University of Hohenheim

About: University of Hohenheim is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Population & Soil water. The organization has 8585 authors who have published 16406 publications receiving 567377 citations.

Strategies of plants for acquisition of iron

Abstract: Two different types of root response to Fe deficiency (strategies) have been identified in species of the Plant Kingdom. In Strategy I which occurs in all plant species except grasses, a plasma membrane-bound reductase is induced with enhanced net excretion of protons. Often the release of reductants/chelators is also higher. In Strategy II which is confined to grasses, there is an increase in the biosynthesis and secretion of phytosiderophores which form chelates with FeIII. Uptake of FeIII phytosiderophores is mediated by a specific transporter in the plasma membrane of root cells of grasses. From results based mainly on long-term studies under non-axenic conditions this classification into two strategies has been questioned, and the utilization of Fe from microbial siderophores has been considered as an alternative strategy particularly in grasses. Possible reasons for controversial results are discussed in some detail. The numerous effects of microorganisms in non-axenic cultures, and the as yet inadequate characterization of the so-called standard (basic) reductase present major limitations to understanding different mechanisms of Fe acquisition. In comparison with the progress made in identifying the cellular mechanisms of root responses in Strategy I and Strategy II plants, our understanding is poor concerning the processes taking place in the apoplasm of root rhizodermal cells and of the role of low-molecular-weight root exudates and siderophores in Fe acquisition of plants growing in soils of differing Fe availability.

Synchronized terrestrial-atmospheric deglacial records around the North Atlantic

Abstract: On the basis of synchronization of three carbon-14 (C-14)-dated lacustrine sequences from Sweden With tree ring and ice core records, the absolute age of the Younger Dryas-Preboreal climatic shift was determined to be 11,450 to 11,390 +/- 80 years before the present. A 150-year-long cooling in the early Preboreal, associated with rising Delta(14)C values, is evident in all records and indicates an ocean ventilation change. This cooling is similar to earlier deglacial coolings, and box-model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the North Atlantic heat conveyor, although the Younger Dryas may have begun as an anomalous meltwater event.