Abstract
Total and soluble leaf chloroplast protein levels were directly related to severity of bloat in cattle and sheep. The highest correlation was found between Fraction I chloroplast protein and bloat. Chlorophyll to protein ratios demonstrated a preferential synthesis of protein in chloroplasts during high-bloat stages. Progressing from non- to high-bloat-provoking forage, the percentage of soluble protein localized in chloroplasts increased from 45 to 77 per cent. Chloroplast lipids were inversely related to bloat. The percentages of total lipids in the chloroplasts suggest that preferential synthesis of chloroplast lipids occurs in non-bloat forage. Progressing from non- to high-bloat forage, the percentage of total leaf lipids localized in chloroplasts decreased from 71 to 27 per cent. Electron micrographs showed numerous large osmiophilic lipid granules in non-bloat chloroplasts. The number and size of the granules were highly correlated with changes in chloroplast lipids and bloat. Chloroplast fragments containing osmiophilic granules, starch grains and grana lamellae were observed in bolus juice and rumen fluid. Lamellae and osmiophilic granules were the only identifiable plant components found in rumen foam, while the chloroplast stroma was dispersed. These results strongly suggest that a stable foam is produced by an imbalance of protein and lipid chloroplast components which are specifically located within the stroma.
Published Version
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