Re: embryogenesis/organogenesis from callus

[Wayne Parrott <wparrott@ARCHES.UGA.EDU>]

At 04:20 PM 2/21/01 +0000, you wrote:
Dear all,
has anyone made studies of the number of cells involved in
embryogenesis/organogenesis from callus. Is it highly variable?

I am particularly interested to know if a single (or multiple)cell
origin was found in explants such as leaves/flower stem etc whether the same
was found in callus from the same plant.

many thanks,
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Excellent questions, and tough to answer. I am going out on a limb
with my answer, so I will look very much forward to what other people
have to say.

The following references document single cell origin from callus:

Street, H. E. and L. A. Withers. 1974. The anatomy of embryogenesis in
culture, p. 71-100. In: H. E. Street (ed.), Tissue culture and
plant science. Academic Press, London and New York.

Haccius,B. 1977. Question of unicellular origin of non-zygotic embryos in
callus cultures. Phytomorphology 28:74-81.

But the following reference makes it clear that multicellular origins are
common:

Williams,E.G. and G.Maheswaran. 1986. Somatic embryogenesis: factors
influencing coordinated behaviour of cells as an embryogenic group. Ann.
Bot. 57:443-462.

As I understand your question, you are asking if embryo origin from
callus may be different than origin from an explant. Generally
speaking, I find that the ability to undergo embryogenesis from
both true callus and from an explant is not common within the same
species. I do not really think there are that many species that can
undergo embryogenesis from true callus. The term "embryogenic
callus" is common in the literature, but the term is frequently a
misnomer. Usually what is meant by the term is either embryogenic
tissue or masses of proliferating embryos.

Nevertheless, I do think it is possible for somatic embryos-- for
example, primary embryos (those that arise from the explant tissue) to be
multicellular in origin, while secondary embryos-- those that arise from
primary embryos or from embryogenic tissue, to originate from single
cells. I do not have incontrovertible evidence for this, just
inferences that can be made by looking at the transformation
literature. This is not to say that primary embryos are always
multicellular in origin. The ability to bombard immature zygotic
embryos of some cereals and recover transgenic embryos from them suggests
a single cell origin.

Any other takes on this matter?

Darren Sage

Horticulture Research International
Wellesbourne
UK

Wayne Parrott
Dept. Crop & Soil Sciences
University of Georgia
Athens, GA 30602-7272
(706) 542-0928/fax 0914
http://www.cropsoil.uga.edu/~parrottlab

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