Prior to and/or accompanying lipolytic degradation of triacylglycerols (TAGs) during seed germination in oilseeds, certain enzymatic and non-enzymatic signaling molecules are expressed on the oil body membranes. These include certain proteases, lipoxygenase, phospholipase A2 and lipase. Although enough biochemical investigations have demonstrated their activities, recent developments in the in situ localization of these signaling molecules in germinating oilseeds, have enhanced our understanding in this field. This is evident from the temporal and spatial changes observed in the expression pattern of some of these molecules. Present review aims at providing an up-to-date account of these recent developments in the author's and other laboratories, which are largely based on fluorescence microscopic and confocal laser scanning microscopic (CLSM) imaging of the molecular changes using specific fluorescent probes. A model for the molecular events associated with oil body mobilization is also being presented.

Biochemical and fluorescence microscopic imaging approach has been adopted to investigate the accumulation of oil bodies at specific stages of seed development in Helianthus annuus L. cv. Morden. Seed filling in sunflower is marked with a rapid accumulation of proteins and lipids upto 30 DAA, after which protein accumulation declines whereas lipids continue to accumulate. Earliest signs of lipid accumulation are evident as early as during globular stage of embryo development. Spatially, a developing seed exhibits enhanced lipid deposition in peripheral cells. Oil body biogenesis is observed as early as 10 DAA, as is evident from the fluorescence microscopic detection of Nile red-positive entities in the protoplasts. To begin with, expression of one of the oleosin (the principal oil body membrane proteins) isoforms (16 kDa), is slower than the other two (17.5 and 20 kDa). Fatty acid composition of oil body lipids is quite similar to that of total seed lipids. An enhanced accumulation of linoleic acid is evident during later stages of seed filling. The proportion of major saturated fatty acids, palmitic (16: 0) and stearic (18: 0), however, do not alter much during the later phases of seed development. Present findings provide new information on oil body development, lipid accumulation and fatty acid composition, for a better understanding of the phasing of physiological and biochemical events associated with oilseed development.