The Effects of Light and Gravity on the Horizontal Curvature of Roots of Gravitropic and Agravitropic Arabidopsis thaliana L

In an attempt to study and distinguish the effects of light and gravity on the direction of horizontal root growth, wild-type and an agravitropic mutant of Arabidopsis thaliana L., aux-1 were examined. The mutant aux-1 seedling roots are agravitropic but do respond to light, thus allowing the effects of light and gravity on roots to be studied separately. It is shown that in addition to the recognized negative phototropic and positive gravitropic responses of the root, there are also horizontal curvatures (clockwise or counterclockwise) induced by both unilateral light and gravity. The effects of light and gravity in inducing the horizontal curvature of roots are synergistic when both act in the same direction, and are antagonistic when acting in opposite directions. The results indicate that light and gravity interact to determine the direction and magnitude of the horizontal curvature of roots.     

Mechanism of hyperoxia-induced pulmonary vascular paralysis: effect of antioxidant pretreatment

We designed experiments using isolated rabbit lungs to determine the effect of hyperoxia on the pulmonary vasoconstriction caused by the infusion of the lipid peroxide tert-butyl hydroperoxide (t-bu-OOH), which produces vasoconstriction by stimulating the pulmonary synthesis of thromboxane. Exposure to 48-60 h of 100% O2 at 1 ATA markedly reduced the increase in pulmonary artery pressure caused by t-bu-OOH infusion. We also investigated whether the mechanism for the attenuated vasoconstriction was due to altered production of arachidonate mediators or oxidant-induced damage to the contractile mechanism. In addition to infusing t-bu-OOH, which selectively stimulates thromboxane production, we also infused Intralipid, an esterified fatty acid emulsion that stimulates production of both thromboxane and prostacyclin. These experiments were done to study the effect of hyperoxia on prostacyclin synthesis. To determine if antioxidant therapy would prevent the changes in mediator production and vascular reactivity caused by hyperoxia, we pretreated animals with the antioxidants butylated hydroxyanisole (BHA) or vitamin E. The lack of vascular reactivity to t-bu-OOH was not due to a decrease in thromboxane synthesis or an increase in prostacyclin synthesis. Hyperoxia did not affect thromboxane synthesis during basal conditions or after stimulation of synthesis by t-bu-OOH. 100% O2 also did not effect the basal synthesis of prostacyclin by the lung. Hyperoxia did, however, markedly reduce prostacyclin synthesis when it was stimulated by Intralipid infusion. Antioxidant pretreatment did not reverse the inhibition of prostacyclin synthesis but did prevent the loss of vascular reactivity caused by hyperoxia. Thus hyperoxia causes vascular paralysis through oxidant-induced injury to the pulmonary vasculature.     

Free radical damage to cultured porcine aortic endothelial cells and lung fibroblasts: Modulation by culture conditions

Summary Culture conditions modulating cell damage from xanthine plus xanthine oxidase-derived partially reduced oxygen species were studied. Porcine thoracic aorta endothelial cells and porcine lung fibroblasts were maintained in monolayer culture. Cells were prelabeled with⁵¹Cr before xanthine plus xanthine oxidase exposure. Endothelial cells showed 30 to 100% more lysis than fibroblasts and thus seemed more sensitive to this oxidant stress. The effect of cell culture age, as indicated by population doubling level (PDL), was examined. Response of low PDL endothelial cells and fibroblasts subjected to oxidant stress was compared with the response of PDL 15 cells. Both low PDL endothelial cells and fibroblasts responded differently to the lytic effect of xanthine oxidase-derived free radicals than did higher PDL cells. Specific activities of the antioxidant enzymes catalase, managanese superoxide dismutase, copper-zinc superoxide dismutase, glutathione peroxidase, and glucose-6-phosphate dehydrogenase were measured in both low and high PDL fibroblasts and endothelial cells. Antioxidant enzyme specific activities could only partially explain the differences in response to oxidant stress between fibroblasts and endothelial cells and between low and high PDL cells. Cell culture medium composition modulated the rate of production, and relative proportions of xanthine plus xanthine oxidase-derived partially reduced species of oxygen, i.e. superoxide, hydrogen peroxide, and hydroxyl radical. Serum content of medium was important in modulating free radical generation; superoxide production rates decreased 32%, H₂O₂ became undetectable, and hydroxyl radical generation decreased 54% in the presence of 10% serum. The medium protein and iron content also modulated free radical generation. The data suggest that cell culture media constituents, cell type, and cell culture age greatly affect in vitro response of cells subjected to oxidant stress. Research supported by American Lung Association Fellowship Training Grant and Research Training Grant, the R. J. Reynolds Corporation, and National Institutes of Health Grants HL29784 and 1 HL 23805.     

Mechanisms by which endothelin 1 induces pulmonary vasoconstriction in the rabbit.

To investigate the mechanisms by which endothelin 1 (ET-1) causes pulmonary vasoconstriction, we studied the effect of synthetic ET-1 on pulmonary vascular tone in the buffer-perfused isolated rabbit lung. In nanomolar concentrations (1.2-8 nM), ET-1 causes a dose-dependent increase in pulmonary arterial pressure that persists for greater than or equal to 1 h (increase in pressure 19 +/- 2 mmHg with ET-1 vs. 2 +/- 1 with vehicle, P less than 0.0001). Reduction of calcium availability with verapamil, cadmium, or a calcium-free buffer significantly blunts the increase in pressure caused by ET-1. Pretreatment with a calcium-free buffer plus the chelator ethylene glycol-bis(beta-aminoethyl ether)-N,N,N', N'-tetraacetic acid (EGTA) completely eliminates the vasoconstriction. Three different inhibitors of protein kinase C, phloretin, staurosporine, and dihydrosphingosine, significantly diminish the response to ET-1. Indomethacin and a thromboxane synthase inhibitor partially decrease the response to the highest concentration of ET-1. Isoproterenol and dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP) are significantly more effective in preventing the vasoconstriction caused by ET-1 than are nitroprusside and guanosine 5'-cyclic monophosphate (cGMP) analogues. ET-1 in doses of 1.2-8 nM is a potent pulmonary vasoconstrictor in the isolated rabbit lung. ET-1 appears to cause pulmonary vasoconstriction by increasing calcium entry and by activating protein kinase C. Vasodilators that increase cAMP are substantially more effective in preventing the increase in pressure than are drugs that increase cGMP.     

The role of sexual isolation during rapid ecological divergence: Evidence for a new dimension of isolation in Rhagoletis pomonella

The pace of divergence and likelihood of speciation often depends on how and when different types of reproductive barriers evolve. Questions remain about how reproductive isolation evolves after initial divergence. We tested for the presence of sexual isolation (reduced mating between populations due to divergent mating preferences and traits) in Rhagoletis pomonella flies, a model system for incipient ecological speciation. We measured the strength of sexual isolation between two very recently diverged (~170 generations) sympatric populations, adapted to different host fruits (hawthorn and apple). We found that flies from both populations were more likely to mate within than between populations. Thus, sexual isolation may play an important role in reducing gene flow allowed by early-acting ecological barriers. We also tested how warmer temperatures predicted under climate change could alter sexual isolation and found that sexual isolation was markedly asymmetric under warmer temperatures – apple males and hawthorn females mated randomly while apple females and hawthorn males mated more within populations than between. Our findings provide a window into the early speciation process and the role of sexual isolation after initial ecological divergence, in addition to examining how environmental conditions could shape the likelihood of further divergence.     

Lipase Induction in Mucor hiemalis

The influence on lipase induction in Mucor hiemalis of different types of triglycerides containing mainly oleic acid (olive oil), erucic acid (mustard oil), or saturated fatty acids of 8 to 16 carbons (coconut oil) was studied. The fungus was grown in shake flasks in a fermentation medium containing peptone, minerals, and glucose or one of the oils as the carbon source. Maximum lipase was produced when the initial pH of the fermentation medium was kept at 4.0. Addition of Ca²⁺ to the medium did not increase lipase production. The optimum pH for activity of both the mycelial and extracellular lipases was found to be 7.0. The fungus produced a significant amount of lipase in the presence of glucose, but the lipase activity increased markedly when olive oil was added to the medium at the beginning of the fermentation. Addition of olive oil at a later stage did not induce as much enzyme. Studies with washed mycelia showed that a greater amount of lipase was released when olive oil was present than when glucose was present. Among the various types of triglycerides used as the carbon source, olive oil was found to be most effective in inducing the lipase. Olive oil and mustard oil fatty acids inhibited the lipase more than those of coconut oil. The lipase induced by a particular type of triglyceride did not seem to be specific for the same triglyceride, nor was it inhibited specifically by it. Irrespective of the triglyceride used in the fermentation medium, the lipase produced was most active against coconut oil triglyceride, and this specificity, as shown by lipase activities in an n-heptane system, was not found to be due to a better emulsification of this oil. The lipase of M. hiemalis can be considered to be both constitutive and inducible.     

The fauna of benthic sediments from the organically enriched Oslofjord,Norway

The macrobenthic fauna of the organically enriched Oslofjord was sampled in Sept.–Nov. 1977. Seventy-six stations were sampled using a stratified random plan. A total of 146 species were identified, dominated by polychaetes, molluscs and echinoderms. The faunal data were analysed by a variety of methods including diversity indices, log-normal distribution of individuals among species, factor analysis and numerical classification. The primary aim was the detection of pollution-induced disturbance and to delimit the extent of pollution on the benthic fauna of Oslofjord. All of the methods used showed a gradient from heavy pollution at the innermost part of the fjord where few species occurred, together with high dominance and low diversity, to normal unpolluted conditions at the Drøbak sill with high species diversity. From the classification analysis a combination of both site and species data revealed a trend in species groupings which were broadly similar to data from other Scandinavian fjords and from Scotland. Hydrographical and biological data taken at the turn of the century and in the 1960's compared with the present data show declining conditions in Oslofjord, due primarily to organic enrichment combined with a naturally poor water exchange which leads to stagnation of the water mass.