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Key message: A new Tau class GST gene was cloned from Pinus brutia Ten. cDNA sequence was analysed for conserved sequences. Substrate specificity, optimum pH, and temperature values of the recombinant PbGST Tau enzyme were determined. Tau class glutathione S-transferases (GSTs) are essential enzymes for detoxification in plants. To date, a lot of the members of this family have been characterized from different plants but the studies on the conifers are very scarce. This study investigates for the first time molecular cloning and biochemical characterization of a Tau class GST gene (PbGST Tau) from Pinus brutia Ten. The full length PbGST Tau ORF was 687 bp having a molecular mass of 27.37 kDa. Catalytic and ligand binding sites of PbGST Tau are well conserved and shared maximum identity with Pinus tabulaeformis GST Tau. Kinetic analysis with respect to 1-chloro-2,4-dinitrobenzene (CDNB) and ethacrynic acid (ECA) as substrates exhibited a Km of 3.66 mM and 0.3 mM, respectively. PbGST Tau enzyme had an optimum activity at pH 6.0 and 8.0 when CDNB and ECA were used as substrate, respectively. The highest activity was measured at 25 °C. Through enzyme assays, phylogenetic analysis and structural modelling, we provide a detailed characterization of the PbGST Tau gene and the enzyme. This study is going to provide new insights into the phylogenetic and biochemical analysis of GST family in conifers. [ABSTRACT FROM AUTHOR]

Although plant species with either animal or wind pollination modes are widespread and usually sympatric in nature, the degree of pollen interference from wind‐pollinated species on animal‐pollinated species remains little known. Conifer trees generally release a huge number of pollen grains into the air, floating into our noses and sometimes causing an allergic response. Here we document airborne pollen from two conifers (Pinus densata Mast. and Picea likiangensis (Franch.) E. Pritz.) deposited on the stigmas of eight coflowering insect‐pollinated angiosperms over 2 years in a mountainous forest community, in Shangri‐La, southwest China. Pollen density in the air as well as conifer pollen deposited onto stigmas at short and long distances from the airborne pollen source were quantified. Our results showed that conifer pollen as a proportion of total stigmatic pollen loads in the insect‐pollinated plants varied from 0.16% to 8.67% (3.16% ± 0.41%, n = 735) in 2016 and 0.66% to 5.38% (2.87% ± 0.86%, n = 180), and pollen quantity per unit area was closely related to that of airborne pollen in the air. Conifer pollen deposition on stigmas of insect‐pollinated species decreased greatly with increased distance from the pollen source. In the 10 plant species flowering in summer after conifer pollen release had finished, heterospecific pollen deposited on these stigmas came mainly from other insect‐pollinated flowers, with little contribution from airborne conifer pollen. The results indicate that there might be little interference with coflowering angiosperms by airborne pollen from dominant conifers in natural communities. [ABSTRACT FROM AUTHOR]

Rubisco specificity factor (Sc/o), a measure of the relative capacities of an enzyme to catalyze carboxylation and oxygenation of ribulose-1,5-bisphosphate, determines the extent of photosynthetic CO2 assimilation and photorespiratory CO2 release. The current model of C3 photosynthesis, the Farquhar–von Caemmerer–Berry (FvCB) model, requires a species-specific Sc/o. However, Sc/o values have never been reported in conifers, likely because in vitro kinetic analysis of conifer Rubisco presents difficulties. To estimate the Sc/o of conifers and compare it with angiosperm Sc/o, we measured changes in leaf CO2 compensation points (Γ) in response to O2 partial pressure for a variety of leaves, with different rates of day respiration (Rday) and maximum Rubisco carboxylation (Vcmax) in gymnosperms (Ginkgo biloba), conifers (Metasequoia glyptostroboides and Cryptomeria japonica), and angiosperms (Nicotiana tabacum and Phaseolus vulgaris). As predicted by the FvCB model, the slope of a linear function of Γ vs O2 partial pressure, d, increased alongside increasing Rday/Vcmax. The Sc/o was obtainable from this relationship between d and Rday/Vcmax, because the d values at Rday/Vcmax = 0 corresponded to α/Sc/o, where α was the photorespiratory CO2 release rate per Rubisco oxygenation rate (generally assumed to be 0.5). The calculated Sc/o values of N. tabacum and P. vulgaris exhibited good agreement with those reported by in vitro studies. The Sc/o values of both conifers were similar to those of the two angiosperm species. In contrast, the Sc/o value of G. biloba was significantly lower than those of the other four studied species. These results suggest that our new method for Sc/o estimation is applicable to C3 plants, including those for which in vitro kinetic analysis is difficult. Furthermore, results also suggest that conifer Sc/o does not differ significantly from that of C3 angiosperms, assuming α remains unchanged. [ABSTRACT FROM AUTHOR]

• The stem CH 4 emissions in wetlands are significantly higher than in uplands. • The stem CH 4 emissions of angiosperm are higher than gymnosperm trees. • The stem CH 4 emissions in coastal wetlands are less than in inland wetlands. • The source of stem CH 4 emissions in wetlands is from the soil. Growing evidence suggests that methane (CH 4) emissions from tree stems are a potentially significant atmospheric source. However, a comprehensive global assessment of the general pattern and the controlling factors of stem CH 4 emissions is still unavailable. Here, we present a global data-synthesis of 1081 observations from 62 studies to explore the patterns of stem CH 4 emission rate in upland and wetland ecosystems and their controlling factors. The global average stem CH 4 emission rate in uplands was 2.04 ± 0.61 nmol m −2 s −1, which was significantly lower than in wetlands (87.08 ± 19.49 nmol m −2 s −1). Angiosperm stem CH 4 emission rates were significantly higher than gymnosperm in both upland and wetland ecosystems. Meanwhile, stem CH 4 emission rate in inland wetlands (101.78 ± 27.44 nmol m −2 s −1) was significantly higher than in coastal wetlands (56.21 ± 19.23 nmol m −2 s −1). In both wetland and upland ecosystems, stem CH 4 emission rate decreased with increasing sampling height, but increased as soil CH 4 emission rate increased. However, the relationship between stem CH 4 emissions and soil CH 4 fluxes was much weaker for uplands, but very strong for wetlands. In wetlands, stem CH 4 emission rate was also regulated by plant properties, as it was negatively correlated with wood specific density, but positively correlated with stem lenticel density. In uplands, tree diameter negatively affected stem CH 4 emission rate. Overall, our results shed light on the magnitude and controlling factors of stem CH 4 emissions in upland and wetland ecosystems and could facilitate their upscaling to ecosystems and identify the role of stem CH 4 emissions in global CH 4 budgets. [Display omitted] [ABSTRACT FROM AUTHOR]

Cycads, which primarily consist of the families Cycadaceae and Zamiaceae, possess intrinsic therapeutic attributes that are prominently expressed across their morphological spectrum, including roots, leaves, flowers, and seeds. In Chinese traditional medicine, the leaves of cycads are particularly revered for their profound healing capabilities. This meticulous review engages with existing literature on cycads and presents insightful avenues for future research. Over 210 phytoconstituents have been isolated and identified from various cycad tissues, including flavonoids, azoxy metabolites, sterols, lignans, non-proteogenic amino acids, terpenoids, and other organic constituents. The contemporary pharmacological discourse highlights the antineoplastic, antimicrobial, and antidiabetic activities inherent in these ancient plants, which are of particular importance to the field of oncology. Despite the prevalent focus on crude extracts and total flavonoid content, our understanding of the nuanced pharmacodynamics of cycads lags considerably behind. The notoriety of cycads derived toxicity, notably within the context of Guam's neurological disease cluster, has precipitated an established emphasis on toxicological research within this field. As such, this critical review emphasizes nascent domains deserving of academic and clinical pursuit, whilst nested within the broader matrix of current scientific understanding. The systematic taxonomy, traditional applications, phytochemical composition, therapeutic potential, and safety profile of cycads are holistically interrogated, assimilating an indispensable repository for future scholarly inquiries. In conclusion, cycads stand as a veritable treasure trove of pharmacological virtue, displaying remarkable therapeutic prowess and holding vast promise for ongoing scientific discovery and clinical utilization. Cycads represent a rich, therapeutic resource, exhibiting exceptional medicinal efficacy and enormous potential for continued exploration and application. [Display omitted] • Up to now, more than 210 phytochemicals have been identified from cycads. • Cycads is a double-edged sword, and its toxicity should not be overlooked. • Cycads has great medical development and application value. [ABSTRACT FROM AUTHOR]

A reference genome sequence for Pseudotsuga menziesii var. menziesii (Mirb.) Franco (Coastal Douglas-fir) is reported, thus providing a reference sequence for a third genus of the family Pinaceae. The contiguity and quality of the genome assembly far exceeds that of other conifer reference genome sequences (contig N50 = 44,136 bp and scaffold N50 = 340,704 bp). Incremental improvements in sequencing and assembly technologies are in part responsible for the higher quality reference genome, but it may also be due to a slightly lower exact repeat content in Douglas-fir vs. pine and spruce. Comparative genome annotation with angiosperm species reveals gene-family expansion and contraction in Douglas-fir and other conifers which may account for some of the major morphological and physiological differences between the two major plant groups. Notable differences in the size of the NDH-complex gene family and genes underlying the functional basis of shade tolerance/intolerance were observed. This reference genome sequence not only provides an important resource for Douglas-fir breeders and geneticists but also sheds additional light on the evolutionary processes that have led to the divergence of modern angiosperms from the more ancient gymnosperms.

Premise of research. Recent research on evolutionarily old species has uncovered mesophyll conductance (g m) as a key player in realized assimilation, but considerable variation was found. However, in gymnosperms, photosynthetic limitations, particularly how limitation combinations contribute to realized photosynthetic rates, have been studied in very few species, precluding any broad conclusions about the share of different controls and hindering reliable global modeling of the gymnosperm forest's contributions to the global carbon cycle and responses to climate change. Methodology. Using combined gas exchange and fluorescence measurements, we studied photosynthetic limitations in 67 species of gymnosperms (7% of all extant species) to uncover the share of photosynthetic limitations and the consequences of the variation in g m. These studied species were grown in a common garden but originated from globally contrasting habitats and evolutionary histories and represent species with flat leaves, scales, and needle-shaped foliage. Pivotal results. Remarkably, g m varied 21-fold, extending almost across the whole range of values observed in vascular plants to date, and this variation was associated with 6- and 12-fold differences in the net assimilation rate per area and mass and with more than 3-fold differences in the CO2 drawdown from the intercellular airspace to chloroplasts. Photosynthetic limitation analysis revealed that mesophyll and stomatal limitations were dominant, correspondingly spanning 8%–72% and 5%–57% of the total photosynthetic limitation. Both limitations were correlated with foliage structural characteristics, challenging the hypothesis that the phylogenetic background of a species directly determines the partitioning of photosynthetic limitations. Conclusions. The results of the current study emphasize that highly variable gymnosperm leaf structure results in major variations in mesophyll diffusion conductance that needs to be included in carbon gain estimations, especially in evolutionarily old species. [ABSTRACT FROM AUTHOR]

Our power to predict the future relies on our knowledge of the past. Paleoproxies are a powerful tool for understanding environmental and ecological conditions and changes across different time periods. However, constructing a functioning paleoproxy requires a well-constrained and robustly tested model. This is challenging, especially if ecological traits are involved. In the current study, we constructed an extended data set to test the reliability of the derivation of leaf dry mass per unit area (LMA) from the thickness of fossil gymnosperm cuticle. Specifically, we tested whether different leaf types (broad leaves, needles, and scales), intraspecific variability in cuticle thickness, and growing conditions affect the functioning of the proxy. Taxonomic groups were analyzed to uncover the possible taxonomic influence on LMA, cuticle thickness (CT), and the LMA-CT relationship. Our results indicate that the CT versus LMA relationship depends on multiple factors that can have various and incongruous effects on this relationship, depending especially on leaf type and growing conditions. We conclude that CT measured from gymnosperm fossils could be used as a proxy for LMA in past ecosystems for some broad- and scale-leaved gymnosperms but not for needle-leaved gymnosperms. However, caution must be taken when comparing species from different environments or growth conditions. [ABSTRACT FROM AUTHOR]

Background: Small RNAs (sRNAs) are regulatory molecules impacting on gene expression and transposon activity. MicroRNAs (miRNAs) are responsible for tissue-specific and environmentally-induced gene repression. Short interfering RNAs (siRNA) are constitutively involved in transposon silencing across different type of tissues. The male gametophyte in angiosperms has a unique set of sRNAs compared to vegetative tissues, including phased siRNAs from intergenic or genic regions, or epigenetically activated siRNAs. This is contrasted by a lack of knowledge about the sRNA profile of the male gametophyte of gymnosperms. Results: Here, we isolated mature pollen from male cones of Norway spruce and investigated its sRNA profiles. While 21-nt sRNAs is the major size class of sRNAs in needles, in pollen 21-nt and 24-nt sRNAs are the most abundant size classes. Although the 24-nt sRNAs were exclusively derived from TEs in pollen, both 21-nt and 24-nt sRNAs were associated with TEs. We also investigated sRNAs from somatic embryonic callus, which has been reported to contain 24-nt sRNAs. Our data show that the 24-nt sRNA profiles are tissue-specific and differ between pollen and cell culture. Conclusion: Our data reveal that gymnosperm pollen, like angiosperm pollen, has a unique sRNA profile, differing from vegetative leaf tissue. Thus, our results reveal that angiosperm and gymnosperm pollen produce new size classes not present in vegetative tissues; while in angiosperm pollen 21-nt sRNAs are generated, in the gymnosperm Norway spruce 24-nt sRNAs are generated. The tissue-specific production of distinct TE-derived sRNAs in angiosperms and gymnosperms provides insights into the diversification process of sRNAs in TE silencing pathways between the two groups of seed plants. [ABSTRACT FROM AUTHOR]

Key message: A Gretchen Hagen 3-like gene, LaGH3 from hybrid larch (Larix leptolepis × Larix olgensis), was identified, and the effects of abscisic acid (ABA) and indole-3-acetic acid (IAA) on its transcriptional levels and expression patterns during somatic embryogenesis were analyzed. A full-length cDNA sequence of a Gretchen Hagen 3 (GH3) gene was isolated from hybrid larch (Larix leptolepis × Larix olgensis) and designated LaGH3. The cDNA was 2053 bp in length and contained an 1848-bp open-reading frame encoding a predicted protein of 615 amino acids, characterized by four conserved motifs of the GH3 protein family: P-loop, α5, α6, and β8–β9. The 5′-flanking promoter region of LaGH3 was cloned using an improved TAIL-PCR technique. In this region, we identified several auxin- and abscisic acid (ABA)-inducible elements. Expression analysis showed that LaGH3 was induced by indole-3-acetic acid and that its transcript accumulation was inhibited by ABA. Further experiments demonstrated that ABA was the main factor in LaGH3 downregulation during the early stage of somatic embryogenesis, although the absence of auxin decreased LaGH3 expression slightly. LaGH3 transcripts gradually increased and peaked at 28 days with the rapid development of somatic embryos and then declined as the somatic embryos matured. We suggest that the level of LaGH3 transcripts partly represents the dynamics of endogenous auxin during somatic embryo development in larch. Taken together, our results provide evidence that GH3 genes play important roles in the crosstalk between auxin and ABA by maintaining auxin homeostasis during somatic embryo development. [ABSTRACT FROM AUTHOR]

Premise of research. Mississippian (Lower Carboniferous) anatomically preserved ovules are pivotal to our present understanding of the Paleozoic primary seed plant radiation, but few are known from the late Viséan stratigraphic interval approximately 330 million years ago. Here, we document an exceptionally well-preserved mesoscopic charcoalified ovule from late Viséan limestones that is adapted for wind dispersal and for deterring herbivory. Methodology. We use synchrotron radiation X-ray tomographic microscopy (SRXTM) and low-vacuum scanning electron microscopy (LVSEM) to analyze histological features not identifiable through traditional methods. Pivotal results. The ovule is small, 2 mm long and 1.25 mm in maximum diameter, and has a dense covering of spirally arranged, long, slender, hollow hairs with glandular apexes and a distal papilla. The nucellus is fused to the integument up to the nucellar apex, and above this, the integument comprises eight apical lobes, each with a single vascular bundle. The nucellar apex has a domed pollen chamber and large central column characteristic of hydrasperman-type (lagenostomalean) pteridosperms, but it lacks the distal salpinx seen in most hydrasperman ovules, leaving an exposed distal opening to the pollen chamber for pollination. Differences with existing taxa lead to the erection of Hirsutisperma rothwellii gen. et sp. nov. Conclusions. The apical glands presumably functioned as granivory deterrents; coprolites (fossilized feces) from herbivorous arthropods are abundant in the fossiliferous horizon and at this stratigraphic interval. The small ovule size and its dense covering of hairs indicate Hirsutisperma was adapted for wind dispersal and was an r -selected species, producing large numbers of small offspring in unstable or changing environments. Taphonomic implications are discussed, including preservational biases for charcoalification. Hirsutisperma provides the first clear evidence for ecological niche partitioning in Mississippian hydrasperman-type ovules. [ABSTRACT FROM AUTHOR]

A silicified gymnospermous wood, Protophyllocladoxylon zhaobishanensis sp. nov., is described from the Induan (Lower Triassic) Jiucaiyuan Formation in Zhaobishan section, Shanshan County, southern Bogda Mountains, Xinjiang Uygur Autonomous Region, northwestern China. The pycnoxylic wood contains thick-walled tracheids and parenchymatous ray cells. It is characterized by uni- to triseriate araucarian radial tracheidal pitting, uniseriate rays, one to two large, simple pits in each cross-field, and uni- to biseriate tangential tracheidal pits. The presence of distinct and extensive growth rings in all fossil woods from the Induan of the research area were probably caused by the seasonal climate with great precipitation variability during the earliest Triassic in the Turpan–Hami Basin. This is also supported by the occurrence of Calcisols, vertic Calcisols, and calcic Argillisols from coeval deposits nearby. The occurrence of fossil wood with anatomical structures from the Induan confirms that woody gymnosperms, probably conifers, were crucial elements on the Early Triassic landscape in northeastern Pangaea. It appears that some gymnosperms had survived the end-Permian biotic crisis based on the continuous records of Protophyllocladoxylon -type woods from the Wuchiapingian (upper Permian) to Norian (Upper Triassic) in Bogda Mountains. • A new species of Protophyllocladoxylon wood has been described. • Gymnosperms were crucial elements on the Early Triassic landscape in northeastern Pangaea. • Growth rings on fossil woods and paleosols indicate seasonal environmental stresses. [ABSTRACT FROM AUTHOR]

Biphenyl structures (5–5 linkages) are one of the significant structural units in plant cell wall lignin. They can potentially play a role in providing branch points in lignins and influence the polymer structure of lignins. Variation of the biphenyl content was investigated for 21 wood species by alkaline nitrobenzene oxidation. The total yields of biphenyl-type products were similar among the six softwoods, and at least 6% of the phenylpropanoid units in lignin were involved in the biphenyl structures (>0.06 per C6-C3). The biphenyl product yield of the 15 hardwoods ranged widely (0.002–0.05 per C6-C3) and was lower in species having a higher syringyl/guaiacyl ratio (i.e. a species with less guaiacyl units). In addition, the proportion of biphenyl products in all guaiacyl-type products was not constant but decreased as the proportion of syringyl units increased. This indicates that the content of guaiacyl units is not likely the only factor influencing the biphenyl content. [ABSTRACT FROM AUTHOR]

The simultaneous over-accumulation of Fe, hydrogen peroxide and superoxide can result in the generation of hydroxyl radicals, which play a significant role in the interactions between plant hosts and invading fungi. The physiological response to infection by pathogenic or mycorrhizal fungi may, however, be determined by the root zone. The objective of the present study was to use light microscopy to determine whether iron and hydrogen peroxide are differentially distributed in P. sylvestris roots in response to colonization by necrotrophic pathogens (Fusarium oxysporum and Rhizoctonia solani) vs. mycorrhizal fungi (Hebeloma crustuliniforme and Laccaria bicolor) in in vitro culture. It was also of interest to determine how hydrogen peroxide, superoxide, and iron added to substrate in vitro impacted the ability of trophically different fungi to grow. Infection by necrotrophic fungi, especially by F. oxysporum, were associated with a significantly higher accumulation of both forms of iron (Fe2+ and Fe3+) in the meristematic root zone, relative to the accumulation of these forms of iron in response to ectomycorrhizal fungi. Iron supplementation of solid culture medium reduced the growth of pathogenic fungi to a greater extent than the growth of mycorrhizal fungi. In contrast to the distribution of iron, cells in the elongation zone of P. sylvestris roots generally exhibited the highest accumulation of hydrogen peroxide. The growth of mycorrhizal fungi was more inhibited by the presence of hydrogen peroxide in the solid culture medium than by any other supplemented compounds. This research indicate that the distribution of iron and hydrogen peroxide in roots of P. sylvestris is related to the trophic strategy of the colonizing fungi. [ABSTRACT FROM AUTHOR]

Sugar pine (Pinus lambertiana Douglas) is within the subgenus Strobus with an estimated genome size of 31 Gbp. Transcriptomic resources are of particular interest in conifers due to the challenges presented in their megagenomes for gene identification. In this study, we present the first comprehensive survey of the P. lambertiana transcriptome through deep sequencing of a variety of tissue types to generate more than 2.5 billion short reads. Third generation, long reads generated through PacBio Iso-Seq have been included for the first time in conifers to combat the challenges associated with de novo transcriptome assembly. A technology comparison is provided here to contribute to the otherwise scarce comparisons of second and third generation transcriptome sequencing approaches in plant species. In addition, the transcriptome reference was essential for gene model identification and quality assessment in the parallel project responsible for sequencing and assembly of the entire genome. In this study, the transcriptomic data were also used to address questions surrounding lineage-specific Dicer-like proteins in conifers. These proteins play a role in the control of transposable element proliferation and the related genome expansion in conifers.

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.

Pinus plants are the largest existing group of gymnosperms and one of the most highly differentiated taxa. Due to its huge ecological, economic, and scientific value, the genetic diversity and the relationship between the intraspecific evolution of Pinus plants have gained wide attention. In this study, the chloroplast genomes of several common pine trees in southwest and south China, including P. massoniana (masson pine), P. yunnanensis (yunnan pine), P. latteri (south asia pine), P. crassicorticea (la ya pine), and P. elliottii (slash pine), and entire cpDNA sequences were obtained. Characteristics including the structure, repeated sequence, and codon bias of the cpDNA for these five pine tree species were analyzed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The gymnosperm genus Cycas is the sole member of Cycadaceae, and is the largest genus of extant cycads. There are about 115 accepted Cycas species mainly distributed in the paleotropics. Based on morphology, the genus has been divided into six sections and eight subsections, but this taxonomy has not yet been tested in a molecular phylogenetic framework. Although the monophyly of Cycas is broadly accepted, the intrageneric relationships inferred from previous molecular phylogenetic analyses are unclear due to insufficient sampling or uninformative DNA sequence data. In this study, we reconstructed a phylogeny of Cycas using four chloroplast intergenic spacers and seven low-copy nuclear genes and sampling 90% of extant Cycas species. The maximum likelihood and Bayesian inference phylogenies suggest: (1) matrices of either concatenated cpDNA markers or of concatenated nDNA lack sufficient informative sites to resolve the phylogeny alone, however, the phylogeny from the combined cpDNA-nDNA dataset suggests the genus can be roughly divided into 13 clades and six sections that are in agreement with the current classification of the genus; (2) although with partial support, a clade combining sections Panzhihuaenses  +  Asiorientales is resolved as the earliest diverging branch; (3) section Stangerioides is not monophyletic because the species resolve as a grade; (4) section Indosinenses is not monophyletic as it includes Cycas macrocarpa and C. pranburiensis from section Cycas ; (5) section Cycas is the most derived group and its subgroups correspond with geography. [ABSTRACT FROM AUTHOR]

Plant cell walls (CWs) are dynamic in that they can change conformation during ontogeny and in response to various stresses. Though seeds are the main propagatory units of higher plants, little is known of the conformational responses of zygotic embryo CWs to drying. This study employed cryo-scanning electron microscopy to compare the effects of desiccation on zygotic embryo CW morphology across three gymnosperm species that were shown here to differ in seed desiccation sensitivity: Podocarpus henkelii (highly desiccation-sensitive), Podocarpus falcatus (moderately desiccation-sensitive), and Pinus elliottii (desiccation-tolerant). Fresh/imbibed (i.e. fresh Podocarpus at shedding and imbibed Pi. elliottii) embryos showed polyhedral cells with regular walls, typical of turgid cells with an intact plasmalemma. Upon desiccation to c. 0.05 g g−1 (dry mass basis), CWs assumed an undulating conformation, the severity of which appeared to depend on the amount and type of dry matter accumulated. After desiccation, intercellular spaces between cortical cells in all species were comparably enlarged relative to those of fresh/imbibed embryos. After rehydration, meristematic and cotyledonary CWs of P. henkelii and meristematic CWs of P. falcatus remained slightly undulated, suggestive of plasmalemma and/or CW damage, while those of Pi. elliottii returned to their original conformation. Cell areas in dried-rehydrated P. henkelii root meristem and cotyledon were also significantly lower than those from fresh embryos, suggesting incomplete recovery, even though embryo water contents were comparable between the two states. Electrolyte leakage measurements suggest that the two desiccation-sensitive species incurred significant plasmalemma damage relative to the tolerant species upon desiccation, in agreement with the CW abnormalities observed in these species after rehydration. Immunocytochemistry studies revealed that of the four CW epitopes common to embryos of all three species, an increase in arabinan (LM6) upon desiccation and rehydration in desiccation-tolerant Pi. elliottii was the only difference, although this was not statistically significant. Seed desiccation sensitivity in species like P. henkelii and P. falcatus may therefore be partly based on the inability of the plasmalemma and consequently CWs of dried embryos to regain their original conformation following rehydration. [ABSTRACT FROM AUTHOR]

Summary: A defining feature of angiosperms is double fertilization involving the female gametophyte central cell and formation of a nutrient‐storing tissue called endosperm. The route for the evolutionary origin of endosperm from a gymnosperm ancestor, particularly the molecular steps involved, has remained elusive. Recently, the histidine kinase gene Cytokinin‐Independent 1 (CKI1), an activator of cytokinin signaling, was described as a key to specification of the endosperm precursor central cell in Arabidopsis. Here, we have investigated the function and expression of a putative ortholog of CKI1 in the gymnosperm Ginkgo biloba. We demonstrate that Ginkgo CKI1 can partially rescue an Arabidopsis cki1 mutant and promote weak activation of the cytokinin signaling pathway in the Arabidopsis embryo sac, but does not confer central cell specification. Ginkgo CKI1 is expressed in both male and female gametophytes of Ginkgo. In the latter, it is expressed in the ventral canal cell, which is sister to the egg cell in the archegonium. As in Arabidopsis, Ginkgo CKI1 is not expressed in the egg cell. The similarities in expression patterns of CKI1 in Ginkgo and Arabidopsis female gametophytes suggest that extant gymnosperms possess an essential component of the molecular machinery required for angiosperm endosperm development, and provide new insights into endosperm origin from a gymnospermous ancestor. [ABSTRACT FROM AUTHOR]

• Background and Aims Form and function relationships in plant reproductive structures have long fascinated biologists. Although the intricate associations between specific pollinators and reproductive morphology have been widely explored among animal-pollinated plants, the evolutionary processes underlying the diverse morphologies of wind-pollinated plants remain less well understood. Here we study how this diversity may have arisen by focusing on two conifer species in the pine family that have divergent reproductive cone morphologies at pollination. • Methods Standard histology methods, artificial wind pollination assays and phylogenetic analyses were used in this study. • Key Results A detailed study of cone ontogeny in these species reveals that variation in the rate at which their cone scales mature means that pollination occurs at different stages in their development, and thus in association with different specific morphologies. Pollination experiments nevertheless indicate that both species effectively capture pollen. • Conclusions In wind-pollinated plants, morphological diversity may result from simple variation in development among lineages rather than selective pressures for any major differences in function or performance. This work also illustrates the broader importance of developmental context in understanding plant form and function relationships; because plant reproductive structures perform many different functions over their lifetime, subtle differences in development may dramatically alter the specific morphologies that they use to meet these demands. [ABSTRACT FROM AUTHOR]

Background and Aims Polyamines are small metabolites present in all living cells and play fundamental roles in numerous physiological events in plants. The aminopropyltransferases (APTs), spermidine synthase (SPDS), spermine synthase (SPMS) and thermospermine synthase (ACL5), are essential enzymes in the polyamine biosynthesis pathway. In angiosperms, SPMS has evolved from SPDS via gene duplication, whereas in gymnosperms APTs are mostly unexplored and no SPMS gene has been reported. The present study aimed to investigate the functional properties of the SPDS and ACL5 proteins of Scots pine (Pinus sylvestris L.) in order to elucidate the role and evolution of APTs in higher plants. Methods Germinating Scots pine seeds and seedlings were analysed for polyamines by high-performance liquid chromatography (HPLC) and the expression of PsSPDS and PsACL5 genes by in situ hybridization. Recombinant proteins of PsSPDS and PsACL5 were produced and investigated for functional properties. Also gene structures, promoter regions and phylogenetic relationships of PsSPDS and PsACL5 genes were analysed. Key Results Scots pine tissues were found to contain spermidine, spermine and thermospermine. PsSPDS enzyme catalysed synthesis of both spermidine and spermine. PsACL5 was found to produce thermospermine, and PsACL5 gene expression was localized in the developing procambium in embryos and tracheary elements in seedlings. Conclusions Contrary to previous views, our results demonstrate that SPMS activity is not a novel feature developed solely in the angiosperm lineage of seed plants but also exists as a secondary property in the Scots pine SPDS enzyme. The discovery of bifunctional SPDS from an evolutionarily old conifer reveals the missing link in the evolution of the polyamine biosynthesis pathway. The finding emphasizes the importance of pre-existing secondary functions in the evolution of new enzyme activities via gene duplication. Our results also associate PsACL5 with the development of vascular structures in Scots pine. [ABSTRACT FROM AUTHOR]

Background and Aims Investigating the biology of trees that were growing at high latitudes during warmer geological periods is key to understanding the functioning of both past and future forest ecosystems. The aim of this study is to report the first co-occurrence of epicormic shoots and traumatic growth zones in fossil trees from the Triassic of Antarctica and to discuss their biological and environmental implications. Methods Permineralized woods bearing scars of epicormic shoots were collected from the Triassic Fremouw Formation in Gordon Valley, Central Transantarctic Mountains, Antarctica in 2010. Samples from different portions of three specimens were prepared using standard thin section and hydrofluoric (HF) acid peel techniques, and anatomical details were studied in transmitted light. Key Results The fossil woods represent the outer part of trunks, with at least 40 growth rings that are 0.2-4.8 mm in width. Anatomical comparisons suggest that they represent a new tree taxon for the Triassic of Antarctica. Numerous small epicormic shoots can be seen crossing the wood almost horizontally and are locally branched. Each specimen also contains several occurrences of traumatic growth zones located in the early wood, in the cells produced either at the very start of the growing season or slightly later. Conclusions This is the first report of epicormic shoots and traumatic growth zones in the wood of a Triassic tree from Antarctica. Their co-occurrence indicates that these trees from Gordon Valley were subjected to environmental stresses not seen in Triassic trees previously described from this region. This suggests that they had a different biology and/or were growing in a different habitat, which offers a new glimpse into the diversity of high-latitude trees in the Triassic greenhouse climate. [ABSTRACT FROM AUTHOR]

The Miocene Lake deposit in Clarkia, Idaho is composed of highly fossiliferous silty clays. These rocks were formed in an anoxic and likely toxic deep lacustrine environment which facilitated the fossilization of plant material with a high amount of morphological detail. Many of the plant compression fossils exhibit exceptional preservation, including the preservation of original biomolecules. Pyritized plant specimens are much less common and the details of plant pyritization at this site are not yet fully understood. Pyritized male pollen cones from Taxodium dubium provide an opportunity to explore the processes of pyrite preservation in the Clarkia deposit. One specimen was examined using scanning electron microscopy (SEM) and energy-dispersive x-ray analysis (EDS). The only pyrite textures observed on this specimen were framboids and framboidal microcrystals. Pyrite was found in abundance on the surface of the pollen cones and to a much lesser extent on the surface of the stem. Underneath the pyrite coating, both the cones and stem were carbon-rich, indicating organic preservation. Some pyrite crystals were found in the interior of the stem, but likely originated from the exterior and developed through cracks or tears in the fossil. Pyrite crystals did not form inside the cell walls of the stem. The decaying specimen likely provided a scaffold that could facilitate the formation of pyrite upon the specimen surface. Gypsum crystals found in close association with pyrite likely formed as a product of oxidation after the specimens were taken from the rock. • Two plant fossils preserved with pyrite were found in Clarkia, Idaho. • Pyrite crystals formed either as spherical framboids or associated microcrystals. • Pyrite found only on the exterior of the plant or infilling cracks or tears. • The decaying plant matter formed a scaffold for pyrite formation. • Gypsum found in association with pyrite likely formed after excavation. [ABSTRACT FROM AUTHOR]

Sampling standardization has not been fully addressed for the study of insect herbivory in the fossil record. The effects of sampling within a single locality were explored almost a decade ago, but the importance of sampling standardization for comparisons of herbivory across space and time has not yet been evaluated. Here, we present a case study from the Permian in which we evaluate the impact of sampling standardization on comparisons of insect herbivory from two localities that are similar in age and floral composition. Comparisons of insect damage type (DT) diversity change dramatically when the number of leaves examined is standardized by surface area. This finding suggests that surface area should always be taken into account for comparisons of DT diversity. In addition, the three most common metrics of herbivory—DT diversity, proportion of leaves herbivorized and proportion of leaf surface area herbivorized—are inherently decoupled from each other. The decoupling of the diversity and intensity of insect herbivory necessitates a reinterpretation of published data because they had been conflated in previous studies. Future studies should examine the divergent ecological factors that underlie these metrics. We conclude with suggestions to guide the sampling and analysis of herbivorized leaves in the fossil record.

Abundant gymnosperm pollen grains associated with the oedemerid beetle Darwinylus marcosi Peris, 2016 were found in Early Cretaceous amber from Spain. This discovery provides confirmatory evidence for a pollination mutualism during the mid Mesozoic for the family Oedemeridae (Coleoptera), which today is known to pollinate only angiosperms. As a result, this new record documents a lateral host-plant transfer from an earlier gymnosperm to a later angiosperm, indicating that pollination of the latter is a derived condition within Oedemeridae. This new fossil record exemplifies one of the 4 ecological-evolutionary pollinator cohorts now known to have existed during the global shift from a gymnosperm to an angiosperm dominated global flora. Currently, all direct evidence for pollination during the 35 million-year interval of the mid Cretaceous gymnosperm-to-angiosperm transition entails recognition of gymnosperm pollen grains on insect mouthparts and other body contact surfaces, while analogous records involving angiosperms are lacking. The gathering evidence indicates that angiosperm pollination was preceded by at least 4 gymnosperm pollination modes that served as a functional and ecological prelude to the rise and expansion of angiosperms.