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Angiosperms
*Micro/mega gametogenesis
Pollination
Embryogenesis
• Tapetal tissues are not only found in angiosperms but older groups like ferns- have a
variety of functions associated with them
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• Genreal result in meiosis is 4 haploid cells
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• Immature haploid spore- then you’ll have a process of maturation that occurs- and will
create a protective layer around it to avoid damage to the insides- its a tough
process
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The complexity is that usually you would think about cells as
distinct separate cells but in fact if you think of the maturation process they are
both embedded and look like they are in the same cell
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• The vegetative nucleus is important in controlling the growth of the pollen- the pollen
will then germinate and this is driven by the DNA contained in the vegetative
nucleus
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• When and how this occurs varies depends on the type of species you’re working onbut generally occurs within the anthers of the flower
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• Things get strange in plants because its not a single fertilization event that occurs- its
actually 2 and is known as the double fertilization
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The
triploid endosperm then surrounds the developing zygote
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• Above- microgametogenic process
Megagametogenic process
• Fairly similar complexity associated with it- occurs in the angiosperms
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Will show
where the triploid and zygote is created in terms of fertilization
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In the context of thinking about what occurs here,
there are some variations on a theme which are associated whether or

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not all those haploid cells continue to develop and embryo sac or not
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All of this
occurs within a well defined and protected environment in the carpel
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So get a single haploid spore then undergoes mitotic divisions which
generates 2 cells- get more mitosis which gives you 4 haploid cells and
then another mitotic process which gives you 8 haploid cells in total
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It is surrounded by an integument and
contains a micropile- its an 8 cell mega gametophyte (multinuclei
structure)- the cells then undergo by particular names- the egg cell is
where you’ll get fertilization from the pollen which contains 2 generative
nuclei which will then fuse with the egg cell to form the zygote
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These cells probably
play a role in protecting and allowing fusion to occur between the
generative pollen and the egg cell
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The central cells
are known as the central cells
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At this point you’ve got the final structure of the ovule structure surrounding
the integument and the spore structure inside it
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The
two polar nuclei present in the central cell have actually already fused and
then the 2nd generative cell fuses and forms the triploid endosperm
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Ability of which cell
fuses and creates the zygote or the triploid endosperm is of great
interest
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Why is there a double
fertilization occurring- no idea
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All of this creates what actually fixed
this that allows this to occur and is there any elective advantage
associated with the complex processes of micro and mega
gametogenesis
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