Annals of botany最新文献

Background and aims: Botanical literature is filled with studies which tried to demonstrate that leaves of many gymnosperms have an endodermis with Casparian bands or a sheath of sclerified cells around leaf veins. Direct photographic evidence of an endodermis with Casparian bands (strips) is lacking for the leaves of many gymnosperms. Our goal was to confirm with direct evidence an endodermis with Casparian bands or a vein sheath in leaves of representative gymnosperms via histochemical staining and epifluorescence microscopy, while extending previous work by examining understudied petioles and leaf bases.

Methods: We sectioned leaves fresh with razor blades and viewed them unstained or stained, usually with berberine hemisulfate, counterstained with gentian violet, and phloroglucinol HCl. Bright-field, epifluorescence and/or laser confocal microscopies on a Zeiss LSM700 were used for viewing and imaging.

Key results: Most members of Pinaceae of Pinophyta (13 species of genera Cedrus, Pseudotsuga, Larix, Picea and Pinus) had endodermis with distinct Casparian bands in needles. We identified endodermis in the distal petiolar regions of nine of these same species. Sclerified vein sheaths or partial vein sheaths were observed in 10 species of 41 studied among Cycadophyta (Cycas), Ginkgophyta (Ginkgo) and the Pinophyta Podocarpaceae (Dacrycarpus, Dacrydium), Cupressaceae (Metasequoia), Taxaceae (Amentotaxus) and Pinaceae (Keteleeria, Abies, Tsuga).

Conclusions: Endodermis with Casparian bands is only characteristic of most species of Pinaceae; vein sheaths are found in three genera of Pinaceae and six genera of the other families of gymnosperms, but most gymnospermous leaves lack endodermis and vein sheath, particularly in petiolar and leaf base regions. The presence of endodermis with Casparian bands could have contributed to the adaptation of the Pinaceae to extreme environments; members of genera such as Picea and Pinus are the typical treeline species in many mountain ranges across the world.

Background: Brown algae developed multicellularity independently of plants and animals. Once formed, the embryo rapidly establishes growth hotspots that lay the foundation for the development of the adult stage. The mechanisms that control the establishment of these growth hotspots are unknown.

Scope: Using diagrams and 3-D schematics, this review unpacks the different growth strategies of these organisms, focusing on localized 3-D growth in a particular cell or tissue. The sequence of cell divisions leading to the formation of 3-D tissues is compared among algae of the orders Sphacelariales, Dictyotales, Laminariales and Fucales, thereby providing an overview of the range of growth strategies selected in this phylum. I specifically focus on the orientation of cell divisions, which generally alternates in most brown algae, being perpendicular to the previous plane of cell division. These cell division characteristics, specific to brown algae, implement the building plans of 3-D bodies.

Conclusions: This review highlights the diversity of 3-D growth strategies within the brown algae, illustrating several cases and providing a framework for a broader comparison with other multicellular organisms, which developed 3-D tissues elsewhere within the eukaryote tree. It also addresses the potential underlying cellular mechanisms that control cell division plane orientation, and questions the level of cell autonomy with respect to neighbouring cells and the external environment.

Background and aims: Recent studies on desiccation-tolerant Australian rainforest seeds demonstrated that some were short-lived in storage. We sought to understand structural changes of storage lipids that might occur during storage at -20 °C that could contribute to a short lifespan.

Methods: We used differential scanning calorimetry (DSC) to examine exothermic and endothermic transitions during freezing and thawing in dry seed samples of 23 species. Seed samples and extracted triacylglycerols (TAGs) were cooled to -150 °C and rewarmed to 50 °C at 10 °C min-1; slower and faster rates of cooling/warming were used for a subset of species to examine lipid crystallization and melting kinetics. Thermograms were analysed for temperature and enthalpy of observed peaks, and these were compared with expected values to detect anomalies. Extracted lipids were further analysed using gas chromatography to characterize fatty acid composition. The thermal profiles of six species were used to design experiments comparing the impact of storage at -20 °C with storage at temperatures outside the range of thermal transitions.

Key results: Thermal activity was detected in 22 species within the narrow temperature range of -30 and -10 °C; activity at broader temperature ranges was also detected depending on species, cooling protocol and fatty acid composition. A profound interaction between DSC parameters and time at low temperature, as well as fatty acid composition, suggested that TAG crystallization rates contribute to low-temperature sensitivity. We confirmed that damage from TAG crystallization could be avoided by storing seeds at temperatures above TAG crystallization and melting events; storage at cryogenic temperatures improved survival over storage at -20 °C but requires further optimization to maintain pre-storage germination potential.

Conclusions: We conclude that the crystallization and melting of TAGs during storage may negatively impact seed longevity. Seed thermal profiles and rate of TAG crystallization may serve as predictive tools for sensitivity to storage at -20 °C.

Background and aims: Current grassland management, including fertilization, mowing and livestock grazing, substantially influences plant communities; however, it is not fully understood how management can affect plant growth at the individual level. Most herbaceous dicotyledonous plant species form distinct annual rings in the xylem that reveal age, but their annual width can also respond to changes in environmental conditions. It is also unclear at what scale, from the local plot level to the regional level, such secondary growth varies most.

Methods: Using cross-sections of the oldest well-preserved detectable part of the rhizome of Galium mollugo agg., we determined the response of secondary growth to the intensity, timing and type of grassland management for 1220 individuals across 60 populations in three different regions in Germany. In addition, we used environmental variables to examine the effects of climatic, soil and diversity-related characteristics on variation in ring width.

Key results: The age of the studied G. mollugo individuals ranged between 1 and 17 years (average age 6 years). Secondary growth varied most among individuals within sites and only slightly among sites within regions and among regions, indicating a strong influence of local plant-plant interactions. Increasing overall management and land-use intensity decreased secondary growth, whereas a late start of annual land use increased it. In addition, summer soil moisture was positively related whereas neighbour species richness was negatively related to secondary growth.

Conclusions: Our results indicate that annual secondary growth of a widespread herbaceous grassland species is sensitive to timing and intensity of land use and seasonal water regimes. The results imply that trends of increasing land-use intensity along with prolonged summer heat waves will further hamper growth of G. mollugo, which might translate to reduced performance and subsequently affect the overall plant community.

Background and aims: Many mechanisms respond simultaneously when plants are under drought stress. We examined physiological traits across six Zea mays genotypes varying in grain productivity under water limitation to identify plant strategies associated with greater productivity under limited water.

Methods: Data were collected on diurnal stomatal conductance (gs), maximum shoot hydraulic conductivity, pressurized root flow, light-adapted chlorophyll fluorescence and gas exchange on well-watered and water-limited plants in the field and greenhouse to identify traits and general strategies associated with grain production under water limitations in the field.

Key results: Results indicated that greater grain production was associated with greater peak gs among genotypes and treatments, and, when grown under limited water, maximum whole shoot hydraulic conductivity and pressurized root flow, the last of which may be linked to refilling of capacitance tissues to support plant gas exchange under limited water availability. Additionally, genotypes with greater grain production under limited water availability had reduced effective quantum yield of chlorophyll fluorescence relative to lower-yielding genotypes, suggesting trade-offs limiting maximum electron transport for the safety of photosynthetic apparatuses aligned with a productive strategy under limited water availability. Because both photosynthesis and gs declined similarly among genotypes grown with limited water, instantaneous water use efficiency determined under limited water in the greenhouse was similar among genotypes and did not show any relationship with grain production under limited water availability in the field.

Conclusions: A successful strategy for maize under cyclic water limitation appears to be to maintain growth with greater stomatal conductance and hydraulic conductivity, while protecting photosynthetic apparatuses. Finding a strong linkage between grain productivity and pressurized root flow, with its potential connection to capacitance tissues, emphasizes the need to explore hydraulic mechanisms that have received little attention to date but could provide a crucial mechanism for maintaining productivity when water availability is limited.

Background and aims: Aridity drives plant adaptations such as reduced stature, sclerophyllous leaves and increased phenolic production. While these patterns are well documented, the role of soil properties in modulating the impact of aridity remains understudied. Trait responses may also vary - converging, diverging, or remaining uncorrelated - across intraspecific and community levels, adding complexity to predictions of ecological responses to arid conditions.

Methods: We investigated how aridity influences six plant functional traits - lateral spread, maximum height, leaf area, specific leaf area (SLA), and the concentrations of total phenolics and flavonoids - at both the species level (focusing on Helichrysum italicum, the dominant species across the surveyed sites) and the community level across 24 dune ecosystems along the Atlantic-Mediterranean coastline of the Iberian Peninsula. We also collected soil samples and used piecewise structural equation modelling to assess whether physico-chemical soil variables - water-holding capacity, nutrient availability, pH and organic matter content - mediate the effects of aridity on plant functional traits.

Key results: We found a significant negative relationship between aridity and both plant height and lateral spread in H. italicum, while leaf area, SLA, total phenolics and flavonoids were not significantly affected. At the community level, aridity was also negatively associated with plant height and lateral spread, positively associated with SLA, and showed no significant relationship with the concentrations of phenolic compounds. Importantly, water-holding capacity was strongly correlated (positively) with aridity; however, the influence of aridity on plant functional traits was not mediated by variation in this factor.

Conclusions: This study demonstrates that aridity consistently influences structural plant traits across species and community levels in Iberian dune ecosystems, with largely convergent responses across organismal scales, and these patterns occur independently of key soil variables such as water-holding capacity.

Backgrounds and aims: In palms, many dioecious species have emerged from at least eight independent events; the mechanisms of sex determination remain poorly understood. Here, we identify and compare the sex chromosomes of Kerriodoxa elegans with those of the well-studied date palm (Phoenix dactylifera), which evolved dioecy independently from a monoclinous common ancestor.

Methods: We developed target sequence capture kits and inferred sex-linked genes using a probabilistic approach in both species.

Key results: We find a striking similarity between the sex-linked regions of K. elegans and P. dactylifera, with the majority of sex-linked genes being common between the two species. However, we confirm that these regions evolved independently, much later than the split between the lineages.

Conclusions: This case of convergent evolution seems to be unique in plants so far, and raises questions on the mechanisms of sex determination. This could be explained by the presence of genes related to floral sex development and sex determination in this region, which have been recruited during the evolution of sex chromosomes, even though the genes involved may differ between the two species.

Background and aims: Viola tricolor subsp. macedonica and Viola arsenica are metallophytes from the abandoned Allchar mine site in the Republic of North Macedonia, an area extremely enriched in thallium and arsenic, with up to 5750 and 12 800 mg kg-1 in the soil, respectively. This study aimed to infer tolerance mechanisms evolved in the two Viola species by analysis of the tissue-level distribution of arsenic and thallium.

Methods: Seedlings of V. tricolor subsp. macedonica and V. arsenica were grown under different thallium and arsenic treatments in hydroponics. Synchrotron-based micro-X-ray fluorescence (µXRF) analysis was used to elucidate elemental distribution in hydrated plant organs and tissues.

Key results: Plants dosed with increasing concentrations of arsenic and thallium had higher accumulation of these elements, especially in the roots. In V. arsenica, thallium mainly accumulated in the shoots, with the mature leaves being the main site of deposition. In the leaves of V. tricolor subsp. macedonica, the highest thallium concentrations occured around the stomata.

Conclusions: Foliar accumulation of thallium is the main tolerance strategy in V. arsenica, whereas the limited translocation into the shoot and potentially excreting excess thallium through the stomata in V. tricolor subsp. macedonica appears to be an important mechanism for survival in the extremely toxic habitat at the Allchar site.

Background and aims: Pollen:ovule ratios are often lower in species and populations with higher selfing rates. This may be due either to higher pollination efficiency through selfing, or to lower male competition when less allo-pollen is available. Changes in pollination can also impact pollen traits, such as the number of apertures. Viola arvensis has experienced a rapid recent increase in selfing rates, and a rapid floral trait evolution towards the selfing syndrome. This study tests the hypothesis that V. arvensis is also undergoing a rapid evolution in its pollen:ovule ratio and pollen heteromorphism.

Methods: Using the resurrection ecology methodology, we compared four ancestral populations (from ca. 30 years ago) to their descendants (from 2021). We counted ovules and pollen and measured the different pollen aperture morphs in 50 individuals per population. We also developed a model to better understand the links between the number of apertures and the mating system.

Key results: We found no temporal change in pollen or ovule production. However, populations with the lowest pollen:ovule ratios were also those with the highest ancestral selfing rates, suggesting that the pollen:ovule ratio could have evolved on a similar timescale to population differentiation. Our model predicts a positive correlation between number of apertures and selfing rates, if pollination parameters remain constant. However, this positive correlation was not found in our results, neither across populations nor through time.

Conclusions: Unlike floral morphology, pollen and ovule production did not evolve rapidly with increased selfing rates, suggesting a delayed change of the pollen:ovule ratio compared to other traits of the selfing syndrome. The absence of correlation between pollen heteromorphism and selfing rate can be explained by multiple (non-mutually exclusive) factors: a decrease in allo-pollen deposition correlated with the evolution of the selfing syndrome, pollinator declines or the absence of selection in this trait.