Studies on metabolic changes accompanying imbibition and vernalisation of a spring and a winter wheat.

Abstract

Changes in protein content, amino acid, fatty acid and phosphate metabolism were followed in the morphologically distinct parts and whole grains of Marquis (spring) and Rideau (winter) wheats during imbibition'and vernalisation. Vernalisation had a negligible effect on the protein content of the grains of either wheats. However, large increases in the total alcohol soluble amino acid and amide fractions were observed in the grain parts (embryo-scutellum and endosperm) of vernalised wheats. The percentage distribution varied both between grain parts and between spring and winter wheats. The duration of the imbibition period prior to vernalisation was another important variant. Despite these variations, the embryo fractions of both wheats consistently contained larger amounts of nine amino acids following vernalisation. After vernalisation the ratio of acidic to total basic amino acids decreased in the grain parts. Three methods of computing the amino acid data were used in all cases; namely, per protein content, dry weight or grain part. Whereas the general trends outlined were consistent throughout, differences in the magnitude of change were observed to be dependent upon the base from which the data were calculated. With regard to fatty acid composition, it was observed that vernalisation increased the degree of unsaturation in the plumule, radicle and scutellum of Marquis grains (largely as a result of the increased proportions of oleic and linoleic acids), while under the same conditions the degree of unsaturation in these three grain parts of Rideau grains were decreased (largely as a result of a decrease in the proportion of linoleic acid). The major fatty acid components of the Marquis endosperm and all the grain parts of Rideau wheat were oleic and linoleic acids. The proportions of these acids did not change with vernalisation in the endosperm of either variety. Only traces of linoleic acid were noted before and after vernalisation in all the grain parts of both varieties except in the plumules of the partially and fully vernalised Marquis wheat. 32P-orthophosphate taken up by both varieites during imbibition was incorporated largely into water-soluble organic phosphates and this incorporation continued during vernalisation. Chilling accelerated the uptake of 32P into the total nucleic acids of the grain parts and whole grains of Rideau wheat, relative to the uptake of 32P into the nucleic acids of the controls. Incorporation of 32P into the total nucleic acids of Marquis whole grains was low and varied only slightly during vernalisation. The 32P incorporated into the phospholipids of the various Rideau and Marquis grain parts was concentrated in the "lysophos - phatidic acid" and lecithin components. In all the Rideau grain parts, the uptake of 32P into lecithin increased with vernalisation; simultaneously, the incorporation of 32P into the "lysophosphatidic acid" component decreased. The 32P incorporation data suggest that the scutellum of both varieties act as a "sink" for the phosphate metabolites from the other grain parts. From the results obtained in these studies, a hypothesis has been suggested to account for the mode of action of vernalisation in winter wheat grains.