Unconventional Method for Determining Groat-oil Content in Oats
I.G. Loskutov and G.I. Moskaleva
N.I.Vavilov Institute of Plant Industry, St.Petersburg,
B.Morskaya str., 190000, Russia
Studying oil content in the accessions of wild oat species and hybrids constantly faces the problem of identifying an optimum quantity of materials to be analyzed by biochemical methods. In view of this, in 1994-1995 methodological attempts have been undertaken to search for a possibility of using anatomical criteria for preliminary assessment of oat accessions for oil content.

This research was performed on the following materials of 20 accessions of the species Avena sativa, A.byzantina, A.sterilis, A.ludoviciana, A.fatua and A.magna (reproductions of 1990-1992); and 11 accessions with different periods of caryopsis storage under room condition.

Anatomical preparations were received as follows: cross-sections were taken from dry caryopses (in the middle part) and stained with alcohol solution of Sudan III. The stained cross-sections were placed in 60% water solution of glycerol. Immediately after the microchemical reaction, entire staining of cytoplasm was observed. Some time later oil started forming drops.

Fat content reactions were demonstrated by all accessions studied. Differences were observed in the intensity of endosperm colouring, pattern of aleurone layer or main parenchyma staining (which can be entire, uniform or interrupted with colouring of separate cells or cell groups), localization of oil and size (diameter) of drops. The analyzed accessions to a greater extent differed in the size of parenchymal cells of the endosperm (which were broader and shorter in A.sterilis accessions from Algeria and in A.byzantina from India), and to a lesser extent in the size of aleurone layer cells. Noteworthy was in A.byzantina accession from Mexico which manifested brighter colouring of most of the aleurone layer cells and formation of larger and more numerous oil drops in the endosperm's parenchyma after staining. In A.sativa accession from New Zealand had parenchymal cells smaller and intensity of aleurone layer and main parenchyma were lighter. The content of fats is possibly influenced by the size of the cells where they concentrate and the density of their distribution. It was confirmed by the results of the biochemical analysis: in A.sterilis accession from Algeria and in A.sativa accession from India oil content was 9%, in A.byzantina accessions from Mexico was till 6% and from New Zealand - 2% only.

Similarly, the dipper intensity of aleurone layer colouring helped to identify A. udoviciana from Azerbaijan and Georgia and 4 accessions of A.magna - all of them were reproduced in 1990-1992. Biochemical analysis of groat-oil in these accessions showed its high content within the scope of 8.9% to 11.1%. Part of the accessions of A.magna and all the accessions of later reproductions were coloured less intensely, oil content in these accessions were within the scope of 6% to 8%. Comparison of accessions with different storage periods evidenced that the kernels of 1990-1992 reproductions formed fat drops immediately after staining them with Sudan III, while accessions with a longer storage period (since 1971) demonstrated colouring of either the entire cell contents, or a part of them, but no formation of fat drops was observed.

The results of this study showed that although the links between the anatomical structure of the caryopsis' aleurone layer and its oil content existed, these links were not plainly explicit. It was also discovered that caryopses of different reproductions had different structure of the fat drops that filled the aleurone layer, i.e. caryopses of earlier reproductions formed smaller, but more numerous drops, as compared with those of fresher reproductions. Probably this phenomenon was determined by certain biochemical processes that took place in oat caryopses during storage.

Biochemical analysis was shown that on the accessions that had been stored from 1971 concentration of saturated (palmitate, stearate) and monounsaturated (oleate) acids increased, but concentration of polyunsaturated (linoleate and linolenate) ones decreased compare with analysis the same accessions of 1990-1992 reproductions.

The process of work also involved development of methods for making preparations and performing microchemical reactions for fats by using specific dyes Sudan III and black Sudan B. It was found out that staining with black Sudan B was better for identification of oil in the aleurone layer (more drops were formed). The use of fresh (non-fixed) materials proved to be more efficient in evaluating the localization of lipids. It is difficult to obtain whole cross-sections after continuous fixation process, while colouring of parenchymal tissue in the endosperm is too intense, which hampers the work with such material.

The anatomical method of lipid identification with the help of microchemical reactions based on the accumulation of the dye in lipids made it possible to accelerate their identification in the cells of the aleurone layer and the endosperm parenchyma and to define more precisely the degree of their localization in caryopsis tissues. This method consumes little time and material and may be recommended for preliminary assessment of oat accessions by the mentioned parameter, especially if the materials for the research are available only in very limited quantities.


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