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Oldenburgia grandis, Botany RUOldenburgia grandis, Botany RU
a quick lesson in embryogenesis
FERTILIZATION MEIOSIS
seed
sporophyte
megaspores microspores
megagametophyte
microgametophyte
sperm egg
2N
N
The triangle of differentiation
Where do we start?
embryo
initiation of SAM, RAM (polarity?)
cell division, formation of axes
expansion growth
axis & coleoptiles form
gametogenesisgametogenesis seed
[differentiation, maturation]
[differentiation]
- - - - - - - - - - - - - - - - -
totipotency
Seed to plant
graviperception
phototropism
Seed
monocotyledon
dicotyledon
expansion, cell elongation
activation of SAM & RAM
(genes, hormones)cell division
procambium
Embryo proper ofCapsella
Post-Germination: Rapid growth
Growth in this bean plant is due in part to cell division, but, to a larger extent, DUE to longitudinal elongation of cells – all controlled by genes.
2h2h
2h20min 2h20min
2h 40 min2h 40 min
Apical organizationApical organization
Organization in plants is dependent upon programmed, controlled cell division, followed by growth, further cell division and ultimately, differentiation.
Programmed and controlled cell division occurs within the domain of the vegetative apex.
the apexthe apex
All the tissues within the apex differentiate rapidly. By about 150 µm, cells within the apical region are starting to differentiate. In the pine apex (above), you can see developing leaflets.
The Coleus apex to the right, shows rapidly developing leaflets beneath the apical dome.
cell divisioncell division
Cell division is responsible for the formation of all cells and tissues in the primary plant body as well as in the secondary plant body.
Cell source
apical and sub apical primary divisionapical and sub apical primary division
apical meristemapical meristem
provascular tissue
provascular tissue
epidermisepidermis pithpith cortexcortexprimary phloem
primary phloem
primary xylem
primary xylem
ground meristem
ground meristemprotodermprotoderm
undifferentiated
generative source
Secondary celllineage
fascicular cambium
fascicular cambium
primary lineage
the ground tissuethe ground tissue
cortexcortex
parenchyma collenchyma sclerenchyma
filling tissue mechanical, supportive
STOP
the secondary lineagethe secondary lineage
fascicular cambium
fascicular cambium
secondary xylem
secondary xylem
vascular cambium
vascular cambium
secondary phloem
secondary phloem
cork cambium
cork cambium
ASSOCIATED WITH THE VASCULAR BUNDLE ONLY
COMPLETE RING OF CAMBIUM
the secondary protective lineagethe secondary protective lineage
sub-epidermal
layers
sub-epidermal
layers
phellemphellem
phellogenphellogen
phellodermphelloderm
thecork cambium(bark layer)
the periderm a protective barrier
Development of the peridermDevelopment of the periderm
sub-epidermal
layers
sub-epidermal
layers
phellemphellem
phellogenphellogen
phelloderm
phelloderm
The first periderm is formed just beneath the epidermis
phellem
phellogenphelloderm
a waterproof, fireproofinsulator
primary organizationprimary organization
groundmeristem
groundmeristem
PITHPITH CORTEXCORTEX
interfascicular
cambium
interfascicular
cambium
phellem/cork cambium
phellem/cork cambium
Click for Filling spaces notes
fascicular cambium
fascicular cambium
secondary xylem
secondary xylem
vascular cambium
vascular cambium
secondary phloem
secondary phloem
cork cambium
cork cambium
primary mechanical tissuesprimary mechanical tissues
groundmeristem
groundmeristem
PITHPITHCORTEXCORTEX
collenchymacollenchyma
sclerenchymasclerenchyma sclerenchymasclerenchyma
collenchyma(rare)
collenchyma(rare)
groundmeristem
groundmeristem
PITHPITH CORTEX
CORTEX
interfascicularcambium
interfascicularcambium
phellem/cork cambium
phellem/cork cambium
development of the vascular cambiumdevelopment of the vascular cambium
fascicular cambium
fascicular cambium
fusiform initials
fusiform initials
ray initials
ray initials
axialxylem
axialxylem
axial phloem
axial phloem
fascicular cambium
fascicular cambium
secondary xylem
secondary xylem
vascular cambium
vascular cambium
secondary phloem
secondary phloem
cork cambium
cork cambium
xylemrays
xylemrays
phloemrays
phloemrays
to cambial derivatives notes pages
cambial divisioncambial division
radial
axia
linitial
xylem Cell division within the ray and fusiform initials results in the formation of derivative cells that are placed either on the outside of the mother cell, in which case they add to the secondary phloem, or on the inside endarch to) the mother cell, thus adding to the secondary xylem
Cell sourceCell source
The apical meristem is the principle source of new cells in the primary as well as within the secondary plant body. All cell division linked to vegetative growth, involves mitosis, and, as a result, the cells that are produced are exact copies of each other. Lineage depends on the position of the initial within the meristem.
the periderm a protective barrierthe periderm a protective barrier
During secondary growth, the diameter of stems and roots increases rapidly, which results in tension and splitting of the existing dermal tissues, which subsequently, will stretch and become disrupted.
The generative layer of the first periderm (phellogen) is initiated within parenchymatous elements in the outer cortex of stems and roots. It offers protection from invasion by insects, pathogens and fungi.
As the stem or root continues to increase in diameter, so successive periderms are formed. These are formed within the secondary phloem.
The periderm is a natural waterproof, fireproof insulator.
Filling spacesFilling spaces
Within all plants the primary packaging tissues are composed of cells that either fill in spaces, or support other areas of the stem, root or leaf. Thus, the parenchymatic elements that are produced (and have lineage back to the apical meristems) are produced from what is termed the ground meristem. In simple terms, the ground meristem is that region of a shoot or root apical meristem that is NOT involved in the production of vascular tissue.
cambial derivativescambial derivatives
The vascular cambium is the source of all needed (secondary) differentiation in plants. It contains two systems, the secondary xylem, and the secondary phloem tissue. Each of these tissues is complex, and is developed and has evolved for specific functions – the xylem for the transport of water and water soluble molecules, the phloem for the transport of assimilated, and the, which consist of sugars and related carbohydrates translocated in water.
click here for the next page
Physiologically, the transport xylem is dead at maturity, has secondarily-lignified cell walls, and functions under extreme negative pressure potentials. Transport phloem on the other hand, contains a majority of living cells, with specialized sieve elements, which are geared for rapid, long-distance translocation of the assimilated carbohydrate pool. These transport elements, have thickened walls, are living at maturity and function under a high positive pressure potential.
transport functionalitytransport functionality
The xylem and phloem conduits form axial tubes. These tubes facilitate rapid, long-distance movement of water and dissolved materials. It follows therefore that the fascicular cambial derivatives that form these transport cells are longer than they are wide, and that the cells will, depending on position form either xylem or phloem.
click here for cambial derivatives
click the need for lateral communication
back
the need for lateral communicationthe need for lateral communication
As the secondary plant body enlarges, so the carbohydrate conducting, and water transporting systems become laterally spatially and physiologically further removed from each other. The core of a stem or root, for example, may well contain a number of living cells, that not only require water and a supply of assimilate and other carbohydrates, in order to maintain their functional state. If this does not happen or if the supply is cut off for some reason, then the core will die.
Lateral communication, and the production of these cells in the lateral communication pathway, is due to the activity of specialised cambial cells, called the ray cells. These cells are sort, often cubic in shape and the produce rows (files) of parenchymatous living cells, that interconnect the phloem with the inner xylem core, thereby facilitating exchange of carbohydrate inwards, and water outwards in the living plant.
zipping organ formation
Plant signals
Figure 1 Model of how CLASS III HD-ZIP1 and KANADI activities pattern lateral organs and vasculature. A centrally derived signal (red) activates CLASS III HD-ZIP genes, whose activity is antagonistic with that of KANADI activity. Both KANADI and MIR165/166 negatively regulate CLASS III HD-ZIP genes, (relationship between the two is not presently known). In lateral organs, CLASS III HD-ZIP activity promotes adaxial fates and KANADI activity promotes abaxial fates. In the vascular bundles, interactions between the two gene classes pattern the arrangement of xylem and phloem tissues. The vascular bundle shown is already differentiated, but the initial patterning events likely occur just below the apical meristem where provascular cells are being specified.
–––––––––––––––-–1Class III homeodomain-leucine zipper proteins See http://www.nature.com/nrm/journal/v5/n5/full/nrm1364.html
Arabidopsis class III homeodomain-leucine zipper (HD-Zip III) proteins play overlapping, distinct, and antagonistic roles in key aspects of development that have evolved during land plant evolution.
Scarecrow
Laura Di Laurenzio et al., Cell, Vol. 86, 423–433, August 9, 1996, Copyright ã1996 by Cell Press
The formation of the cortex and endodermal layers inthe Arabidopsis root requires two asymmetric divisions.In the first, an anticlinal division of the cortex/endodermalinitial generates two cells with different developmentalpotentials. One will continue to function as aninitial, the other undergoes a periclinal division togenerate the first cells in the endodermal and cortexcell files. This second asymmetric division is eliminatedin the scr mutant, resulting in a single cell layer insteadof two.
Homework:
Spend a bit of time researching other gene systems (in Arabidopsis, or higher plants) that are involved in SAM or RAM development, expression of morphology, size and shape.
Insert into a word doc, CITE the references as well please and send them to me – I will collate and redistribute useful information back to you via RUConnected
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