79 research outputs found
A Model for the Development of the Rhizobial and Arbuscular Mycorrhizal Symbioses in Legumes and Its Use to Understand the Roles of Ethylene in the Establishment of these two Symbioses
We propose a model depicting the development of nodulation and arbuscular mycorrhizae. Both processes are dissected into many steps, using Pisum sativum L. nodulation mutants as a guideline. For nodulation, we distinguish two main developmental programs, one epidermal and one cortical. Whereas Nod factors alone affect the cortical program, bacteria are required to trigger the epidermal events. We propose that the two programs of the rhizobial symbiosis evolved separately and that, over time, they came to function together. The distinction between these two programs does not exist for arbuscular mycorrhizae development despite events occurring in both root tissues. Mutations that affect both symbioses are restricted to the epidermal program. We propose here sites of action and potential roles for ethylene during the formation of the two symbioses with a specific hypothesis for nodule organogenesis. Assuming the epidermis does not make ethylene, the microsymbionts probably first encounter a regulatory level of ethylene at the epidermis–outermost cortical cell layer interface. Depending on the hormone concentrations there, infection will either progress or be blocked. In the former case, ethylene affects the cortex cytoskeleton, allowing reorganization that facilitates infection; in the latter case, ethylene acts on several enzymes that interfere with infection thread growth, causing it to abort. Throughout this review, the difficulty of generalizing the roles of ethylene is emphasized and numerous examples are given to demonstrate the diversity that exists in plants
THE EFFECT OF PLASMA GLUCOSE ON THE GROWTH HORMONE RESPONSE TO HUMAN PANCREATIC GROWTH HORMONE RELEASING FACTOR IN NORMAL SUBJECTS
“Medical Education in the Shadow of ‘Stealth Euthanasia’” among Catholics: Are we Fighting Secularism or Heresy?
Untersuchungen mit einer empfindlichen radioimmuno-logischen Doppelantik�rpermethode f�r menschliches Wachs-tumshormon (HGH): Wachstumshormonspiegel im Serum nach rascher Infusion von Tolbutamid
Mapping tree density at a global scale
The global extent and distribution of forest trees is central to our understanding of the terrestrial biosphere. We provide the first spatially continuous map of forest tree density at a global scale. This map reveals that the global number of trees is approximately 3.04 trillion, an order of magnitude higher than the previous estimate. Of these trees, approximately 1.39 trillion exist in tropical and subtropical forests, with 0.74 trillion in boreal regions and 0.61 trillion in temperate regions. Biome-level trends in tree density demonstrate the importance of climate and topography in controlling local tree densities at finer scales, as well as the overwhelming effect of humans across most of the world. Based on our projected tree densities, we estimate that over 15 billion trees are cut down each year, and the global number of trees has fallen by approximately 46% since the start of human civilization
IS THE GROWTH-HORMONE RESPONSE TO INSULIN DUE TO HYPOGLYCAEMIA, HYPERINSULINAEMIA OR A FALL IN PLASMA FREE FATTY ACIDS?
Television Viewing Habits of Preclinical UK Medical Undergraduates: Further Potential Implications for Bioethics
Effect of chromium picolinate on histopathological alterations in STZ and neonatal STZ diabetic rats
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