摘要:

Filtrates (conditioned medium) from high‐densityChlorella vulgariscultures in photobioreactors were obtained and tested for autoinhibitory activity under different conditions. Exponentially growing cells were inoculated at low initial cell concentration (2 × 105cells/ml) in 90% conditioned medium (CM) supplemented with 10% fresh medium (FM) at low (atmospheric) CO2levels. The time sequence of DNA histograms of cells in CM cultures showed that there is an accumulation of cells with two and four DNA equivalents in the culture over a period of time, signifying a blockage of cells at the division stage of the cell cycle. Examination of the chemical composition of CM showed the presence of high concentrations (>10 mM) of bicarbonate. Adding similar bicarbonate concentrations to FM were found to have similar effects as CM cultures, causing blockage of cell division, though the intensity of the blocking effect was lower. The bicarbonate‐free CM did not show any cell cycle modulating or inhibitory activity. The growth of cells cultivated at high (5%) CO2levels in 90% CM supplemented with 10% FM was comparable to 10% FM cultures, indicating nutrient limitation in 90% CM culture. When the 90% CM culture was supplemented with 100% nutrients, the growth rate and final cell concentration was similar to 100% FM culture. Based on these results we conclude thatC. vulgarisdoes not secrete any autoinhibitor(s) or cell cycle modulating compound(s) under the conditions from which the CM was obtained.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11559.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Isoflavonoids, some of which are highly fluorescent, are produced by soybean [Glycine max(L.) Merr.] and serve as chemical signals for certain aspects of nitrogen fixation and microbial resistance. This study was conducted to determine whether soybean mutants with nonfluorescent roots contained abnormal concentrations of isoflavonoids. Isoflavonoids were extracted from the root and hypocotyl of 4‐d‐old wild‐type soybean seedlings (cv. Hark) having fluorescent roots and from four nonallelic mutant, near isogenic lines of Hark having nonfluorescent roots. In addition, isoflavonoids were extracted from the root and hypocotyl of 4‐d‐old seedlings of near isogenic lines of Hark harboring two pairs of the mutant alleles for nonfluorescent roots. Malonyl daidzin, daidzin, malonyl genistin, and genistein were the most abundant isoflavonoids extracted from either the root or hypocotyl of seedlings with either fluorescent or nonfluorescent roots. Extracted malonyl daidzin, malonyl genistin, and malonyl glycitin decomposed readily, yielding daidzin, genistin, and glycitin, respectively. The concentrations of malonyl genistin and genistein, two highly fluorescent compounds, were similar in both fluorescent and nonfluorescent roots. Thus, root fluorescence was not correlated with abundance per se of fluorescent isoflavonoids in roots. In addition, the abundance of isoflavonoids extractable from the hypocotyl did not correlate with root fluorescence.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11560.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

The systematically problematic fernMetaxya rostrata, commonly regarded as an ally of the cyatheoid and dicksonioid tree ferns, is investigated, and features of its organography, shoot vascular anatomy and development, soral initiation and early development, and gametophyte structure are described. The rhizome is creeping, dorsiventral, with an unusual four‐seriate phyllotaxis. Typical protoxylem is lacking from the intemodes of the solenostele, but are present in the leaf trace and end blindly proximally. Tangential cells are found in the phloem of the stem. The early maturing “protoxylem” of the stem is scattered, and, apart from some identifiable protoxylem strands, is not clearly associated with the young leaves. Sori are initiated as groups of large cells on the abaxial side of developing leaflets, distant from the marginal meristem initials, and in close association with a lateral vein. Two sori may arise by the subdivision of a single large patch of cells. Soral maturation is of the simple type. Gametophytes are cordate to ribbonlike, with moderately primitive gametangia. Morphologically and systematically,Metaxyaappears isolated. It shares few significant derived conditions with the tree ferns, and a separate family Metaxyaceae seems well justified.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11561.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Detailed analysis of the three‐dimensional vascular organization in species ofDiplaziumandBlechnumindicates that these ferns possess reticulate (dictyostelic) vascular systems that closely reflect the helical phyllotaxis of the shoot. In each species, the vascular pattern shows a specific relationship to the phyllotaxis, so that the phyllotactic fraction can be determined by examination of the number of cauline vascular bundles (meristeles) in cross section of the stem. The number of meristeles in a cross section equals the denominator of the phyllotactic fraction, i.e., the number of foliar orthostichies on the stem. The same numerical relationship also exists in the eusteles of seed plants between the number of axial (sympodial) stem bundles and the phyllotaxis. There is a further parallel between the three‐dimensional reticulate pattern of fern dictyosteles and the reticulate patterns that characterize some herbaceous dicotyledons. However, the hypothesized separate origins of seed plant eusteles and fern dictyosteles from protostelic precursors preclude any direct homologies between these similar patterns. The parallel evolution of presumably more physiologically efficient reticulate systems in herbaceous seed plants and in ferns that have only a primary plant body is noteworthy. The similar relationships between the primary stem vascular patterns and phyllotaxy in both ferns and seed plants further emphasize the likely similarity of the morphogenetic events that occur at the shoot apex in these taxonomically disparate groups.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11562.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

In plant species with an obligate species‐specific pollinator, gamete encounter is a critical phase in the success of reproductive strategies. One of the key factors in the success of gamete encounter, the length of female receptivity, has been rarely studied experimentally. InFicusspecies (Moraceae), each exclusively associated with its specific pollinating wasp, the receptive female phase of individual syconia was believed to last only a few days. This estimate, based on field observations of pollinator arrivals, neglected the possibility that unpollinated syconia may remain receptive for a prolonged period. In two distantly related fig species (F. caricaandF. aurea), we measured experimentally the duration of receptivity of individual syconia protected from pollinator visits. For these two species, receptivity lasted from 2 to 3 wk. Syconia pollinated at any time during this period of receptivity are capable of setting seeds. Furthermore, it has been assumed that female syconium receptivity stops quickly after pollinator visitation. Our experiments showed that syconia of both species are able to extend their receptive period for a few days longer when visited only by a single wasp. The demonstration of a long duration of female receptivity has important consequences for understanding the maintenance of the fig‐wasp mutualism.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11563.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

As plant populations decrease in size, reduced seed set may contribute to their ultimate extirpation. In this study, effects of pollen quantity and compatibility relationships (quality) on seed set were investigated in a rare species (Eupatorium resinosum) and a closely related common species (E. perfoliatum). The impact of pollen quantity was studied through pollen supplementation experiments in two populations of each species. Addition of pollen increased seed set only in the smaller population ofE. resinosum.Compatibility relationships (pollen quality) were investigated in a diallel crossing experiment using ten genotypes from the same populations. Plants from the smaller population ofE. resinosumwere found to be 40% cross‐incompatible, which was higher than the larger population ofE. resinosumand the two populations ofE. perfoliatum, the latter showing signs of self‐compatibility in some individuals. In addition the variance in number of compatible matings per individual was higher in the smaller population ofE. resinosum.These results are consistent with a computer simulation model that investigated the effect of small population size on S‐allele diversity. Sufficient pollination accompanied by a partial breakdown of the incompatibility system may account, in part, for the relative success ofE. perfoliatum.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11564.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Selfing has evolved repeatedly in outcrossing taxa, and theory predicts that an increase in the level of self‐fertilization should occur in concert with changes in reproductive allocation and the magnitude of inbreeding depression. Here we characterize the mating system of two sympatric congeners,Epilobium ciliatumandE. angustifolium, and compare the taxa for 1) reproductive allocation patterns and 2) the fitness consequences of self‐fertilization. ForE. ciliatum, autogamy rates were high, pollinator visitation was low, and electrophoresis revealed no genetic variation at 11 putative isozyme loci. ForE. angustifolium, autogamy rates were low, pollinator visitation was relatively high, and electrophoresis generated an outcrossing rate estimate oft =0.64 (SE = 0.08). The pollen/ovule ratio was ten times higher forE. angustifoliumthan forE. ciliatum, due to a decline in pollen production in the selfing species. The proportion of total flower biomass allocated to female function was significantly greater inE. ciliatum, while that allocated to male function and attractive structures was greater inE. angustifolium.We quantified the fitness consequences of selfing at three life stages: seed number, percent germination, and mature biomass. Relative performance (RP) measures indicated less inbreeding depression forE. ciliatumthan forE. angustifoliumat all stages; differences in RP between the species were significant for seed number and cumulative total, but not for germination or biomass. RP was correlated among life history stages for only one comparison, suggesting that the genetic basis of inbreeding depression differs among life history stages. Variation among maternal parents for RP was significant at almost all stages in both species, with the exception of seed number inE. ciliatum.The striking variation among maternal parents inE. angustifolium, ranging from strong inbreeding depression to strong outbreeding depression, may reflect both variation in the history of inbreeding and the long‐distance migration of individuals from different populations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11565.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Two new recessive male‐sterile mutants ofZea mays(Poaceae), or maize, were studied to identify the timing of pollen abortion and to examine the involvement of anther wall cell layers. The results of test crosses indicated that these mutants were not allelic with any known male‐sterile mutants of maize. Light and transmission electron microscopy were used to compare pollen development in homozygous male‐sterile mutants to that in fertile heterozygous siblings. In both mutants, microspores abort soon after release from the meiotic tetrad. However, the two mutations have strikingly different phenotypes. Large lipid bodies accumulate in the tapetal cells as the microspores vacuolate and die in the mutantms25. Large vacuoles appear in both the tapetal cells and the young microspores as they begin to disintegrate in the mutantms26. Because abnormal tapetal cell morphology is detected in both mutants, it is possible that both of these mutations affect the expression of genes in tapetal cells.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11566.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

From 1975 to 1993, aboveground net primary production (NPP) at the Konza Prairie Research Natural Area in NE Kansas varied from 179 g/m to 756 g/m. Across a variety of sites, NPP was significantly related to precipitation (r=0.37), but much variability was unexplained. Thus, we evaluated the relationship between NPP with meteorological variables and soil moisture measurements in tallgrass prairie sites that varied in fire frequency and topographic position. Annually burned lowland sites had significantly higher NPP than either annually burned upland or unbumed sites. NPP in burned sites was more strongly related to meteorological variables and soil moisture when compared to unbumed sites. The lack of significant correlation between soil moisture with NPP on unbumed sites suggests that factors other than water availability limit production in these sites. When NPP data were analyzed separately by life forms, interannual variability in forb NPP was not correlated with any meteorological variables, but was negatively correlated with grass NPP (r= ‐0.49). The inability of a single factor, such as precipitation to explain a large portion of the interannual variability in NPP is consistent with the concept that patterns of NPP in tallgrass prairie are a product of spatial and temporal variability in light, water, and nutrients, driven by a combination of topography, fire history, and climate.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11567.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Setaria glauca(yellow foxtail),S. geniculata(knotroot foxtail), and S.faberii(giant foxtail) are important cosmopolitan weeds of temperate and tropical regions. Isozyme markers were used to investigate genetic diversity and population genetic structure in 94 accessions of yellow foxtail, 24 accessions of knotroot foxtail, and 51 accessions of giant foxtail, collected mainly from North America and Eurasia. Giant foxtail populations were nearly identical genetically, with only one population exhibiting isozyme polymorphism. Yellow and knotroot foxtail populations had low genetic diversity but marked population differentiation. Although the latter species are similar morphologically, they are readily distinguished electrophoretically, with Nei's genetic identity being 0.83. In both species, genetic divergence between accessions from Eurasia and North America was minimal. Populations from the native ranges had slightly greater genetic diversity than those from the respective introduced ranges. Yellow foxtail populations genetically clustered into Asian, European, and North American groups. Within North America, yellow foxtail populations from Iowa were genetically diverse whereas populations collected from other North American locations were nearly monomorphic for the same multilocus genotype. Knotroot foxtail populations in North America were genetically differentiated into northern and southern groups on either side of a line at ≈37° N latitude. No genetic patterning was evident in knotroot foxtail populations from Eurasia. In both yellow and knotroot foxtail, patterns of population genetic structure have been influenced by several factors, including genetic bottlenecks associated with founder events, genetic drift, and natural selection.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11568.x

出版商:Wiley    

年代:1995

数据来源: WILEY