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1.
Season of fire have marked effects on the germination and establishment of serotinous shrubs of the family Proteaceae in fynbos vegetation. To investigate reasons for this, we simulated the effects of different fire seasons by planting seeds into cleared fynbos and then followed their progress. Four species of Proteaceae were planted monthly at four sites over two and a half years. Exclosures were used to exclude rodent seed predators. Germination was confined largely to the three winter months (June–Aug.). Seeds planted from January–June had higher germination than those planted in the second half of the year. Higher levels of regeneration noted after fires in the first half of the year, were previously hypothesised to be results of predation. However, we obtained similar results despite the exclusion of seed predators. Monthly minimum temperature was strongly correlated with germination percentage but monthly rainfall was not. Loss of seed viability may be important, in determining post-fire seedling densities. Differential seedling mortality of earlier and late germinants appears to be unimportant in determining establishment levels. Our results nevertheless support the current practice of restricting management fires in fynbos to the summer-autumn period. 相似文献
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J L Slonczewski T N Gonzalez F M Bartholomew N J Holt 《Journal of bacteriology》1987,169(7):3001-3006
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The cell cycle of the photosynthetic unicellular alga Euglena gracilis growing in phototrophic medium is regulated by light. To investigate the relationship of this cell cycle response to light stimulated photosynthesis, we have tested the effect of the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on Euglena cell cycle transit. While DCMU does not block light stimulated cells from entering the S phase of the cell cycle, it does inhibit the transit through G2/M. The specificity of this response and its relationship to photosynthesis was studied by looking at the effect of DCMU on dark grown wild-type cells, and on two bleached variants of Euglena (W3BUL and W10BSmL) that lack chloroplasts. The drug does block G2/M in these cells, but not entrance into the cell cycle. Our studies show that entrance of cells into the cell cycle from a quiescent state does not require active photosynthesis, and that DCMU has effects on G2/M transit that are independent of the photosynthetic capacity of the cells. 相似文献
5.
Temporal Patterns of Reported Single-Vehicle Car and Truck Accidents in Texas, U.S.A. During 1980-1983 总被引:1,自引:0,他引:1
Peter H. Langlois Michael H. Smolensky Bartholomew P. Hsi Francis W. Weir 《Chronobiology international》1985,2(2):131-140
Reported single car and truck accidents due specifically to driver 'fatigue' for the 4-year span of 1980-1983 were analyzed for 24-hr, 7-d and 1-yr patterns. Three types of data were examined: (1) accidents in rural Texas, (2) accidents only in San Antonio, the fourth largest city in Texas and (3) accident ratio (number of accidents per time interval divided by traffic volume for the interval) in this city.
A statistically significant seasonal variation of relatively low amplitude with peaks in May and July was detected only for accidents in rural areas. High-amplitude periodicities of 7 d were evident in all the data sets, with a peak on the weekend. A very prominent 24-hr pattern was detected as well, with the acrophase determined by single cosinor around 0300. A slight secondary peak in accidents, around 1500, was evident in the data from the rural areas. This secondary peak represented a 12-hr rhythm in addition to the 24-hr. Overall, features of the temporal patterns in accidents over 24 hr and over the year in urban and rural areas differed only slightly. Accident ratios yielded results similar to accident frequencies. However, with regard to the rural data, the shape of the 24-hr temporal pattern varied with driver age; older drivers exhibited a flatter curve with a more pronounced afternoon rather than early morning (around 0300) peak. 相似文献
A statistically significant seasonal variation of relatively low amplitude with peaks in May and July was detected only for accidents in rural areas. High-amplitude periodicities of 7 d were evident in all the data sets, with a peak on the weekend. A very prominent 24-hr pattern was detected as well, with the acrophase determined by single cosinor around 0300. A slight secondary peak in accidents, around 1500, was evident in the data from the rural areas. This secondary peak represented a 12-hr rhythm in addition to the 24-hr. Overall, features of the temporal patterns in accidents over 24 hr and over the year in urban and rural areas differed only slightly. Accident ratios yielded results similar to accident frequencies. However, with regard to the rural data, the shape of the 24-hr temporal pattern varied with driver age; older drivers exhibited a flatter curve with a more pronounced afternoon rather than early morning (around 0300) peak. 相似文献
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C Bartholomew W Charles C Saxinger W Blattner M Robert-Guroff C Raju P Ratan W Ince D Quamina K Basdeo-Maharaj et al. 《BMJ (Clinical research ed.)》1985,290(6477):1243-1246
Adult T cell leukaemia/lymphoma was first recognised as a clinical entity in southwest Japan. Subsequently the Caribbean has been found to be another area where the disease is endemic, and sporadic cases have been identified in different parts of the world. The human T cell leukaemia/lymphoma virus (HTLV-I) is causally related to adult T cell leukaemia/lymphoma. A subgroup of HTLV, designated HTLV-III, has recently been isolated from many patients with the acquired immunodeficiency syndrome (AIDS) and preAIDS, and there is now evidence that this variant is the primary cause of AIDS. This is the first report from Trinidad to describe 12 cases of adult T cell leukaemia/lymphoma and 14 of AIDS. All were in patients of African descent. No cases were seen in subjects of East Indian descent, who, like those of African descent, comprise as much as 40% of the population. West Indians of African descent may have increased susceptibility to infection with both HTLV-I and HTLV-III. 相似文献
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The effect of 3-sulphation and taurine conjugation on the uptake of chenodeoxycholic acid by rat hepatocytes 总被引:1,自引:0,他引:1
The hepatic uptake of chenodeoxycholic acid, taurochenodeoxycholic acid, chenodeoxycholic acid 3-sulphate and taurochenodeoxycholate acid 3-sulphate by isolated rat hepatocytes was examined. Taurochenodeoxycholic acid, taurochenodeoxycholic acid 3-sulphate and chenodeoxycholic acid 3-sulphate uptake occurred by a saturable, energy-dependent process while chenodeoxycholic acid uptake was predominantly non-saturable, possibly simple diffusion. Apparent Km (mumol/l) and Vmax (nmol/mg protein per min) values (mean +/- S.D.), respectively, were: chenodeoxycholic acid (saturable component), 33 +/- 6.4 and 4.8 +/- 0.6; taurochenodeoxycholic acid, 11.1 +/- 2.0 and 3.1 +/- 0.5; chenodeoxycholic acid 3-sulphate, 6.1 +/- 0.9 and 2.3 +/- 0.4; and taurochenodeoxycholic acid 3-sulphate, 5.0 +/- 0.7 and 0.9 +/- 0.15. Both conjugation with taurine and sulphation at the 3 position resulted in a reduction in the values of Km and Vmax. Uptake of each of the bile acids taurochenodeoxycholic acid, taurochenodeoxycholic acid 3-sulphate and chenodeoxycholic acid 3-sulphate was competitively inhibited by the other two, with taurochenodeoxycholic acid a potent inhibitor of both taurochenodeoxycholic acid 3-sulphate and chenodeoxycholic acid 3-sulphate uptake. Other bile acids also inhibited. Uptake was inhibited by albumin in the order chenodeoxycholic acid 3-sulphate greater than taurochenodeoxycholic acid 3-sulphate greater than taurochenodeoxycholic acid and was dependent on the extent of bile acid binding to albumin. 相似文献
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Use of the gas chromatograph and a mercury-to-glass sealed respirometer adapted for gas syringe sampling, allowed the rapid, accurate characterization of CO2 evolution rates from live and from dead-sterile Zea mays L. grain dried to moisture levels of 12.6 to 1.4%. The live grain at the lowest moisture level showed an elevated rate inconsistent with the exponential increase in rate of CO2 evolution with increasing moisture found for maize with moisture contents from 4 to 12.6%. At the lowest moisture level, rates of CO2 evolution from dead-sterile grain were greater than for live grain. Moisture had no effect on CO2 evolution from dead-sterile grain. Increasing temperature and increasing levels of O2 in the storage atmosphere resulted in increased rates of CO2 evolution from both live and dead-sterile maize. CO2 production rates from live and from dead-sterile grain decreased with increasing storage time, even though respirometer CO2 concentrations were less than 1% at the end of the experiment. Our results indicate that CO2 production is not a dependable measure of respiration in dry seeds. Other experiments indicate that oxygen absorption also is not reliable in maize grain. 相似文献