The distribution of oil in the oat grain

Abstract

High-lipid oat is a potential oil crop. Chemical and microscopical analyses have shown that the major part of the grain lipids are stored in the endosperm. While oil bodies are intact in the aleurone layer, scutellum and embryo, they have less associated proteins (oleosins) and undergo fusion in the starchy endosperm. In this report, we document the distribution of lipids in the endosperm microscopically. Underneath the aleurone layer, lipids are most abundant in the subaleurone cells and in the endosperm cells in the vicinity of the scutellum and embryo. Thus the major areas of oil storage are close to the living tissues of the grain, the sites of enzyme production in connection with germination and mobilization. The documentation of cellular structural changes, and implication of the fused state of oil bodies, during germination, remains to be elucidated.Oat (Avena sativa L.) is a cereal crop that accumulates up to 18% of lipids. 1 Most of the lipids are stored in the endosperm tissues of the grain. [2][3][4] This has been also demonstrated using fluorescence microscopy, 1,5 light microscopy as well as scanning and transmission electron microscopy. 4,6 White et al., 7 on the other hand, interpreted their transmission electron microscopy pictures as if indicating scarcity or absence of lipids beneath the subaleurone layer. Applying different microscopical approaches, it has been shown that oil bodies appear as distinct entities in the embryonic axis and the aleurone layer, and that they loose their integrity and fuse with each other into large masses in the rest of the endosperm during grain development. 6 The fusion of oil bodies in the starchy endosperm is probably correlated with the reduced amount of the protecting oil-body associated proteins (oleosins) documented in this tissue. 6 The aim of this report is to present microscopical data on the distribution of oil throughout the oat endosperm, not shown in Heneen et al. 6 The structural observations were made on the highlipid oat cultivar Matilda with 10.3% lipids. 6 Sectioned sectors of grains at early and late developmental stages, 14 and 40 days after anthesis, were stained with Sudan Black B or Toluidine Blue O. 6 The low magnifications of whole sectors of the grain and higher magnifications of defined sites (Fig. 1) provide information on the distribution and appearance of lipids throughout the grain. A further step would be simultaneous visualization and quantification of lipids, as has been elegantly demonstrated in developing barley grains and soybean seeds in vivo, applying frequency-selected magnetic resonance imaging. 8 At the early developmental stage of oat grains (Fig. 1A), lipids were less densely stained in the aleurone layer than in the rest of the endosperm, inferring tissue-specific differences. Oil was not evenly distributed in the starchy endosperm. It was most frequent in the subaleurone cells, and decreased in cells of middle and inner endosperm, in accordance with earlier findings. 5 This was valid for the discrete oil bodies observe...

Preferred carbon precursors for lipid labelling in the heterotrophic endosperm of developing oat (Avena sativa L.) grains

“…The results clearly showed that cultivar differences in carbon partitioning into lipid synthesis was localized to the oat endosperm, and not to the small but lipid (oil) dense embryo, which might indicate a higher FA synthesis in the endosperm of the HO as compared to the MO cultivar. This is well in agreement with previous determined spatial distribution of 14 C from sucrose fed to grains through detached panicles (Ekman et al, 2008) as well as with analytical data and microscope analysis on lipid accumulation in grains of these oat cultivars (Banas et al, 2007;Heneen et al, 2009). This localization of cultivar differences in lipid metabolism to the endosperm is of great importance since this tissue makes out the largest part of the grain and should therefore be the target for the potential development of high-oil yielding cereals.…”

“…Previous studies on quantification and localization of oil in the oat grain both during seed filling and germination (Banas et al, 2007;Leonova et al, 2010;Heneen et al, 2008Heneen et al, , 2009, as well as transcriptome and metabolite analyses of developing grains (Hayden et al, 2011), have increased the understanding of oil metabolism in cereals. However, the knowledge of metabolic and genetic factors that explain why oat is unusual among the cereals in having high amounts of endosperm oil, as well as why some oat varieties have high oil content as compared to others, remains incomplete.…”

Processing of oats and the impact of processing operations on nutrition and health benefits

“…Oats are also used to make products such as granola, snack bars, cookies and pancakes, and are used as an extender in meat products such as black and white puddings and haggis, and as a carbohydrate source for fermented foods such as beer. The lipid in many grains including oat can exist as lipid bodies ( 15 ) , which are like emulsion droplets with the lipids surrounded by phospholipids and proteins. The lipid bodies, along with proteins, can be extracted from oats using water and salt to produce oat milk ( 16 , 17 ) .…”

Cofactome analyses reveal enhanced flux of carbon into oil for potential biofuel production

“…Exhaustive breeding and engineering efforts directed at the development of high-oil maize only led to increases in the size and oil concentration of the embryo and scutellum without a significant impact on the endosperm oil levels, maintained at <1% (Leng, 1961;Alexander et al, 1967;Shen et al, 2010;Alonso et al, 2011). Oat (Avena sativa) is unique among cereals, as there are oat varieties that contain up to 18% oil (Alexander et al, 1967 ; Price and Parsons, 1975;Alonso et al, 2011), mainly (up to 90%) deposited in the endosperm (Price and Parsons, 1979;Banas et al, 2007;Heneen et al, 2008;Heneen et al, 2009). Detailed examina-tion of two closely related oat cultivars, cv.…”