Gametophytic Chromosome Number Research Articles

Genetic characterization and pollen viability of a natural putative hybrid of Begonia boliviensis × B. micranthera (Begoniaceae) from Argentina

ABSTRACT An orange-flowered natural putative hybrid of Begonia boliviensis × B. micranthera was recently discovered from Calilegua National Park in Jujuy Province, Argentina. Propionic hematoxilyn method was applied to study its chromosomal behavior during meiosis, Müntzing’s stain solution was used to determine pollen grain fertility and ITS2 and rbcL sequences were amplified to help confirm the parentage of the putative hybrid. This plant has a gametophytic chromosome number of n = 13, very regular meiotic behavior and an intermediate percentage of viable pollen compared to other studied natural putative hybrids. The ITS2 sequence data support the parentage of the putative hybrid begonia but sequence comparison shows its ITS2 sequence is more similar to B. micranthera than to B. boliviensis. The molecular marker rbcLa revealed that there are no differences between the sequences for B. boliviensis, B. micranthera and the putative hybrid. Begonia boliviensis × B. micranthera is a diploid plant that, due to its moderately high pollen fertility (43.3%) compared to other natural Begonia hybrids (which are often sterile) and regular meiosis, would likely be able to self-cross or cross with other begonia taxa.

Double Haploids for Vegetable Crop Improvement: A Review

Vegetables are the richest source of vitamins and minerals and play a major role in nutritional security. The primary objective of vegetable breeding is enhancing production and productivity. Breeders use various conventional and non-conventional breeding approaches for genetic advance. Recent advances in biotechnology helps to enhance the efficiency and shorten the time required to achieve the fixed goals in a breeding program, as well as to address the economic and ecological goals. Among these, haploid (H) and doubled haploid (DH) production through gametic embryogenesis has long been recognized as a valuable tool to help crop improvement. Haploid plants are the sporophytes with a gametophytic chromosome number and doubled haploids (DH) are haploids that have undergone chromosome duplication. Haploids and double haploids occur spontaneously in nature. Haploids can also be induced artificially by various techniques such as wide hybridization, pollination with irradiated pollens androgenesis, gynogenesis and finally further chromosome doubling results in double haploids. Production of double haploids in vegetables will shorten the breeding cycle and also DH technology is useful in reverse breeding, CMS line production, gene stacking and various other genetic studies.

CENH3-GFP: a visual marker for gametophytic and somatic ploidy determination in Arabidopsis thaliana.

BackgroundThe in vivo determination of the cell-specific chromosome number provides a valuable tool in several aspects of plant research. However, current techniques to determine the endosystemic ploidy level do not allow non-destructive, cell-specific chromosome quantification. Particularly in the gametophytic cell lineages, which are physically encapsulated in the reproductive organ structures, direct in vivo ploidy determination has been proven very challenging. Using Arabidopsis thaliana as a model, we here assess the applicability of recombinant CENH3-GFP reporters for the labeling of the cell’s chromocenters and for the monitoring of the gametophytic and somatic chromosome number in vivo.ResultsBy modulating expression of a CENH3-GFP reporter cassette using different promoters, we isolated two reporter lines that allow for a clear and highly specific labeling of centromeric chromosome regions in somatic and gametophytic cells respectively. Using polyploid plant series and reproductive mutants, we demonstrate that the pWOX2-CENH3-GFP recombinant fusion protein allows for the determination of the gametophytic chromosome number in both male and female gametophytic cells, and additionally labels centromeric regions in early embryo development. Somatic centromere labeling through p35S-CENH3-GFP shows a maximum of ten centromeric dots in young dividing tissues, reflecting the diploid chromosome number (2x = 10), and reveals a progressive decrease in GFP foci frequency throughout plant development. Moreover, using chemical and genetic induction of endomitosis, we demonstrate that CENH3-mediated chromosome labeling provides an easy and valuable tool for the detection and characterization of endomitotic polyploidization events.ConclusionsThis study demonstrates that the introgression of the pWOX2-CENH3-GFP reporter construct in Arabidopsis thaliana provides an easy and reliable methodology for determining the chromosome number in developing male and female gametes, and during early embryo development. Somatically expressed CENH3-GFP reporters, on the other hand, constitute a valuable tool to quickly determine the basic somatic ploidy level in young seedlings at the individual cell level and to detect and to quantify endomitotic polyploidization events in a non-destructive, microscopy-based manner.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0700-5) contains supplementary material, which is available to authorized users.

Haploid Breeding in Palms-A Brief Review

Haploids are sporophytic plants with gametophytic chromosome number, and they originate from a single gamete. The chromosome number of haploid could be doubled spontaneously or artificially to obtain doubled haploids carrying two sets of chromosomes from a single parent (homozygous). The important use of haploids is based on the fact that marked improvements in the economics of plant breeding can be achieved through doubled haploid production, since selection and other procedural efficiencies can be markedly improved through the provision of elite true-breeding (homozygous) progenies. Haploids have value in allowing the isolation of mutants, which may be masked in a diploid, particularly where the mutant allele is non-functional. Haploids also have value in transformation programmes. If haploids are transformed directly, then true breeding diploid transgenic plants can be produced in one step, following doubling of chromosomes. Using an integrated approach, including biotechnological tools and conventional methods, it is possible to achieve main goals of crop improvement in short time. Hence, efforts were made to exploit the potential of haploids in breeding of perennial monocots such as palms. The present paper discusses various developments in haploid breeding with respect to economically important palm species.

Microlepia boluoensis sp. nov. (Dennsteadtiaceae) from Guangdong, China

Microlepia boluoensis Y. Yuan & L. Fu, a new species of the genus Microlepia from Luofu mountain, Boluo county, Guangdong province, China, is described and illustrated. Its gametophytic chromosome number is n =47. Microlepia boluoensis has a similar morphology to M. scyphoformis, M. speluncae and M. hancei, such as creeping rhizomes, bipinnate‐tripinnatified laminas, intramarginal sori, cup‐shaped indusium and trilete spores, but it has a shorter creeping rhizome, larger frond (up to 351 cm), dry chartaceous, longer stipe (up to 139 cm), 23 pairs of primary pinnae, 1–13 sori, and spores with a distinct and raised laesurae.

Gametic embryogenesis and haploid technology as valuable support to plant breeding

Plant breeding is focused on continuously increasing crop production to meet the needs of an ever-growing world population, improving food quality to ensure a long and healthy life and address the problems of global warming and environment pollution, together with the challenges of developing novel sources of biofuels. The breeders' search for novel genetic combinations, with which to select plants with improved traits to satisfy both farmers and consumers, is endless. About half of the dramatic increase in crop yield obtained in the second half of the last century has been achieved thanks to the results of genetic improvement, while the residual advance has been due to the enhanced management techniques (pest and disease control, fertilization, and irrigation). Biotechnologies provide powerful tools for plant breeding, and among these ones, tissue culture, particularly haploid and doubled haploid technology, can effectively help to select superior plants. In fact, haploids (Hs), which are plants with gametophytic chromosome number, and doubled haploids (DHs), which are haploids that have undergone chromosome duplication, represent a particularly attractive biotechnological method to accelerate plant breeding. Currently, haploid technology, making possible through gametic embryogenesis the single-step development of complete homozygous lines from heterozygous parents, has already had a huge impact on agricultural systems of many agronomically important crops, representing an integral part in their improvement programmes. The aim of this review was to provide some background, recent advances, and future prospective on the employment of haploid technology through gametic embryogenesis as a powerful tool to support plant breeding.

Anther culture for haploid and doubled haploid production

Haploids are plants with a gametophytic chromosome number and doubled haploids are haploids that have undergone chromosome duplication. The production of haploids and doubled haploids (DHs) through gametic embryogenesis allows a single-step development of complete homozygous lines from heterozygous parents, shortening the time required to produce homozygous plants in comparison with the conventional breeding methods that employ several generations of selfing. The production of haploids and DHs provides a particularly attractive biotechnological tool, and the development of haploidy technology and protocols to produce homozygous plants has had a significant impact on agricultural systems. Nowadays, these biotechnologies represent an integral part of the breeding programmes of many agronomically important crops. There are several available methods to obtain haploids and DHs, of which in vitro anther or isolated microspore culture are the most effective and widely used. This review article deals with the current status of knowledge on the production of haploids and DHs through pollen embryogenesis and, in particular, anther culture.

Gynogenesis in the vine cacti Hylocereus and Selenicereus (Cactaceae)

Gynogenesis was investigated on the allotetraploid Selenicereus megalanthus and the diploid Hylocereus polyrhizus and Hylocereus undatus vine cactus species. Unpollinated ovules from developing flower buds containing microspores at middle uninucleate developmental stage were cultured on MS basal medium containing 2,4-D/TDZ with different sucrose concentrations. Ovule size increased under dark culture conditions in all the three species and the level of response was species and sucrose concentration dependent. The best responses were achieved in the two S. megalanthus accessions, E-123 and J-80, at 0.18 and 0.26 M sucrose. Only ovule enlargement was obtained in H. undatus and both ovule enlargement and callus were obtained in H. polyrhizus. Development in both species ceased and embryoids were not formed. Plant regeneration was directly and indirectly obtained in both S. megalanthus accessions. Ploidy level was determined for a total of 29 S. megalanthus gynogenic plants using flow cytometry: 15 were found to be dihaploid (plants with the gametophytic chromosome number) and the other 14 were found to have higher ploidy levels. This is the first report of successful gynogenesis in Cactaceae. The dihaploids of S. megalanthus successfully produced by ovule culture techniques opens new perspectives in vine cacti breeding.

Chromosome Numbers of the East African Giant Senecios and Giant Lobelias and their Evolutionary Significance

The gametophytic chromosome number for the giant senecios (Asteraceae, Senecioneae, Dendrosenecio) is n = 50, and for the giant lobelias (Lobeliaceae, Lobelia subgenus Tupa section Rhynchopetalum) it is n = 14. Previous sporophytic counts are generally verified, but earlier reports for the giant senecios of 2n = 20 and ca. 80, the bases for claims of intraspecific polyploidy, are unsubstantiated. The 14 new counts for the giant senecios and the ten new counts for the giant lobelias are the first gametophytic records for these plants and include the first reports for six and four taxa, respectively, for the two groups. Only five of the 11 species of giant senecio and three of the 21 species of giant lobelia from eastern Africa remain uncounted. Although both groups are polyploid, the former presumably decaploid and the latter more certainly tetraploid, their adaptive radiations involved no further change in chromosome number. The cytological uniformity within each group, while providing circumstantial evidence of monophyly and simplifying interpretations of cladistic analyses, provides neither positive nor negative support for a possible role of polyploidy in evolving the giant-rosette growth-form.

CHROMOSOME NUMBERS OF THE EAST AFRICAN GIANT SENECIOS AND GIANT LOBELIAS AND THEIR EVOLUTIONARY SIGNIFICANCE

The gametophytic chromosome number for the giant senecios (Asteraceae, Senecioneae, Dendrosenecio) is n = 50, and for the giant lobelias (Lobeliaceae, Lobelia subgenus Tupa section Rhynchopetalum) it is n = 14. Previous sporophytic counts are generally verified, but earlier reports for the giant senecios of 2n = 20 and ca. 80, the bases for claims of intraspecific polyploidy, are unsubstantiated. The 14 new counts for the giant senecios and the ten new counts for the giant lobelias are the first gametophytic records for these plants and include the first reports for six and four taxa, respectively, for the two groups. Only five of the 11 species of giant senecio and three of the 21 species of giant lobelia from eastern Africa remain uncounted. Although both groups are polyploid, the former presumably decaploid and the latter more certainly tetraploid, their adaptive radiations involved no further change in chromosome number. The cytological uniformity within each group, while providing circumstantial evidence of monophyly and simplifying interpretations of cladistic analyses, provides neither positive nor negative support for a possible role of polyploidy in evolving the giant‐rosette growth‐form.

Scopelophila cataractae(Mitt.) Broth. in North Wales

Abstract Scopelophila cataractae (Mitt.) Broth., discovered in abundance at its third British site, is highly gemmiferous. The plants attain a height of 5 cm, up to twice that previously known, and morphologically differentiated inner perigonial bracts occur. A gametophytic chromosome number of n = 13 is discussed in the wider context of the Pottiaceae.

Nuclear and cell divisions in isolated pollen of Petunia hybrida in agar suspension cultures.

IN VITRO cultivation of anthers leading to androgenesis provides a new approach to the production of angiosperms possessing the gametophytic number of chromosomes. Kameya and Hinata1 reported cell cluster formation from isolated pollen grains of Brassica oleracea. This study explores the use of isolated Petunia pollen to study the conditions leading to vegetative growth.

Note on the chromosome numbers obtained from crosses with the “peculiar” aposporous type ofScolopendrium vulgare

1. From crosses between the peculiar type ofScolopendrium vulgare andvulgare type the gametic chromosome numbers 15–30 are obtained, whereas the gametophytic chromosome number is 30.

The Life History of Cutleria

The nuclear conditions in the life history of Cutleria multifida may be summarized as follows: 1. The nucleus of both male and female plants contains 24 chromosomes, and the male and female gametes contain the same number. 2. In the union of gametes the number is doubled, and 48 chromosomes appear in the sporelings, which develop into the Aglaozonia form of Cutleria. Therefore, the individual bearing the name of Cutleria multifida represents the gametophytic phase of the species, 24 being the gametophytic number of chromosomes; and the Aglaozonia form of Cutleria represents the sporophytic phase, 48 being the sporophytic number. 3. Aglaozonia reptans contains 48 chromosomes, and the number is reduced in zoospore formation, the zoospore containing 24 chromosomes The zoospore with the reduced number of chromosomes germinates without conjugation. The individual grown from the germinating zoospore presents a striking similarity to the young form of Cutleria in nature and contains 24 chromosomes, the same number as the latter. Therefore it is evident that the individual bearing the name of Aglaozonia reptans represents the sporophytic phase of the species, 48 being the sporophytic number of chromosomes, and that the gametophytic phase is represented by the individual grown from the zoospore and resembling the young form of Cutleria in nature. It is certain that Aglaozonia reptans as it occurs in nature is identical with the Aglaozonia form of Cutleria multifida as developed in cultures and now determined to be the sporophytic phase of the species. 4. Therefore, Cutleria multifida and Aglaozonia reptans represent respectively gametophytic and sporophytic generations of a single species, the two generations alternating in the life history of Cutleria. 5. The female gamete of Cutleria may germinate apogamously. There is no irregularity in the mitotic process, 24 chromosomes being invariably present. The individual produced, in its early development differs somewhat from the product of the fertilized gamete, but the fate of the apogamous individual was not determined.

Cytology of Cutleria and Aglaozonia. A Preliminary Paper

The nuclear conditions during the life-history of Cutleria multifida and Aglaozonia reptans may be summarized as follows: 1. The nucleus of both male and female plants of Cutleria multifida contains 24 chromosomes; and the male and female gametes produced contain the same number. 2. In the union of gametes the number is doubled, and 48 chromosomes appear in the sporelings, which develop into the Aglaozonia form of Cutleria. Therefore it is evident that the individual bearing the name of Cutleria multifida represents the gametophytic phase of the species, 24 being the gametophytic number of chromosomes; and the Aglaozonia form of Cutleria represents the sporophytic phase of the species, 48 being the sporophytic number. 3. Aglaozonia reptans contains 48 chromosomes, and the number is reduced in zoospore formation, the zoospore containing 24 chromosomes. The zoospore with the reduced number of chromosomes germinates without conjugation. Although the nuclear details of the sporelings of Aglaozonia reptans have not yet been followed, it seems evident that Aglaozonia reptans represents the sporophytic phase of the individual whose gametophytic and sporophytic numbers of chromosomes are respectively 24 and 48. Probably Aglaozonia reptans as it occurs in nature is identical with the Aglaozonia form of Cutleria multifida which we have grown under culture and is now determined to be the sporophytic phase of the species.