Biology Reference
In-Depth Information
Identifi cation and understanding of the biological function of any
novel gene is a more ambitious goal than merely determining its
sequence. Proteomics approach supported with genome-sequence
data is thus a powerful tool to identify novel proteins and to follow
temporal changes in protein expressions. In spite of the agricultural
importance, soybean yield increment through conventional breed-
ing over the past few decades has lagged behind those of cereals.
Different abiotic and biotic impediments including fl ooding,
drought, salinity, metal toxicity, nutrient limitations, and pathogen
attacks curtail yield potential in soybean. Stress-induced changes in
gene expression modulate metabolic processes through alteration
of cellular protein abundance and function. Therefore, understand-
ing how the function of proteins changes under stressed conditions
is crucial for clarifying the molecular mechanisms underlying stress
tolerance and crop injury.
The proteomic research done so far in soybean has mainly
focused on the comparative analyses of protein abundance between
control and stressed or tolerant/susceptible cultivars (Table
1
).
In addition, changes in protein expression profi ling at various organ
developmental stages including seed fi lling period of soybean have
been well exploited. In the present review, an attempt has been
made to summarize all signifi cant contributions in the fi eld of soy-
bean proteomics. Special emphasis is given to subcellular pro-
teomics in response to abiotic stresses for better understanding of
changes in the protein abundance and plant stress tolerance.
2
Protein Extraction of Soybean
Protein extraction is the most critical step in a two-dimensional gel
electrophoresis (2-DE) approach, as the amount and quality of the
extracted proteins ultimately determine the protein spot number,
resolution and intensity. Phenolic compounds, proteolytic and oxi-
dative enzymes, terpenes, pigments, organic acids, inhibitory ions,
and carbohydrates are the most common interfering substances
present in recalcitrant plant tissues, resulting inferior results such as
proteolytic breakdown, streaking and charge heterogeneity. Efforts
have been made to standardize sample preparation protocols to get
optimized yield. Instead of having physicochemical limitations of
each and every protocol, the trichloroacetic acid (TCA)-acetone
precipitation and phenol extraction methanol-ammonium acetate
precipitation methods are most used as standard methods for
removing interfering substances to obtain high quality gels [
5
].
Soybean seeds contain approximately 36 % protein, 30 % car-
bohydrate, 20 % oil, 9 % crude fi ber and 5 % ash [
6
]. In addition,
large amounts of secondary metabolites like kaempferol and
quercetin are present in both seeds and leaves of soybean [
7
].
Increased activities of enzymes involved in phenolic biosynthetic
