apical dome
what are the three types of genes that regulate floral identity?
- meristem identity genes
- floral organ identity genes
- cadastral genes
- These are groups of genes from which individual genes continue to be discovered via “loss of
function mutants”
meristem identity genes
encode transcription factors that induce organ identity
- Must be active for the immature primordia at the shoot or inflorescence apical
meristem to become a floral meristem
floral organ identity genes
encode transcription factors that directly control floral
identity
- Homeotic genes that act as major developmental switches to activate the
genetic programing for a specific structure
cadastral genes
encode transcription factors that act as spatial regulators of the floral
organ identity genes by setting boundaries for their expression
- from French word cadastre, meaning ‘register of property’
ABC model
Floral organ identity genes determine floral organ patterning according to an elegant system, as
predicted by the ABC model proposed in 1991
how is each whorl determined by the three gene activities?
- Type A activity alone specifies sepals
- Type A activity with type B activity specifies petals
- Type B activity with type C activity specifies stamens
- Type C activity alone specifies carpels
type A
Type A activity controls organ identity in the first and second whorl
Type B
Type B activity controls organ identity in the second and third whorls
Type C
Type C activity controls organ identity in the third and fourth whorls
what is a loss in type A?
loss of type A activity results in the formation of carpels instead of sepals in the first whorl
and of stamens instead of petals in the second whorl
what is a loss in type B?
Loss of type B activity results in the formation of sepals instead of petals in the second whorl
and of carpels instead of stamens in the third whorl
what is a loss in type C?
Loss of type C activity results in the formation of petals instead of stamens in the third whorl,
and the formation of a new flower instead of carpels into the fourth whorl
what is a loss in type A, B, and C?
- Loss of A, B, and C activity results in the formation of a pseudoflower in which all floral organs are replaces with green leaf-like structures - Since AB and C genes were identified another class of floral homeotic genes, class E genes (D genes are required for ovule formation).
when do annual plants produce flowers?
- within a few weeks after germinating
when do perennial plants grow flowers?
- example: forest trees
- may grow 20+ yeas before producing flowers
- Thus size or age of a plant is an internal factor controlling the switch to reproductive
development
autonomous regulation
plants flower entirely according to internal cues
obligate response
plants that exhibit an absolute requirement for environmental cues in order to flower
