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11.
Kinetic studies were performed on fresh-cut and aged leaf discsof Spinacia oleracea L. in order to investigate the regulatoryprocesses involved in sugar transport across the mesophyll plasmamembrane. A comparison of the kinetic profiles for fructose,glucose, sucrose and arginine obtained on freshly-cut and ageddiscs revealed that during wound-recovery, uptake is enhanced,but that this enhancement varies considerably for the differentsubstrates tested. Variation in the saturable and first-orderkinetic components of uptake was also observed. The involvementof a phosphoinositide-signalling mechanism in the wounding processwas examined by pretreating spinach leaves with lithium. Lithiuminhibited the enhancement of uptake and this effect was reversedby the addition of miro-inositol. However, in some experimentsthe tissue appeared to be insensitive to Li+. Gas chromatographicanalyses performed on cut discs indicated that ethylene wasproduced in response to wounding and that the addition of cobaltto the ageing media inhibited this ethylene production. Comparativekinetic studies of control and cobalt-treated discs indicatedthat ethylene was essential for the enhancement of transportacross the plasma membrane. However, addition of ethylene touncut tissue caused only a partial increase in the uptake offructose, which indicates that some additional wound-signallingcomponent is involved. Addition of cycloheximide to the recoverymedia completely inhibited this enhancement phenomenon. Thecycloheximide-response was not due to an inhibition of ACC synthasesynthesis nor to a reduction of ATP levels. We concluded thatthe effect of cycloheximide was on protein synthesis. Our resultsare discussed in terms of possible cellular and molecular mechanismsregulating sugar transport. Key words: Sugar transport, wounding, ethylene production, spinach leaves 相似文献
12.
LEONARD B. RADINSKY 《Biological journal of the Linnean Society. Linnean Society of London》1984,22(1):31-41
Skull length is the measurement most commonly used as a standard against which other aspects of cranial morphology are compared to derive an index of relative size or proportions. However, skull length is composed of two different functional components, facial skull and cerebral skull, which vary independently and have different scaling relationships with body size. An analysis of carnivore skull shape with measurements standardized against basicranium length produced very different results than an analysis using skull length as the standard. For example, expressions of relative size of cranial measurements were reduced by 13% in mustelids and increased by 20% in canids, reflecting removal of jaw length (short in mustelids and long in canids) from the comparative standard (basicranial axis length). Cranial measurements scale with higher allometric exponents against basicranial axis length than against skull length. 相似文献
13.
SYNOPSIS. In the present study the timing of metamorphosis inan anural ascidian, Molgula pacifica, was compared to metamorphosisin a urodele species Boltenia villosa. Metamorphosis in M. pacificawas triggered at a fixed time in development (3236 hoursafter fertilization), just prior to hatching. In contrast, metamorphosiswas triggered in B. villosa after the hatched larvae respondedto substrate cues. The timing of metamorphosisin B. villosawas often delayed for up to four days, whereas delays in M.pacifica were not observed. An antibody, termed Epi-3, was foundto cross-react exclusively with epidermal cells in both species.The binding of FITC-labelled Epi-3 was very low prior to metamorphosisand then it increased dramatically after metamorphosis was triggered.The cytoplasm of ampulla tip cells and the tunic immediatelysurrounding each ampulla showed the highest levels of Epi-3fluorescence. The histological and ultrastructural featuresof the ampulla cells suggest that Epi-3 antibody recognizesgranules localized in the apical cytoplasm. How the evolution of an internal "clock" mechanism responsiblefor initiating metamorphosis may be beneficial to anural speciesis discussed. One possibility is that the anural type of timingmechanism reduces mortality rates during this critical phaseof its life cycle. 相似文献
14.
TELFER WILLIAM H.; WOODRUFF RICHARD I.; HUEBNER ERWIN 《Integrative and comparative biology》1981,21(3):675-686
SYNOPSIS. In the oocyte-nurse cell syncytium of meroistic insectovaries a gradient in electrical potential is shown to drivea micro-injected basic protein (fluorescein-labeled lysozyme)and its methylcarboxylated, acidic derivative in opposite directions.In the polytrophic Cecropia ovary the electrophoretic effectis greatest in the intercellular bridges, while in the telotrophicRhodnius ovary it is greatest within the nurse chamber. We speculatethat in both systems the potential gradient prevents the freediffusion of cell cycle and differentiative control proteins,while at the same time reinforcing the transport of acidic precursorstoward the ooplasm. Because of its apparent ability to affectthe distribution of polyions that govern nuclear function, electricalpolarity can also be envisioned to have a more general rolein the control of differentiation. The possibility is consideredthat it serves as a relay mechanism for the non-diffusing determinantthat is already known to govern the differentiation of oocytesfrom nurse cells. 相似文献
15.
16.
Phyletic Relationships of Living Sharks and Rays 总被引:3,自引:1,他引:2
A set of hypotheses are developed for the origin of living sharksand rays and the interrelationships of their major groups, usingsome methods of cladistic analysis to relate groups with sharedderived characters. Comparative studies on living sharks andrays combined with new data on fossil sharks suggests that theliving groups ultimately stem from a common ancestral groupof "neoselachian" sharks with many modern characters. Reinterpretationsof "amphistyly" in modern sharks is presented on new data. 相似文献
17.
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
18.
LEONARD B. RADINSKY 《Biological journal of the Linnean Society. Linnean Society of London》1981,15(4):369-388
Fifteen variables, selected primarily to reflect functionally significant aspects of cranial morphology, were measured on one skull each of 62 species of modern carnivores, including viverrids, canids, mustelids and felids. To allow comparisons between species of different sizes without the potentially confounding effects of allometric shape changes, the measurements were transformed to dimensionless variables, based on the residuals from allometric equations. Fourteen out of 15 of the transformed variables distinguish one or more of the four family groups and the rotated first two axes of a principal components analysis distinguish all four families from each other. The following functional hypotheses are proposed: mustelids and felids have the most powerful bites and canids the weakest among the four family groups studied; mustelids and, to a lesser degree, felids have more powerful neck musculature than do canids and viverrids; and visual abilities are best developed among felids and least developed among mustelids. The first two functional hypotheses suggest possible differences in killing behaviour, which are supported by a preliminary survey of the literature on such behaviour. Allometric analysis of the 15 cranial measures shows that the neurocranial components scale with negative allometry, while most of the other measures scale approximately isometrically. 相似文献
19.
WILLIAM TRAGER 《The Journal of eukaryotic microbiology》1979,26(1):125-129
SYNOPSIS. A new design of flow vessel provides a method for continuous culture of P. falciparum in a settled layer of human erythrocytes with a slow flow of culture medium over them. The parasitemia is kept fluctuating from ? 1%, just after addition of fresh erythrocytes. to ? 10%, 2 or 3 days later. Each vessel provides each week 3 harvests, each containing ? 0.6–1 × 109 parasites. 相似文献
20.
Nitrate Reductase Activity in Calcifugous and Calcicolous Tomatoes as Affected by Iron Stress 总被引:1,自引:0,他引:1
Calcicolous plants are generally more Fe-efficient than calcifugous plants, because they respond to Fe stress by releasing H-ions and “reductants” from their roots that causes Fe to become available. The objective of our study was to determine if differential response to Fe stress in calcicolous and calcifugous varieties affects nitrate reductase activity. T3238FER (Fe-efficient) and T3238fer (Fe-inefficient) tomato (Lycopersicon esculentum Mill.) cultivars were grown in nutrient solutions supplied with N as NH4+-N plus NO3?-N, and as NO3?-N only. The chemical reactions induced by Fe stress concomitantly increased nitrate reductase activity in roots and tops of calcicolous, but not in calcifugous tomato. This nitrate reductase activity decreased, however, when Fe was made available to the plants. When Fe stress was eliminated by adding Fe, nitrate reductase activity was comparable in the two cultivars. 相似文献