Biology Reference
In-Depth Information
the seeds are naked. Seeds comprise an outer covering (the seed
coat, which developed from the integuments of the ovule), the
endosperm, cotyledons, and embryonic axes [
1
,
2
]. The reserve
polymers necessary for the support of postgerminative seedling
growth are contained either within the endosperm (endosperm-
dominant) or cotyledons (cotyledon-dominant) of the seeds [
3
,
4
]. In cotyledon-dominant angiosperm seeds, such as those from
legumes, the endosperm at maturity can be as thin as 2-3 cells, or
be absent entirely. Conversely, the endosperm is the more promi-
nent organ in grains, and the cotyledons are relatively small.
Embryos of cotyledon-dominant seeds generally have two cotyle-
dons (dicot) while those of endosperm-dominant seeds have a
single cotyledon (monocot) or cotyledon-like (e.g., scutellum)
storage organ.
There is an enormous range in the size of seeds, from the dust-
like seeds of orchids (e.g.,
Gomesa crispa
, 810 ng dry weight/seed)
to the formidable seeds of Coco de Mer (
Lodoicea maldivica
),
samples of which have been reported to exceed 18 kg dry weight!
The more familiar seeds of soybean (
Glycine max
(L.) Merr, cv
Jack) and “mouse-eared cress” (
Arabidopsis thaliana
L. ecotype
Columbia) weigh in at 225 mg dry weight and 30
g dry weight,
respectively [
5
]. Size is one of many criteria that can impinge on
the choice of a research subject by the seed biologist. While I am
unaware of specifi c supporting data, it seems likely that the smaller
seeds have the greater biological variation.
One seldom sees reference to, e.g., “leaf proteomics,” or “stem
proteomics.” Are seeds then actually deserving of their own unique
sub-discipline? Well … yes! Any one of multiple seed-specifi c char-
acteristics is adequate to justify unique treatment, and together
they virtually require it. For any sort of meaningful comparisons,
sample uniformity is an important issue. In addition to anatomical
considerations, any meaningful analysis of seed composition must
accommodate their physiological state; quiescent or dormant [
6
],
dry or hydrated [
7
,
8
], orthodox or recalcitrant [
9
]. The occur-
rence of seed storage proteins (SSP) is a major technical problem
because of the extended protein dynamic range [
10
].
As a discipline, proteomics is a broad, instrument-intensive
research area that has progressed rapidly since its genesis 20 years
ago. While methods of protein isolation and separation have
improved during this period, it has been the improvements in
instrumentation that have driven expansion of the fi eld [
11
-
14
].
Signifi cant improvements in sensitivity, mass accuracy, and frag-
mentation in recent years have led to widespread adoption of pro-
teomic strategies. As proteomics has matured as a discipline, there
have been an increasing number of specialized studies; organism-
specifi c, cell or organelle-specifi c, and specifi c for increasingly nar-
row physiological or developmental targets. Herein I address the
burgeoning fi eld of seed proteomics.
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