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Ancient hybridization leading to plastid capture is a likely cause of cytonuclear discordance, although discordance may also be attributed to other mechanisms. Cytonuclear discordance is ubiquitous in a clade of southern African Oxalis known as the Hirta clade, despite a notable lack of documented field hybrids for this genus. The aims of this study were to determine whether hybridization is possible between different Hirta clade species, what the fitness effects on seed set of possible hybridizations are, and to determine the mode of inheritance of plastid DNA in Oxalis. We tested these aims using manual interspecific and conspecific crosses, as well as self-pollination control crosses of species within this clade, conducted in a research collection context. Roughly 10% of interspecific crosses produced seed, most of which were confirmed as unambiguous hybrid plants using DNA sequencing of the Internal Transcribed Spacer (ITS). Low levels of self-compatibility were recorded in several species, while one accession showing very high levels of self-compatibility (accession MO1218). Interspecific crosses produced significantly less seed per capsule compared to conspecific crosses with respective parents, suggesting decreased fitness in the establishment of the F1 hybrids. Selfing seed set was significantly lower than interspecific and conspecific seed set upon removal of MO1218. Using plastid fragment length polymorphisms, Oxalis was found to have predominantly or exclusively maternally inherited plastid DNA. This study establishes the viability of the earliest stages of plastid capture in Oxalis, and provides context relevant to the lack of documented field hybrids in the southern African members of this genus. Future studies should focus on F1 survival and fertility and the maternal fitness effects of subsequent backcrosses to the maternal parent, as well as on hybridization rates under field conditions, to assess whether hybridization occurs at rates sufficient to affect Oxalis evolution in southern Africa.

Chloroplasts are typically inherited from the female parent and are haploid in most angiosperms, but rare intra-individual heteroplasmy in plastid genomes has been reported in plants. Here, we report an example of plastome heteroplasmy and its characteristics in Gentiana tongolensis (Gentianaceae). The plastid genome of G. tongolensis is 145,757 bp in size and is missing parts of petD gene when compared with other Gentiana species. A total of 112 single nucleotide polymorphisms (SNPs) and 31 indels with frequencies of more than 2% were detected in the plastid genome, and most were located in protein coding regions. Most sites with SNP frequencies of more than 10% were located in six genes in the LSC region. After verification via cloning and Sanger sequencing at three loci, heteroplasmy was identified in different individuals. The cause of heteroplasmy at the nucleotide level in plastome of G. tongolensis is unclear from the present data, although biparental plastid inheritance and transfer of plastid DNA seem to be most likely. This study implies that botanists should reconsider the heredity and evolution of chloroplasts and be cautious with using chloroplasts as genetic markers, especially in Gentiana.

Plastid inheritance in angiosperms is presumed to be largely maternal, with the potential to inherit plastids biparentally estimated for about 20% of species. In Passiflora, maternal, paternal and biparental inheritance has been reported, however, these studies were limited in the number of crosses and progeny examined. To improve the understanding of plastid transmission in Passiflora, the progeny of 45 interspecific crosses were analyzed in the three subgenera: Passiflora, Decaloba and Astrophea. Plastid types were assessed following restriction digestion of PCR amplified plastid DNA in hybrid embryos, cotyledons and leaves at different developmental stages. Clade-specific patterns of inheritance were detected such that hybrid progeny from subgenera Passiflora and Astrophea predominantly inherited paternal plastids with occasional incidences of maternal inheritance, whereas subgenus Decaloba showed predominantly maternal and biparental inheritance. Biparental plastid inheritance was also detected in some hybrids from subgenus Passiflora. Heteroplasmy due to biparental inheritance was restricted to hybrid cotyledons and first leaves with a single parental plastid type detectable in mature plants. This indicates that in Passiflora, plastid retention at later stages of plant development may not reflect the plastid inheritance patterns in embryos. Passiflora exhibits diverse patterns of plastid inheritance, providing an excellent system to investigate underlying mechanisms in angiosperms.

Organellar genomes may shed light on complicated patterns of plant evolution at inter- and intraspecies level. Primary structure of plastid genomes sequenced in this study and taken from public databases was characterised and compared in 22 diverse, mostly wild representatives of the genus Pisum (peas). Phylogenetic trees reconstructed via Bayesian approach on the basis of entire plastid genomes resembled those reconstructed on the basis of a nuclear gene His5 coding for a minor histone H1 subtype. They reveal Pisum fulvum as an early divergence of the genus but do not support other taxonomical subdivisions. The positions of three accessions, classified as P. sativum subsp. elatius (the wild subspecies of the common pea), appeared quite unexpected. On the entire plastid genome tree, two accessions, from the Black Sea area of Turkey and Georgia, clustered with representatives of another species, P. fulvum, while the other, from Greece, was the first divergence of the P. sativum branch. We suppose these unusual plastid genomes to be ancient lineages ascending to a ‘missing link’ between P. fulvum and P. sativum, represented by accession Pe 013 from Turkey. Accessions with common pea appearance but deeply diverged plastids could occur through occasional crossing of diverged pea lines in the past and biparental plastid inheritance, both events being possible in peas.

A number of plant groups have been proposed as ideal systems to explore plastid inheritance, plastome evolution and plastome-nuclear genome coevolution. Quick generation times and a compact nuclear genome in Arabidopsis thaliana, the relative ease of plastid isolation from Spinacia oleracea and the tractability of plastid transformation in Nicotiana tabacum are all desirable attributes in a model system; however, these and most other groups all lack novelty in terms of plastome structure and nucleotide sequence evolution. Contemporary sequencing and assembly technologies have facilitated analyses of atypical plastomes and, as predicted by early investigations, Geraniaceae plastomes have experienced unprecedented rearrangements relative to the canonical structure and exhibit remarkably high rates of synonymous and nonsynonymous nucleotide substitutions. While not the only lineage with unusual plastome features, likely no other group represents the array of aberrant phenomena recorded for the family. In this chapter, Geraniaceae plastomes will be discussed and, where possible, compared with other taxa.

We applied a series of intra- and interspecific in situ cross-pollination experiments under greenhouse conditions to evaluate the breeding systems in four Fosterella species (Pitcairnioideae s.str.; Bromeliaceae). Viable hybrids were produced between each pair of the investigated species, suggesting that reproduction barriers may be low also under natural conditions. Seed germination rates proved to be high in each crossing treatment, indicating a high viability of the artificial hybrids. Large numbers of seeds were produced after both closed and open pollination treatments, suggesting that autogamy may be a major reproductive strategy in the genus. Our results support the concept that self-compatibility is an appropriate way to avoid natural hybridization in Bromeliaceae and could assist in maintaining species integrity in the presence of pollen flow. Paternity was verified in all crosses by genotyping parents and offspring with a set of polymorphic nuclear microsatellite markers. To study the mode of chloroplast inheritance, we developed a novel set of 24 chloroplast microsatellite markers using 454 pyrosequencing technology, and applied four of these markers for genotyping parents and offspring from all crosses. Our results clearly demonstrated a maternal inheritance of plastids.

The difference between the uniparental maternal and biparental type of plastid inheritance is based upon a relatively simple mechanism. In the uniparental type plastids are excluded from the generative or siperm cells during the firts pollen mitosis or during pollen development. In some angiosperms this exclusion is completely lacking or carried out partially.

Plastid sequences are a cornerstone in plant systematic studies and key aspects of their evolution, such as uniparental inheritance and absent recombination, are often treated as axioms. While exceptions to these assumptions can profoundly influence evolutionary inference, detecting them can require extensive sampling, abundant sequence data, and detailed testing. Using advancements in high-throughput sequencing, we analyzed the whole plastomes of 65 accessions ofPicea,a genus of ~35 coniferous forest tree species, to test for deviations from canonical plastome evolution. Using complementary hypothesis and data-driven tests, we found evidence for chimeric plastomes generated by interspecific hybridization and recombination in the clade comprising Norway spruce (P. abies) and ten other species. Support for interspecific recombination remained after controlling for sequence saturation, positive selection, and potential alignment artifacts. These results reconcile previous conflicting plastid-based phylogenies and strengthen the mounting evidence of reticulate evolution inPicea.Given the relatively high frequency of hybridization and biparental plastid inheritance in plants, we suggest interspecific plastome recombination may be more widespread than currently appreciated and could underlie reported cases of discordant plastid phylogenies.

We report here the isolation of spectinomycin-resistant mutants in cultured cells of Medicago sativa line RegenSY-T2. Spectinomycin induces bleaching of cultured alfalfa cells due to inhibition of protein synthesis on the prokaryotic type 70S plastid ribosomes. Spontaneous mutants resistant to spectinomycin bleaching were identified by their ability to form green shoots on plant regeneration medium containing selective spectinomycin concentrations in the range of 25-50 mg/l. Sequencing of the plastid rrn16 gene revealed that spectinomycin resistance is due to mutations in a conserved stem structure of the 16S rRNA. Resistant plants transferred to the greenhouse developed normally and produced spectinomycin-resistant seed progeny. In light of their absence in soybean, a related leguminous plant, the isolation of spectinomycin-resistant mutants in M. sativa was unexpected. The new mutations are useful for the study of plastid inheritance, as demonstrated by detection of predominantly paternal plastid inheritance in the RegenSY-T2 × Szapko57 cross, and can be used as selective markers in plastid transformation vectors to obtain cisgenic plants.

Summary Plastids and mitochondria, the DNA-containing cytoplasmic organelles, are maternally inherited in the majority of angiosperm species. Even in plants with strict maternal inheritance, exceptional paternal transmission of plastids has been observed. Our objective was to detect rare leakage of plastids via pollen in Nicotiana sylvestris and to determine if pollen transmission of plastids results in co-transmission of paternal mitochondria. As father plants, we used N. sylvestris plants with transgenic, selectable plastids and wild-type mitochondria. As mother plants, we used N. sylvestris plants with Nicotiana undulata cytoplasm, including the CMS-92 mitochondria that cause cytoplasmic male sterility (CMS) by homeotic transformation of the stamens. We report here exceptional paternal plastid DNA in approximately 0.002% of N. sylvestris seedlings. However, we did not detect paternal mitochondrial DNA in any of the six plastid-transmission lines, suggesting independent transmission of the cytoplasmic organelles via pollen. When we used fertile N. sylvestris as mothers, we obtained eight fertile plastid transmission lines, which did not transmit their plastids via pollen at higher frequencies than their fathers. We discuss the implications for transgene containment and plant evolutionary histories inferred from cytoplasmic phylogenies.

BACKGROUND: Tea is the most consumed beverage worldwide after water. Yet very little is known about the genetics of tea in comparison with other crop species. Here we have taken advantage of the polymorphic nature of microsatellite DNA to investigate the mode of chloroplast inheritance in tea, Camellia sinensis (L.) O. Kuntze. This is important for the correct interpretation of phylogeny and introgression data as well as assessing the suitability of chloroplast transformation as a means for transgene containment in tea. RESULTS: The study was based on six Japanese tea cultivars, namely Aj2, CK23, Hatsumomiji, Nka05, Yamanoibuki and Kanayamidori used to generate four informative families. The parental pairs in the crosses differed at a single chlroroplast locus with respect to an imperfect microsatellite repeat of 16 nucleotide bases. In agreement with earlier cytological studies, all 61 progeny displayed a cpDNA profile that was consistent with the maternal inheritance of chloroplasts in tea. CONCLUSIONS: The data generated here provide the first molecular evidence of the plastid inheritance in tea. However, we suggest that additional families and polymorphic markers be screened for increasing the confidence in the observed maternal inheritance of chloroplasts in this important crop species. Copyright © 2011 Society of Chemical Industry

This review bridges functional and evolutionary aspects of plastid chromosome architecture in land plants and their putative ancestors. We provide an overview on the structure and composition of the plastid genome of land plants as well as the functions of its genes in an explicit phylogenetic and evolutionary context. We will discuss the architecture of land plant plastid chromosomes, including gene content and synteny across land plants. Moreover, we will explore the functions and roles of plastid encoded genes in metabolism and their evolutionary importance regarding gene retention and conservation. We suggest that the slow mode at which the plastome typically evolves is likely to be influenced by a combination of different molecular mechanisms. These include the organization of plastid genes in operons, the usually uniparental mode of plastid inheritance, the activity of highly effective repair mechanisms as well as the rarity of plastid fusion. Nevertheless, structurally rearranged plastomes can be found in several unrelated lineages (e.g. ferns, Pinaceae, multiple angiosperm families). Rearrangements and gene losses seem to correlate with an unusual mode of plastid transmission, abundance of repeats, or a heterotrophic lifestyle (parasites or myco-heterotrophs). While only a few functional gene gains and more frequent gene losses have been inferred for land plants, the plastid Ndh complex is one example of multiple independent gene losses and will be discussed in detail. Patterns of ndh-gene loss and functional analyses indicate that these losses are usually found in plant groups with a certain degree of heterotrophy, might rendering plastid encoded Ndh1 subunits dispensable.

Plants with transgenic plastid (chloroplast) genomes represent a promising production platform in molecular farming, mainly because of the plastids' potential to accumulate foreign proteins to very high levels and the increased biosafety conferred by the maternal mode of plastid inheritance. Although some transgenes can be expressed to extraordinarily high levels, the expression of others has been unsuccessful. Lack of detectable transgene expression is usually attributable to either RNA instability or protein instability. Here, we have investigated the possibilities to improve the production of a pharmaceutical protein that is difficult to express in chloroplasts: the HIV-1 fusion inhibitor cyanovirin-N (CV-N). Testing various N-terminal and C-terminal fusions to peptide sequences from two proteins known to accumulate to high levels in transgenic plastids (GFP and the protein antibiotic PlyGBS), we show that both low mRNA stability and low protein stability contribute to the lack of detectable CV-N expression in chloroplasts. Both problems can be alleviated by N-terminal fusions to the CV-N coding region, thus highlighting a suitable strategy for optimization of plastid transgene expression.

In 1909 two papers by Correns and by Baur published in volume 1 of Zeitschrift für induktive Abstammungs- und Vererbungslehre (now Molecular Genetics and Genomics) reported on the non-Mendelian inheritance of chlorophyll deficiencies. These papers, reporting the very first cases of extranuclear inheritance, laid the foundation for a new field: non-Mendelian or extranuclear genetics. Correns observed a purely maternal inheritance (in Mirabilis), whereas Baur found a biparental inheritance (in Pelargonium). Correns suspected the non-Mendelian factors in the cytoplasm, while Baur believed that the plastids carry these extranuclear factors. In the following years, Baur's hypothesis was proved to be correct. Baur subsequently developed the theory of plastid inheritance. In many genera the plastids are transmitted only uniparentally by the mother, while in a few genera there is a biparental plastid inheritance. Commonly there is random sorting of plastids during ontogenetic development. Renner and Schwemmle as well as geneticists in other countries added additional details to this theory. Pioneering studies on mitochondrial inheritance in yeast started in 1949 in the group of Ephrussi and Slonimski; respiration-deficient cells (petites in yeast, poky in Neurospora) were demonstrated to be due to mitochondrial mutations. Electron microscopical and biochemical studies (1962-1964) showed that plastids and mitochondria contain organelle-specific DNA molecules. These findings laid the molecular basis for the two branches of extranuclear inheritance: plastid and mitochondrial genetics.

Albinism is a common problem encountered in interspecific crosses and tissue culture experiments including anther culture and generation of doubled haploids. It is characterized by partial or complete loss of chlorophyll pigments and incomplete differentiation of chloroplast membranes. This in turn impairs photosynthesis and the plants eventually die at a young stage without reaching maturity. Environmental conditions such as light, temperature, media composition and culture conditions play some role in determining the frequency of albino plant formation. Genetic factors are even more important, and are major determinants in albinism. Genetic studies in different crops show that it is a recessive trait governed by many loci. Both the nuclear and chloroplast genomes affect albinism and incompatibilities between the two are a probable cause of many pigment defects in hybrid progenies. Such incompatibility has been reported in a large number of angiosperms. The mechanisms behind these incompatibilities are p...

It is widely held that organelles inherit from the maternal lineage. However, the plastid genome in quite a few angiosperms appears to be biparentally transmitted. It is unclear how and why biparental inheritance of the genome became activated. Here, we detected widespread occurrence of plastids in the sperm cells (a cellular prerequisite for biparental inheritance) of traditional Caprifoliaceae. Of the 12 genera sampled, the sperm cells of Abelia, Dipelta, Heptacodium, Kolkwitzia, Leycesteria, Linnaea, Lonicera, Symphoricarpos, Triosteum and Weigela possessed inheritable plastids. The other genera, Sambucus and Viburnum, lacked plastids in sperm cells. Interestingly, such exclusion of plastids in the sperm cells of some Caprifoliaceae appeared to be associated with the divergence of Dipsacales phylogeny. Closer examination of Weigela florida revealed that both plastids and plastid DNA were highly duplicated in the generative cells. This implies that the appearance of plastids in sperm cells involved cellular mechanisms. Because such mechanisms must enhance the strength of plastid transmission through the paternal lineage and appear ubiquitous in species exhibiting biparental or potential biparental plastid inheritance, we presume that biparental plastid genetics may be a derived trait in angiosperms. This is consistent with our extended phylogenetic analysis using species with recently discovered modes of potential plastid inheritance. The results show that basal and early angiosperms have maternal plastid transmission, whereas all potential biparental transmission occurs at terminal branches of the tree. Thus, unlike previous studies, we suggest that biparental plastid inheritance in angiosperms was unilaterally converted from the maternal transmission mode during late angiosperm evolution.

The plastid, which originated from the endosymbiosis of a cyanobacterium, contains its own plastid DNA (ptDNA) that exhibits a unique mode of inheritance. Approximately 80% of angiosperms show maternal inheritance, whereas the remainder exhibit biparental inheritance of ptDNA. Here we studied ptDNA inheritance in the model legume, Medicago truncatula. Cytological analysis of mature pollen with DNA-specific fluorescent dyes suggested that M. truncatula is one of the few model plants potentially showing biparental inheritance of ptDNA. We further examined pollen by electron microscopy and revealed that the generative cell (a mother of sperm cells) indeed has many DNA-containing plastids. To confirm biparental inheritance genetically, we crossed two ecotypes (Jemalong A17 and A20), and the transmission mode of ptDNA was investigated by a PCR-assisted polymorphism. Consistent with the cytological observations, the majority of F(1) plants possessed ptDNAs from both parents. Interestingly, cotyledons of F(1) plants tended to retain a biparental ptDNA population, while later emergent leaves tended to be uniparental with either one of the parental plastid genotypes. Biparental transmission was obvious in the F(2) population, in which all plants showed homoplasmy with either a paternal or a maternal plastid genotype. Collectively, these data demonstrated that M. truncatula is biparental for ptDNA transmission and thus can be an excellent model to study plastid genetics in angiosperms.

The genus Triticum L. includes the major cereal crop, common or bread wheat (hexaploid Triticum aestivum L.), and other important cultivated species. Here, we conducted a phylogenetic analysis of all known wheat species and the closely related Aegilops species. This analysis was based on chloroplast matK gene comparison along with trnL intron sequences of some species. Polyploid wheat species are successfully divided only into two groups – Emmer (sections Dicoccoides and Triticum) and Timopheevii (section Timopheevii). Results reveal strictly maternal plastid inheritance of synthetic wheat amphiploids included in the study. A concordance of chloroplast origin with the definite nuclear genomes of polyploid species that were inherited at the last hybridization events was found. Our analysis suggests that there were two ancestral representatives of Aegilops speltoides Tausch that participated in the speciation of polyploid wheats with B and G genome in their genome composition. However, G genome species are younger in evolution than ones with B genome. B genome-specific PCR primers were developed for amplification of Acc-1 gene.

Plastids are usually uni-parentally inherited and genetic recombination between these organelles is seldom observed. The genus Pseudo-nitzschia, a globally relevant marine diatom, features bi-parental plastid inheritance in the course of sexual reproduction. This observation inspired the recombination detection we pursued in this paper over a ~1,400-nucleotide-long region of the plastidial rbcL, a marker used in both molecular taxonomy and phylogenetic studies in diatoms. Among all the rbcL-sequences available in web-databases for Pseudo-nitzschia, 42 haplotypes were identified and grouped in five clusters by Bayesian phylogeny. Signs of hybridization were evident in four of five clusters, at both intra- and interspecific levels, suggesting that, in diatoms, (i) plastidial recombination is not absent and (ii) hybridization can play a role in speciation of Pseudo-nitzschia spp.

Understanding how new species form is one of the central goals of evolutionary biology. While historically studies have focused on the role of nuclear genetic incompatibilities in speciation, cytonuclear incompatibilities have been proposed to be among the first genetic incompatibilities to arise, influencing the early stages of the speciation process. However, due to the lack of studies characterizing reproductive isolation at the intraspecific level, little is known regarding the role of cytonuclear incompatibilities at these early stages. The effect of cytonuclear incompatibility could be mitigated though biparental plastid inheritance, by increasing the likelihood of individuals inheriting a compatible chloroplast. Alternatively, accelerated plastid evolution could speed up the co-evolution of the plastid and nuclear genomes, increasing the propensity for cytonuclear incompatibility when crossing between populations. This dissertation uses Campanulastrum americanum as a system to study how biparental plastid inheritance and accelerated plastid evolution may impact the evolutionary dynamics of cytonuclear incompatibilities and their contribution to incipient speciation. Analysis of chloroplast and nuclear markers distinguished four geographically structured, genetically divergent lineages in C. americanum. Crossing studies found substantial reductions in germination and survival when crossing between these lineages. There was also evidence for cytonuclear incompatibility underlying reproductive isolation in survival, supporting the idea that cytonuclear incompatibilities arise early in the speciation process. However, reproductive isolation between divergent lineages appeared to be reduced in the Appalachians where these lineages are likely in secondary contact. In addition, analysis of plastid inheritance patterns found that C. americanum has biparental plastid inheritance, which in genetically-divergent crosses mitigates the impact of cytonuclear incompatibility on reproductive isolation, potentially slowing the speciation process. In contrast, analysis of plastid sequence divergence and polymorphism in C. americanum found evidence for increased nucleotide substitution rates acting at the among and within species level, suggesting that accelerated plastid evolution may facilitate the development of cytonuclear incompatibility in this species. Altogether, cytonuclear incompatibility appears to be contributing to incipient speciation in C. americanum, but the dynamics of this contribution are being influenced, often in opposing ways, by a variety of mechanisms, including gene flow, biparental plastid inheritance and accelerated plastid evolution.

Four chloroplast (cp), one mitochondrial (mt), and one ribosomal nuclear (ITS) DNA regions were studied in four artificial and one natural interspecific Passiflora hybrids. The ITS results confirmed their hybrid origin and all mtDNAs were maternally inherited. The same, however, was not true for cpDNA. The four hybrids (three artificial and one natural) derived from species of the Passiflora subgenus showed a cpDNA paternal inheritance, while the one involving taxa of the Decaloba subgenus gave evidence of maternal transmission. These results are of significance for the ongoing studies which are being performed on the molecular evolution of this genus and furnish important background for investigations aimed at clarifying the factors which determine cpDNA inheritance.

IN the late 1930s when Tracy Sonneborn was in graduate school and just starting his work on the genetics of protozoa, classical studies on genetics were almost finished. The second edition of Principles of Genetics by E. W. Sinnott and L. C. Dunn (1932) that appeared in that period was quite sophisticated, containing a good account of chromosome theory, segregation ratios produced by complex gene interactions, chromosome and genetic maps, polyploidy, aneuploidy, multiple factor inheritance, sex determination, and evolution. The authors argued strongly that virtually all inheritance was ascribable to nuclear genes. Only Correns's work on plastid inheritance was cited as an example of cytoplasmic inheritance, and it was pointed out that this should be considered only a minor exception to the general rule that chromosomal genes determine the hereditary characters of the organism. Other biologists, particularly cell physiologists such as L. V. Heilbrunn at the University of Pennsylvania, were not so sure. They thought that classical genetics dealt only with superficial characters and that the fundamental characters of organisms such as membrane permeability, metabolism, etc., were controlled by the cytoplasm. It is not clear what Sonneborn thought of this controversy, but from what I know about Sonneborn, he must, at least, have had an open mind about the matter. All classical genetics was based on multicellular organisms, in which characters were seen after a complex developmental process. Once Sonneborn had discovered mating types in the protozoa it became possible to carry out classical genetic studies with the protozoa and study their inheritance without an intervening period of somatic development. Perhaps the genetics of single-cell organisms, the protozoa, would prove to be a bit different from the classical picture.

The ultrastructure and ontogeny of bicellular pollen in Tillandsia seleriana Mez (Bromeliaceae) before anther dehiscence has been here investigated. The development, after the first mitosis, is described to consist in three stages. The aim of the present report, which is part of a more extensive study on the reproductive mechanisms in the genus, is to compare the development of the male gametophyte of Tillands with information available from other an-giosperms. Aspects on water, starch and soluble carbohydrate contents of the pollen of T. seleriana are discussed in the light of the current ecological classification of pollens. The generative cell did not show any plastid in its cytoplasm, hence plastid inheritance in Tillandsia is confirmed as totally maternal (Lycopersicon type). Contrarily to other pollen grains, those of T. seleriana maintain a considerable amount of starch in the vegetative cell until dehiscence. The inulin test was negative, indicating that T. seleriana pollen lacks of Fructa...

Epifluorescence microscopic detection of organelle DNA in the mature generative cell is a rapid method for determining the potential for the mode of cytoplasmic inheritance. We used this method to examine 19 of the known 22 to 27 species in the genus Syringa. Organelle DNA was undetectable in seven species, all in the subgenus Syringa, but was detected in the 12 species examined of the subgenera Syringa and Ligustrina. Therefore, species within the genus Syringa display differences in the potential cytoplasmic inheritance. Closer examination revealed that the mature generative cells of the species in which organelle DNA was detected contained both mitochondria and plastids, but cells of the species lacking detectable organelle DNA contained only mitochondria, and the epifluorescent organelle DNA signals from the mature generative cells corresponded to plastid DNA. In addition, semiquantitative analysis was used to demonstrate that, during pollen development, the amount of mitochondrial DNA decreased greatly in the generative cells of the species examined, but the amount of plastid DNA increased remarkably in the species containing plastids in the generative cell. The results suggest that all Syringa species exhibit potential maternal mitochondrial inheritance, and a number of the species exhibit potential biparental plastid inheritance. The difference between the modes of potential plastid inheritance among the species suggests different phylogenies for the species; it also supports recent conclusions of molecular, systematic studies of the Syringa. In addition, the results provide new evidence for the mechanisms of maternal mitochondrial inheritance in angiosperms.

The majority of angiosperms display maternal plastid inheritance. The cytological mechanisms of this mode of inheritance have been well studied, but little is known about its genetic relationship to biparental inheritance. The angiosperm Chlorophytum comosum is unusual in that different pollen grains show traits of different modes of plastid inheritance. About 50% of these pollen grains exhibit the potential for biparental plastid inheritance, whereas the rest exhibit maternal plastid inheritance. There is no morphological difference between these two types of pollen. Pollen grains from different individuals of C. comosum all exhibited this variability. Closer examination revealed that plastid polarization occurs, with plastids being excluded from the generative cell during the first pollen mitosis. However, the exclusion is incomplete in 50% of the pollen grains, and the few plastids distributed to the generative cells divide actively after mitosis. Immunoelectron microscopy using an anti-DNA antibody demonstrated that the plastids contain a large amount of DNA. As there is a considerable discrepancy between the exclusion and duplication of plastids, resulting in plastids with opposite fates occurring simultaneously in C. comosum, we propose that the species is a transitional type with a mode of plastid inheritance that is genetically intermediate between the maternal and biparental modes.