A comparison between ammonium and nitrate nutrition of young sugar-beet plants grown in nutrient solutions at constant acidity. 1. Production of dry matter, ionic balance and chemical composition.

Diploid sugar beet was grown in nutrient culture with ammonium and nitrate N in solutions kept at constant pH by automatic titration. Since plants given nitrate N yielded only 12% more than those given ammonium N, the effects of form of N on plant chemical composition could be determined. The excess of cations in the plant (C-A) was >3 times as great in plants given nitrate as in those given ammonium. The acidity evolved into the culture medium was a good measure of ammonium uptake, whereas with nitrate the amount of alkalinity evolved was unrelated to and small in comparison with the amount of nitrate absorbed. The rate of H+ production decreased during darkness and that of OH- decreased during or just after the dark phase. Levels of soluble carbohydrates in plants given nitrate were over twice as high as in those given ammonium. Data are given on levels of 6 organic acids, K, Na, Ca Mg, P, S and Cl. (Abstract retrieved from CAB Abstracts by CABI’s permission

Effect of ammonium nutrition on uptake and metabolism of nitrate in wheat.

Wheat plants 1 month old grown in nitrate culture were exposed for 2 days to media containing 4 meq NO3 and 0-4 meq NH4/l. Where solutions contained both forms of N the uptake of NH4 exceeded that of NO3 even at the lowest NH4 level. NH4 metabolism predominated over NO3 assimilation and resulted in a higher free amino acid content, a lower carboxylate content and lower nitrate reductase activity in the tops than with NO3 alone. NH4 inhibited nitrate reductase activity whereas amino acids did not. The fall in activity of this enzyme in wheat tops caused by NH4 nutrition could not be related to the low level of tissue NH4 and it was suggested that changes in the redox situation in the cells might be involved. (Abstract retrieved from CAB Abstracts by CABI’s permission

Nitrate reductase activity and oxalate content of sugar-beet leaves.

Diploid sugar beet was grown in controlled environment at 25/17 deg C in 14-h photoperiods in well aerated, regularly changed nutrient solution containing 6 meq NO3/l. When 6 leaves had been expanded, the total carboxylate content of the oldest leaf (leaf 1) was found to be 5836 meq/kg DM, while that of leaf 6 was only 2312 meq/kg; the difference was mainly due to oxalate content, which was 5236 meq/kg in leaf 1 and 1744 meq/kg in leaf 6. Nitrate-N content was about 50% higher in leaf 1 than in leaf 4. Nitrate-reductase activity fell to very low values as leaves aged. Experiments in which young and old leaf material was mixed, or oxalate at 0-4000 meq/kg DM was added to leaf samples, showed that oxalate had no substantial effect on nitrate-reductase activity. (Abstract retrieved from CAB Abstracts by CABI’s permission

Naar een duurzaam beheer van de aal in Nederland?

Het gaat al decennia lang erg slecht met de aal en de aal-visserij in Nederland en de rest van Europa. De Europese Unie heeft daarom besloten tot een Herstelprogramma. In dit kader moet Nederland voor het eind van dit jaar een beheersplan maken. Dit artikel geeft een samenvatting van de achtergronden, de resultaten van recent onderzoek en de mogelijkheden voor bescherming

A REVISION OF THE AFRICAN GENERA PAROPSIOPSIS AND SMEATHMANNIA (PASSIFLORACEAE - PAROPSIEAE), INCLUDING A NEW SPECIES OF PAROPSIOPSIS FROM CAMEROON

The African genera Paropsiopsis Engl. and Smeathmannia R.Br. (Passifloraceae - Paropsieae) are revised. The two genera are well separated based on the presence or absence of a second, annuliform, corona, as well as the number of stamens and curvature of their filaments. An overview of important characters and a key to all genera of Paropsieae is provided. In Paropsiopsis all previously recognised species are united under P. decandra (Baill.) Sleumer. In addition one species, Paropsiopsis atrichogyna J.M.de Vos & Breteler, is newly described and illustrated. In Smeathmannia both previously recognised species are maintained, but infraspecific taxa are rejected. Descriptions of both genera and their species, keys to species, illustrations and distribution maps are provide