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Plant Physiology 43:1297-1308 (1968) © 1968 American Society of Plant Biologists Levels of Phosphate Esters in SpirodelaFruit Research Division, Department of Scientific and Industrial Research, Auckland, New Zealand The duckweed Spirodela oligorrhiza was grown in sterile nutrient solutions that contained 1 mM phosphate-32P at various specific activities. In solutions with activities higher than 2 µc per µmole per ml, plant growth was inhibited after a time, and the physical appearance of the plants was affected. The critical level of radiation, at which growth was first affected, corresponded to 5 kilorads. Plants were grown for 9 days (5 generations) in a culture solution containing phosphate at 0.5 µc per µmole per ml (radiation load approx 0.5 kilorads) so that all phosphorus-containing materials in the tissue became uniformly labeled. The various radioactive compounds were extracted, chromatographed, identified, and their radioactivity was measured. From this radioactivity plus the specific activity of the supplied phosphate, the amount of each compound was calculated. The data constitute a complete balance-sheet for phosphorus in a plant tissue. The identity of 98% of the phosphorus in the tissue was determined. Inorganic phosphate (32,700 mµmoles/g fr wt) was the predominant phosphorus-containing compound; RNA (5100 mµmoles P/g fr wt) was the main organic phosphate; phosphatidyl choline (1600 mµmoles/g fr wt) was the main phospholipid, and glucose-6-phosphate (500 mµmoles/g fr wt) the main acid-soluble phosphate ester. Amounts of other phosphorus compounds are given.
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