Floral diagrams
Floral Diagrams
The first symbol in a floral formula describes the symmetry of a flower.Radial symmetry Divisible into equal halves by two or more planes of symmetry.Bilateral symmetry – Divisible into equal halves by only one plane of symmetry. ($) Asymmetrical – Flower lacking a plane of symmetry, neither radial or bilateral.
Floral Formula Symbol 2
The second major symbol in the floral formula is the number of sepals, with “K” representing “calyx”. Thus, K5 would mean a calyx of five sepals.
Floral Formula Symbol 3
The third symbol is the number of petals, with “C” representing “corolla”. Thus, C5 means a corolla of 5 petals.
Floral Formula Symbol 4
The fourth symbol in the floral formula is the number of stamens (androecial items), with “A” representing “androecium”. A∞ (the symbol for infinity) indicates numerous stamens and is used when stamens number more than twelve in a flower. A10 would indicate 10 stamens.
Floral Formula Symbol 5
The fifth symbol in a floral formula indicates the number of carpels, with “G” representing “gynoecium”. Thus, G10 would describe a gynoecium of ten carpels.
Basic Floral Formula
*, K5, C5, A∞, G10
•Radial symmetry (*),
•5 sepals in the calyx (K5)
•5 petals in the corolla (C5)
•Numerous (12 or more) stamens (A∞)
•10 carpels (G10)
Floral FormulasAt the end of the floral formula, the fruit type is often listed.ample:•*, K5, C5, A∞, G10, capsule
Three Types of Genes Regulate Floral
Development
Mutations have identified three classes of genes that regulate
floral development: floral organ identity genes, cadastral
genes, and meristem identity genes.
1. Floral organ identity genes directly control floral
identity. The proteins encoded by these genes are
transcription factors that likely control the expression
of other genes whose products are involved in the formation
and/or function of floral organs.
2. Cadastral genes act as spatial regulators of the floral
organ identity genes by setting boundaries for their
expression. (The word cadastre refers to a map or survey
showing property boundaries for taxation purposes.)
3. Meristem identity genes are necessary for the initial
induction of the organ identity genes. These genes
are the positive regulators of floral organ identity.
Meristem Identity Genes Regulate Meristem
Function
Meristem identity genes must be active for the primordia
formed at the flanks of the apical meristem to become floral
meristems. (Recall that an apical meristem that is forming
floral meristems on its flanks is known as an inflorescence
meristem.) For example, mutants of Antirrhinum
(snapdragon) that have a defect in the meristem identity
gene FLORICAULA develop an inflorescence that does not
produce flowers. Instead of causing floral meristems to
form in the axils of the bracts, the mutant floricaula gene
results in the development of additional inflorescence
meristems at the bract axils. The wild-type floricaula (FLO)
gene controls the determination step in which floral meristem
identity is established.
Once activated, AGL20 triggers the expression of LFY,
and LFY turns on the expression of AP1 (Simon et al. 1996).
In Arabidopsis, LFY and AP1 are involved in a positive feedback
loop; that is, AP1 expression also stimulates the
expression of LFY.
Homeotic Mutations Led to the Identification of
Floral Organ Identity Genes
The genes that determine floral organ identity were discovered
1 Also known as SUPPRESSOR OF OVEREXPRESSION OF
CONSTANS 1 (SOC1).
. Such genes act as major developmental switches that activate the entire
genetic program for a particular structure. The expression
of homeotic genes thus gives organs their identity.
As we have seen already in this chapter, dicot flowers
consist of successive whorls of organs that form as a result
of the activity of floral meristems: sepals, petals, stamens,
and carpels. These organs are produced when and where
they are because of the orderly, patterned expression and
interactions of a small group of homeotic genes that specify
floral organ identity.The floral organ identity genes were identified through
homeotic mutations that altered floral organ identity so that
some of the floral organs appeared in the wrong place. For
example, Arabidopsis plants with mutations in the APETALA2
(AP2) gene produce flowers with carpels where sepals
should be, and stamens where petals normally appear.
The homeotic genes that have been cloned so far encode
transcription factors—proteins that control the expression
of other genes. Most plant homeotic genes belong to a class
of related sequences known as MADS box genes, whereas
animal homeotic genes contain sequences called homeoboxes
Many of the genes that determine floral organ identity
are MADS box genes, including the DEFICIENS gene of
snapdragon and the AGAMOUS, PISTILLATA1, and
APETALA3 genes of Arabidopsis. The MADS box genes
share a characteristic, conserved nucleotide sequence
known as a MADS box, which encodes a protein structure
known as the MADS domain. The MADS domain enables
these transcription factors to bind to DNA that has a specific
nucleotide sequence.
Not all genes containing the MADS box domain are
homeotic genes. For example, AGL20 is a MADS box gene,
but it functions as a meristem identity gene.
Three Types of Homeotic Genes Control Floral
Organ Identity
Five different genes are known to specify floral organ
identity in Arabidopsis: APETALA1 (AP1), APETALA2
(AP2), APETALA3 (AP3), PISTILLATA (PI), and AGAMOUS
(AG) (Bowman et al. 1989; Weigel and
Meyerowitz 1994). The organ identity genes initially were
identified through mutations that dramatically alter the
structure'
Floral diagrams are stylized cross sections of flowers that represent the floral whorls as viewed from above. Rather like floral formulas, floral diagrams are used to show symmetry, numbers of parts, the relationships of the parts to one another, and degree of connation and/or href="https://www.blogger.com/goog_1862822130">adnation.www.chempapy.blogspot.com Such diagrams cannot easily show ovary position
Floral Diagram Symbols 1
.Floral Formula Symbol 1
Floral Diagram Symbols II
Sample floral diagrams
Sample Floral Diagrams Described
The first symbol in a floral formula describes the symmetry of a flower.Radial symmetry Divisible into equal halves by two or more planes of symmetry.Bilateral symmetry – Divisible into equal halves by only one plane of symmetry. ($) Asymmetrical – Flower lacking a plane of symmetry, neither radial or bilateral.
Floral Formula Symbol 2
The second major symbol in the floral formula is the number of sepals, with “K” representing “calyx”. Thus, K5 would mean a calyx of five sepals.
Floral Formula Symbol 3
The third symbol is the number of petals, with “C” representing “corolla”. Thus, C5 means a corolla of 5 petals.
Floral Formula Symbol 4
The fourth symbol in the floral formula is the number of stamens (androecial items), with “A” representing “androecium”. A∞ (the symbol for infinity) indicates numerous stamens and is used when stamens number more than twelve in a flower. A10 would indicate 10 stamens.
Floral Formula Symbol 5
The fifth symbol in a floral formula indicates the number of carpels, with “G” representing “gynoecium”. Thus, G10 would describe a gynoecium of ten carpels.
Basic Floral Formula
*, K5, C5, A∞, G10
•Radial symmetry (*),
•5 sepals in the calyx (K5)
•5 petals in the corolla (C5)
•Numerous (12 or more) stamens (A∞)
•10 carpels (G10)
Floral FormulasAt the end of the floral formula, the fruit type is often listed.ample:•*, K5, C5, A∞, G10, capsule
Three Types of Genes Regulate Floral
Development
Mutations have identified three classes of genes that regulate
floral development: floral organ identity genes, cadastral
genes, and meristem identity genes.
1. Floral organ identity genes directly control floral
identity. The proteins encoded by these genes are
transcription factors that likely control the expression
of other genes whose products are involved in the formation
and/or function of floral organs.
2. Cadastral genes act as spatial regulators of the floral
organ identity genes by setting boundaries for their
expression. (The word cadastre refers to a map or survey
showing property boundaries for taxation purposes.)
3. Meristem identity genes are necessary for the initial
induction of the organ identity genes. These genes
are the positive regulators of floral organ identity.
Meristem Identity Genes Regulate Meristem
Function
Meristem identity genes must be active for the primordia
formed at the flanks of the apical meristem to become floral
meristems. (Recall that an apical meristem that is forming
floral meristems on its flanks is known as an inflorescence
meristem.) For example, mutants of Antirrhinum
(snapdragon) that have a defect in the meristem identity
gene FLORICAULA develop an inflorescence that does not
produce flowers. Instead of causing floral meristems to
form in the axils of the bracts, the mutant floricaula gene
results in the development of additional inflorescence
meristems at the bract axils. The wild-type floricaula (FLO)
gene controls the determination step in which floral meristem
identity is established.
Once activated, AGL20 triggers the expression of LFY,
and LFY turns on the expression of AP1 (Simon et al. 1996).
In Arabidopsis, LFY and AP1 are involved in a positive feedback
loop; that is, AP1 expression also stimulates the
expression of LFY.
Homeotic Mutations Led to the Identification of
Floral Organ Identity Genes
The genes that determine floral organ identity were discovered
1 Also known as SUPPRESSOR OF OVEREXPRESSION OF
CONSTANS 1 (SOC1).
. Such genes act as major developmental switches that activate the entire
genetic program for a particular structure. The expression
of homeotic genes thus gives organs their identity.
As we have seen already in this chapter, dicot flowers
consist of successive whorls of organs that form as a result
of the activity of floral meristems: sepals, petals, stamens,
and carpels. These organs are produced when and where
they are because of the orderly, patterned expression and
interactions of a small group of homeotic genes that specify
floral organ identity.The floral organ identity genes were identified through
homeotic mutations that altered floral organ identity so that
some of the floral organs appeared in the wrong place. For
example, Arabidopsis plants with mutations in the APETALA2
(AP2) gene produce flowers with carpels where sepals
should be, and stamens where petals normally appear.
The homeotic genes that have been cloned so far encode
transcription factors—proteins that control the expression
of other genes. Most plant homeotic genes belong to a class
of related sequences known as MADS box genes, whereas
animal homeotic genes contain sequences called homeoboxes
Many of the genes that determine floral organ identity
are MADS box genes, including the DEFICIENS gene of
snapdragon and the AGAMOUS, PISTILLATA1, and
APETALA3 genes of Arabidopsis. The MADS box genes
share a characteristic, conserved nucleotide sequence
known as a MADS box, which encodes a protein structure
known as the MADS domain. The MADS domain enables
these transcription factors to bind to DNA that has a specific
nucleotide sequence.
Not all genes containing the MADS box domain are
homeotic genes. For example, AGL20 is a MADS box gene,
but it functions as a meristem identity gene.
Three Types of Homeotic Genes Control Floral
Organ Identity
Five different genes are known to specify floral organ
identity in Arabidopsis: APETALA1 (AP1), APETALA2
(AP2), APETALA3 (AP3), PISTILLATA (PI), and AGAMOUS
(AG) (Bowman et al. 1989; Weigel and
Meyerowitz 1994). The organ identity genes initially were
identified through mutations that dramatically alter the
structure'
References
- Bakker,Robert.(1978).dinosaur feeding behaviour and orgin of flowering plant.Macimillan london
- Stevens.P.F.(2011).Angiosperm phylogeny Website (at missouri botanical Garden)
- Dutta, A.C. 1999. Botany for Degree Students. Oxford University Press, Calcuta.
- Pandey, SN; Trivedi, PS and Misra, SP. 1996. A text book of botany. Vol I. Vikas Publishing House PVT ltd.
- Pandey, SN; Trivedi, PS and Misra, SP. 1998. A text book of botany. 11th revised Edition Vol II. Vikas Publishing House PVT ltd.
- Jensen, WA & Salisbury, FB. Botany: An ecological Approach. Wadsworth Publishing Company inc., California.
- Gorge B. Johnson 2000. The living world. Second edition
- Murray W. Nabors 2004. Introduction to Botany. Pearson Benjamin Cummings. University of Mississippi
- Berg, LR. 1997. Introductory Botany: Plants, People and the Environment. St Pettersburg Junior college.
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