A tobacco mutant with a reduced cell number in embryo sacs

 The semisterile tobacco plant BG-141.4 was produced using both irradiation with X-rays and anther culture. The embryological investigation of the progeny of this plant following selfing (R1) revealed disturbances in the structure of the mature embryo sacs (ESs). The major abnormality was a decrease in cell number in the ESs. Other abnormalities included disturbances in the distribution of nuclei and in cell differentiation. The overall frequency of abnormal ESs in individual plants investigated varied from 8% to 83%, while the frequency of ESs with a reduced number of cells varied from 5% to 72%. Since the examination of three subsequent generations - R2, R3 and R4 - showed similar results, it is concluded that a mutation has been induced. Its main phenotypic manifestation is most likely related to its lacking one or two nuclear division(s) during the coenocytic stage of megagametogenesis. The penetrance of the mutation varies widely. Received: 18 November 1996 / Revision accepted: 16 May 1997     

Seed germination and seedling fitness in Mesua ferrea L. in relation to fruit size and seed number per fruit

Effect of fruit size and seediness (seed number per fruit) was examined on germination and early growth of seedlings in Mesua ferrea L. Fruiting incidence (number of fruited trees in a population) and fruit loading (number of fruits per tree) vary from one year to the other, and were greater in 1997 than in 1998. Seeds from large fruits (> 40 g) are preferred for forestry plantations and those from small fruits (< 40 g) are discarded, despite a greater proportion of small fruits (63.2 %) than large fruits (36.8 %). A fruit, large or small in size, may contain one, two, three or four seeds. The germination percentage of seeds increased from 1-seeded through 4-seeded fruits both in laboratory and greenhouse conditions, and both in case of large and small fruits. Conversely, the mean seed weight and germination time decreased along this gradient, i.e. seeds from 1-seeded fruits were the heaviest and required maximum time for germination, and the seeds from 4-seeded fruits were the lightest and required minimum time for germination. The seeds from small fruits were lighter in weight, achieved lower germination percentages and required greater germination time than the seeds from large fruits in all four seeded categories. Seedlings from seeds from 1-seeded fruits survived better and with stronger vigour after 1 year of growth than seedlings from 2-, 3- and 4-seeded fruits. Further, seedling survival and vigour were greater for seeds from large rather than small fruits.     

Variance in number of eggs per patch: oviposition behaviour and population dispersion in a seed parasitic moth

ABSTRACT. 1. The relationship between oviposition behaviour and population dispersion was analysed for Grey a subalba Braun (Lep., Incurvariidae), a species in which females usually, but not invariably. lay eggs in only a few schizocarps (seed-pairs) on each umbellet they visit on Lomatium dissectum (Umbelliferae). During each of four years females exhibited a constant probability of leaving an umbellet after each egg was laid. Hence, some umbellets received more eggs than others and the behaviour matched a geometric distribution of eggs among umbellets.
2. The variance in number of schizocarps attacked per umbellet by individual females did not result from females choosing schizocarps of particular sizes or avoiding schizocarps that already contained eggs or larvae. A potential, but speculative, explanation of the variance is that females distribute their eggs among umbellets in a way that maximizes unpredictability on larval dispersion to a searching parasitoid, The pattern of oviposition by Greya females fits the truncated geometric distribution that is predicted if information, as indexed by the Shannon-Wiener entropy measure, is minimized. None the less, other measures of unpredictability or minimum information are possible, and the results highlight the problem of how to identify patterns of movement that may result from selection for unpredictability to enemies.
3. In systematic surveys of the L.dissectum population during three consecutive years, virtually all plants had between 10% and 65% of their seeds attacked. Hence, the separation of oviposition bouts between umbellets and the constant probability of leaving an umbellet after each egg was laid resulted in a broad distribution of Greya attack among L.dissectum plants.     

Selective seed abortion affects the performance of the offspring in Bauhinia ungulata

BACKGROUND AND AIMS: Under the microgametophytic competition hypothesis, a non-random pattern of seed abortion is expected, in which only the most vigorous seeds reach maturity. In a previous study, it was found that Bauhinia ungulata (Fabaceae) exhibits a pattern of seed abortion dependent on the position of the ovule within the ovary; ovules located in the stylar half of the fruit, close to the point of entry of pollen tubes to the ovary, have a low probability of seed abortion, whereas ovules in the basal half of the fruit are aborted with a high probability. METHODS: A series of experimental fruits was generated, in which ovules from either the stylar (treatments 1 and 2) or the basal (treatments 3 and 4) half of fruits were destroyed, to evaluate whether these patterns of selective seed abortion have an effect on the vigour of the offspring in B. ungulata. KEY RESULTS: Only 53 % of the seed from control fruits germinated. Seed set in fruits from treatments 1 and 2 showed a significantly lower (33-43 %) percentage of germination; the germination of seeds from fruits in treatments 3 and 4 (49-51 %) did not differ from control seeds. In addition, it was found that the differences in vigour of the offspring are not random with respect to the position of the ovule in the pod. CONCLUSIONS: The overall performance of the seeds correlated with their likelihood of maturation. Seeds located at the basal half of the treatment fruits showed lower values of vigour than seeds located on the stylar half. The differences were more marked for early measures of fitness.     

Pollen limitation,fruit abortion,and autonomous selfing in three populations of the perennial herb Ruellia nudiflora

Multiple factors determine plant reproductive success and their influence may vary spatially. This study addresses several factors influencing female reproductive success in three populations of Ruellia nudiflora, specifically we: (i) determine if fruit set is pollen‐limited and if pollinator visitation rates are related to this condition; (ii) estimate fruit set via autonomous self‐pollination (AS) and relate it to the magnitude of herkogamy; and (iii) evaluate if fruit abortion is a post‐pollination mechanism that determines the magnitude of pollen limitation. At each site we marked 35 plants, grouped as: unmanipulated control (C) plants subjected to open pollination, plants manually cross‐pollinated (MP), and plants excluded from pollinators and only able to self‐pollinate autonomously (AS). Fruit set was greater for MP relative to C plants providing evidence for pollen limitation, while a tendency was observed for lower fruit abortion of MP relative to C plants suggesting that fruit set is influenced not only by pollen delivery per se, but also by subsequent abortion. In addition, although pollinator visits varied significantly among populations, the magnitude of pollen limitation did not, suggesting that pollinator activity was not relevant in determining pollen limitation. Finally, fruit set tended to decrease with the degree of herkogamy for AS plants, but this result was inconclusive. These findings have contributed to identify which factors influence reproductive success in populations of R. nudiflora, with potentially relevant implications for population genetic structure and mating system evolution of this species.     

Ceratitis capitata: Effect of host fruit size on the number of eggs per clutch

A laboratory strain of Ceratitis capitata (Wiedemann) was presented with grapes, plums, apples and peaches for oviposition. Fruit diameter was highly correlated with the number of eggs/oviposition. Clutch size was 3.9±0.3 for grapes (20 mm) compared with 14.0±0.7 for apples (70 mm). When Parafilm^®-enveloped whole peeled fruits and smaller spheres of fruit flesh were offered, fruit size proved more important than fruit type in determining egg clutch sizes. Ovipositions that required the puncture of fruit skin gave larger clutches than ovipositions through Parafilm or into punctured fruit.

---

Zusammenfassung Einem Laboratoriumsstamm von Ceratitis capitata (Wiedemann) wurden Trauben, Pflaumen, Aepfel und Pfirsiche zur Eiablage vorgelegt. Der Fruchtdurchmesser war stark korreliert mit der Eizahl pro Eiablage. Die Grösse der Eihaufen war 3,9±0,3 bei Trauben (20 mm) und 14,0±0,7 bei Aepfeln (70 mm). Wenn geschälte und mit Parafilm^® eingehüllte ganze Früchte und Fruchtscheiben vorgelegt wurden, war die Fruchtgrösse wichtiger als der Fruchttyp für die Grösse der Eiablage. Eiablagen, bei denen die Fruchthaut durchbohrt werden musste, waren grösser als Eiablagen durch Parafilm oder in perforierte Früchte.

     

Ovule number per flower in a world of unpredictable pollination

The number of ovules per flower varies over several orders of magnitude among angiosperms. Here we consider evidence that stochastic uncertainty in pollen receipt and ovule fertilization has been a selective factor in the evolution of ovule number per flower. We hypothesize that stochastic variation in floral mating success creates an advantage to producing many ovules per flower because a plant will often gain more fitness from occasional abundant seed production in randomly successful flowers than it loses in resource commitment to less successful flowers. Greater statistical dispersion in pollination and fertilization among flowers increases the frequency of windfall success, which should increase the strength of selection for greater ovule number per flower. We therefore looked for evidence of a positive relationship between ovule number per flower and the statistical dispersion of pollen receipt or seed number per flower in a comparative analysis involving 187 angiosperm species. We found strong evidence of such a relationship. Our results support the hypothesis that unpredictable variation in mating success at the floral level has been a factor in the evolution of ovule packaging in angiosperms.     

Competition and the compensatory regulation of fruit and seed set in the perennial herb Epilobium dodonaei (Onagraceae)

I studied the effects of competition and soil fertilization on variation of seed yield components of the outcrossing perennial Epilobium dodonaei Vill. using a randomized complete block design. Fertilization as a main effect was not significant. Competition, however, reduced the number of flower buds per shoot (-29%), the number of ovules per fruit (-12%), and the number of ripe fruits per shoot (-51%). In addition, competition caused an increase in abortion of flower buds. Consequently the fruit/flower bud ratio decreased from 0.71 to 0.47. Average seed mass was not reduced significantly by competition. Some of the negative effects of competition on fruit production were mitigated by fertilization. However, competition considerably reduced the proportion of late-aborted seeds, which resulted in an increase of the seed/ovule ratio from 0.31 to 0.49 (+58%). As a consequence of this compensation, the reduction in the number of seeds per shoot due to competition was not significant. At the level of the genet, competition had a strong effect on seed yield due to decreases in the number of shoots produced. I discuss patterns of regulation at consecutive levels of reproduction. Shoots of plants suffering from competition initially invested less in reproductive structures than the control and showed a higher abortion rate of less costly structures early in reproductive development, but also had a lower abortion rate later in their development. The observed compensatory pattern in yield components illustrates the fine-tuning regulation capacity at different levels of reproductive development in plants.     

Analysis of stunter1, a maize mutant with reduced gametophyte size and maternal effects on seed development

Many higher eukaryotes have evolved strategies for the maternal control of growth and development of their offspring. In higher plants this is achieved in part by postmeiotic gene activity controlling the development of the haploid female gametophyte. stunter1 (stt1) is a novel, recessive, maternal effect mutant in maize that displays viable, miniature kernels. Maternal inheritance of stt1 results in seeds with reduced but otherwise normal endosperms and embryos. The stt1 mutation displays reduced transmission through the male and female parents and causes significant changes in the sizes of both male and female gametophytes. stt1 pollen grains are smaller than wild type, have reduced germination efficiency, and reduced pollen tube growth. stt1 embryo sacs have smaller central cells and abnormal antipodal cells that are larger, more vacuolated, and fewer in number than wild type. Embryos and endosperms produced by fertilization of stt1 embryo sacs develop and grow more slowly than wild type. The data suggest that the morphology of mutant embryo sacs influences endosperm development, leading to the production of miniature kernels in stt1. Analysis of seeds carrying a mutant maternal allele of stt1 over a deletion of the paternal allele demonstrates that both parental alleles are active after fertilization in both the endosperm and embryo. This analysis also indicates that embryo development until the globular stage in maize can proceed without endosperm development and is likely supported directly by the diploid mother plant.     

Freezing of bovine embryos: Effects of embryo quality,time from thawing to transfer and number frozen per vial

Over a ten-month period 736 embryos were collected from 103 cows induced to superovulate. Embryos were frozen in 10% glycerol and, after thawing, 655 appeared viable and were transferred nonsurgically to synchronous recipients. When embryos did not appear degenerative before freezing and transfers were performed within 3 hr of thawing, 40% of the embryos resulted in pregnancies. If embryos showed signs of degeneration before freezing, only 27% resulted in pregnancies after thawing and transfer. Similarly, when non-degenerative embryos were kept in Casou straws for more than 3 hr after thawing, fewer produced pregnancies (25%) following transfer. The number of embryos frozen in each vial ranged from one to 18 and this had no significant effect on success. By selecting embryos to be frozen and transferring them soon after thawing, the proportion of embryos surviving the freeze-thaw process can be very high.     

Dynamics of maternal and paternal effects on embryo and seed development in wild radish (Raphanus sativus)

Background and Aims

Variability in embryo development can influence the rate of seed maturation and seed size, which may have an impact on offspring fitness. While it is expected that embryo development will be under maternal control, more controversial hypotheses suggest that the pollen donor and the embryo itself may influence development. These latter possibilities are, however, poorly studied. Characteristics of 10-d-old embryos and seeds of wild radish (Raphanus sativus) were examined to address: (a) the effects of maternal plant and pollen donor on development; (b) the effects of earlier reproductive events (pollen tube growth and fertilization) on embryos and seeds, and the influence of embryo size on mature seed mass; (c) the effect of water stress on embryos and seeds; (d) the effect of stress on correlations of embryo and seed characteristics with earlier and later reproductive events and stages; and (e) changes in maternal and paternal effects on embryo and seed characteristics during development.

Methods

Eight maternal plants (two each from four families) and four pollen donors were crossed and developing gynoecia were collected at 10 d post-pollination. Half of the maternal plants experienced water stress. Characteristics of embryos and seeds were summarized and also compared with earlier and later developmental stages.

Key Results

In addition to the expected effects of the maternal plants, all embryo characters differed among pollen donors. Paternal effects varied over time, suggesting that there are windows of opportunity for pollen donors to influence embryo development. Water-stress treatment altered embryo characteristics; embryos were smaller and less developed. In addition, correlations of embryo characteristics with earlier and later stages changed dramatically with water stress.

Conclusions

The expected maternal effects on embryo development were observed, but there was also evidence for an early paternal role. The relative effects of these controls may change over time. Thus, there may be times in development when selection on the maternal, paternal or embryo contributions to development are more and less likely.     

E-Screen evaluation of sugar beet feedstuffs in a case of reduced embryo transfer efficiencies in cattle: the role of phytoestrogens and zearalenone

The E-Screen assay was used to evaluate the estrogenicity of sugar beet by-products obtained from a dairy farm experiencing low success rates of embryo transfer. The beet tailings had ~3-fold the estradiol equivalents of the pelleted beet pulp (3.9 and 1.2 μg estradiol equivalents or E₂Eq/kg dry matter, respectively). Whole sugar beets, sugar beet pellets, and shreds from several Midwest US locations were also evaluated by E-Screen. All pellets examined were found to have some estrogenic activity (range ~0.1–2.0 μg E₂Eq/kg DM) with a mean of 0.46 μg/kg dry matter and median of 0.28 μg/kg dry matter. Relative E₂Eq ranked as follows: pellets?>?shreds?>?most unprocessed roots. Using recommended feeding levels and conservative absorption estimates (10%), the estrogenic activity in the original samples could result in blood estradiol equivalents?≥?those found at estrus (10 pg/mL, cows). Chemical analyses revealed no known phytoestrogens, but the estrogenic mycotoxin, zearalenone, was found in 15 of 21 samples. Of significance to those using the E-Screen are our findings that contradict previous reports: ß-sitosterol has no proliferative effect and genistein’s glucuronidated form—genistin—is equal to genistein in proliferative effect. The latter is the result of deconjugation of genistin to genistein in the presence of fetal bovine serum (determined by LC MSMS). These data show the usefulness and caveats of the E-Screen in evaluation of feedstuffs, and indicate a potential for sugar beet by-products to contain zearalenone at concentrations that may impact reproduction.     

Limited carbohydrate availability as a potential cause of fruit abortion in Rubus chamaemorus

Fruit abortion can be caused by a range of abiotic and biotic factors. To gain a better understanding of the causes of the high fruit abortion frequency in cloudberry ( Rubus chamaemorus L.), we manipulated different sources of carbon, that is, leaves and rhizome. We also manipulated flower number to see if competition between floral ramets explained fruit abortion in cloudberry. Reducing the number of flowers had no impact on fruit abortion frequency. In fact, the species forms an extensive rhizome network with only a few ramets per clone and competition between floral ramets is unlikely. Ramet defoliation had limited impact on fruit abortion, but successful fruit development was affected by rhizome length. The longer the rhizome, the higher the chances to mature a fruit. These results suggest that current photoassimilate production by the reproductive ramet alone is insufficient to insure fruit development. Carbon can come from other ramets but distances are usually high between ramets. Fruit production might thus depend on the use of stored carbohydrates in the rhizome to balance insufficient photosynthetic contribution during fruit production.     

Forest fragmentation and plant reproductive success: a case study in four perennial herbs

We assessed the effects of habitat fragmentation on reproductive success in natural populations of four forest herbs with differing life-history traits and whose distribution patterns appeared to be negatively affected by decreased habitat size and/or increased isolation: Carex sylvatica, Galium odoratum, Sanicula europaea and Veronica montana. Our aims were to test (1) whether habitat size and isolation are positively correlated with population size and isolation, respectively, (2) whether plant reproductive success, a major component of plant fitness, is reduced in small and/or isolated populations when also accounting for differences in habitat quality (edaphic conditions, light intensity) and the effects of plant size, and (3) whether species with different life histories are affected differently. There were significant positive relationships between habitat and population size and between habitat and population isolation in some, but not all of the species. We mostly found no negative effects of small population size or isolation on reproduction. However, reproductive success was reduced in small populations of Sanicula, and this effect was independent of differences in plant size and environmental conditions. The reduced fecundity in small populations may be a consequence of the Allee-effect, a possible mechanism being pollen limitation. Furthermore, the proportion of flowering ramets was reduced in small and isolated populations of Galium, which may have been caused by changes in population structure. Lastly, we found some evidence for largely outcrossing, non-clonal species to be more sensitive to reductions in population size, at least in terms of their reproductive success.     

Measurement of gene number for seed storage proteins in Pisum.

We have measured the numbers of genes coding for the three seed storage proteins, vicilin, convicilin and legumin, in a number of Pisum genotypes of variant protein composition. No difference in gene number existed among P. sativum genotypes for any of the proteins. There were differences in the number of genes coding for individual proteins with approximately 11 genes (per haploid genome) for vicilin, 8 genes for legumin and 1 gene for convicilin.     

Differences in life history traits of relatedEpilobium species: Clonality, seed size and seed number

Small changes in morphology can affect the performance and functions of organisms and hence their ecological success. In modular constructed plants, contrasting growth strategies may be realized by differences in the spatial arrangement and size of shoots. Such differences change the way in which meristems and resources are assigned to various functions during the lifespan of a plant. If such changes include the capacity to spread clonally, sexual reproduction may also be affected. I compare patterns in vegetative growth and sexual reproductive traits in four allopatric species ofEpilobium which are sometimes considered as subspecies of a single polymorphic taxon. The four species differ in the location of the buds which annually renew the aerial shoot system.E. dodonaei andE. steveni do not spread clonally and are characterized by a shrub-like habit.E. fleischeri, a species occurring only in the Alps, andE. colchicum, which occurs in the upper region of the Caucasus mountains, both produce buds on horizontal roots or plagiotropic shoots. Both alpine species exhibiting clonal growth have smaller shoots, fewer fruits and smaller seeds than the lowland species. An intraspecific trade-off between seed number per fruit and seed mass is realized. Both alpine species produce more seeds per fruit at the expense of seed mass. The morphological relationship between the four species and their geographical distribution suggest that clonal growth inE. fleischeri (restricted to the Alps) andE. colchicum (restricted to the Caucasus) is adaptively associated with the stressful conditions of alpine habitats. Our results suggest that clonal growth is not necessarily correlated with reduced reproduction by seeds. The success of plants which are already established may largely depend on clonal spread, but the colonization of new habitats depends on the production of a large number of small seeds with high dispersability.     

Fine mapping and candidate gene prediction of a major QTL for kernel number per ear in maize

Kernel number per ear (KNE) is a maize yield component and an important breeding target for improving grain yield. As a complex quantitative trait, KNE has been assumed to be controlled by a set of quantitative trait loci (QTLs) with minor effects. Identification and genetic evaluation of these QTLs are prerequisites for improving KNE with a molecular breeding approach. In this study, we developed the chromosome segment introgression line SL19-41, which exhibited 95.60% recovery of the Ye478 background and showed a higher KNE and grain yield. The plant architecture and flowering time of SL19-41 were not significantly different from those of Ye478. We employed introgression line (IL)-derived mapping populations and identified a major QTL, KNE4, which is partially dominant. KNE4 was validated in a backcross population and a set of sub-introgression lines and was delimited to a 440-kb genomic region in Bin4.07. An allele included in the introgression fragment had a synergistic effect, noticeably increasing KNE and showing the potential to improve KNE in Ye478. Subsequently, the association between sequence polymorphism in the QTL interval and KNE variation revealed a putative candidate gene that encoded a long-chain acyl-CoA synthetase responsible. This result provides an available locus for the molecular improvement of KNE and for the isolation of functional genes underlying this QTL.