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71.
72.
The vacuolar pH (pHv) and the cytoplasmic pH (pHc) of the marinegiant-celled green alga Chaetomorpha darwinii were measuredby pH microelectrode techniques on extracted vacuolar sap, andby the [I4C]DMO distribution method respectively. Equilibrationof DMO occurred with a half-time of about 2 h, with an apparentPDMO of 3.6 x 105 cm s1, but the vacuolar concentrationof free, undissociated DMO was always less than the externalconcentration. The explanation offered for freshwater giant-celledalgae of net DMO leakage across the plasmalemma cannotapply to Chaetomorpha darwinii, since electrically-driven DMOexit from the cytoplasm should be similar across the plasmalemmaand the tonoplast in these cells with large, vacuole-positivepotential differences across the tonoplast. pHc was accordinglycomputed assuming either tonoplast or plasmalemma equilibrationof DMO, with correction for DMO metabolism within the cell.pHc was 8.08.3 in the light in artificial seawater (pHoabout 8.0), was some 0.5 units lower in the dark, and was slightlylower with an external pH of 7. Vacuolar pH was 6.56.9,without consistent effects of illumination or of external pHof 7 rather than 8. While µH+ at the tonoplast was similarto that in giant-celled freshwater algae (although with a greatercontribution from relative to pH), µH+ at the plasmalemmawas less than 8 kJ mol1, i.e. less than one-third ofthe value in freshwater green algae. µNa+ was some 13kJ mol1 at the plasmalemma. The possibility that theprimary active transport process at the plasmalemma of Chaetomorphadarwinii (and certain other marine algae) is Na+ efflux ratherthan H+ efflux is discussed. 相似文献
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Influence of crop background on aphids and other phytophagous insects on Brussels sprouts 总被引:1,自引:0,他引:1
JUDITH G. SMITH 《The Annals of applied biology》1976,83(1):1-13
More Brevicoryne brassicae and other alate aphids were caught in yellow water-traps in a weed-free crop of Brussels sprouts than in a crop with a weedy background. More B. brassicae colonized Brussels sprout plants in bare soil than in weeds; very few alatae were attracted to cruciferous weeds in the crop. Results in 1 yr suggest that initially larger populations on the weed-free sprouts became smaller than populations on the weedy sprouts because the larger aphid population attracted more natural enemies. Aleyrodes brassicae and certain Lepidoptera were also more abundant on sprout plants in bare soil than on sprouts surrounded by weeds; more adult A. brassicae were caught in water traps over the bare soil. More A. brassicae were present on sprout plants surrounded by a green than by a brown cloth background but the differences were not significant (P < 0–05). Numbers of B. brassicae on sprout plants with green and brown backgrounds varied greatly and did not differ significantly. In field cages, B. brassicae alatae were more attracted to potted sprout plants surrounded by bare soil than to ones surrounded by rings of living or cut grass or by artificial green rings. This effect was greater with small than with large sprout plants surrounded by grass rings. The maintenance of a limited weed cover is considered potentially useful in integrated control of some brassica pests. 相似文献
75.
J. R. COOK SANDRA SMITH HAGGARD PATRICIA HARRIS 《The Journal of eukaryotic microbiology》1976,23(3):368-373
SYNOPSIS. In populations of Euglena gracilis strain Z synchronized by cultivation on a repetitive light-dark cycle, chloroplasts undergo cyclic changes in structure. During most of the light period chloroplasts are relatively compact with closely appressed lamellae; during the dark (division) period the chloroplasts become quite distended. This change persists for at least one cycle even when the cells are left in continuous light, suggesting that the periodicity may be related more to the age of the cell than to a direct effect of light. In addition, the pyrenoid in synchronized cells has a transient existence, being present only in the first half of the light period. 相似文献
76.
JOSEPH J. NAPOLITANO BARBARA-HELENE SMITH 《The Journal of eukaryotic microbiology》1975,22(2):196-199
Nuclear division in synchronized cultures of the ameboflagellate Adelphamoeba galeacystis has been described. Division in this organism is typically promitotic. It occurs within an intact nuclear membrane and is characterized by the persistence of the nucleolus and its transformation into 2 polar masses. The nucleolus is stained with pyronin-Y by the methyl green pyronin-Y technic, and with Heidenhain's hematoxylin, but is unstained by the Feulgen reaction. The reaction with these stains is removed after digestion of the nucleolus by ribonuclease. During mitosis the nucleolus undergoes an orderly series of vacuolizations before forming the polar masses. The chromatin is Feulgen positive, stains with methyl green by the methyl green pyronin-Y technic and undergoes a series of characteristic changes during the division process. Synchronization of amebae grown on coverglasses was accomplished by transfer of cells from 30 to 38.5 C for a period of 100 min. A temporal sequence of nucleolar and chromatin participation in the nuclear division of this organism is suggested. 相似文献
77.
The flexibility and self-healing properties of animal cell surface membranes are well known. These properties have been best exploited in various micrurgical studies on living cells (2, 3), especially in amoebae (7, 20). During nuclear transplantation in amoebae, the hole in the membrane through which a nucleus passes can have a diameter of 20-30 μm, and yet such holes are quickly sealed, although some cytoplasm usually escapes during the transfer. While enucleating amoebae in previous studies, we found that if a very small portion of a nucleus was pushed through the membrane and exposed to the external medium, the amoeba expelled such a nucleus on its own accord. When this happened, a new membrane appeared to form around the embedded portion of the nucleus and no visible loss of cytoplasm occurred during nuclear extrusion. In the present study, we examined amoebae that were at different stages of expelling partially exposed nuclei, to follow the sequence of events during the apparent new membrane formation. Unexpectedly, we found that a new membrane is not formed around the nucleus from inside but a hole is sealed primarily by a constriction of the existing membrane, and that cytoplasmic filaments are responsible for the prevention of the loss of cytoplasm. 相似文献
78.
Seasonal Dynamics of Biomass and Mineral Nutrient Partitioning in Mature Kiwifruit Vines 总被引:1,自引:0,他引:1
The accumulation of dry matter plus macro- and micronutnentsby various components of 6-year-old, field-grown kiwifruit vines(Actinidia deliciosa var deliciosa cv Hayward) was recordedover one season Twenty vines were harvested periodically throughoutthe year and separated into perennial components (roots <20 mm diameter, structural roots, stump, stem, cordon, one-year-oldfruiting wood) and current season's growth (non-fruiting shoots,laterals on fruiting wood, leaves and fruit) There was minimalseasonal variation (CVs < 7%) in biomass change in perennialcomponents of the vine Concentrations in these components eitherfluctuated about a constant value, or indicated a strong seasonaldependence Changes in biomass and nutnent concentrations incurrent season's growth, however, were very regular Prior tobudbreak, below-ground components contained between 48 and 81% of the total content of each element Roots < 20 mm diametercontained more total nutrient than any other perennial componentof the vine during the season, with the exception of Zn andCu, which were concentrated in the cordon There was consistentaccumulation of each nutrient from budbreak until harvest Ratesof greatest uptake occurred in the month following budbreak,or in the 3 weeks after anthesis Between dormancy and harvest,whole-vine contents increased for all nutrients Increases inFe, Mg, P, S and Zn ranged from 21 % (Zn) to 88% (Mg), and inB, Ca, Cl, Cu, K, N and Mn from 109% (Cu) to 302% (Cl) Despitethe large requirements of the current season's growth, net changesin the seasonal content of perennial components were relativelysmall Copper, Mg, P, N and Cl were the elements in which perennialreserves were utilized to the greatest extent to meet transientdeficits between nutnent demand for the current seasonsgrowth, and that recently taken up from soil Generally, reserves utilized during the period of vegetativegrowth were replaced by harvest-time These observations, basedon application of a single fertiliser dressing before budbreak,suggest the vine maintains satisfactory fertility without theneed for late-season or post-harvest applications of fertiliserto supplement nutrient reserves, as occurs with some other fruitingcrops Actinidia deliciosa, kiwifruit, mineral nutrition, seasonal accumulation, whole-plant harvesting 相似文献
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80.