Post on 06-Jan-2016
description
Fig. 24.3 T&Z3
Normal Floral Organ Identity
Organs (LDOs) are always produced by the Flower Shoot Apical Meristem (Flower SAM) in the following order, from lower/outer to upper/inner:
Sepals Petals
Stamens Carpels
Names of Flower Organs
Individual Collectively, DistinctOrgan or Connate
Carpel Gynoecium (G), Ovary, Pistal
Stamen Androecium (A)
Petal Corolla (Co, C) Perianth (P)Sepal Calyx (Ca, K)
If the organs of the two whorls/spirals of the Perianth are not differentiated from each other (that is, are both showy appear similar to each other), they may be called Tepals (T) or simply P
When you cannot easily count the organs
Number of Petals usually equals number of Sepals(Sepals are usually easy to see from below the flower)
Sepals and Petals are usually Alternate/Rotationally offset(If true for part of its circumference, true for entire flower)
wt ap2 pi ag1
Fig. 2 Meyerowitz 2002
S P St C C St St C S S C C [S P P S] n
Homeotic Mutants that Transform the Identity of Adjacent Whorls
Arabidopsis
B B B A C C A C A
Wild Type A is Null B is Null C is Null
The ABC Model based only on phenotypes of single mutants
Each Function acts in two adjacent whorls
Functions include Organ Identity and, forA and C, inhibition of each others function
The ABC Model of Floral Organ Identity
Y SUP
AP3+PI AP3+PI AP3+PI AP3+PI
LUG+SEU LUG+SEU LUG+SEU LUG+SEU
AP1 SEP3 AP1 SEP3 AP1 SEP3 AP1 SEP3
AG AG AG AG
AP2+BLR AP2+BLR AP2 AP2
LFY+WUS LFY+WUS
Sepals Petals Stamens Carpels
AG AG
ABCE Model: Regulators Y (inhibits AP3+PI), BLR (activates AP2), and LFY+WUS (activates AG) are differentially expressed
C A B C A B C A B C A B
Y SUP
AP3+PI AP3+PI AP3+PI AP3+PI
LUG+SEU LUG+SEU LUG+SEU LUG+SEU
AP1 SEP3 AP1 SEP3 AP1 SEP3 AP1 SEP3
AG AG AG AG
AP2+BLR AP2+BLR AP2 AP2
LFY+WUS LFY+WUS
Carpels Stamens Stamens Carpels
AG AG
Why ap2 lacks both A Functions: Expansion of AG into Whorls 1 and 2 inhibits the Specification Function of AP1
C A B C A B C A B C A B
Tepals in Monocots
First two whorls are identical, looking like two whorls of Petals, three organs in each whorl
Expression of ABC Genes indicates that both whorls are Petals: the whorl of Sepals has been transformed into a whorl
of Petals
Imperfect Flowers: Male and Female Flowers
Studies of the development of the whorls in Male and Female flowers indicate that both male and female whorls start
development, but either the male or female whorl aborts, resulting in a unisexual (imperfect and incomplete) flower
There is an extensive taxonomy based on the types of flowers (hemaphorditic vs unisexual) on individuals and in populations
monoecious (one house): male and female flowers on same plant
dioecious (two houses): male and female flowers on different plants
Floral Symmetry
Actinomorphic: Radially Symmetric (Actually Rotationally Symmetric)Probably the Ancestral State
Zygomorphic: Bilaterally SymmetricLocal Inhibition of Organ Development and/or Differential Growth of Organs,
resulting in one or two mirror planes
If any part of the flower is even weakly zygomorphic the entire flower is considered to be zygomorphic
Irregular: No obvious Symmetry
23.11 Stern9
All Ovaries start out Superior (4th Whorl)
The first three whorls may be elevatedon an outgrowth of the receptacle on whichthey are borne/inserted
This outgrowth is called an Hypanthium
It may be entirely adnate (fused) to with the ovary, adnate to the ovary only in the ovary’s basal region, or entirely distinct (free)
Hypogynous: Apparent insertion of thefirst 3 whorls below the gynoecium
Perigynous: Apparent insertion of the first 3 whorls at level of gynoecium
Epigynous: Apparent insertion of the first 3 whorls above the gynoecium
Hypanthium
Receptacle
MS Simpson (and many taxonomists?): An hypanthium is not an hypanthium if it is adnate (fused) to the ovary. It is an hypanthium only if it is distinct (free of the ovary).
Have not discovered how they think the corolla and androecium crawled up the sides of the ovary.
Agree Agree Duh?
A More Narrow Definition of an Hypanthium
RAB Glossary: A Broad Definition of an Hypanthium
Hypanthium: May be adnate to ovary (epigyny) or free from ovary (perigyny).
Superior ovary: Hypanthium adnate to ovary for less than ¼ the length of the ovary.
Inferior ovary: Hypanthium adnate to the ovary for ¾ or more of its length.
Sensible, and the Keys and Descriptions of Rosaceae use these definitions. But at least one lead to some taxa of Rosaceae does not.
Partial to complete Connation/Fusion of Carpels
Minimum Number of carpels can be inferred from whichever is the larger number: number of locules, number of lobes, number of
(paired) rows of ovules, number of styles, or number of stigmas.
Warning: In some taxa, a carpel develops a false septum, resulting in two pseudo-locules
Fuse Carpels before Closing Them
Close Carpels before Fusing Them
septate
axial parietal
marginal axial parietal free central apical
marginal axial parietal free central
basal
Walters and Keil
Ovaries from Fused Carpels
nonseptate
3 Carpellate3 Loculate3 Septa
3 Carpellate1 Loculate0 Septa