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The following enzyme activities were determined in the mitochondria of cucumber leaves (Cucumis sativus L. cv. Suisei No. 2) during ammonium toxicity: malate dehydrogenase, succinate dehydrogenase, glutamate dehydrogenase, cytochrome c oxidase, NADH diaphorase, NADH oxidase, succinate: cytochrome c oxidoreductase, NADH: cytochrome c oxidoreductase and adenosine triphosphatase. The activities of all enzymes except ATPase increased more or less during ammonium toxicity. Generally speaking the marked increase was found at 7 days treatment with 200 mg/l NH3-N. The adenosine triphosphatase activity of injured plants was lower than that of normal plants through treatment. The addition of various organic acids (15 mM) to the culture solution contaning 200 mg/l NH3-N (14.3 mM NH4Cl) suppressed the ammonium toxicity. The accumulation of free ammonia in the leaves was also repressed by the addition of organic acids. The results of present and previous reports suggest that the increase of respiratory metabolism due to ammonium toxicity is required for the supply of organic acids, specially α-ketoglutaric acid, to counteract ammonia. Uncoupling in mitochondria resulting in the increase of respiration does not seem to occur during ammonium toxicity. [ABSTRACT FROM AUTHOR]

The following enzyme activities were determined in the cucumber (Cucumis sativus L. cv Suisei No 2) during ammonium toxicity; glucose-6-phosphate dehydrogenase, phosphoglucoisomerase, phosphofructokinase, aldolase, glyceraldehyde-3-phosphate dehydrogenase, enolase, pyruvate kinase, aconitase, NADP-isocitrate dehydrogenase, malate dehydrogenase, glutamic dehydrogenase, isocitratase, peroxidase, glycolic acid oxidase and ascorbic acid oxidase. The activities of glucose-6-P dehydrogenase, phosphoglucoisomerase, phosphofructokinase, glyceraldehyde-3-P dehydrogenase, enolase, aconitase, NADP-isocitrate dehydrogenase, glutamic dehydrogenase, and peroxidase in the leaves indicated distinct increases during ammonium toxicity. The highest increase, nearly 5 fold, was found in the phosphofructokinase which is the key enzyme of glycolysis. Aldolase was the only enzyme in the leaves which distinctly decreased due to ammonium treatment. Generally speaking the enzymes in the roots did not show distinct changes except for five enzymes. Glutamic dehydrogenase, isocitratase and aconitase increased distinctly, whereas, glyceraldehyde-3-phosphate dehydrogenase and malate dehydrogenase decreased noticeably during ammonium toxicity. The respiration in the leaves slightly increased by the ammonium treatment. The increases of many enzyme activities and respiration due to ammonium toxicity suggest that the energy metabolism could be affected by the ammonium treatment.

The changes of granule bound starch synthetase activity in cucumber leaves (Cucumis sativus L. cv. Suisei No. 2) were investigated during ammonium toxicity. Generally speaking the quantity of starch granules of injured plants were less than that of normal plants. ADPG is a more effective glucose donor to starch synthesis than UDPG. It was found that the starch synthetase activity of injured plants was decreased compared to the normal plants. This variation of enzyme activity was higher when UDPG was used as glucose donor. The addition of K+ and NH4+ generally inhibited the enzyme activity when UDPG was used as glucose donor, but stimulated it when ADPG was used. This stimulation was found to be more effective in enzymes prepared from injured plants than from normal plants. The level of potassium bound to starch granules was not changed markedly between normal and injured plants. [ABSTRACT FROM AUTHOR]

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/1 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 hand, the rate of 14C incorporation in 80 % ethanol soluble fraction was higher in the treatment of 200 mg/1 NH3-N. In the latter half of experiment, phosphate esters in the leaves 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 glucose-1- phosphate (G-l-P) and fructose-6-phosphate (F-6-P) were higher in injured plants. These results further suggested the disorder of carbohydrate metabolism due lo ammonium toxicity which was reported previously. [ABSTRACT FROM AUTHOR]

Toxic effects of high concentrations of ammonia were studied in the cucumber plant (Cucumis sativus cv. Suisei No. 2). When the cucumber plant was cultured with 200 mg/1 NH3-N (as NH4CI), some characteristic symptoms, probably due to ammonium toxicity, appeared in the leaves after about 1 week, while no such symptoms were observed in the plants cultured with 20 mg/l NH3-N. The level of free sugars in 20 mg/1 NH3-N treated plants decreased with time and was lower than that in plants treated with 200 mg/I NH3-N. Specially distinct differences were found as regards the levels of fructose and glucose. After 9 days' culture the content of glucose in 200 mg/1 NH3-N plants was 17 times higher than that of 20 mg/1 NH3-N plants. From the results of an incorporation of photosynthesized 14CO2 for 3 hour into newly synthezied glucose it is evident that this accumulation of glucose can not be the degradative product of a glucose polymer such as starch. The levels of starch were also studied, and it was found that the starch level decreased due to ammonium toxicity. These results suggest that the translocation of glucose after its synthesis is inhibited by ammonium toxicity, at least up to starch synthesis. [ABSTRACT FROM AUTHOR]

Nicotinamide nucleotide coenzymes were estimated enzymatically in cucumber leaves (Cucumis sativus L. cv. Suisei No. 2) during ammonium toxicity. The contents of all the coenzymes (NAD(H)) and NADP(H)) were found to be higher in the ammonium-treated plants than in the control plants, and the difference attained a maximum at 5 days after the initiation of ammonium treatment. Thereafter, the contents of NAD and NADH returned towards the control level, but NADP and NADPH levels were lowered in injured plants. The ratios of NAD/NAD + NADH and NADP/NADP + + NADPH were little altered by the ammonium treatment. Changes of nicotinamide nucleotide coenzymes are discussed in relation to respiratory metabolism in cucumber leaves during ammonium toxicity. [ABSTRACT FROM AUTHOR]

Galactinol, 1-O-(alpha-D-galactopyranosyl)-myo-inositol, was produced from sucrose as a starting material. UDP-Glc was prepared with sucrose and UDP using sucrose synthase partially purified from sweet potato roots. Then, the UDP-Glc was converted to UDP-Gal using yeast UDP-Gal 4-epimerase from a commercial source. Finally, galactinol was produced from the UDP-Gal and myo-inositol using galactinol synthase partially purified from cucumber leaves. The product was identified as galactinol by the retention times of HPLC, alpha-galactosidase digestion, and NMR spectrometry.

Nitrate reduction in roots and shoots and exchange of reduced N between organs were quantitatively estimated in intact 13-d-old seedlings of two-row barley (Hordeum vulgare L. cv. Daisengold) using the (15)N-incorporation model (A. Gojon et al. (1986) Plant Physiol. 82, 254-260), except that NH + (4) was replaced by NO - (2) . N-depleted seedlings were exposed to media containing both nitrate (1.8 mM) and nitrite (0.2 mM) under a light-dark cycle of 12:12 h at 20°C; the media contained different amounts of (15)N labeling. Experiments were started either immediately after the beginning (expt. 1) or immediately prior to the end (expt. 2) of the light period, and plants were sampled subsequently at each light-dark transition throughout 36 h. The plants effectively utilized (15)NO - (3) and accumulated it as reduced (15)N, predominantly in the shoots. Accumulation of reduced (15)N in both experiments was nearly the same at the end of the experiment but the accumulation pattern in roots and shoots during each 12-h period differed greatly depending on time and the light conditions. In expt. 1, the roots accounted for 31% (light), 58% (dark), and 9% (light) of nitrate reduction by the whole plants, while in expt. 2 the contributions of the root were 82% (dark), 20% (light), and 29% (dark), during each of the three 12-h periods. Xylem transport of nitrate drastically decreased in the dark, but that of reduced N rather increased. The downward translocation of reduced (15)N increased while nitrate reduction in the root decreased, whereas upward translocation decreased while nitrate reduction in the shoot increased. We conclude that the cycling of reduced N through the plant is important for N feeding of each organ, and that the transport system of reduced N by way of xylem and phloem, as well as nitrate reduction by root and shoot, can be modulated in response to the relative magnitude of reduced-N demands by the root and shoot, with the one or the other predominating under different circumstances.

Inorganic orthophosphate (25 millimolar in assay media; Pi) was found to increase in vitro activity of NADH-nitrate reductase (NR) isolated from 2-row barley (Hordeum vulgare L.) leaves with a saturating concentration of nitrate (2 millimolar) but to decrease it with low nitrate levels (<0.1 millimolar). The response to nitrate concentrations was Pi specific. The Lineweaver-Burk plot showed that Pi increases the apparent K(m) for nitrate as well as V(max), whereas it does not alter the K(m) for NADH significantly. These results suggest that the interaction between a molybdenum site of the enzyme and Pi results in alteration of the properties of NR molecule.