Application of Two-Phase Regression to Geotechnical Data

2000 Mathematics Subject Classification: 62F10, 62J05, 62P30A method for estimating a transition parameter in two-phase regression is described. The two phases are fitted and simultaneously the transition point is estimated. Practical application of the method is demonstrated on the data for determining soil hydraulic properties.Partly supported by projects FOR 444, Deutsche Forschungsgemeinschaft, Germany, MM1301/2003, National Science Fund, Bulgaria, and PRO-ENBIS: GTC1-2001-43031

The role of nitrate reduction in the anoxic metabolism of roots - II. Anoxic metabolism of tobacco roots with or without nitrate reductase activity

The effects of root anoxia on a tobacco (Nicotiana tabacum) wild type (WT) and a transformant (LNR-H) lacking root nitrate reductase were compared. LNR-H plants were visibly more sensitive to oxygen deprivation than WT, showing rapid and heavy wilting symptoms. LNR-H roots also produced substantially more ethanol and lactate than WT roots under anoxia, and their sugar and sugar-P content, as well as their ATP levels, remained higher. The fermentation rates of WT and LNR-H roots were unaffected by sugar feeding and the higher fermentation rate in the LNR-H roots was associated with a greater acidification of the cytoplasm under anoxia. From these observations it is concluded: (i) that the absence of NR activity in the LNR-H roots does not necessarily limit NADH recycling; and (ii) that nitrate reduction in the WT roots results in a more acidifying metabolism. It is the higher metabolic rate in the LNR-H roots that leads to the greater cytoplasmic acidification under anoxia despite the absence of a contribution from the metabolism of nitrate. Competition for NADH cannot explain this difference in metabolic rate, and it remains unclear why the NR-free LNR-H, and tungstate-treated WT roots, had much higher fermentation rates than WT roots. The difference in anaerobic metabolism could still be due to the presence or absence of nitrate reductase and the possibility that this could occur through the production of nitric oxide is discussed

Discrepancy between nitrate reduction rates in intact leaves and nitrate reductase activity in leaf extracts: what limits nitrate reduction in situ?

Kaiser WM, Stoimenova M, Glaab J, Kandlbinder A. Discrepancy between nitrate reduction rates in intact leaves and nitrate reductase activity in leaf extracts: what limits nitrate reduction in situ? Planta. 2000;210(5):801-807