T19 – Nonzygotic Embryogenesis

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12 Δεκ 2012 (πριν από 4 χρόνια και 6 μήνες)

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Ryan Williams


2/28/10



Nonzytogic Embryogenesis I


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Nonzygotic Embryogenesis

By Dennis J. Gray

An embryo is “the earliest recognizable multicellular stage
of an individual that occurs before it
has developed the structures or organs characteristic of a given species.” Plants are unique
because
viable embryos can arise from many different tissue types from both gametophytes and
sporophytes.

These embryos are functionally equivalent to zygotic embryos. Nonzygotic
embryogenesis
in vitro

is very useful for plant improvement because it allows scien
tists to
genetically engineer somatic cells and then create many new identical individuals without having
to deal with the genetic changes introduced by sexual reproduction.

This is really cool. I find it very interesting that we can reset part of the p
lant back to thinking it
is a baby again.


Nonzygotic embryos are thought to come from a single cell. This is important because
this
means that an individual cell could be genetically engineered and then result in a modified plant.
If this genetically
modified cell was in a bud, the results would be a chimeric plant.

This property is good news for genetic engineers as it allows them greater flexibility in creating
new types of plants.


Generally, nonzygotic embryos can only be made from younger or m
eristematic tissues of plants,
but different genotypes show a lot of variation on what parts they will produce embryos from.
Nobody is totally sure what causes a cell to dedifferentiate and begin embryogenesis. Some
studies have been done, but they were
found to be faulty later so they don’t really shed much
light on the cause of nonzygotic embryogenesis.


The induction of nonzygotic embryogenesis relies on specific types of media. Generally there
are auxins in the media with 2,4
-
D a commonly used one.

Cytokinins are also used in many
dicot species. The most commonly used cytokinin is BA.

Surprise, surprise, the media is the most important part of getting nonzygotic embryogenesis to
happen. Without the proper media (and sometimes multiple types of
media) the magic will not
happen.


Embryos most likely begin when a progenitor cell undergoes unequal division. They then
develop into a dense, organized embryo. Nonzygotic embryos can frequently turn into callus, do
direct secondary embryogenesis, or ge
rminate precociously which can cause problems. These
things are caused by environmental factors.


Monocot
Development
: Globular, scutellar, coleoptilar stages.

Dicot and Conifer Development: Globular, heart, torpedo, cotyledonary stages.


One difference
between zygotic and nonzygotic embryos is the
seed coat which compresses the
zygotic embryos. This causes them to usually be smaller and flatter than nonzygotic embryos.
The affects of this on the adult plant are unknown.


Nonzygotic embryos often fail

to mature, instead becoming disorganized or forming new
embryos. They also frequently have extra cotyledons and apical meristems that are not well
developed. Maturation can be improved by
media with high sucrose content, ABA, or PEG.

Ryan Williams


2/28/10



Nonzytogic Embryogenesis I


Page
2


Nonzygotic embryos
generally don’t exhibit a quiescent period like zygotic embryos do. This
quiescent period is what allows the zygotic embryos to be stored for long periods of time.

This is interesting. I guess this means that we still need to expand our knowledge before

we can
invent
human made seeds.


Generally, it is difficult to get plants from nonzygotic embryos. Research has been done lately
that has found that the conditions for maturation usually promote plant formation, and science
has been able to get some no
nzygotic embryos to produce plants with almost as much success as
with seeds.


Nonzygotic embryos are important in at least 3 areas.

1. Study of plant development

2. Genetic engineering of plants

3.
Clonal Propagation


Synthetic seeds are one application for nonzygotic embryos.
These would be an advantage for
plants such as seedless watermelon which have a very high seed production cost. Also, conifers
might benefit by cloning through nonzygotic embryogenesis since the
y are difficult to breed due
to their very long life cycle.

I think this would be really neat. Synthetic seeds definitely have the potential to have many
advantages over normal seeds.



T
20



Embryogenic Callus and Suspension Cultures from Leaves of
Orchardgrass

By Dennis J. Gray, Robert N. Trigiano, and Bob V. Conger


The family Poaceae is the most economically important group of plants. It includes corn, rice,
oats, wheat, and some other grasses.
Many of these species have been used to successfull
y
create plants by nonzygotic embryogenesis, but it is usually a lot of work. One member of the
family, Orchardgrass, is much easier to work with and some experiments with it will be
described in this chapter. Orchardgrass is self
-
incompatible which make
s creation of new
varieties difficult. Somatic embryos hold lots of promise in cloning of especially good parental
lines. Orchardgrass is a particularly good plant for experimenting with because it grows easily,
the leaves are the required explant materi
al, and their leaves are easier to dissect than the leaves
of other types of poaceae.
This chapter contains protocols for investigating nonzygotic
embryogenesis with orchardgrass.

This appears to be a pretty involved experiment, but it has neat results if

it is successful.



T21



Somatic Embryogenesis from Seeds of Melon

By Dennis J. Gray


Cantaloupe belongs to the family Cucurbitaceae and has hundreds of cultivars. This family is a
very important agricultural family, but it is susceptible to several types of diseases. Genetic
engineering
can put resistance into melon plants and somatic em
bryogenesis is a very efficient
way to regenerate the resistant plant. This chapter contains protocols for investigating somatic
embryogenesis from melon seeds.

Ryan Williams


2/28/10



Nonzytogic Embryogenesis I


Page
3


This
experiment looks like it would be interesting to do, but I think that the orchardgrass
one is
more informative one than this one is.




Questions:

1. Define what a plant embryo is.

2. List one application for nonzygotic embryogenesis.

3. Which types of PGRs are required to induce nonzygotic embryogenesis?

4. What is the term describing a

embryo made in vitro and coated with a artificial seed coat?

5. True or False, nonzygotic embryos created in vitro exhibit a quiescent period much the same
as a naturally forming embryo.