Slide 1:Development of Flower Dr. S.K. Chile


Slide 2:Floral organs develop in the order Sepal-Petal-Stamen- Carpel i.e. outer whorl to inner. The development of Floral organ is determined Genetically. Mutants whose organs develop in the wrong places are called Homeotic Mutants. Double Flowers are good example.


Slide 3:Developmental stages of Floral organs Plant cells do not migrate during development as the animal cells do. Differentiating cells and tissues of Floral organs and Vegetative organs differ a lot in Physiology and Genetics.


Slide 4:Change of vegetative phase takes place into reproductive phase In the preparatory stage. The shoot apex differentiated into the Inflorescence shoot apex. Then the differentiation of Floral bud take place. Orientation of Apical cells changes drastically in these processes.


Slide 5:Activation of these cells is followed by rapid increase in cell numbers by quick cell division. The apex changes from flat to dorm like form. These preparative stage are accompanied by rapid elongation of stalk of Flower (Bolting). Several cauline leaves smaller than true leaves also develop from leaf primordia after bolting.


Slide 6:Flowers develop from floral buds. Floral buds develop from inflorescence shoot apices. Sepal, Petal, Stamen, and finally Carpel. The organ primordia develop in orders from outer to inner. Once the carpel primordia form the floral apex becomes nonmeristematic . However, inflorescence shoot apices retain meristamatic nature and continue to differentiate floral buds.


Slide 7:Vegetative apical meristem Inflorescence apical meristem Conversion of vegetative meristem to inflorescence meristem in Arabidopsis thaliana


Slide 10:Flower Mutant and The Genetic Model


Slide 11:In Arabidopsis thaliana and Antirrhinum majus working models of Flower development are derived from the genetic analysis of homeotic mutation. Homeotic means a normally developed organ occupied a position of different organ/s.


Slide 12:Genetic analysis in these species have described recessive mutations that cause homeotic conversion of floral organs. They either alter the identity of the meristem or affect the identity of floral organs. Many of these mutants have been observed and utilized by Breeders and Horticulturised.


Slide 13:The homeotic mutants of three categories are picked up ; “a type” Carpels-Stamens-Stamens-Carpels “b type” Sepals-Sepals-Carpels-Carpels “c type” Sepals-Petals-Petals-Sepals. The ABC model was elucidated to explain the mechanism of floral morphogenesis.


Slide 14:About "ABC" Model


Slide 15:This model explains how A,B,and C class genes make floral organs in the proper places during flower development. There are three hypotheses;


Slide 16:First Hypothesis


Slide 17:Each of these three class of genes is required to function in adjacent whorls at early flower developmental stages to specify organ type. Class A gene acts at the first and second whorls where sepals and petals develop. Class B gene acts at the second and third whorl. Class C gene acts at the third and forth whorls where stamens and carpels develop.


Slide 18:Second Hypothesis


Slide 19:The second hypothesis is that primordial cells in the flower are specified to develop which types of floral organs by the combinations of A, B, and C gene functions. Sepal develop in first whorl by the function of A class genes alone and petals develop in the second whorl by the function of A class and B class genes. Stamens in the third whorl by the function of B genes alone and carpels develop by the combination of B and C genes.


Slide 20:Third Hypothesis.


Slide 21:The third hypothesis is that A class genes and C class genes repress the function of each other. In the ‘a type mutant’ C function exist in the first and the second whorls since A function is lost and as a result flowers with Carpel-Stamens-Stamens-Carpels are formed The same is occurred in ‘c type mutant’ to make flowers of Sepals-Petals-Petals-Sepals.


Slide 22:To examine the propriety of the "ABC" model


Slide 23:We can easily predict the what kind of flower phenotype will form on plant that lose two of the A, B, and C function at the same time. ‘ab double mutant’ will lose function of A and B genes and has only C function develop a flower with carpels only. ‘bc double mutant’ only has A genes functional will develop flowers of sepals. A triple mutant that lack all three genes would develop a flower with leaf like appendages only.


Slide 24:Se. Pe St Ca A A+B B+C C Wild type


Slide 25:Ca St St Ca C B+C B+C C ‘a’ mutant


Slide 26:Se Se Ca Ca A A C C ‘b’ mutant


Slide 27:Se. Pe Pe Se A A+B A+B A ‘c’ mutant Se. Pe Pe


Slide 28:B A C B C WILD TYPE ABC Apetala 2 aBC


Slide 29:A B A C Agamous ABc Apetala 3 AbC


Slide 30:B A C B C WILD TYPE ABC Apetala 2 aBC


Slide 31:C B A C B A 35 S- AGAMOUS 35 S- APETALA3 WILD TYPE 35 S- AGAMOUS WILD TYPE 35 S- APETALA3


Slide 32:Thanks Dr. S.K. Chile