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61.
Partial residuals for the proportional hazards regression model 总被引:34,自引:0,他引:34
62.
ROS ROC; COOK DAVID T.; MARTINEZ-CORTINA CARMEN; PICAZO ISABEL 《Journal of experimental botany》1992,43(11):1475-1481
Six-day-old rice plants (Oryza sativa L. cv. Bahia) were grownin the presence of 0.5 mol m3 Ni or Cd for 5 or 10 d.Five days after treatment, some plants were transferred to amedium containing no heavy metal for 5 or 10 d. Plasmalemmavesicles from shoots of treated, transferred (recovery experiments)and control plants were isolated, ATPase activity and proton-pumpingwere assessed, and free sterols and phospholipids determined.The ATPase hydrolytic activity was increased by 37% and 34%in 5 and 10 d Cd-treated plants, respectively; and by 66% in5 and 10 d Ni-treated plants. However, neither the initial rateof H+ transport nor the proton-pumping rate at steady-statewere significantly affected by the treatments. The relativeproportion (%) of the plasmalemma sterols campesterol and 5-avenasteroldecreased while sitosterol increased during heavy metal treatment.The overall plasmalemma phospholipid fatty acyl chain lengthand degree of unsaturation were also reduced. In experimentswhere plants recovered from Cd and Ni treatment, differencesbetween treated and control plants were reverted, particularlyin 10 d Ni-recovered plants. The possible involvement of lipidsin the regulation of the plasmalemma ATPase as well as the relationshipbetween growth, ATPase and adaptations to stress conditionsare discussed. Key words: Cadmium, nickel, sterols, phospholipids, ATPase 相似文献
63.
PAUL MATTHEW J.; DRISCOLL SIMON P.; LAWLOR DAVID W. 《Journal of experimental botany》1992,43(2):147-153
Stimulation of the rate of photosynthesis at 2·0 kPaO2 in comparison with 21 kPa O2 and carbohydrate accumulationover 4h were measured during exposure of sunflower (Helianthusannuus L.) and rape (Brassica napus L.), grown at 30 °Cand 13 °C, to temperatures between 7 °C and 35 °C.The effect of reducing source: sink ratio by shading on theresponse of photosynthetic rate to temperature was also determined.Stimulation of photosynthesis by 2·0 kPa O2 in comparisonwith 21 kPa O2 decreased over 4 h at cool temperatures in sunflowerplants grown at 30 °C but not in rape grown at 30 °C.Stimulation did not decrease over 4 h in plants grown at 13CC. Sucrose was the main carbohydrate accumulated over 4 h;its accumulation increased with decreasing temperature. Starchaccumulation either decreased or remained the same with decreasingtemperature. In plants grown at 30 °C more carbohydrateaccumulated between 8 °C and 21 °C in sunflower thanin rape, but more carbohydrate accumulated at 30 °C in rapethan in sunflower. In plants grown at 13 °C much less carbohydrateaccumulated between 13 °C and 23 °C than in plants grownat 30 °C. Photosynthetic rate in plants grown at 30 °Cexposed to between 20 °C and 35 °C over 32 h (14 h light-10h dark-8 h light), declined over 32 h at 20 °C and 25 °Cin sunflower and at 20 °C in rape. This fall over 32 h,especially at 20 °C in sunflower, was significantly reducedby shading the rest of the plant. Shading had little effecton photosynthetic rate above 25 °C. The work confirms thatlow temperature imposes a sink-limitation on photosynthesiswhich occurs at higher temperatures in sunflower than in rape.This limitation may be relieved by decreasing the source:sinkratio. Key words: Sunflower, rape, photosynthesis, carbohydrates, sink demand, temperature 相似文献
64.
Fisher information for a bivariate extreme value distribution 总被引:4,自引:0,他引:4
65.
A Perspective on Protistan Nomenclature 总被引:1,自引:0,他引:1
ABSTRACT. The nomenclature of protists is more complicated than that of plants or animals because more than one code of nomenclature applies (i.e. the taxa may be ambiregnal), because of the frequent absence of type material, and because of changing perspectives of the phylogenetic relationships of various groups of protists. These factors often lead to uncertainty over the meaning of names of taxa. If nomenclatural instability is to be avoided, some changes in current practices are required. The nature of the problems and some possible changes are discussed. 相似文献
66.
THE CONTROL OF SEXUAL MORPHOGENESIS IN THE ASCOMYCOTINA 总被引:2,自引:0,他引:2
PAUL S. DYER DAVID S. INGRAM KEITH JOHNSTONE 《Biological reviews of the Cambridge Philosophical Society》1992,67(4):421-458
(1) A series of factors controls sexual morphogenesis in the Ascomycotina, a process involving the formation of novel structures such as ascocarps (fruit bodies) and asci (sacs containing spores) during sexual reproduction. (2) Environmental and genetic factors must be correct before Ascomycetes may sexually reproduce. Compatibility in many heterothallic species is under polygenic control, with the mating type loci and also other genetic factors determining the productivity of sexual crosses. (3) Classical genetic studies have shown that sexual morphogenesis involves the expression of a series of developmentally regulated genes, and this has been confirmed by recent molecular studies which have demonstrated changes in patterns of mRNA and protein synthesis during ascocarp formation. (4) Hyphal differentiation leading to the formation of mature fruit bodies occurs in response to a series of signals, which include various physical and chemical factors. (5) Chemical sex factors have been identified which are believed to have important regulatory or nutritional roles in sexual morphogenesis. These include the following. (a) Diffusible sex hormones which may regulate developmental switching between asexual and sexual modes of reproduction, including (i) pheromones involved with the induction of gametangia and gamete attraction, and (ii) sex morphogens involved with triggering particular stages of fruit body formation. (b) Sexual growth substances which are required as nutrients, and may be precursors for the production of sex hormones, or metabolites used in the synthesis of novel sexual structures. Most of these sex factors are lipids. (6) Certain sex morphogens and sexual growth substances have been shown to exhibit activity in a variety of fungal species, suggesting that fungi of related phylogenetic descent may utilize similar metabolites or signalling factors during sexual reproduction. (7) Phenoloxidase enzymes may catalyse hyphal aggregation in developing fruit bodies. (8) Initial stages of ascocarp development may occur independently of the events of the sexual cycle. However, a link(s) with the functional ascogenous hyphae is needed for the formation of morphologically mature ascocarps. (9) Suitable environmental conditions are sufficient to trigger sexual morphogenesis in homothallic Ascomycetes. However, an extra level of control is present in heterothallic species, with a compatible partner required to complete sexual reproduction. This may be partly because novel regulatory products, formed by the combined action of the mating type loci of different partners, are required for further ascocarp development. (10) Further research is required to identify more fungal chemical sex factors and to determine the role of environmental stress in controlling sexual morphogenesis, and how this may be related to temporal patterns in the expression of mating type genes. 相似文献
67.
Inhibition of Nitrate Assimilation in Roots in the Presence of Ammonium: The Moderating Influence of Potassium 总被引:11,自引:1,他引:10
RUFTY THOMAS W. Jr; JACKSON WILLIAM A.; RAPER C. DAVID Jr. 《Journal of experimental botany》1982,33(6):1122-1137
Experiments were conducted to investigate the effect of concentrationof NH4+ in nutrient solution on root assimilation of NO3and to determine whether the NH4+NO3 interaction wasmodified in the presence of K+. Dark-grown, detopped corn seedlings(cv. Pioneer 3369A) were exposed for 8 h to 0.15 mM Ca(NO3)2and varying concentrations of (NH4)2SO4 in the absence or presenceof 0.15 mM K2SO4. The accelerated phase of NO3 uptakeappeared most sensitive to restriction by additions of 0.15mM (NH4)2SO4. In the absence of K+, the restriction increasedonly slightly even when solution (NH4)2SO4, was increased from0.15 mM to 12.5 mM which was accompanied by an increase of NH4+in the tissue from about 7.0 to 35 µmol g1 fr.wt. of root. Increasing concentrations of solution NH4+ progressivelyinhibited net K+ uptake. At the highest solution NH4+ concentrations,there was an initial net efflux of K+ and no net influx occurredduring the treatment period. The severity of the NH4)SO4 restrictionof NO3 uptake was moderated considerably in the presenceof K+ as long as a net influx of K+ occurred. However, net influxof K+ was not associated with alteration of NH4+ uptake, assimilation,or accumulation in the root tissue. The lack of correlationbetween the severity of restriction of NO3 uptake andendogenous NHJ suggested the restriction resulted from an effectexerted by exogenous NH4+ which tended to saturate at lowersolution NHJ concentrations or by inhibitory factors generatedduring assimilation of NH4+. Several mechanisms were postulatedto account for the moderating influence of K+. In all experiments,root NO3 reduction was restricted by the presence ofambient NH4+. The quantitative decreases in reduction tendedto be less than decreases in NO3 uptake and therefore,could result from inhibition solely of uptake with subsequentlimitation in availability of substrate for the reduction process,but the possibility of a direct effect on reduction could notbe excluded. 相似文献
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