973. DENDROBIUM HEKOUENSE

Dendrobium hekouense Z.J. Liu & L.J. Chen is illustrated. Its distribution, ecology and successful cultivation are described.     

Effects of superoxide radicals on transport (Na+K) adenosine triphosphatase and protection by superoxide dismutase

Membrane (Na+K)ATPase isolated from rat brain was preincubated in a medium in which superoxide radicals were generated enzymatically. Exposure to superoxide radicals caused an irreversible inactivation, which could be prevented by further addition of superoxide dismutase. (Na+K)ATPase was also protected by addition of allopurinol, a xanthine oxidase inhibitor, during preincubation. The K-activated nitrophenylphosphatase associated with (Na+K)ATPase was also found to be inactivated by preincubation with superoxide radicals, which could be prevented by superoxide dismutase.     

Filament formation in Clostridium acidiurici under conditions of elevated temperatures

Terry, David R. (Brigham Young University, Provo, Utah), Abdul Gaffar, and Richard D. Sagers. Filament formation in Clostridium acidiurici under conditions of elevated temperatures. J. Bacteriol. 91:1625-1634. 1966.-Vegetative cells of Clostridium acidiurici, when grown at temperatures up to 42 C, are straight rods varying from 2.5 to 4 mu in length. When grown at 43 C, the cells show a definite tendency to elongate, and, when grown at 44 C, filaments are formed, often exceeding 500 mu in length. Only an occasional cross wall is apparent in the heat-induced long forms, but as the temperature is lowered they readily form cross walls and fragment into short, single cells. Chromatin material is distributed in evenly spaced clusters throughout the length of the filaments. The filaments grown at 44 C are gram-negative, whereas cells grown at 37 C are gram-positive. However, filament formation and gram-negativity apparently are not due to magnesium deficiency, since the gram-negative filaments are formed in concentrations of magnesium ranging from 10(-6) to 10(-2)m. The rapid transition from filaments to single cells upon lowering the temperature from 44 to 37 C suggests that the temperature-related repression of the cross wall-forming system is a phenotypic response rather than the selection of specific mutants which produce the observed phenomena.     

Hormone regulation of development in plant cells

Summary Hormonal stimulation of dedifferentiation and redifferentiation can be studied in explanted, cultured plant tissues. Some of the questions about development which one would like to answer with such a system revolve around the role of quiescence in the stabilization of the differentiated state, the role of replication in the stimulation of redifferentiation and the means by which cells are brought out of the quiescent state. Such a system also offers the potential for revealing the level(s) at which plant hormones operate in the stimulation of replication and differentiation since the responses to hormones can be achieved in vitro. The pea-root cortical parenchyma system has been utilized as a model system in the study of cytokinin plus auxin stimulation of redevelopment of mature, quiescent root cells. The first detected response of the root parenchyma to excision and culture with both of these hormones is an enhanced rate of RNA synthesis between 9 and 12 hr after the initiation of culture. DNA synthesis is stimulated 36 to 39 hr after RNA synthesis (after 48 hr in culture). During this 48-hr period various cytological changes have been observed which are compatible with renewed nucleic acid synthesis, but cytological changes have not been observed prior to the onset of hormone-stimulated RNA synthesis. The first mitoses and cytokineses occur after 60 and 72 hr, respectively. Terminally differentiated tracheary elements are first formed in these cultures after 120 to 168 hr when both the cytokinin and auxin are present at adequate levels. Studies employing inhibitors suggest that tracheary element differentiation is dependent upon the DNA replication that normally accompanies cell replication. Temperature probes of the period between the initiation of cultures and the appearance of the terminally differentiated tracheary elements have been initiated and, in conjunction with previous studies employing inhibitors and analogues, may allow one to distinguish between a variety of potential models of hormone-stimulated redifferentiation. Presented in the Opening Symposium on Nutritional Factors and Differentiation at the 28th Annual Meeting of the Tissue Culture Association, New Orleans, Louisiana, June 6–9, 1977. Supported in part by grants from the National Science Foundation (GB 36948) and the Public Health Service (RR 07092).     

Effects of scale on interpreting life-history characteristics of ungulates and carnivores

Many life-history characteristics of large mammals are scale sensitive. We provide examples where varying temporal and spatial scales can affect interpretation of data concerning life-history characteristics in large herbivores and carnivores and offer recommendations for selecting the most appropriate sampling scale or scales. We also document that some animals make decisions concerning their spatial distribution at scales well beyond the size of the home range. Conversely, other decisions involving sexual segregation of sexes, or where to give birth, may be made at scales below the level of the habitat patch. Such differences in behaviour affect our understanding of habitat selection in large herbivores, and interpreting tradeoffs between acquiring essential resources and avoiding predators. Moreover, some landscape attributes may be selected at one scale, whereas other characteristics of the environment may be selected at another. We argue that even sophisticated models for explaining the ecology and behaviour of mammals benefit from framing specific hypotheses that are related to the to the life-history characteristics of those animals. We also believe that the failure to consider and select the most appropriate scale, or suite of scales, may lead to the mismanagement of critical natural resources. We forge relationships among scale, life-history characteristics of mammals, and biodiversity. Finally, we synthesize the literature on scale for large mammals and make recommendations for future research.