Annals of botany最新文献

Background: Leaf dark respiration (Rd) responds to short-term temperatures and acclimates to changes in long-term temperatures. Although accurate Rd-temperature (Rd-T) models are crucial for carbon flux prediction in forest ecosystems, two thermodynamically grounded frameworks-the macromolecular rate theory (MMRT) and the general temperature dependence (GTD) model-have not been compared. Moreover, these models can uniquely link molecular processes to leaf-scale Rd, providing mechanistic interpretations of thermal acclimation that empirical models cannot achieve.

Methods: Here, we grew two common subtropical species, Cyclobalanopsis glauc and Schima superba, in artificial climatic chambers under three temperature treatments (daytime/nighttime = 30/25°C, 25/20°C, and 20/15°C). After 15 days of temperature treatment, Rd-T response curves were measured at night.

Key results: Despite both models showed equivalent predictive power (R², AICc, RMSE), MMRT was prioritized for its detailed mechanistic interpretation, which links the molecular conformation to temperature-dependent leaf Rd via temperature-dependent changes in heat capacity (ΔC). Although both species employ type II thermal acclimation, the thermal acclimation strategies differ: for C. glauca, the increase in ΔC under warming suggests a shift toward enhanced enzyme conformational flexibility, achieving partial homeostasis. In contrast, S. superba exhibited overcompensation without changes in ΔC or activation enthalpy (ΔH), indicating a strategy governed by factors independent of these thermodynamic parameters.

Conclusions: In our study, the MMRT model is recommended to fit Rd-T response curves, and ΔC serves as a bridge between thermodynamic principles and species-specific thermal acclimation mechanisms, successfully distinguishing the strategy of C. glauca (associated with changing enzyme thermodynamics) from that of S. superba (independent of such thermodynamic adjustments).

Background: Primed acclimation (PA) is a phenomenon where an abiotic stressor early in a plant's vegetative stage primes defense pathways to the same stressor at later developmental stages. Similarly, cross-stress tolerance is a response where an exposure to one abiotic stressor creates a 'stress memory' that can more quickly respond to a later, different abiotic stressor. Cross-priming is a phenomenon where an early abiotic stressor confers defense to a late season biotic stressor. Peanut (Arachis hypogaea L.), an economically important crop in the United States, has exhibited beneficial primed acclimation responses in previous studies. Sclerotium rolfsii, the causal agent of southern blight, can inflict significant economic damage to peanut operations. The purpose of this study was therefore to test for cross-priming against southern blight in two peanut cultivars.

Methods: In this factorial greenhouse study, we instituted four sequential treatments each with two levels: (1) cv. Florun 331/cv. Georgia-06G, (2) Primary Water Stress (P-50FC)/Primary Well-Watered (P-100FC), (3) Inoculated/Control, and (4) Secondary Water Stress (S-0FC)/Secondary Well-Watered (S-100FC), yielding a total of 16 treatments. The primary water stress (PWS) consisted of irrigating plants to 50% field capacity for 35 days and the secondary water stress (SWS) was the withholding of any water for seven days.

Key results: We documented the absence of a beneficial cross-priming result as we did not see reduced southern blight progression among plants exposed to the PWS. Crucially, we observed a three-way interaction between cultivar, PWS, and SWS in inoculated plants, whereby the treatment combinations "Georgia-06G→P-50FC→S-0FC" and "Florun331→P-50FC→S-100FC" had substantially greater disease severity than their P-100FC counterparts. Serendipitously, we observed reduced secondary transmission of southern blight in P-50FC treated plants. Overall, our results caution that drought acclimation may not only fail to deliver crop production benefits but could even have an adverse influence on peanut yields and disease severity.

Background and aims: DNA methylation plays a crucial role in plant stress response, particularly under abiotic stress. Suaeda aralocaspica (S. aralocaspica), a halophyte with C4 photosynthetic pathway within a single polarized cell, exhibits unique adaptations to environmental challenges. This study investigates cytosine methylation patterns in S. aralocaspica under dark (D), light recovery (LR), and NaCl stress (100 and 500 mM, N100 and N500), focusing on the methylation-mediated regulation of stress-responsive genes, including different phosphoenolpyruvate carboxylase genes (SaPEPCs).

Methods: The whole-genome bisulfite sequencing was used to investigate DNA methylation under different stress treatments. Gene expression and Western blot analyses in photosynthesis and salt response pathways were conducted using a DNA methylation inhibitor (5-azacytidine, 5-azaC) and a methylating agent (methyl trifluoromethanesulfonate, MTFMS) to assess the functional link between methylation and gene regulation.

Key results: Global methylation levels in S. aralocaspica decreased under stress, with non-CG methylation showing the most significant changes. The majority of 81854 and 14653 differentially methylated regions (DMRs) under N500 and darkness, respectively, were hypo-methylated. Dynamic DNA methylation directly regulates the expression of genes involved in both photosynthetic and salt stress responses. In most cases, mRNA expression of these genes increased when their promoters were hypo-methylated. The functional significance of these methylation patterns was further confirmed through DNA methylation inhibitor (5-azaC) or DNA methylating agent (MTFMS). These treatments revealed that hypo-methylation may enhance the gene expression, as observed in key genes such as SaPEPC1, SaPEPC2, PPDK, CPK3, CPK4. Between the two SaPEPC genes, SaPEPC2 showed hypo-methylated DMRs specifically under N500 treatment, by contrast, SaPEPC1 exhibited a hypo-DMR under darkness. Combined with our previous study, our results suggest a functional divergence among these paralogs, and SaPEPC1 may be the key gene in carbon fixation.

Conclusions: This study revealed a stress-induced genome-wide DNA hypo-methylation in S. aralocaspica. SaPEPC1 and SaPEPC2 exhibited distinct methylation responses to darkness and salt stress, respectively. Through methylation alteration experiments, we established the associations between DNA methylation and relevant gene expression, which should improve our understanding of epigenetic regulation in halophyte stress adaptation.

Background and aim: Many plants have complex mating systems involving sexual and asexual reproduction. Investment in different reproductive strategies can vary among sub-populations and is linked to local ecological conditions, but the key drivers are not well understood. We aim to use direct estimates of reproductive investment (flowering and seed production), population genetic surveys and a biophysical model to assess the relationship between connectivity and the relative importance of sexual and asexual reproduction in maintaining seagrass populations. We predict that populations with high levels of connectivity and investment in flowering and seed production will display higher levels of genotypic diversity, while more isolated populations with lower investment in flowering and seed production will display higher levels of clonality.

Methods: We combine field surveys of flowering and seed production with population genetic surveys and a biophysical dispersal model to assess reproductive effort and patterns of connectivity in the seagrass Heterozostera nigricaulis across 16 sites in a large embayment in south-eastern Australia.

Key results: Estimates of genotypic diversity varied widely between locations, ranging from highly clonal (R = 0.18) to highly diverse (R = 0.91). Genotypic diversity correlated strongly with local seed production and the inflow of propagules derived from the biophysical dispersal model (pseudo R2 = 0.73). Sites that receive low numbers of propagules and produce few seeds were more clonal than sites with high propagule inflow and seed density.

Conclusions: These results show that isolated populations have higher levels of clonality and invest less in sexual reproduction. This has important consequences for the managing of declining populations of seagrass where fragmentation and loss of key source populations of propagules may lead to declines in genotypic and genetic diversity and the long-term viability of these important habitat-forming species.

Background and aims: In conifers, leaf length exhibits remarkable variation across and within species, even within the same individual. Leaves are often shorter in drier sites and at the tops of taller trees. Several hypotheses have been proposed to explain this shortening, but a clear causal framework is lacking. We hypothesize that conifer needles should exhibit a low rate of tip-to-base conduit widening leading to higher hydraulic resistance in long needles, explaining adaptive leaf shortening.

Methods: We sampled needles from 22 Pinus species and one Sequoia sempervirens across a range of environmental conditions. We conducted a detailed intraspecific analysis on four Pinus species by measuring tracheid diameter along the needle, and an interspecific comparison by measuring tracheid diameter at the needle base across all species. In both analyses, we fitted tracheid diameter against distance from the needle tip and calculated the slope (b) of tip-to-base tracheid widening.

Key results: A low mean intraspecific widening slope (b = 0.12) was found, indicating that tracheid diameter increases only slightly from tip to base. This low widening rate cannot fully compensate for the increase in hydraulic resistance, which therefore increases with needle length. The interspecific slope of mean tracheid diameter at the needle base vs. needle length (0.25) was higher than the intraspecific mean, suggesting that longer-needled species may have wider conduits at the needle apex, offsetting needle length-imposed resistance.

Conclusions: Our findings suggest that shorter needles should reduce hydraulic resistance under dry conditions or with height growth, maintaining leaf-specific conductance. We offer a novel explanation for the commonly observed pattern of needle shortening, interpreting it as an adaptive response rather than a physiological limitation.

Background and aims: Plant populations can recover from wildfires through resprouting (resprouters), recruiting from in situ surviving seed banks (seeders) or recolonization via seed dispersal. However, it is unclear how complementary these mechanisms can be, especially whether and how specific seed dispersal syndromes are associated with resprouter or seeder potential. In particular, it is unknown whether the occurrence of traits that facilitate seed dispersal and post-fire recolonization are disproportionately frequent among plants that lack other fire-coping strategies (i.e. colonizers).

Methods: Here, we compiled information on the presence of post-fire regeneration mechanisms - resprouting potential, seeding capacity and presence of traits that facilitate seed dispersal - for 705 species from the European Mediterranean Basin. Three-way contingency tables were built and analysed using log-linear models to assess associations between the three mechanisms.

Key results: We found a negative association between resprouting and seeding capacity, and observed that these mechanisms were independent of having any traits related to seed dispersal. However, traits facilitating endozoochory (fleshy fruits) were more common among resprouters than expected by chance.

Conclusions: Our results show that traits enhancing seed dispersal are widespread among post-fire resprouters and seeding species in the Mediterranean Basin flora. We conclude that seed dispersal traits are mostly an independent backup system assisting the recovery of burned sites rather than an alternative to resprouting or post-fire seeding.

Background: Climate change and population growth are major threats to global food security. Many cultivated crops remain vulnerable due to reduced genetic variation. Wild relatives and diverse accessions of crop species are being used to reintroduce diversity into their genomes to help contend with these issues. However, in some species, notably Triticum aestivum, Oryza spp., Solanum lycopersicum, Zea mays and Nicotiana spp., Arabidopsis thaliana and their wild relatives, gamete-killing genes may be responsible for the occurrence of hybrid dysgenesis through the targeting of reproductive cells that do not contain the gene.

Scope: This article explores gametocidal genes, 'pollen killers' or 'gamete killers', and toxin-antidote systems that result in sterility, alongside potential biological mechanisms. Gametocidal genes from wheat wild relatives significantly impact breeding programmes: wild relatives may contain useful germplasm but also gametocidal genes resulting in disastrous effects, including yield reductions. Due to their preferential transmission, gametocidal genes are extremely difficult to remove, therefore gene characterization is necessary. Hybrid sterility loci in Oryza spp. have been addressed, highlighting those that function similarly to gametocidal genes. We collate recent evidence to appraise the merit of biological mechanism hypotheses and suggest how recent innovations may improve characterization. Additionally, the challenges that they contribute to breeding programmes and subsequent successes are highlighted. In light of genetic innovation, we suggest contexts where a revival of using gametocidal genes may be beneficial, alongside novel techniques for research.

Conclusions: Past research has identified unique characteristics of gametocidal genes, leading to theories such as the dual-mechanism and restriction-modification models to explain the mechanisms. However, recent research suggests that complex genetic factors such as transposable elements and epigenetics may account for the phenomenon. Future work towards mapping these genes is hopeful: innovations in sequencing, bioinformatics and genomic data have improved the ability to precisely identify the elusive gametocidal genes.

Background and aims: Spikelets are fundamental units of the inflorescence in many members of Poales, including the species-rich families Poaceae and Cyperaceae. Comparative studies of spikelet morphology have illuminated key aspects of floral evolution, function and homology across these groups. However, spikelets of Restionaceae, a predominantly Australasian and South African family of Poales, remain poorly understood. Female inflorescences of some Restionaceae exhibit highly modified structures that have led to conflicting interpretations of the spikelet-flower boundary. This study clarifies the homology and functional significance of floral units in Restionaceae, with a focus on structural and developmental comparisons that highlight convergence with grasses.

Methods: We used scanning electron microscopy and high-resolution X-ray computed tomography to study reproductive morphology and ontogeny in Leptocarpus denmarkicus, which is remarkable in possessing a grass-like awn. Ontogenetic series were used to trace the development of reproductive structures, focusing on bract arrangement, flower position and awn formation.

Key results: The female units represent compound spikes, each consisting of numerous reduced, single-flowered spikelets. Each spikelet bears two bracts, one of which subtends a flower. Ontogenetic observations and positional data support this interpretation and challenge previous assumptions about bracteole identity in Restionaceae. The awn is formed by the flower-subtending bract and exhibits hygroscopic twisting, which is reported here for the first time for Restionaceae. It is likely to facilitate seed dispersal and provides a striking example of functional parallelism with grasses.

Conclusions: This study redefines the structure and developmental basis of inflorescences and identifies a novel seed dispersal mechanism in Restionaceae. The findings challenge long-standing assumptions on spikelet and bracteole identity and provide compelling evidence for evolutionary plasticity within Poales. The presence of hygroscopic awns in Restionaceae highlights parallel evolution of dispersal strategies with grasses, underscoring the broader significance of functional morphology in understanding inflorescence evolution across monocots.