ABSTRACT
In soybean seeds, lipids are stored in the form of triacyl-glycerol (TAG) which fatty acids are esterified to glycero-lipids. Fatty acids vary in type and content according to genetic and environmental factors, which affect their nutritional value and processing property.). The lipid related changes of seeds during storage revealed decline in phospholipids and polyunsaturated fatty acids leading to marked decline in seed vigour . The source of primary catalysis which initiate lipid peroxidation are free radicals which contain one or more unpaired electrons , as active forms of oxygen, i.e. the superoxide radical (2O), hydrogen peroxide ( H 2O2 ) and the hydroxyl radical (OH°) which can react with biological molecules.
In plants, the pathways for lipid biosynthesis and oil accumulation had been studied and the genes related to fatty acid biosynthesis have been characterized.
The biosynthesis of seed storage oils containing the five major FAs occurs primarily in two subcellular compartments. FA biosynthesis occurs in the plastid of cells and involves the cyclic condensation of two-carbon units in which acetyl coenzyme A (acetyl-CoA) is the precursor.
Lipids accumulate as triacylglycerides that are found in oil storage bodies surrounded by the protein oleasin or occasionally as oil droplets in the cytosol. Predominant fatty acids in triacylglycerides are palmitate (16:0), stearate (18:1), linoleate (18:2) and linolenate (18:3). In soybean, cell division in the seed is completed at an early stage of development (20-25 DAF) while the embryo is still quite small. The major increase in seed size which occurs between 25 to 60 days after flowering (DAF) is brought about through enlargement of pre-existing cells.
A general trend indicated an increase in the saturation level of the oil fraction due to various abiotic stresses has been reported. The proportion of polyunsaturated FAs (PUFA) in soybean oil dropped considerably under heat stress. FA synthesis in oil seeds starts its early steps in the plastids and then C18:1 as the main product of plastidal lipid synthesis is exported to the cytosol. The enzyme activity in which oleate desaturase (OD) moderates the cytosolic desaturation of C18:1 to form PUFA (i.e. C18:2) is believed as an explanation for shifts in C18:1/C18:2 ratio in several crops under various types of stress, including: salinity, drought, and heat.
