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Plant Structure, Growth, and Development
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Cellular differentiation to a large extent depends on positional information and is affected by homeotic genes.

Slide 65

Location and a Cells Developmental Fate

Location and a Cells Developmental Fate

Positional information underlies all the processes of development: growth, morphogenesis, and differentiation.

Cells are not dedicated early to forming specific tissues and organs.

The cells final position determines what kind of cell it will become.

Slide 66

Phase change in the shoot system

Phase change in the shoot system

Leaves produced

by adult phase

of apical meristem

Leaves produced

by juvenile phase

of apical meristem

Slide 67

Genetic Control of Flowering

Genetic Control of Flowering

Flower formation involves a phase change from vegetative growth to reproductive growth.

It is triggered by a combination of environmental cues and internal signals.

Transition from vegetative growth to flowering is associated with the switching on of floral meristem identity genes.

Slide 68

Plant biologists have identified several organ identity genes = plant homeotic genes. These genes regulate the development of floral pattern.

Plant biologists have identified several organ identity genes = plant homeotic genes. These genes regulate the development of floral pattern.

A mutation in a plant organ identity gene can cause abnormal floral development.

Slide 69

(a) Normal Arabidopsis flower

(a) Normal Arabidopsis flower

Ca

St

Pe

Se

Pe

Pe

Pe

Se

Se

(b) Abnormal Arabidopsis flower

Organ identity genes and pattern formation in flower development

Slide 70

Researchers have identified three classes of floral organ identity genes.

Researchers have identified three classes of floral organ identity genes.

The ABC model of flower formation identifies how floral organ identity genes direct the formation of the four types of floral organs.

An understanding of mutants of the organ identity genes depicts how this model accounts for floral phenotypes.

Slide 71

The ABC hypothesis for the functioning of organ identity genes in flower development

The ABC hypothesis for the functioning of organ identity genes in flower development

Sepals

Petals

Stamens

Carpels

(a) A schematic diagram of the ABC hypothesis

A

A + B

gene

activity

B

C

A gene

activity

B + C

gene

activity

C gene

activity

Carpel

Petal

Stamen

Sepal

Active

genes:

Whorls:

Stamen

Carpel

Petal

Sepal

Wild type

Mutant lacking A

Mutant lacking B

Mutant lacking C

A

A

A

A

B

B

B

B

C

C

C

C

B

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