The sperm nuclear basic proteins of the sword fern (Polystichum munitum)

Sperm nuclear basic proteins (SNBPs) were isolated from extracted antheridia-rich male gametophytes raised from spores of the swordfern, Polystichum munitum. Electrophoretic (acetic acid-urea PAGE and SDS-PAGE) and chromatographic (rp-HPLC) characterization of the nuclear proteins exhibited the characteristics of the histone (H-type). In both types of gel electrophoresis, histones H1, H2A, and H2B showed an altered electrophoretic mobility corresponding to that which is routinely observed for the histones in other plants. Histones present during spermatogenesis of the fern P. munitum were compared with the few current SNBPs known to be present in higher and lower evolutionary plant clades. A transition from an early protamine (P-type) SNBPs in charophytes and bryophytes to the (H-type) SNBP observed here is reminiscent of similar reversions observed in the animal kingdom.

Ornamental tobacco floral nectar is a rich source of antimicrobial peptides

Although floral nectar is a rich source of nutrients, it is rarely infected by microorganisms. Defense molecules such as proteins have been identified in this fluid, but defense peptides have been largely overlooked. Thus, the aim of this study was to perform an extensive peptidomic analysis of the ornamental tobacco floral nectar to seek peptides involved in nectar defense. Using LC-MS/MS, 793 peptides were sequenced and characterized. After extensive bioinformatics analysis, six peptides were selected for further characterization, synthesis, and evaluation of their antimicrobial properties against phytopathogenic fungi and bacteria. All six peptides had antimicrobial activity to some extent. However, the activity varied by peptide concentration and microorganism tested. An analysis of the action mechanism revealed damage in the cell membrane induced by peptides. The results show that floral nectar is rich in peptides and that, together with proteins and hydrogen peroxide, they contribute to plant defense against microorganisms during pollination.

Composition of Sexual Fluids in Cycas revoluta Ovules During Pollination and Fertilization

The composition of fluids that mediate fertilization in cycads is described for the first time. Using tandem mass spectrometry, proteomes of two stages of fluid production, megagametophyte fluid and archegonial chamber fluid production, are compared in Cycas revoluta. These were compared with the proteome of another sexual fluid produced by ovules, the pollination drop proteins. Cycad ovules produce complex liquids immediately prior fertilization. Compared with the pollination drops that mainly had few proteins in classes involved in defense and carbohydrate modification, megagametophyte fluid and archegonial chamber fluid had larger proteomes with many more protein classes, e.g. proteins involved in programmed cell death. Using high-performance liquid chromatography, megagametophyte fluid and archegonial chamber fluid were shown to have elevated concentrations of smaller molecular weight molecules including glucose, pectin and glutamic acid. Compared to megagametophyte fluid, archegonial chamber fluid had elevated pH as well as higher osmolality.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12229-021-09271-1.

LC-MS/MS based comparative proteomics of floral nectars reveal different mechanisms involved in floral defense of Nicotiana spp., Petunia hybrida and Datura stramonium

Tobacco floral nectar (FN) is a biological fluid produced by nectaries composed of sugars, amino acids and proteins called nectarins, involved in the floral defense. FN provides an ideal source of nutrients for microorganisms. Understanding the role of nectar proteins is essential to predict impacts in microbial growth, composition and plants-pollinators interactions. Using LC-MS/MS-based comparative proteomic analysis we identified 22 proteins from P. hybrida, 35 proteins from D. stramonium, and 144 proteins from 23 species of Nicotiana. The data are available at ProteomeXchance (PXD014760). GO analysis and secretory signal prediction demonstrated that defense/stress was the largest group of proteins in the genus Nicotiana. The Nicotiana spp. proteome consisted of 105 exclusive proteins such as lipid transfer proteins (LTPs), Nectar Redox Cycle proteins, proteases inhibitors, and PR-proteins. Analysis by taxonomic sections demonstrated that LTPs were most abundant in Undulatae and Noctiflora, while nectarins were more abundant in Rusticae, Suaveolens, Polydicliae, and Alata sections. Peroxidases (Pox) and chitinases (Chit) were exclusive to P. hybrida, while D. stramonium had only seven unique proteins. Biochemical analysis confirmed these differences. These findings support the hypothesis that, although conserved, there is differential abundance of proteins related to defense/stress which may impact the mechanisms of floral defense. SIGNIFICANCE: This study represents a comparative proteomic analysis of floral nectars of the Nicotiana spp. with two correlated Solanaceous species. Significant differences were identified between the proteome of taxonomic sections providing relevant insights into the group of proteins related to defense/stress associated with Nectar Redox Cycle, antimicrobial proteins and signaling pathways. The activity of FNs proteins is suggested impact the microbial growth. The knowledge about these proteomes provides significant insights into the diversity of proteins secreted in the nectars and the array of mechanisms used by Nicotiana spp. in its floral defense.

Complex reproductive secretions occur in all extant gymnosperm lineages: a proteomic survey of gymnosperm pollination drops

Complex protein-containing reproductive secretions are a conserved trait amongst all extant gymnosperms; the pollination drops of most groups include carbohydrate-modifying enzymes and defence proteins. Pollination drops are aqueous secretions that receive pollen and transport it to the ovule interior in gymnosperms (Coniferales, Cycadales, Ginkgoales, Gnetales). Proteins are well established as components of pollination drops in conifers (Coniferales) and Ephedra spp. (Gnetales), but it is unknown whether proteins are also present in the pollination drops of cycads (Cycadales), Ginkgo (Ginkgoales), Gnetum (Gnetales), or in the pollination drops produced by sterile ovules occurring on pollen plants in the Gnetales. We used liquid chromatography-tandem mass spectrometry followed by database-derived protein identification to conduct proteomic surveys of pollination drops collected from: Ceratozamia hildae, Zamia furfuracea and Cycas rumphii (Cycadales); Ginkgo biloba (Ginkgoales); Gnetum gnemon and Welwitschia mirabilis, including pollination drops from both microsporangiate and ovulate plants (Gnetales). We identified proteins in all samples: C. hildae (61), Z. furfuracea (40), C. rumphii (9), G. biloba (57), G. gnemon ovulate (17) and sterile ovules from microsporangiate plants (25) and W. mirabilis fertile ovules (1) and sterile ovules from microsporangiate plants (138). Proteins involved in defence and carbohydrate modification occurred in the drops of most groups, indicating conserved functions for proteins in pollination drops. Our study demonstrates that all extant gymnosperm groups produce complex reproductive secretions containing proteins, an ancient trait that likely contributed to the evolutionary success of seed plants.

The Evolution of Sexual Fluids in Gymnosperms From Pollination Drops to Nectar

A current synthesis of data from modern and fossil plants paints a new picture of sexual fluids, including nectar, as a foundational component of gymnosperm reproductive evolution. We review the morpho-anatomical adaptations, their accompanying secretions, and the functional compounds involved. We discuss two types of secretions: (1) those involved in fertilization fluids produced by gametophytes and archegonia of zooidogamous gymnosperms, i.e., Ginkgo and cycads, and (2) those involved in pollen capture mechanisms (PCMs), i.e., pollination drops. Fertilization fluids provide both liquid in which sperm swim, as well as chemotactic signals that direct sperm to the egg. Such fertilization fluids were probably found among many extinct plants such as ancient cycads and others with swimming sperm, but were subsequently lost upon the evolution of siphonogamy (direct delivery of sperm to the egg by pollen tubes), as found in modern gnetophytes, conifers, and Pinaceae. Pollination drops are discussed in terms of three major types of PCMs and the unique combinations of morphological and biochemical adaptations that define each. These include their amino acids, sugars, calcium, phosphate and proteins. The evolution of PCMs is also discussed with reference to fossil taxa. The plesiomorphic state of extant gymnosperms is a sugar-containing pollination drop functioning as a pollen capture surface, and an in ovulo pollen germination medium. Additionally, these drops are involved in ovule defense, and provide nectar for pollinators. Pollination drops in anemophilous groups have low sugar concentrations that are too low to provide insects with a reward. Instead, they appear to be optimized for defense and microgametophyte development. In insect-pollinated modern Gnetales a variety of tissues produce sexual fluids that bear the biochemical signature of nectar. Complete absence of fluid secretions is restricted to a few, poorly studied modern conifers, and is presumably derived. Aspects of pollination drop dynamics, e.g., regulation of secretion and retraction, are reviewed. Lastly, we discuss pollination drops' control of pollen germination. Large gaps in our current knowledge include the composition of fertilization fluids, the pollination drops of Podocarpaceae, and the overall hydrodynamics of sexual fluids in general.

Sex-Dependent Variation of Pumpkin (Cucurbita maxima cv. Big Max) Nectar and Nectaries as Determined by Proteomics and Metabolomics

Nectar is a floral reward that sustains mutualisms with pollinators, which in turn, improves fruit set. While it is known that nectar is a chemically complex solution, extensive identification and quantification of this complexity has been lacking. Cucurbita maxima cv. Big Max, like many cucurbits, is monoecious with separate male and female flowers. Attraction of bees to the flowers through the reward of nectar is essential for reproductive success in this economically valuable crop. In this study, the sex-dependent variation in composition of male and female nectar and the nectaries were defined using a combination of GC-MS based metabolomics and LC-MS/MS based proteomics. Metabolomics analysis of nectar detected 88 metabolites, of which 40 were positively identified, and includes sugars, sugar alcohols, aromatics, diols, organic acids, and amino acids. There are differences in 29 metabolites between male and female nectar. The nectar proteome consists of 45 proteins, of which 70% overlap between nectar types. Only two proteins are unique to female nectar, and 10 are specific to male nectar. The nectary proteome data, accessible at ProteomeXchange with identifier PXD009810, contained 339 identifiable proteins, 71% of which were descriptively annotatable by homology to Plantae. The abundance of 45 proteins differs significantly between male and female nectaries, as determined by iTRAQ labeling. This rich dataset significantly expands the known complexity of nectar composition, supports the hypothesis of H+-driven nectar solute export, and provides genetic and chemical targets to understand plant-pollinator interactions.

Phylogenetic and functional signals in gymnosperm ovular secretions

BACKGROUND AND AIMS

Gymnosperms are either wind-pollinated (anemophilous) or both wind- and insect-pollinated (ambophilous). Regardless of pollination mode, ovular secretions play a key role in pollen capture, germination and growth; they are likely also involved in pollinator reward. Little is known about the broad-scale diversity of ovular secretions across gymnosperms, and how these may relate to various reproductive functions. This study analyses the sugar and amino acid profiles of ovular secretions across a range of ambophilous (cycads and Gnetales) and anemophilous gymnosperms (conifers) to place them in an evolutionary context of their possible functions during reproduction.

METHODS

Ovular secretions from 13 species representing all five main lineages of extant gymnosperms were sampled. High-performance liquid chromatography techniques were used to measure sugar and amino acid content. Multivariate statistics were applied to assess whether there are significant differences in the chemical profiles of anemophilous and ambophilous species. Data were compared with published chemical profiles of angiosperm nectar. Chemical profiles were placed in the context of phylogenetic relationships.

KEY RESULTS

Total sugar concentrations were significantly higher in ovular secretions of ambophilous species than wind-pollinated taxa such as Pinaceae and Cupressophyta. Ambophilous species had lower amounts of total amino acids, and a higher proportion of non-protein amino acids compared with anemophilous lineages, and were also comparable to angiosperm nectar. Results suggest that early gymnosperms likely had ovular secretion profiles that were a mosaic of those associated with modern anemophilous and ambophilous species. Ginkgo, thought to be anemophilous, had a profile typical of ambophilous taxa, suggesting that insect pollination either exists in Gingko, but is undocumented, or that its ancestral populations were insect-pollinated.

CONCLUSIONS

Chemical profiles of ovular secretions of ambophilous gymnosperms show a clear signal of pollinator-driven selection, including higher levels of carbohydrates than anemophilous taxa, lower levels of amino acids, and the presence of specific amino acids, such as β-alanine, that are known to influence insect feeding behaviour and physiology.

A transcriptomic resource for Douglas-fir seed development and analysis of transcription during late megagametophyte development

Douglas-fir transcriptomics. Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is economically important with extensive breeding programs and seed trade. However, the molecular genetics of its seed development are largely unknown. We developed a transcriptome resource covering key developmental stages of megagametophytes over time: prefertilization, fertilization, embryogenesis, and early, unfertilized abortion. RNA sequencing reads were assembled de novo into 105,505 predicted high-confidence transcripts derived from 34,521 predicted genes. Expression levels were estimated based on alignment of the original reads to the reference. Megagametophytes express a distinct set of genes compared to those of vegetative tissues. Transcripts related to signaling, protein turnover, and RNA biogenesis have lower expression values in vegetative tissues, whereas cell wall remodeling, solute transport, and seed storage protein transcripts have higher expression values in megagametophytes. Seed storage protein transcripts become very abundant in both pollinated and unpollinated megagametophytes over time, even in aborting ovules. However, the absence of protein storage bodies in unfertilized megagametophytes suggests extensive posttranscriptional mechanisms that either inhibit storage protein translation or their aggregation into protein bodies. This novel transcriptome resource provides a foundation for further important insights into conifer seed development.

Insights from the pollination drop proteome and the ovule transcriptome of Cephalotaxus at the time of pollination drop production

BACKGROUND AND AIMS

Many gymnosperms produce an ovular secretion, the pollination drop, during reproduction. The drops serve as a landing site for pollen, but also contain a suite of ions and organic compounds, including proteins, that suggests diverse roles for the drop during pollination. Proteins in the drops of species of Chamaecyparis, Juniperus, Taxus, Pseudotsuga, Ephedra and Welwitschia are thought to function in the conversion of sugars, defence against pathogens, and pollen growth and development. To better understand gymnosperm pollination biology, the pollination drop proteomes of pollination drops from two species of Cephalotaxus have been characterized and an ovular transcriptome for C. sinensis has been assembled.

METHODS

Mass spectrometry was used to identify proteins in the pollination drops of Cephalotaxus sinensis and C. koreana RNA-sequencing (RNA-Seq) was employed to assemble a transcriptome and identify transcripts present in the ovules of C. sinensis at the time of pollination drop production.

KEY RESULTS

About 30 proteins were detected in the pollination drops of both species. Many of these have been detected in the drops of other gymnosperms and probably function in defence, polysaccharide metabolism and pollen tube growth. Other proteins appear to be unique to Cephalotaxus, and their putative functions include starch and callose degradation, among others. Together, the proteins appear either to have been secreted into the drop or to occur there due to breakdown of ovular cells during drop production. Ovular transcripts represent a wide range of gene ontology categories, and some may be involved in drop formation, ovule development and pollen-ovule interactions.

CONCLUSIONS

The proteome of Cephalotaxus pollination drops shares a number of components with those of other conifers and gnetophytes, including proteins for defence such as chitinases and for carbohydrate modification such as β-galactosidase. Proteins likely to be of intracellular origin, however, form a larger component of drops from Cephalotaxus than expected from studies of other conifers. This is consistent with the observation of nucellar breakdown during drop formation in Cephalotaxus The transcriptome data provide a framework for understanding multiple metabolic processes that occur within the ovule and the pollination drop just before fertilization. They reveal the deep conservation of WUSCHEL expression in ovules and raise questions about whether any of the S-locus transcripts in Cephalotaxus ovules might be involved in pollen-ovule recognition.

Host-Parasite Interactions from the Inside: Plant Reproductive Ontogeny Drives Specialization in Parasitic Insects

Host plant interactions are likely key drivers of evolutionary processes involved in the diversification of phytophagous insects. Granivory has received substantial attention for its crucial role in shaping the interaction between plants and their seed parasites, but fine-scale mechanisms explaining the role of host plant reproductive biology on specialization of seed parasites remain poorly described. In a comparative approach using plant histological techniques, we tested the hypotheses that different seed parasite species synchronize their life cycles to specific stages in seed development, and that the stage they target depends on major differences in seed development programs. In a pinaceous system, seed storage products are initiated before ovule fertilization and the wasps target the ovule’s nucellus during megagametogenesis, a stage at which larvae may benefit from the by-products derived from both secreting cells and dying nucellar cells. In a cupressaceous system, oviposition activity peaks later, during embryogenesis, and the wasps target the ovule’s megagametophyte where larvae may benefit from cell disintegration during embryogenesis. Our cytohistological approach shows for the first time how, despite divergent oviposition targets, different parasite species share a common strategy that consists of first competing for nutrients with developing plant structures, and then consuming these developed structures to complete their development. Our results support the prediction that seed developmental program is an axis for specialization in seed parasites, and that it could be an important parameter in models of their ecological and taxonomic divergence. This study provides the basis for further investigating the possibility of the link between plant ontogeny and pre-dispersal seed parasitism.

Effect of light conditions on anatomical and biochemical aspects of somatic and zygotic embryos of hybrid larch (Larix × marschlinsii)

BACKGROUND AND AIMS

In conifers, mature somatic embryos and zygotic embryos appear to resemble one another physiologically and morphologically. However, phenotypes of cloned conifer embryos can be strongly influenced by a number of in vitro factors and in some instances clonal variation can exceed that found in nature. This study examines whether zygotic embryos that develop within light-opaque cones differ from somatic embryos developing in dark/light conditions in vitro. Embryogenesis in larch is well understood both in situ and in vitro and thus provides a suitable system for addressing this question.

METHODS

Features of somatic and zygotic embryos of hybrid larch, Larix × marschlinsii, were quantified, including cotyledon numbers, protein concentration and phenol chemistry. Somatic embryos were placed either in light or darkness for the entire maturation period. Embryos at different developmental stages were embedded and sectioned for histological analysis.

KEY RESULTS

Light, and to a lesser degree abscisic acid (ABA), influenced accumulation of protein and phenolic compounds in somatic and zygotic embryos. Dark-grown mature somatic embryos had more protein (91·77 ± 11·26 µg protein mg(-1) f.wt) than either dark-grown zygotic embryos (62·40 ± 5·58) or light-grown somatic embryos (58·15 ± 10·02). Zygotic embryos never accumulated phenolic compounds at any stage, whereas somatic embryos stored phenolic compounds in the embryonal root caps and suspensors. Light induced the production of quercetrin (261·13 ± 9·2 µg g(-1) d.wt) in somatic embryos. Mature zygotic embryos that were removed from seeds and placed on medium in light rapidly accumulated phenolics in the embryonal root cap and hypocotyl. Delaying germination with ABA delayed phenolic compound accumulation, restricting it to the embryonal root cap.

CONCLUSIONS

In larch embryos, light has a negative effect on protein accumulation, but a positive effect on phenol accumulation. Light did not affect morphogenesis, e.g. cotyledon number. Somatic embryos produced different amounts of phenolics, such as quercetrin, depending on light conditions. The greatest difference was seen in the embryonal root cap in all embryo types and conditions.

Bacterial associates of seed-parasitic wasps (Hymenoptera: Megastigmus)

Background

The success of herbivorous insects has been shaped largely by their association with microbes. Seed parasitism is an insect feeding strategy involving intimate contact and manipulation of a plant host. Little is known about the microbial associates of seed-parasitic insects. We characterized the bacterial symbionts of Megastigmus (Hymenoptera: Torymidae), a lineage of seed-parasitic chalcid wasps, with the goal of identifying microbes that might play an important role in aiding development within seeds, including supplementing insect nutrition or manipulating host trees. We screened multiple populations of seven species for common facultative inherited symbionts. We also performed culture independent surveys of larvae, pupae, and adults of M. spermotrophus using 454 pyrosequencing. This major pest of Douglas-fir is the best-studied Megastigmus, and was previously shown to manipulate its tree host into redirecting resources towards unfertilized ovules. Douglas-fir ovules and the parasitoid Eurytoma sp. were also surveyed using pyrosequencing to help elucidate possible transmission mechanisms of the microbial associates of M. spermotrophus.

Results

Three wasp species harboured Rickettsia; two of these also harboured Wolbachia. Males and females were infected at similar frequencies, suggesting that these bacteria do not distort sex ratios. The M. spermotrophus microbiome is dominated by five bacterial OTUs, including lineages commonly found in other insect microbiomes and in environmental samples. The bacterial community associated with M. spermotrophus remained constant throughout wasp development and was dominated by a single OTU – a strain of Ralstonia, in the Betaproteobacteria, comprising over 55% of all bacterial OTUs from Megastigmus samples. This strain was also present in unparasitized ovules.

Conclusions

This is the first report of Ralstonia being an abundant and potentially important member of an insect microbiome, although other closely-related Betaproteobacteria, such as Burkholderia, are important insect symbionts. We speculate that Ralstonia might play a role in nutrient recycling, perhaps by redirecting nitrogen. The developing wasp larva feeds on megagametophyte tissue, which contains the seed storage reserves and is especially rich in nitrogen. Future studies using Ralstonia-specific markers will determine its distribution in other Megastigmus species, its mode of transmission, and its role in wasp nutrition.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-014-0224-4) contains supplementary material, which is available to authorized users.

Application of proteomics to the study of pollination drops

PREMISE OF THE STUDY

Pollination drops are a formative component in gymnosperm pollen-ovule interactions. Proteomics offers a direct method for the discovery of proteins associated with this early stage of sexual reproduction. •

METHODS

Pollination drops were sampled from eight gymnosperm species: Chamaecyparis lawsoniana (Port Orford cedar), Ephedra monosperma, Ginkgo biloba, Juniperus oxycedrus (prickly juniper), Larix ×marschlinsii, Pseudotsuga menziesii (Douglas-fir), Taxus ×media, and Welwitschia mirabilis. Drops were collected by micropipette using techniques focused on preventing sample contamination. Drop proteins were separated using both gel and gel-free methods. Tandem mass spectrometric methods were used including a triple quadrupole and an Orbitrap. •

RESULTS

Proteins are present in all pollination drops. Consistency in the protein complement over time was shown in L. ×marschlinsii. Representative mass spectra from W. mirabilis chitinase peptide and E. monosperma serine carboxypeptidase peptide demonstrated high quality results. We provide a summary of gymnosperm pollination drop proteins that have been discovered to date via proteomics. •

DISCUSSION

Using proteomic methods, a dozen classes of proteins have been identified to date. Proteomics presents a way forward in deepening our understanding of the biological function of pollination drops.

Lodgepole Pine Cambium (Pinus contorta Dougl. ex Loud. var. latifolia Engelm. ex S. Wats.): a springtime first peoples' food in British Columbia

Lodgepole pine (Pinus contorta var. latifolia) is a tree species utilized for succulent edible cambium and secondary phloem in the spring by Interior First Peoples of the Pacific Northwest. In this article we present a nutritional analysis of this food based on a pooled sample of 17 trees harvested in the Chilcotin region of British Columbia. We also present enzymatic sugar analysis of raw, dried, and cooked lodgepole pine cambium harvested from the Chilcotin and Okanagan regions in British Columbia. In the discussion we interpret the nutrient values of raw lodgepole pine cambium in comparison to dried and cooked cambium, results from other nutritional studies of pine cambium, and nutrients in some other traditional and nontraditional foods.

Marking live conifer pollen for long-distance dispersal experiments

Long-distance dispersal (LDD) theory requires a method for marking live LDD pollen. Such a method must complement more intensive sampling methods inclusive of molecular cytogenetics, proteomics and genomics. We developed a new method for marking live Pinus taeda pollen using two dyes, rhodamine 123 and aniline blue, dissolved in a sucrose solution. Marked and unmarked pollen were compared with respect to in vitro germination, storage, terminal velocity, and in vivo pollen tube penetration of ovules. We found that: (1) both types of marked pollen retained their capacity for germination, (2) both types of marked pollen had similar aerodynamic properties when compared to unmarked pollen controls, (3) marked pollen retained its germination capacity for 48 h, and (4) of the marked pollen, only the aniline-marked pollen penetrated ovules during pollination. Germination declined rapidly for both types of marked pollen after 48 h and before 37 days at -20°C storage, while unmarked pollen lots retained 93% germination at all stages. This method for marking live P. taeda pollen is feasible for tracing LDD pollen only if released and deposited within 48 h of dye treatment.

Nectar and pollination drops: how different are they?

BACKGROUND

Pollination drops and nectars (floral nectars) are secretions related to plant reproduction. The pollination drop is the landing site for the majority of gymnosperm pollen, whereas nectar of angiosperm flowers represents a common nutritional resource for a large variety of pollinators. Extrafloral nectars also are known from all vascular plants, although among the gymnosperms they are restricted to the Gnetales. Extrafloral nectars are not generally involved in reproduction but serve as 'reward' for ants defending plants against herbivores (indirect defence).

SCOPE

Although very different in their task, nectars and pollination drops share some features, e.g. basic chemical composition and eventual consumption by animals. This has led some authors to call these secretions collectively nectar. Modern techniques that permit chemical analysis and protein characterization have very recently added important information about these sugary secretions that appear to be much more than a 'reward' for pollinating (floral nectar) and defending animals (extrafloral nectar) or a landing site for pollen (pollination drop).

CONCLUSIONS

Nectar and pollination drops contain sugars as the main components, but the total concentration and the relative proportions are different. They also contain amino acids, of which proline is frequently the most abundant. Proteomic studies have revealed the presence of common functional classes of proteins such as invertases and defence-related proteins in nectar (floral and extrafloral) and pollination drops. Invertases allow for dynamic rearrangement of sugar composition following secretion. Defence-related proteins provide protection from invasion by fungi and bacteria. Currently, only few species have been studied in any depth. The chemical composition of the pollination drop must be investigated in a larger number of species if eventual phylogenetic relationships are to be revealed. Much more information can be provided from further proteomic studies of both nectar and pollination drop that will contribute to the study of plant reproduction and evolution.

Phytohormones and their metabolites during long shoot development in Douglas-fir following cone induction by gibberellin injection

Changes in plant hormones and metabolites in long-shoot stems of interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) during cone induction by gibberellic acid (GA) treatment were analyzed by high performance liquid chromatography-electrospray ionization tandem mass spectrometry in multiple reaction monitoring mode. A mixture of GA(4) and GA(7), including small amounts of GA(3) and GA(1), was stem-injected into each tree in amounts of 0, 4, 40 or 400 mg. One week after injection, concentrations of GA(4), GA(7) and GA(3) were elevated in all GA-treated samples. The ratio of GA(4) to GA(7) decreased significantly at Week 3. Absolute concentrations of all gibberellins declined sharply at Week 3 after GA application. After 5 weeks, GA(1) and GA(4) were below detection limits in all samples, and GA(7) and GA(3) were found only in the samples from trees treated with 40 or 400 mg of GA. Endogenous indole-3-acetic acid (IAA) concentrations increased following GA injection, and peaked at Week 2 or Week 3 in the trees treated with 40 or 400 mg GA, respectively. Injection of 400 mg of GA brought about a twofold increase in IAA concentration compared with control values. Injection of 40 and 400 mg of GA caused significant increases in stem dry mass in Week 5. Seed orchard data revealed that injection of either 40 or 400 mg GA enhanced female cone formation, whereas male cone formation was enhanced only by 400 mg GA. Slight decreases in concentrations of abscisic acid (ABA) and isopentenyl adenosine were observed after GA application. No significant changes were detected in the concentrations of ABA metabolites except for a slight decrease in the concentration of 7'-hydroxy ABA. The concentration of ABA declined during the growing season and the concentration of ABA glucose ester increased correspondingly.

Identification of two thaumatin-like proteins (TLPs) in the pollination drop of hybrid yew that may play a role in pathogen defence during pollen collection

We describe the proteomic identification of two pathogenesis-related group 5 (PR-5) proteins, an acidic thaumatin-like protein (TLP) and a basic TLP isolated from the pollination drop of hybrid yew (Taxus x media Rehder). The basic TLP (TxmTLPb) was the most abundant protein in the yew pollination drop based on protein spot size after two-dimensional electrophoresis. The acidic TLP (TxmTLPa) is also a major protein component of the yew ovular secretion and appears to be encoded by a number of mRNAs transcribed from a TLP gene family that has undergone limited sequence divergence. We have sequenced five acidic TLP-encoding cDNAs (TxmTLPa-1,2,3,4 and 5) isolated from the yew ovule that vary from each other by no more than five out of 233 amino acid residues in their predicted protein sequences. All of the cDNA variants encode TLPs possessing the 16 conserved cysteine residues and five charged amino acid side chains associated with antifungal activity. Amplification of genomic DNA with TxmTLPa primers indicated that at least 11 acidic TLPs with highly similar amino acid sequences may be expressed in yew tissues. Antibodies against TLPs confirmed the identity of TxmTLPa and TxmTLPb in the yew pollination drop and detected TLPs in the ovular secretions of four other species from three other conifer families. Our results suggest that TLPs are a conserved component of conifer ovular secretions and are involved in broad spectrum pathogen defence of ovules.

Genotype effects on ABA consumption and somatic embryo maturation in interior spruce (Picea glaucaxengelmanni)

Abscisic acid (ABA) plays an important role during somatic embryo development and maturation in coniferous species. The purpose of this research was to study ABA utilization by genotypes with different embryo maturation capabilities in interior spruce. Cell lines ISP11 and ISP48 were of high embryo maturation capability. By contrast, the tissue of line ISP16 contained numerous immature embryos, but only a few mature embryos developed. Exogenous ABA, i.e. S-ABA [(+)-cis, trans-ABA], racemic ABA, or ABA isomers were added into suspension cultures at a final concentration of 30 microM. In comparison to racemic ABA and ABA isomers, S-ABA reduced tissue proliferation the most. In all cell lines, about half of the racemic ABA was used within 2 weeks; the remaining ABA was (-)-cis, trans-ABA. The concentration of ABA showed little change thereafter. In the cultures supplied with ABA isomers, about half of (+/-)-cis, trans-ABA was utilized during 22 d. By contrast, (+/-)-trans, trans-ABA was hardly used, especially in line ISP16. S-ABA was almost completely metabolized by line ISP11. However, approximately 28% and 22% of the S-ABA remained in the culture of cell lines ISP16 and ISP48, respectively. Cell line ISP16 grew the fastest in culture. By 3 weeks, S-ABA consumption by ISP11 and ISP48 on the basis of tissue growth was, respectively, 2.2-fold and 3.4-fold greater than that of ISP16. A higher ratio of dihydrophaseic acid to phaseic acid existed with cell lines of higher embryo maturation capability, especially when the exogenously supplied ABA was chemically synthesized.

Seed parasitism redirects ovule development in Douglas fir

Many parasitic species of insects complete their entire development in seeds. They feed off storage reserves within the ovule. These reserves only normally accumulate in fertilized ovules. Consequently, female insects that oviposit their eggs directly into the plant ovule need to be able to select correctly, as unfertilized ovules of conifers normally become so-called empty seed. We provide clear evidence that in conifers, seed-parasitizing insects do not need to discriminate between fertilized and unfertilized plant ovules when ovipositing their eggs. A host-specific insect, the chalcid Megastigmus spermotrophus Wachtl (Hymenoptera: Torymidae), lays its eggs in ovules of Douglas fir (Pseudotsuga menziesii (Mirbel) Franco) before fertilization has taken place in the plant. Oviposition not only prevents the expected degeneration and death of unfertilized ovules, but it induces energy reserve accumulation. Ovules that would otherwise develop as empty seed are redirected in their development by the insect to provide food for the developing larvae. Instead of the insect exploiting normal events during seed development, the insect manipulates seed development for its own reproductive advantage.

Oviposition strategies of conifer seed chalcids in relation to host phenology

Insects are considered the most important predators of seed cones, the female reproductive structures of conifers, prior to seed dispersal. Slightly more than 100 genera of insects are known to parasitize conifer seed cones. The most diverse (i.e., number of species) of these genera is Megastigmus (Hymenoptera: Torymidae), which comprises many important seed pests of native and exotic conifers. Seed chalcids, Megastigmus spp., lay eggs inside the developing ovules of host conifers and, until recently, oviposition was believed to occur only in fertilized ovules. Ovule development begins just after pollination, but stops if cells are not fertilized. The morphological stage of cone development at the time of oviposition by seed chalcids has been established for many species; however, knowledge of ovule development at that time has been documented for only one species, M. spermotrophus. Megastigmus spermotrophus oviposits in Douglas-fir ovules after pollination but before fertilization. Unlike the unfertilized ovules, those containing a M. spermotrophus larva continue to develop, whether fertilized or not, stressing the need to broaden our understanding of the insect-plant interactions for this entire genus. To achieve this task, we reviewed the scientific literature and assembled information pertaining to the timing of oviposition and to the pollination and fertilization periods of their respective host(s). More specifically, we were searching for circumstantial evidence that other species of Megastigmus associated with conifers could behave (i.e., oviposit before ovule fertilization) and impact on female gametophyte (i.e., prevent abortion) like M. spermotrophus. The evidence from our compilation suggests that seed chalcids infesting Pinaceae may also oviposit before ovule fertilization, just like M. spermotrophus, whereas those infesting Cupressaceae seemingly oviposit after ovule fertilization. Based on this evidence, we hypothesize that all species of Megastigmus associated with Pinaceae can oviposit in unfertilized ovules, whereas those exploiting Cupressaceae cannot, and thus oviposit only in already fully developed fertilized seeds. Furthermore, we predict that the presence of a larva in unfertilized ovules of all Pinaceae will influence the development of the female gametophyte by preventing its abortion. This influence on the Pinaceae can be interpreted as an ability to parasitize any of the potential seeds present in a seed cone, and as such represents a much more efficient oviposition strategy than searching and locating only fertilized seeds. Concomitantly, this ability has likely led to an overestimation of the impact of the species of seed chalcid infesting Pinaceae on seed production.

Charcoal affects early development and hormonal concentrations of somatic embryos of hybrid larch

Embryogenic tissue of hybrid larch (Larix x marschlinsii Coaz) was multiplied on Medium M (modified MSG medium supplemented with the plant growth regulators (PGRs) 2,4-dichlorophenoxyacetic acid (2,4-D; 9 microM) and N-6-benzyladenine (2.25 microM)). After 1 week, cultures were transferred to either MSG lacking PGRs (Medium C-) or MSG lacking PGRs but supplemented with 1% activated charcoal (Medium C+). Embryos were sampled after 1 week on Medium M, C- or C+. Embryos were analyzed by ELISA for abscisic acid (ABA), abscisic acid-glucose ester, 2,4-D, indole-3-acetic acid (IAA), indole-3-aspartate (IAAsp), zeatin (Z), zeatin riboside (ZR), isopentenyladenine (iP) and isopentenyladenosine (iPA). Transfer of embryos to Medium C+ reduced the embryo concentrations of 2,4-D and iPA, but resulted in elevated concentrations of IAA, IAAsp, ABA, Z, ZR and iP. Charcoal reduced 2,4-D concentrations of embryos by an order of magnitude greater than PGR-free medium alone. Charcoal affected embryo concentrations of five of the eight PGRs quantified. Use of either C+ or C- medium as part of the maturation protocols also affected germination and plantlet establishment of the embryos. A 1-week treatment on Medium C+ positively influenced plantlet establishment and generally reduced variability during both germination and plantlet establishment.