SUPPRESSION OF STARCH SYNTHESIS AND ACCUMULATION OF URIDINE DIPHOSPHOGLUCOSE IN CUCUMBER LEAVES DUE TO AMMONIUM TOXICITY

This work is a study of the metabolic disorder due to ammonium toxicity in cucumber (Cucumis sativus L. cv. suisei No. 2) leaves. The cucumber was cultured with 20 and 200 mg/l NH3‐N for 5 days. In the first half of this experiment, the plant leaves were photosynthesized for 3 hours to study the distribution of 14C in starch and other fractions. The incorporation of photosynthesized 14C into not only starch but also other higher polymers was suppressed by ammonium toxicity. On the other band, the rate of 14C incorporation in 80 % ethanol soluble fraction was higher in the treatment of 200 mg/l NH3‐N. In the latter half of experiment, phosphate esters in the loaves were analyzed by column chromatography. The opposing contents of uridine diphosphoglucose (UDPG) and the uridine compound containing sugar or sugar derivative (UDPX) were determined by different ammonia levels. Toxicity of ammonia resulted in an increase of UDPG and a decrease of UDPX. The level of ATP was not changed so much. The content of glucose‐6‐phosphate (G‐6‐P) in injured plants was lower than that of normal plants, while ghicose‐1‐phosphate (G‐1‐P) and fructose‐6–phosphate (F‐6‐P) were higher in injured plants. These results further suggested the disorder of carbohydrate metabolism due to ammonium toxicity which was reported previously. Copyright © 1969, Wiley Blackwell. All rights reserved