摘要:

Indirect immunofluorescence microscopy was used to survey the three‐dimensional distribution of microtubules throughout the cell cycle in the green algaMougeotia.The network of microtubules present in the cortex of the cells at interphase gradually disappeared before mitosis. A band of cortical microtubules reminiscent of the preprophase band of higher plants surrounded the nuclei of some preprophase cells undergoing cortical microtubule disassembly. Longitudinally oriented bundles of microtubules appeared at the future spindle poles on either side of the nuclei in prophase. These bundles disappeared gradually as the spindle microtubule arrays formed. New spindles had broad poles but these became quite pointed before anaphase. Interzonal microtubules appearing at anaphase persisted until the end of nuclear migration, by which time they were concentrated into narrow bundles on either side of the centripetally forming crosswalls. During decondensation of the chromosomes and early nuclear migration, the spindle poles persisted as sites of microtubule concentration. New arrays of microtubules radiated from these microtubule centers into the cytoplasm ahead of the migrating nuclei. After cytokinesis, reinstatement of cortical microtubules was best observed in regions of the cells remote from the nuclei and associated microtubules. In contrast to higher plants, the first detectable cortical microtubules were short and already oriented transverse to the long axes of the cells.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15211.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Echinochloa phyllopogonwas grown hydroponically under four root zone gassing treatments to determine aeration effects on the growth and development of the plant root system. Although mesocotyl growth and the number of nodal roots were unaffected by the treatments, other aspects of plant growth were altered. Shoot growth was reduced by hypoxic (5 kPa partial pressure O2in nitrogen gas) and anoxic conditions (O2free nitrogen gas), but not by ethylene (0.1 ppm in air). Seminal root growth was unaffected by hypoxia or ethylene treatments, but was reduced under anoxia. Hypoxic environments stimulated the emergence of roots along the length of the mesocotyl when compared to aerobic controls; anoxic and ethylene treatments had no significant effects. Mesocotyl roots elongated from primordia that were produced de novo in response to the hypoxic treatment. Under hypoxic conditions, aerenchyma was present in the cortex of nodal roots and to a lesser extent in seminal roots, but mesocotyl roots were devoid of aerenchyma under these conditions. The results are compared with the literature concerning flooding and aeration effects on growth and development in other species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15212.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Variation in sex expression, flowering pattern, and seed production was studied in the self‐compatible perennial herbGeranium maculatumin Illinois and Indiana. In a survey of eight populations, female (male‐sterile) plants were found in seven (frequencies ranging from 0.5% to 24.3% [median 4.2%]), and intermediate plants (with partly reduced male function) were found in all populations. Gender variation and sexual differences in reproductive characters were studied in detail in two populations. One population consisted of 5% female, 27% intermediate, and 68% hermaphrodite plants; the other consisted of 1% female, 20% intermediate, and 79% hermaphrodite plants. Females produced smaller flowers and began flowering earlier than hermaphrodites. Intermediates produced flowers of an intermediate size and began flowering as early as females. Females and hermaphrodites did not differ in flower number, vegetative size, flowering frequency, survival, or seed size. However, females produced 1.6 times more seeds than hermaphrodites. Intermediates produced 1.3–1.6 times more seeds than hermaphrodites. Some between‐year variation in sex expression was observed. Hand‐pollination with outcross pollen produced two to four times as many seeds as hand‐pollination with self‐pollen. A lower outcrossing rate in hermaphrodites than in females may at least partly explain the lower seed set in hermaphrodites. The higher seed production of females, and possibly the high fecundity of the intermediates, should contribute to the maintenance of this sexual polymorphism.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15213.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Buchloe dactyloidesis a perennial dioecious grass in which male and female inflorescences are so strikingly dimorphic that they were originally assigned to different genera. The objective of this paper is to present the results of tests for sex‐specific vegetative characters, ecological differences, and sexual niche‐partitioning, combining them with prior information on the reproductive biology ofBuchloefor an evaluation of the key factors leading to the evolution of dioecy and sexual dimorphism. Field and greenhouse data were collected from Oklahoma and Kansas populations on vegetative characters, allocation to reproduction, and relative growth and competitive success along resource gradients. Except for greater susceptibility to leaf rust by males, there were no significant differences between males and females in vegetative characters, total biomass, or reproductive effort. Field studies of spatial distributions of males and females failed to show any relation to soil, topography, or soil moisture. In a 45‐month greenhouse experiment starting at the seedling stage, the relative growth and competitive success of randomly paired individuals showed no evidence for differential competitive success or for niche‐partitioning of males and females. The “outcrossing advantage” and subsequent sexual specialization of the female inflorescence appear to be the major factors underlying this dimorphic system.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15214.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Archaeocalamites lazarii, sp. nov., is based on a few vegetative compressions from the mid‐Lower Permian Leonard Series near Fulda, north‐central Texas. It is a minor component of a rich biota that includes sphenophylls, pteridophylls, conifers, conchostracan crustaceans, eurypterids, arachnids, insects, xenocanth sharks, and coprolites attributed to tetrapods. Biota and sedimentology indicate deposition in a small freshwater body on a deltaic floodplain. Leaves ofA. lazariidiffer in size and posture from those of the widespread and characteristically Mississippian aggregate speciesA. radiatus;nonpreservation of rooting and reproductive organs prevents interpretation of its phylogenetic relationship with other equisetaleans. The main significance ofA. lazariiis that it extends the recorded stratigraphic range of the Archaeocalamitaceae from the lowermost Pennsylvanian (Namurian B) to the mid‐Lower Permian (Artinskian), leaving a hiatus in records of approximately 55 Ma. This Lazarus taxon also occurs with possibly the youngest recorded eurypterid.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15215.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Field studies on two populations ofAgalinis strictifoliawere conducted over a 3‐year period to investigate the relationship between flowering time of individuals and plant size, flowering duration, flower and fruit production, fruit predation, and growth rate. Seasonal patterns of pollinator visitation were compared with those of individual flowering time, flower density, percent fruit production, and mean seeds/fruit. In general, early and middle flowering individuals (as determined by either first flowering date or peak flowering) were larger, flowered longer, and produced more flowers and fruits than late flowering individuals. Early and middle flowering individuals (based on first flowering date) also grew faster than late flowering individuals. Although early and middle flowering individuals produced more fruits, fruit predators did not damage a disproportionate number of fruits compared to late flowering individuals. Patterns of bee visitation showed no association with seasonal patterns of flower density, percent fruit production, mean seed/fruit, or individual flowering time. In populations ofA. strictifolia, it would seem that biotic or environmental determinants of growth rate (hence size and reproductive success) may be more important in generating variation in individual flowering time than patterns of pollinator visitation or fruit predation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15216.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Hermaphroditism is the normal mode of sex expression in diploid species ofFragaria(Rosaceae,2n =14,x =7) with one known exception, gynodioeciousF. vescaL. ssp.bracteata.The polyploid species ofFragariaare all trioecious. An extensive study involving appropriate hybridization, testcrossing, selling, and backcrossing revealed that the repression of sporangia and the inhibition of sporogenesis are controlled by a single gene (or a gene complex) with at least three alleles in the sporophytes of trioecious octoploid species (2n= 56,x =7). A male suppressor (allele F) reduces microsporangia and represses microsporogenesis completely, but it allows normal development of the stigma, style, and ovary. A female suppressor (allele M), in the absence of modifier genes, inhibits megasporogenesis and drastically reduces the number of carpels and size of receptacles. The allele H, conferring perfect flowers at an early stage of flower organogenesis, acts as an inducer of microsporogenesis in females, but leaves both microand megasporangial development intact. At the sex locus, the F allele (femaleness) is dominant to H and M and the H allele (hermaphroditism) is dominant to M (maleness). Females are exclusively heterogametic (F/H or F/M), hermaphrodites may be homo‐ or heterogametic (H/H or H/M), and males are homogametic (M/M). The sex gene is expressed precisely in the genetic background of octoploid × diploid hybrids ofFragariaand their derivatives and in crosses with closely related hermaphroditic diploidPontentilla glandulosaL. Gene dosage phenomena are absent. First generation progeny of colchi‐decaploids (F/F, –/–) are exclusively female, but all generations thereafter segregate in a normal diploidized manner (1:1). Application of phytohormones alters sex expression to a limited extent.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15217.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

TheIpomopsis aggregatacomplex consists of diploid, outcrossing, perennial herbs. The group is highly variable morphologically and is treated as three species:I. aggregata, I. tenuituba, andI. arizonica.Geographic races ofI. aggregataandI. tenuitubaare recognized as subspecies. Enzyme electrophoresis was used to examine genetic relationships among populations and taxa in theIpomopsis aggregatacomplex and some related species. Genetic data for 23 allozyme loci from 60 populations were also used to determine how genetic variation is distributed geographically. Populations in the southwestern United States were more variable than those in the northwest: the center of genetic diversity corresponded to the center of species diversity. Allozymic data provided no evidence of loss of genetic variability associated with recent and rapid divergence. Genetic relationships based on Nei's genetic identity did not correspond to taxonomic relationships. For example, populations of bothI. arizonicaandI. tenuitubaclustered withinI. aggregata.Despite relatively high levels of genetic diversity among populations, diversity among taxa was low. Results indicated that floral divergence and concomitant speciation have occurred recently in theIpomopsis aggregatacomplex. Allozymic patterns also reflected convergent evolution for floral morphology and possible introgression. Despite morphological differences among species, insufficient evolutionary time has elapsed for allelic fixation at neutral or near‐neutral allozyme loci.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15218.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Population studies involving the grassAgrostis hiemalisinfected with the endophytic fungusEpichloë typhinawere made. Grass individuals were assessed for infection state (presence or absence of fungus), number of culms and fungal stromata, and location within plot. Using clustering and ANOVA procedures available in SAS, geometric groups were identified and analyzed. The tendency of plants to bear stromata was found to be significant with respect to both the plot (P<0.05) and the cluster (P<0.0001) within which plants occurred. A cultural study was made of the endophytes from one of the plots. Here isolates from a cluster containing stroma‐bearing grass individuals were found to grow more rapidly than those from grass clusters without stromata on a variety of sugars naturally available in vivo. Histological studies of the host demonstrate that the endophyte is seed transmitted in a comparable fashion to endophytes in other grasses. It is suggested that the clustering of stromata‐bearing plants inAgrostis hiemalisis the result of the presence of aggressive strains of endophyte within proximally located plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15219.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Leaf flavonoid chemistry was examined from the three subgenera and 11 species of the endemic genusDendroseris(Compositae, Lactuceae) of the Juan Fernandez Islands, Chile. Eight of the species are restricted to the older island (Masatierra, ca. 4 million years old), which is also closer to the mainland. Three species, one from each subgenus, are restricted to Masafuera, which is younger geologically (1–2 million years old) and 145 km further west of Masatierra. A total of 16 compounds was identified, with the 7‐0‐glucosides of the flavones apigenin and luteolin accounting for 12 of the constituents. Two glucosides of the flavonol quercetin were detected. Despite considerable interpopulation variation within species, six of the taxa have distinctive flavonoid profiles. Although there are few absolute differences among the subgenera, they can be distinguished chemically. SubgenusReacontains the greatest number of compounds, and a previous cladistic analysis based on morphological features suggested this subgenus as most primitive. SubgenusPhoenicoserisis considered highly derived morphologically, and it has a reduced flavonoid chemistry. Very little reduction in flavonoid diversity was seen in the morphologically specialized subg.Dendroserisas compared to subg.Rea.A trend in reduction of numbers of compounds was seen for two of the three species on the younger island of Masafuera when compared to their presumed ancestors on Masatierra. Flavonoids of selected species ofHieraciumandHypochaeris, presumptive mainland progenitors ofDendroseris, reveal a close chemical affinity with the former genus.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15220.x

出版商:Wiley    

年代:1991

数据来源: WILEY