Levels of Phosphate Esters in Spirodela

Abstract

The duckweed Spirodela oligorrhiza was grown in sterile nutrient solutions that contained 1 mm phosphate-(32)P at various specific activities. In solutions with activities higher than 2 muc per mumole 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 muc per mumole 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 mmumoles/g fr wt) was the predominant phosphorus-containing compound; RNA (5100 mmumoles P/g fr wt) was the main organic phosphate; phosphatidyl choline (1600 mmumoles/g fr wt) was the main phospholipid, and glucose-6-phosphate (500 mmumoles/g fr wt) the main acid-soluble phosphate ester. Amounts of other phosphorus compounds are given.