Callose in Frankia-Infected Tissue of Datisca glomerata is an Artifact of Specimen Preparation

Abstract: Callose, or β-1,3-glucan, is a plant cell wall polysaccharide that occurs endogenously at distinct sites in a variety of tissues. Callose is also formed in response to stress involving cell membrane perturbation. In sections of chemically-fixed nodule tissue of the actinorhizal host, Datisca glomerata, callose was cytochemically detected within the Frankia -infected cortical cells, as an extensive network of wall material surrounding the microsymbiont, but not in uninfected cortical cells. Callose formation was completely inhibited within the infected cells when 2-deoxy-D-glucose, an inhibitor of callose formation, was included in the tissue fixative. The study concludes that callose deposition in the Datisca nodule infected zone is apparently a stress response to tissue preparation and fixation. However, the rapidity and extent of callose deposition primarily at the symbiotic interface in Frankia -infected cells suggests an unusual predisposition to biosynthesis of β-1,3-glucan in the nodule cortical cells that is related to their interaction with the microsymbiont.     

雄全异株植物瘿椒树（省沽油科）的传粉生物学

从开花动态、传粉昆虫、花的形态结构、繁育系统、花粉活力和柱头可授性等方面研究了我国特有珍稀植物瘿椒树（Tapiscia sinensis Oliv.）的传粉生物学特性。瘿椒树是典型的雄全异株植物,两性花中含有功能性花粉,且自交亲和,但雄花花粉活力和萌发力是两性花的10倍以上。雄株和两性植株具有相同开花物候期,花期均为5月下旬至6月上旬,单花期为4-5天,雄花和两性花的5枚花药开裂的不同步性明显延长了散粉时间。两性花雌蕊先熟,柱头可授性较长。具有适应风媒和虫媒传粉的花部特征。传粉昆虫主要为蜜蜂科（Apidae）和食蚜蝇科（Syrphidae）昆虫,访花高峰期为8：30-10：30。维持瘿椒树雄全异株的可能机制是：雄株总体上增加了异交花粉的数量和质量;两性花的雄蕊为该物种提供了繁殖保障,同时为传粉者提供了报酬。     

雄全异株植物瘿椒树(省沽油科)的传粉生物学

从开花动态、传粉昆虫、花的形态结构、繁育系统、花粉活力和柱头可授性等方面研究了我国特有珍稀植物瘿椒树(Tapiscia sinensis Oliv.)的传粉生物学特性。瘿椒树是典型的雄全异株植物,两性花中含有功能性花粉,且自交亲和,但雄花花粉活力和萌发力是两性花的10倍以上。雄株和两性植株具有相同开花物候期,花期均为5月下旬至6月上旬,单花期为4-5天,雄花和两性花的5枚花药开裂的不同步性明显延长了散粉时间。两性花雌蕊先熟,柱头可授性较长。具有适应风媒和虫媒传粉的花部特征。传粉昆虫主要为蜜蜂科(Apidae)和食蚜蝇科(Syrphidae)昆虫,访花高峰期为8:30-10:30。维持瘿椒树雄全异株的可能机制是:雄株总体上增加了异交花粉的数量和质量;两性花的雄蕊为该物种提供了繁殖保障,同时为传粉者提供了报酬。     

Polymorphic microsatellite loci in the parasitic wasp Cotesia glomerata (Hymenoptera: Braconidae)

Five polymorphic microsatellite loci were isolated in a gregarious endoparasitoid, Cotesia glomerata, using an enrichment protocol. We detected two to 15 alleles per locus in a sample of 50 female wasps collected from a field population near Zürich, Switzerland. The observed heterozygosities ranged from 0.21 to 0.92. These markers are currently being used in our studies of sex determination in this species.     

Pollination of Androdioecious Xerospermum intermedium Radlk. (Sapindaceae) in a rain forest

Xerospermum intermedium, a fairly common understorey species in the West Malesian lowland dipterocarp forest is androdioecious, with delayed self-compatibility. It flowers annually, and has an extended flowering period, with individuals flowering somewhat asynchronously, presenting small flowers with minimal visual lures. The flowers are visited by an unrestricted array of apparently imprecise opportunistic feeders, predominated by trigonid bees and butterflies. Most of these visitors exhibit low fidelity and forage opportunistically on numerous competing tree species. Presentation of nectar in alternating rhythms between the male and hermaphrodite trees appears to induce pollinator movement between them. Out of such alternating visits between the sexes, a low level of short-range inter-tree pollen transfer by trigonids and butterflies seems to occur. Despite the elaborate system which promotes pollinator movement between the sexes, this species has retained a low level of self-compatibility. The physical barriers to pollinator movement in the understorey, and high interspecific competition for pollinators by a large number of tree species, appear therefore to make it difficult to maintain an obligate outbreeding system. Hence, androdioecism may be one of the explanations for the survival of X. intermedium.     

Ultrastructure of the male gonad and male gametogenesis in the clam shrimp Eulimnadia texana (Crustacea, Branchiopoda, Spinicaudata)

Abstract. The ultrastructure of the male gonad of Eulimnadia texana (Branchiopoda, Spinicaudata) has been observed for the first time to investigate the sexuality of a well-studied case of androdioecy in the animal kingdom. The male gonad is a double structure located in the hemocoel throughout the entire body length on each side of the midgut. Male gametes originate from the wall and mature centripetally toward the lumen; the proliferative activity is very high and continuous and therefore the mature gonad is full of numerous germ cells. Inside the lumen several degenerative stages are found mixed with sperm cells and spermatids, the latter two being not easily distinguishable because of the slight differences between them. The evolutionary meaning of the degenerative process in E. texana male gametes is difficult to explain, and we propose some hypotheses about its possible role or cause in the studied population: (a) to help build spermatophores, (b) to act as a trophic component for viable sperm, (c) as a manifestation of inbreeding depression, and/or (d) to regulate the number of sperm cells.     

Breeding systems in the clam shrimp family Limnadiidae (Branchiopoda, Spinicaudata)

Abstract. Crustaceans in the class Branchiopoda exhibit a wide range of breeding systems, including dioecy (gonochorism), androdioecy, parthenogenesis, cyclic parthenogenesis, and hermaphroditism. The largest subgroup of the Branchiopods, the Diplostraca, is reported to encompass all five of these breeding systems. However, many of these reports are based primarily on simple observations of sex ratios in natural populations. Herein we report the beginnings of a more rigorous approach to breeding system determination in the Diplostraca, starting with the family Limnadiidae. We combine measurements of sex ratio, offspring rearings, and behavior to identify three breeding systems within the Limnadiidae: dioecy, androdioecy, and selfing hermaphroditism. To date, no instances of parthenogenetic reproduction have been identified in this family. Comparisons of breeding system determination via simple population sex ratios with our more controlled studies show that simple sex ratios can be useful when these sex ratios are ∼50% males (=dioecy) or 5–30% males (androdioecy). However, population sex ratios of 0–5% males or 35–45% males necessitate further investigation because estimates in these ranges cannot distinguish selfing hermaphroditism from androdioecy or androdioecy from dioecy, respectively. We conclude by noting that the genetic sex-determining system outlined for one of these limnadiid species, Eulimnadia texana , provides a parsimonious framework to describe the evolution of the three breeding systems observed within the Limnadiidae.     

Low genetic diversity among Frankia spp. strains nodulating sympatric populations of actinorhizal species of Rosaceae, Ceanothus (Rhamnaceae) and Datisca glomerata (Datiscaceae) west of the Sierra Nevada (California)

Frankia spp. strains typically induce N2-fixing root nodules on actinorhizal plants. The majority of host plant taxa associated with the uncultured Group 1 Frankia strains, i.e., Ceanothus of the Rhamnaceae, Datisca glomerata (Datiscaceae), and all actinorhizal members of the Rosaceae except Dryas, are found in California. A study was conducted to determine the distribution of Frankia strains among root nodules collected from both sympatric and solitary stands of hosts. Three DNA regions were examined, the 5' end of the 16S rRNA gene, the internal transcribed spacer region between the 16S and 23S rRNA genes, and a portion of the glutamine synthetase gene (glnA). The results suggest that a narrow range of Group 1 Frankia spp. strains dominate in root nodules collected over a large area of California west of the Sierra Nevada crest with no apparent host-specificity. Comparisons with Group 2 Frankia strain diversity from Alnus and Myrica within the study range suggest that the observed low diversity is peculiar to Group 1 Frankia strains only. Factors that may account for the observed lack of genetic variability and host specificity include strain dominance over a large geographical area, current environmental selection, and (or) a past evolutionary bottleneck.     

Sex determination in the androdioecious barnacle Scalpellum scalpellum (Crustacea: Cirripedia)

How androdioecy (coexistence of hermaphrodites and males) is maintained is still poorly understood. Therefore, sex determination was studied in the androdioecious barnacle Scalpellum scalpellum L. First, 247 cypris larvae from seven broods were investigated for sexual dimorphism in larval morphology and found to be all identical. Second, experiments with cyprids showed that males and hermaphrodites differ distinctly in morphology as soon as 4–5 days after settlement. Third, 14 252 cyprids were allowed to settle on the bottom of their culture cages, and all surviving larvae developed into hermaphrodites and none into dwarf males. Fourth, larvae settled in hermaphrodite receptacles (i.e. future males) were removed at increasing intervals after settlement to study if the male and hermaphrodite sexual expressions are fixed or plastic. All larvae became dwarf males if allowed to stay there for more than 8 h after settlement. But if removed within 3 h after settlement, half of them developed into hermaphrodites. We conclude that an environmental sex determination mechanism operates in S. scalpellum. Together with a 1:1 hermaphrodite/male ratio observed in previously reported experiments offering a free choice of settlement, we suggest that all larvae are potential hermaphrodites, but only 50% can settle in hermaphrodite receptacles and yield males.     

Superparasitism in Cotesia glomerata: response of hosts and consequences for parasitoids

Abstract.  1. Superparasitism occurs in Cotesia glomerata (Hymenoptera: Braconidae), a gregarious endoparasitoid of Pieris spp. (Lepidoptera: Pieridae). The response of P. brassicae larvae to superparasitism and the consequences for the parasitoid were examined in order to elucidate the ecological significance of this behaviour.
2. Field surveys of a Swiss population revealed that C. glomerata brood sizes from P. brassicae larvae ranged from three to 158, and both the female ratio and the body weight of emergent wasps correlated negatively with brood size. In the laboratory, single oviposition on P. brassicae larvae did not produce any brood size larger than 62, but brood size increased with superparasitism.
3. Laboratory experiments demonstrated that both naive and experienced female wasps were willing to attack hosts that had been newly parasitised by themselves or conspecifics. Superparasitism reduced survivorship but increased food consumption and weight growth in P. brassicae larvae. Superparasitism lengthened parasitoid development and prolonged the feeding period of host larvae.
4. Despite a trade-off between maximising brood size and optimising the fitness of individual offspring, two or three ovipositions on P. brassicae larvae resulted in a greater dry female mass than did a single oviposition on the host. Thus, superparasitism might be of adaptive significance under certain circumstances, especially when host density is low and unparasitised hosts are rare in a habitat.     

Embryogenic cells in Dactylis glomerata L. (Poaceae) explants identified by cell tracking and by SERK expression

 Single mesophyll cells in leaf explants of Dactylis glomerata L. (Dactylis) that were competent to form somatic embryos directly or through callus were identified by semi-automatic cell tracking. These competent cells were a subpopulation of small, isodiametric, cytoplasm-rich cells located close to the vascular bundles. Using whole mount in situ hybridization, we showed that a similar subpopulation of cells expressed the Somatic Embryogenesis Receptor-like Kinase (SERK) gene during the induction of embryogenic cell formation. In both leaf explants and suspension cultures, a transient pattern of SERK gene expression was found during early embryo development, up to the globular stage. In later embryo stages, SERK mRNA was present in the shoot apical meristem, scutellum, coleoptile and coleorhiza. Received: 14 May 1999 / Revision received: 27 August 1999 / Accepted: 8 September 1999     

Microsatellite markers for the Sydney rock oyster,Saccostrea glomerata,a commercially important bivalve in southeastern Australia

The Sydney rock oyster (Saccostrea glomerata) is a commercially important bivalve in southeastern Australian. We describe the isolation and characterization of nine microsatellite markers for S. glomerata. The loci are highly polymorphic, with between five and 20 alleles identified among 30 individuals. Expected heterozygosity levels ranged from 0.608 to 0.936. The markers will be used to study natural dispersal, translocations and population structure. We will also use the microsatellites to test the genetic effects of QX disease on oyster populations. This infectious parasitic disease has decimated S. glomerata productivity in a number of areas over the past few decades.     

An acidic esterase as a biochemical marker for somatic embryogenesis in orchardgrass (Dactylis glomerata L.) suspension cultures

 The isoenzyme pattern of esterases (EC 3.1.1.2) secreted into the medium of orchardgrass (Dactylis glomerata L.) embryogenic suspension cultures during defined stages of somatic embryogenesis was compared with that of non-embryogenic suspension cultures during unorganised cell proliferation. Isoelectric focusing revealed the presence of 7–14 predominantly acidic isoforms. Comparison with the corresponding cell-wall isoenzyme pattern showed minor, mainly quantitative differences. The pattern of intracellular soluble esterases did not change markedly during somatic embryo development. A unique esterase whose migration in two-dimensional gel electrophoresis corresponds to an apparent molecular mass of 36 kDa and pI=3.8 was detected only in embryogenic cultures at very early stages of development. Since this isoform appeared long before morphological changes had taken place, it could possibly be used as a biochemical marker for embryogenic potential in D. glomerata L. suspension cultures. Received: 6 June 2000 / Revision received: 17 July 2000 / Accepted: 17 July 2000     

Subandrodioecy and male fitness in Sagittaria lancifolia subsp. lancifolia (Alismataceae)

Sagittaria lancifolia subsp. lancifolia is described as cosexual (monoecious), but the study population consisted of 84% cosexuals that typically had 35% pistillate buds and 16% predominant males that typically had 0-2% pistillate buds. Hand-pollinations showed that pistillate flowers required pollination to set seed, and pollen from both male and cosexual plants was potent. No gender switching was seen in the field or greenhouse. From 24 experimental crosses, 890 offspring were grown to maturity. Among these, all offspring of cosexual sires were cosexual, but approximately half the offspring of male sires were male, implying that maleness was inherited as a single, dominant allele. These results indicate that S. lancifolia is subandrodioecious, a very rare breeding system. It is rare, in part because its maintenance requires a large male-fitness differential between male and cosexual plants. In the study population, this condition was met by the differential survival of staminate buds on male racemes. Larvae of the weevil Listronotus appendiculatus killed many staminate buds. They did so in a vertical gradient, with buds lower on racemes safer. Male plants have replaced pistillate with staminate buds at these safer positions and thereby enjoy disproportionally higher male fitness.     

Properties of cocksfoot streak and cocksfoot cryptic, two viruses infecting cocksfoot (Dactylis glomerata) in Scotland

A Scottish isolate of cocksfoot streak virus (CSV-S) was found to have flexuous filamentous particles which, in sap of infected cocksfoot plants, had a modal length of 712 nm. It was transmitted from infected to healthy cocksfoot plants in a non-persistent manner by Myzus persicae and by mechanical inoculation of infective sap extracts containing an anti-oxidant. Apart from cocksfoot, mechanical inoculation of infective sap succeeded in infecting only four of 22 plant species tested. The infectivity of sap extracts containing 0.2% thioglycerol was lost after heating for 10 min at 55^oC but not 50^oC, storage at room temperature for 48 but not 24 hours, and after diluting 10^-2to 10^-3. Highly purified preparations of CSV-S particles sedimented as a single component with a sedimentation coefficient of 139S and had a buoyant density in rubidium bromide of 1.31 g/cm³. Virus particles were composed of one protein and one ssRNA species with estimated M_r of 31 000 and 3.2 times 10⁶respectively. In ELISA, an antiserum prepared to CSV-S detected the virus in all aerial parts of infected cocksfoot plants and, when present in the ratio of 1 infected leaf: 1000 healthy leaves. Both CSV-S-infected and -uninfected cocksfoot also contained a previously undescribed virus with isometric particles c. 30 nm in diameter. This virus, named cocksfoot cryptic virus (CCV), was seed-borne in two cvs of cocksfoot tested and its particles contained two dsRNA species of estimated M_r of 1.14 times 10⁶and 1.27 times 10⁶. Despite the fact that particles of CSV-S were largely free from CCV particles following exclusion chromatography on agarose beads prior to immunisation, immunoelectron microscopy (IEM) showed that the antiserum prepared to CSV-S also contained some antibodies to CCV. Evidence from IEM suggested a possible distant serological relationship of CCV to ryegrass and beet (BCV 1 or BCV 2, or both) cryptoviruses, all members of sub-group A of crypto viruses.     

Geographic partitioning of chloroplast DNA variation in the genusDatisca (Datiscaceae)

Datisca (Datiscaceae) is a ditypic genus with an intercontinentally disjunct distribution. Chloroplast DNA restriction site data was obtained from 23 populations and four 10–20 year old herbarium specimens ofD. glomerata and three populations ofD. cannabina from throughout their geographic ranges in western North America and southwest-central Asia, respectively. InD. glomerata, plastome diversity is partitioned geographically. All populations from southern California have a common plastome, while most populations north of this region share a relatively divergent plastome (0.49% sequence divergence). Likewise, these plastomes are highly divergent (0.87% mean sequence divergence) from those found inD. cannabina. Biogeographic processes dating to the Pleistocene and Late Miocene may be responsible for these intra- and interspecific patterns of chloroplast DNA divergence.     

Pollen discounting and the evolution of selfing in Arenaria uniflora (caryophyllaceae)

Although most models of mating system evolution assign a central role to the male transmission advantage of selfing genotypes, empirical data on the male fitness consequences of increased self-pollination are still uncommon. Here, I use measures of pollen import and export by focal plants in genotyped arrays to investigate the effects of floral morphology and pollination environment on self and outcross male function. Plants from an autogamous population of Arenaria uniflora (Caryophyllaceae) exhibit complete pollen discounting relative to closely related outcrossers, as do morphologically intermediate F1 hybrids between the two populations. However, the low cumulative male fitness of hybrids probably results from reduced pollen number or competitive ability, rather than a nonlinear relationship with floral morphology. When surrounded by selfers, plants from the outcrosser population self-fertilize at nearly the same rate as selfers (>80%), but have much lower self male fitness due to reduced fruit set. Because outcross siring success is also extremely low (<8%) in this treatment, these mate-limited outcrossers are at male fitness disadvantage to both pseudocleistogamous selfers and nonlimited outcrossers. The relative male fitness of plants with different mating systems appears dependent on the ecological context, as well as on morphological trade-offs.     

Pistil Receptivity and Pollen Tube Growth in Relation to the Breeding System of Eucalyptus woodwardii (Symphyomyrtus: Myrtaceae)

Pistil structure, stigma receptivity and pollen tube growthwere investigated in relation to seed set of Eucalyptus woodwardii.Self-pollination resulted in reduced capsule retention and seeddevelopment as compared with cross-pollination. The pistil consistedof an ovary with five locules, a long style with a canal extendingfor two-thirds of its length, and a papillate stigma. Therewas no change in style length with time after anthesis, butboth stigma secretion and ability to support pollen germinationand tube growth increased to reach a peak at 7 d. Pollen germinatedon the stigma surface and in the stylar canal, but most tubegrowth occurred intercellularly in the transmitting tissue surroundingthe canal. At the base of the style the pollen tubes split intofive groups following the transmitting tissue strands to theovary. Each group grew through a septum dividing two loculesand entered the placenta. The tubes then emerged from the placentato penetrate the ovules at between 10 and 20 d after pollination.Fewer ovules were penetrated following self- than cross-pollination. Eucalyptus woodwardii Maiden, Lemon-flowered gum, Pistil receptivity, Pollen tube growth, Breeding system, Self-incompatibility