Sexual Plant Reproduction

Segregating progenies of crosses between sexual and apomictic genotypes of Paspalum simplex were analysed for the formation of meiotic versus aposporous embryo sacs, zygotic versus parthenogenetic embryos, and autonomous versus pseudogamous endosperms by using cytoembryological and flow cytometric analyses. Reduced and unreduced 8-nucleated embryo sacs were the final product of female gametophyte development in sexual and aposporous genotypes, respectively. An incomplete penetrance of parthenogenesis was detected in aposporous genotypes. The relative DNA content of endosperm nuclei revealed the normal 2:1 maternal to paternal ratio in sexuals and a 4:1 ratio in apomicts, indicating insensitivity of the apomictic genotypes to endosperm imprinting. Apospory, parthenogenesis and pseudogamy are located on a relatively large linkage group and are inherited together with previously developed molecular markers as a single genetic unit in segregating progenies

 We describe a new method to determine stigma receptivity by using a Peroxtesmo esterase indicator paper liquid (one paper+1 ml water). This technique enables the researcher to check instantly the receptivity of various types of stigmas and to locate the receptive area.

 Cork oak (Quercus suber L.) is a monoecious wind-pollinated species with a protandrous system to ensure cross-pollination. To the best of our knowledge, this report provides the first insight into the sexual reproduction cycle in this species. The cork oak flowering season extends from April until the end of May. Our results show that, at anthesis, the pistillate flower is not completely formed and ovules are just starting to develop. Pollen reaching the dry stigmatic surface adheres to the receptive cells, germinates and penetrates the epidermis in aproximately 24 h, and grows through the intercellular spaces of a solid transmitting tissue. In cross-pollination, a sequential arrest of pollen tubes was observed along the style, providing preliminary evidence for a pollen tube competition mechanism. As a consequence, few pollen tubes reach the basal portion of the style. Furthermore, pollen tube growth is a discontinuous process since tubes are arrested in the basal portion of the style about 10–12 days after pollination. While tubes are latent, the ovarian loculus starts to develop from an emerging mass of sporogeneous cells which later will differentiate into the placenta and ovules. One and a half months after pollination ovules complete their differentiation, tubes resume growth and fertilisation occurs. Ovular abortion is frequent at this stage, and only one ovule will successfully mature during autumn into a monospermic seed.

Polyploidy is a key process in plant evolution, with the asexual formation of embryos representing a way through which polyploids can escape sterility. The association between polyploidy and polyembryony is known to occur in Bignoniaceae. In this study, we investigate polyembryony in four polyploid species of Anemopaegma: A. acutifolium, A. arvense, A. glaucum and A. scabriusculum as well as in one diploid species, A. album. Polyembryony was observed only in polyploid species. We used seed dissection and germination tests to compare the number of polyembryonic seeds. We tested how the pollen source influences the number of polyembryonic seeds and the number of embryos per seed and tested the correlation between the number of viable seeds per fruit and mean number of embryos per seed. The number of polyembryonic seeds observed by seed dissection was higher than the number of polyembryonic seeds determined by the germination test, with the number of embryos produced per seed being higher than the number of seedlings. The dissection of seeds of A. glaucum indicated that a higher number of polyembryonic seeds and a higher number of embryos were present in seeds from cross-pollination than in seeds from self-pollination. On the other hand, germination tests indicated that a higher number of polyembryonic seeds were present in fruits from self-pollination than from cross-pollination. The mean number of embryos per seed was not influenced by the number of viable seeds per fruit in fruits from open pollination. These results indicate a positive relationship between polyembryony and polyploidy in Anemopaegma.

AGP update: plant reproduction. Arabinogalactan proteins (AGPs) are a large family of hydroxyproline-rich proteins, heavily glycosylated, ubiquitous in land plants, including basal angiosperms and also in many algae. They have been shown to serve as important molecules in several steps of the reproductive process in plants. Due to their special characteristics, such as high sugar content and their means of association with the membrane, they are often perceived as likely candidates for many different aspects of the reproductive process such as signalling molecules, cell identity determinants, morphogens, nutrient sources and support for pollen tube growth, among others. Nevertheless, the study of these proteins pose many difficulties when it comes to studying them individually. Most of the work done involved the use of the β-glucosyl Yariv reagent and antibodies that recognize the carbohydrate epitopes only. Recently, new approaches have been used to study AGPs largely based in the ...

A tobacco pollen tube glycoprotein, p69 is encoded by the pollen-specific gene ntp303 that is transcribed during pollen development and pollen tube growth, but it is abundantly translated only after pollen germination. To investigate the translational repression of ntp303 mRNA during pollen development the compartmentation of ntp303 mRNA was examined and compared against another transcript (ntp52), which is efficiently translated during pollen maturation. Three subcellular fractions were isolated: a post-polysomal fraction enriched with messenger ribonucleoprotein particles, a polysomal fraction and a novel fraction of EDTA/ puromycin-resistant particles co-sedimentating with polysomes (EPP). At all developmental stages studied, ntp303 mRNA was found to be present in all fractions. Surprisingly, most of the translationally inactive ntp303 mRNA was localised in the polysomal fraction and EPPs, whereas ntp52 mRNA was distributed between the post-polysomal fraction and polysomes but was virtually undetectable in EPPs. This differential mRNA distribution pattern may help to explain the developmentally regulated translational repression of the ntp303 gene during pollen maturation, highlighting a potential role of EPPs. A model of how this differential mRNA compartmentation pattern regulates ntp303 mRNA translation is proposed.

What differentiates human males from human females? Is it the number of sex chromosomes? Is it the possession of the appropriate sex organs? Is it the amount of testosterone or estrogen? By what non-arbitrary universal standard can we judge?
In this brief article, I argue for such a standard and that this standard entails there are two and only two biological sexes.  Please click on the above link for the published article currently tracking over 20,000 views.

The frequency of aborted fruits and the changes and abnormalities that occur during the embryo development in intraspecific crosses of sweet-potato Ipomoea batatas (2n=6x=90) and interspecific crosses between I. batatas and I. trifida (2n=2x=30) were investigated in order to study the causes of the low seed production. Three genotypes of I. batatas and 18 genotypes of I. trifida were intermated. The frequency of aborted fruits was below 25% in the intraspecific crosses and over 90% in the interspecific crosses. Paraffin sections were used to examine the developmental stages of fruits and seeds. Embryos in different developmental stages were observed to determine the stage of abortion. These observations permitted the identification of developmental stages of embryo rescue in interspecific crosses. There were no significant differences in the frequency of embryo abortion before the early globular stage among female sweet-potato progenitors for the intraspecific and interspecific crosses. The frequency of the late occurrence of embryo abortion (when embryo abortion occurs after the pre-globular stage) was higher in interspecific crosses (19.1%) than in intraspecific crosses (5.5%). The frequency of the late occurrence of embryo abortion in interspecific crosses was higher at the globular stage (9.6%) than at the heart stage (4.3%). Providing that embryo rescue is conducted in interspecific crosses, the estimated number of potentially viable embryos could be increased: 30 times with embryos at the globular stage; 20 times with embryos at the heart stage; and 11 times if embryos at the torpedo stage were used for the rescue with respect to the seed set. The results suggested that the appropriate time for embryo rescue in interspecific crosses is at the globular stage. If embryos could be rescued at the globular stage, it would be possible to increase the number of surviving embryos up to 30 times in interspecific crosses and 0.02 times in intraspecific crosses with respect to natural conditions without embryo rescue.

All members of Rosa section Caninae, dogroses are polyploid and characterized by their unbalanced meiosis, which in most cases leads to a pronounced morphological influence from the maternal parent. In a previous investigation on a pair of reciprocal crosses between two species in this section, Rosa dumalis and R. rubiginosa (2n=35), nine offspring plants (approximately 10%) did not receive any of the 21 RAPD markers present in the respective pollen parent. This was interpreted as a possible occurrence of apomixis. These nine plants have now been subjected to a further study with additional markers. Thirteen new RAPD markers showed the same result as in the previous investigation: none of the nine plants inherited any of the pollen donor markers. The reproducibility of the RAPD markers was checked by mixing DNA samples to obtain a series of artificial hybrids between the two parent plants. Twelve RAPD markers gave the expected result, whereas one marker appeared only 50% of the time. In addition, pollen viability, mean number of seeds per hip, mean seed weight, and mean weight of fruit flesh per hip have been studied on the four progeny groups: R. dumalis×R. rubiginosa plants which received pollen donor markers (PM plants), R. dumalis×R. rubiginosa plants which did not receive any pollen donor markers (NPM plants), R. rubiginosa×R. dumalis PM plants and R. rubiginosa×R. dumalis NPM plants. A canonical discriminant analysis based on these four reproductive characters separated the four progeny groups. There were significant differences between the two PM groups in all investigated characters, and also between the PM and the NPM groups in pollen viability. The result from the RAPD markers together with the differences in pollen viability between the PM and NPM progeny groups is taken as an indication that apomixis occurs within the Caninae section.

Olive trees have a plentiful bloom but a low percentage of normal fruit set. To improve fruit set, numerous investigations have sought to identify the obstacles that prevent full production. In this work, flower development in five DOP Umbria cultivars (Leccino, Frantoio, Moraiolo, Dolce Agogia and San Felice) was studied throughout different developmental phases, from before microsporogenesis and megasporogenesis to post-anthesis, by morphological and cyto-histological observations. Dolce Agogia was the most precocious cultivar, while full flowering was simultaneous in Leccino, Frantoio, Moraiolo and San Felice. Frantoio and Leccino were also good pollen producers, having the highest percentage of pollen viability and germinability. Dolce Agogia can also be considered a good pollen producer in terms of the high quantity of released pollen, but it had the lowest levels of pollen viability and germinability and the highest percentage of aborted flowers and ovaries. Morphological and cyto-histological observations on the number of flowers per inflorescence and the number of aborted flowers and ovaries suggest that fruit set was not influenced by the number of flowers per inflorescence, but rather by the number of inflorescences, which depends on the global fruiting potential of the tree.

Isozymes and random amplified polymorphic DNA (RAPD) markers were used for precocious identification of non-maternal plants in progenies of the facultative apomict Poa pratensis. Four progenies obtained from controlled crosses that showed different degrees of apomixis on isozyme analysis of phospho-gluco-isomerases, esterases and peroxidases were chosen for RAPD analysis to generate genomic fingerprints using species-specific primers. At an advanced vegetative stage, a morphological analysis was also performed and characteristics related to growth habit and leaf morphology were observed and recorded. On the basis of the isozyme and RAPD electrophoretic pattern and the morphological appearance, each plant was classified as maternal or aberrant. All three classes of genetic markers employed were able to identify plants that exhibited aberrant traits in the four progenies. Overall, the results of RAPD analysis supported those of isozyme and morphology studies. However, in each progeny, some plants which both isozyme and morphological analyses distinguished as of maternal origin were aberrant according to RAPD analysis. Therefore, the RAPD method proved the most precise screening technique. The greater cost of the molecular approach was offset by its higher accuracy. The use of either three isozyme systems or six primers for PCR amplification seems to be sufficient for reliable estimation of the degree of apomixis. Histological analyses were carried out and the aposporic development of the plant material studied.

From anthesis to mature seed formation, burrs from cross-pollinated adult Castanea sativa Miller trees were characterized and seven developmental stages defined based on macro and micromorphological traits. In order to get an insight into the involvement of epigenetic mechanisms in sexual embryogenesis and to define somatic embryogenesis induction capability, global DNA methylation and the somatic embryogenic competence were quantified. On cross-pollinated trees once fertilization takes place, at least one ovule per ovary becomes dominant, and transient DNA demethylation occurs coinciding with the start of the sexual embryogenic programme. Unfertilized ovules from the same cluster, which maintain their prior size, increase their methylation level and undergo degeneration. These results were validated using non-cross-pollinated trees and the asynchrony of flower receptivity. When testing in vitro somatic embryogenesis response of isolated dominant ovules and axes from zygotic embryos under cross-pollinated conditions, the highest competence was found for reaching seed maturity. Thus, a “developmental window” of somatic embryogenesis in chestnut has been characterized. It includes from fertilization to embryo maturity, and a transient decrease in methylation is necessary after fertilization for the development of the somatic embryogenesis response.

An ovule culture technique has been established for barley that allows the regeneration of plants from zygotes. An average of 1.3 plantlets per ovule could be regenerated from more than 60% of the cultured ovules and about 75% of the regenerated plantlets developed into normal, fertile plants. The same regeneration frequencies were obtained in intact ovules and in ovules where the two integuments had been removed from the micropylar region. Unfertilized ovules and ovules where the fertilized eggs had been destroyed by a microinjection needle did not give rise to embryo-like structures. Plants could be regenerated from the zygote at the same frequency at developmental stages from immediately after fertilization until the formation of bicellular embryos. This tissue culture system appeared to be largely independent of genotype since similar regeneration frequencies were obtained in two different barley cultivars, Igri and Alexis, that in anther and microspore culture behave differently. The same technique has also been applied successfully in the wheat cultivar Walter.