Adaptation of Active Proton Pumping and Plasmalemma ATPase Activity of Corn Roots to Low Root Medium pH1

Corn (Zea mays L.) root adaptation to pH 3.5 in comparison with pH 6.0 (control) was investigated in long-term nutrient solution experiments. When pH was gradually reduced, comparable root growth was observed irrespective of whether the pH was 3.5 or 6.0. After low-pH adaptation, H+ release of corn roots in vivo at pH 5.6 was about 3 times higher than that of control. Plasmalemma of corn roots was isolated for investigation in vitro. At optimum assay pH, in comparison with control, the following increases of the various parameters were caused by low-pH treatment: (a) hydrolytic ATPase activity, (b) maximum initial velocity and Michaelis constant (c) activation energy of H+-ATPase, (d) H+-pumping activity, (e) H+ permeability of plasmalemma, and (f) pH gradient across the membranes of plasmalemma vesicles. In addition, vanadate sensitivity remained unchanged. It is concluded that plasmalemma H+-ATPase contributes significantly to the adaptation of corn roots to low pH. A restricted net H+ release at low pH in vivo may be attributed to the steeper pH gradient and enhanced H+ permeability of plasmalemma but not to deactivation of H+-ATPase. Possible mechanisms responsible for adaptation of plasmalemma H+-ATPase to low solution pH during plant cultivation are discussed.

Untersuchungen zur Ikonizität von Technischen Grafiken in Hinblick auf ihren Einsatz in Anwenderunterstützungen : eine Usability Studie

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Organic geochemistry on sediment profiles from the Arctic Ocean

During the ARCTIC '91-Expedition with RV 'Polarstern', several Multicorer and Kastenlot-cores were recovered along a profile crossing the eastern part of the Arctic Ocean. The investigated cores consist mainly of clayey-silty sediments, and some units with a higher sand content. In this thesis, detailed sedimentological and organic-geochemical investigations were performed. In part, the near surface sediments were AMS-14C dated making it possible to Interpret the results of the organic-geochemical investigations in terms of climatic changes (isotopic stage 2 to the Holocene). The more or less absence of foraminifers within the long cores prevented the development of an oxygen isotope stratigraphy. Only the results of core PS2174-5 from the Amundsen-Basin could be discussed in terms of the climatic change that could be dated back to oxygen isotope stage 7. Detailed organic-geochemical investigations in the central Arctic Ocean are rare. Therefore, several different organic-geochemical methods were used to obtain a wide range of data for the Interpretation of the organic matter. The high organic carbon content of the surface sediments is derived from a high input of terrigenous organic matter. The terrigenous organic material is most likely entrained within the sea-ice On the Siberian shelves and released during ice-drift over the Arctic Ocean. Other factors such as iceberg-transport and turbidites are also responsible for the high input of terrigenous organic matter. Due to the more or less closed sea-ice Cover, the Arctic Ocean is known as a low productivity system. A model shows, that only 2 % of the organic matter in central Arctic Ocean sediments is of a marine origin. The influence of the West-Spitsbergen current increases the marine organic matter content to 16 %. Short chain n-alkanes (C17 and C19) can be used as a marker of marine productivity in the Arctic Ocean. Higher contents of short chain n-alkanes exist in surface sediments of the Lomonosov-Ridge and the Makarov-Basin, indicating a higher marine productivity caused by a reduced sea-ice Cover. The Beaufort-Gyre and Transpolar-Drift drift Patterns could be responsible for the lower sea-ice distribution in this region. The sediments of Stage 2 and Stage 3 in this region are also dominated by a higher content of short chain-nalkanes indicating a comparable ice-drift Pattern during that time. The content and composition of organic carbon in the sediments of core PS2174-5 reflect glaciallinterglacial changes. Interglacial stages 7 and 5e show a low organic carbon content (C 0,5 %) and, as indicated by high hydrogen-indices, low CIN-ratios, higher content of n-alkanes (C17 and C19) and a higher opal content, a higher marine productivity. In the Holocene, a high content of foraminifers, coccoliths, ostracodes, and sponge spicules indicate higher surface-water productivity. Nevertheless, the low hydrogenindices reveal a high content of terrigenous organic matter. Therefore, the Holocene seems to be different from interglacials 7 and 5e. During the glacial periods (stages 6, upper 5, and 4), TOC-values are significantly higher (0.7 to 1.3 %). In addition, low hydrogen-indices, high CIN-ratios, low short chain n-alkanes and opal contents provide evidence for a higher input of terrigenous organic matter and reduced marine productivity. The high lignin content in core sections with high TOC-contents, substantiates the high input of terrigenous organic matter. Changes in the content and composition of the organic carbon is believed to vary with the fluctuations in sea-level and sea-ice coverage.