Annals of botany最新文献

Background: In epiphytic bromeliads, the roots were previously considered to be poorly functional organs in the processes of absorption and metabolization of water and nutrients, while the leaves were considered to always act as protagonists in both functions. More recent discoveries have been changing this old view of the root system.

Scope: In this review, we address previous ideas regarding the function performed by the roots of epiphytic bromeliads (mere holdfast structures with low physiological activity) and the importance of a reduced or lack of a root system for the emergence of epiphytism. We present indirect and direct evidence that contradicts this older hypothesis. Furthermore, the importance of the root absorptive function mainly for juvenile tankless epiphytic bromeliads and the characteristics of the root absorption process of adult epiphytic tank bromeliads are discussed thoroughly from a physiological perspective. Finally, some factors (species, substrate, environmental conditions) that influence the absorptive capability of the roots of epiphytic tank bromeliads are also be considered, highlighting the importance that the absorptive role of the roots has for the plasticity of bromeliads that live on trees, which is an environment characterized by intermittent availability of water and nutrients.

Conclusions: The roots of tank-forming epiphytic bromeliads play important roles in the absorption and metabolization of nutrients and water. The importance of roots is greatest for juvenile tankless bromeliads since the root is the main absorptive organ. In larger plants with a tank, although the leaves become the protagonists in the resource acquisition process, the roots complement the absorptive function of the leaf trichomes, resulting in improved growth of these bromeliad. The physiological and biochemical properties of the processes of absorption and distribution of resources in the tissues appear to differ between absorption by trichomes and roots.

Background: The evolutionary success of flowering plants is associated with the vast diversity of their reproductive structures. Despite recent progress in understanding angiosperm-wide trends in floral structure and evolution, a synthetic view of the diversity in seed form and function across angiosperms is lacking.

Scope: Here we present a roadmap to synthesize the diversity of seed forms in extant angiosperms, relying on the morphospace concept, i.e. a mathematical representation which relates multiple traits and describes the realized morphologies. We provide recommendations on how to broaden the range of measurable traits beyond mass, by using key morphological traits representative of the embryo, endosperm and seed coat but also fruit attributes (e.g. dehiscence, fleshiness). These key traits were used to construct and analyse a morphospace to detect evolutionary trends and gain insight into how morphological traits relate to seed functions. Finally, we outline challenges and future research directions, combining the morphospace with macroevolutionary comparative methods to underline the drivers that gave rise to the diversity of observed seed forms.

Conclusions: We conclude that this multidimensional approach has the potential, although still untapped, to improve our understanding of covariation among reproductive traits, and further elucidate angiosperm reproductive biology as a whole.

Background and aims: Diversity in pappus shapes and size in Asteraceae suggests an adaptive response to dispersion challenges adjusting diaspores to optimal phenotypic configurations. Here, by analysing the relationship among pappus-cypsela size relationships, flight performance and pappus types in an evolutionary context, we evaluate the role of natural selection acting on the evolution of diaspore configuration at a macro-ecological scale in the daisy family.

Methods: To link pappus-cypsela size relationships with flight performance we collected published data on these traits from 82 species. This allowed us to translate morphometric traits in flight performance for 150 species represented in a fully resolved backbone phylogeny of the daisy family. Through ancestral reconstructions and evolutionary model selection, we assessed whether flight performance was associated with and constrained by different pappus types. Additionally, we evaluated, through phylogenetic regressions, whether species with different pappus types exhibited evolutionary allometric pappus-cypsela size relationships.

Results: The setose pappus type had the highest flight performances and represented the most probable ancestral state in the family. Stepwise changes in pappus types independently led from setose to multiple instances of pappus loss with associated reduction in flight performance. Flight performance evolution was best modelled as constrained by five adaptive regimes represented by specific pappus types which correspond to specific optimal diaspore configurations that are distinct in pappus-cypsela allometric relationships.

Conclusions: Evolutionary modelling suggests natural selection as the main factor of diaspore configuration changes which proceeded towards five optima, often overcoming constraints imposed by allometric relationships and favouring evolution in certain directions. With the perspective that natural selection is the main process driving the observed patterns, various biotic and abiotic are suggested as principal drivers of transitions in diaspore configurations along space and time in the daisy family history. The results also allow discussion of evolutionary changes in a historical context.

Background and aims: The global supply of phosphorus is decreasing. At the same time, climate change reduces the availability of water in most regions of the world. Insights on how decreasing phosphorus availability influences plant architecture are crucial to understanding its influence on plant functional properties, such as the root system's water uptake capacity.

Methods: In this study, we investigated the structural and functional responses of Zea mays to varying phosphorus fertilization levels focusing especially on the root system's conductance. A rhizotron experiment with soils ranging from severe phosphorus deficiency to sufficiency was conducted. We measured the architectural parameters of the whole plant and combined them with root hydraulic properties to simulate time-dependent root system conductance of growing plants under different phosphorus levels.

Key results: We observed changes in the root system architecture, characterised by decreasing crown root elongation and reduced axial root radii with declining phosphorus availability. Modeling revealed that only plants with optimal phosphorus availability sustained a high root system conductance, while all other phosphorus levels led to a significantly lower root system conductance, both under light and severe phosphorus deficiency.

Conclusion: We postulate that phosphorus deficiency decreases root system conductance, which could mitigate drought conditions through a more conservative water use strategy, but ultimately reduces biomass and impairs root development and overall water uptake capacity. Our results also highlight that the organisation of the root system, rather than its overall size, is critical for estimating important root functions.

Background and aims: Both plants and animals display considerable variation in their phe- notypic traits as they grow. This variation helps organisms to adapt to specific challenges at different stages of development. Masting, the variable and synchronized seed production across years by a population of plants, is a common reproductive strategy in perennial plants that can enhance reproductive efficiency through increasing pollination efficiency and decreasing seed predation. Masting represents a population-level phenomenon generated from individual plant behaviors. While the developmental trajectory of individual plants influences their masting be- havior, the translation of such changes into benefits derived from masting remains unexplored.

Methods and key results: We used 43 years of seed production monitoring in European beech (Fagus sylvatica) to address that gap. The largest improvements in reproductive efficiency from masting happen in the largest trees. Masting leads to a 48-fold reduction in seed predation in large, compared to 28-fold in small trees. Masting yields an 6-fold increase in pollination efficiency in large, compared to 2.5-fold in small trees. Paradoxically, although the largest trees show the biggest reproductive efficiency benefits from masting, large trees mast less strongly than small trees.

Conclusions: That apparently suboptimal allocation of effort across years by large plants may be a consequence of anatomical constraints or bet-hedging. Ontogenetic shifts in individual mast- ing behavior and associated variable benefits have implications for the reproductive potential of plant populations as their age distribution changes, with applications in plant conservation and management.

Background and aims: Eocene foliage formerly attributed to the extant araliaceous genus Oreopanax was found attached to twigs bearing inflorescences and infructescences unlike those of Araliaceae. Using newly observable characters of phyllotaxy, vegetative and floral buds, infructescences and seeds, we sought to reassess the affinities of this strange angiosperm.

Methods: Fossils were studied from the Parachute Creek Member of the Green River Formation from near Bonanza, Utah and Douglas Pass, Colorado (ca. 47 Ma). Macrofossil impression remains were investigated by low angle reflected light and subtle details of the vegetative and floral buds, stamens, mature fruits, and seeds were revealed by optical shadow effect microscopy documenting previously obscure topographic surface features.

Key results: Othniophyton elongatum (MacGinitie) Manchester, Judd, Correa-Narvaez gen. et comb. nov. has simple, short-petiolate, elongate, entire-margined leaves with thick midveins, pinnate, brochidodromous secondaries, common intersecondary veins and finely reticulate higher order venation. Inflorescences are small axillary cymes; flower buds are subglobose and pedicellate, in bract axils. The flowers are actinomorphic, bisexual, with ca. five imbricate perianth parts, ca. 24 stamens with elongate anthers and short filaments, arising from a hypanthium. The whorl of stamens persists to fruiting stage. The ovary is superior, with probable basal placentation and five stigmatic arms. Fruits are pedicellate berries with a cup-shaped hypanthium and contain ca. 15 lensoidal reniform seeds, each with a curved embryo and ornamented with concentric ridges. The combined characters refute the prior placement in Araliaceae, and rule out affinities with most extant clades of angiosperms.

Conclusions: The distinctive combination of observed features does not coincide with any extant family. Among extant orders of Eudicots, the fossil seems to conform most closely to the order Caryophyllales, but key differences remain. This example indicates that the vegetation of ca. 47 million years ago included some taxa that cannot readily be placed in modern families and genera.

Background and aims: The transformation of sieve elements (SEs) from meristematic cells, equipped with a full complement of organelles, to specialized transport tubes devoid of a nucleus, has long been enigmatic. We hypothesized a strong involvement of various degradation pathways, particularly macroautophagy in this context, emphasizing the importance of autophagic selectivity in the remaining viability of these cells.

Methods: Experiments were performed on pioneer roots of Populus trichocarpa cultivated in rhizotrons under field conditions. Through anatomical, ultrastructural and molecular analyses, we delineate the stages of phloemogenesis and the concurrent alterations in the cytoplasmic composition of SEs.

Key results: Notably, we observed not only macroautophagic structures, but also the formation of autophagic plastids, the selective degradation of specific organelles, vacuole disruption and the release of vacuolar contents. These events initially lead to localized reductions in cytoplasm density, but organelle-rich cytoplasmic phase is safeguarded from the extensive damage by a membrane system derived from the endoplasmic reticulum. SE ultimately develops into a conduit containing electron-translucent cytoplasm. Eventually, mature SE is a tube filled only by the translucent cytoplasm, with sparse organelles tethered to the cell wall.

Conclusions: Although the activation of programmed cell death pathways was postulated, the persistence of SEs indicates that protoplast depletion is meticulously regulated by hitherto unidentified mechanisms. This research elucidates the sequential processes occurring in these cells during phloemogenesis and unveils novel insights into the mechanisms of selective autophagy.

Background: The CLV3/EMBRYO-SURROUNDING REGION (CLE) peptides control plant development and response to the environment. Key conserved roles include the regulation of shoot apical meristems and the long-distance control of root colonisation by nutrient-acquiring microbes, including the widespread symbioses with arbuscular mycorrhizal fungi and nodulation with nitrogen-fixing bacteria in legumes. At least some signalling elements appear to operate across both processes but clear gaps in our understanding remain. In legumes, although CLE peptide signalling has been examined in detail in symbioses, the role of this pathway in SAM development of legumes is poorly understood.

Scope: In this Research in Context, we review the literature to clarify the conserved and divergent elements of the CLAVATA-CLE peptide signalling pathways that control SAM, mycorrhizal colonisation and nodulation. We used novel pea mutants to determine the role of CLE signalling in regulating SAM development of a model legume, including interaction with temperature.

Conclusions: We found that in pea both genetic and environmental buffering of the CLE pathway influences SAM development. In pea, the CLAVATA2 (CLV2) CLE receptor-like protein and the unknown gene product encoded by the K301 gene are required to limit SAM size and floral organ production under cool temperatures. In contrast, the CLAVATA1 receptor-like kinase promotes SAM proliferation and appears to do so via a CLV2-independent pathway. In contrast, we found no role for the RDN1 enzyme, capable of arabinosylating CLE peptides, in SAM development. Future studies in other legumes are required to examine the role of other CLE peptide signalling elements in SAM control. Studies in non-vascular mycorrhizal hosts could explore if symbioses control is also an ancestral role for this signalling pathway.

Background and aims: Spatial variation in plant-pollinator interactions is a key driver of floral trait diversification. A so far overlooked qualitative aspect of this variation is the behavioural component on flowers that relates to the pollinator fit. We tested the hypothesis that variation in pollinator behaviour influences the geographical pattern of phenotypic selection across the distribution range of the oil-producing Krameria grandiflora (Krameriaceae). This variation mainly involves the presence or absence of flag petal grasping, which is only performed by representatives of Centris (Centridini, Apidae), an oil-collecting bee group highly associated with Krameriaceae pollination.

Methods: We quantified variation in floral traits and fitness and estimated pollinator-mediated selection in five populations at a large geographical scale comprising the entire species range. In each population, we sampled individual pollen arrival and germination as a fitness measure, indicating pollination success and pollination performance, which was then relativized and regressed on standardized flower-pollinator fit (flag-stigma distance), advertisement (sepal length) and reward (oil volume) traits. This generated mean-scaled selection gradients used to calculate geographical selection dispersion.

Key results: Unexpectedly, stronger selection was detected on the flower-pollinator fit trait in populations highly associated with the absence of flag petal grasping. Geographical variation in selection was mainly attributed to differential selection on the flag-stigma distance generating a selection mosaic. This may involve influences of a spatial variation in pollinator behaviour as well as composition and morphology.

Conclusions: Our results show the adaptive significance of the specialized flag petals of Krameria in the absence of the grasping behaviour and highlight the contribution of geographical variation in pollinator behaviour on flowers in driving selection mosaics, with implications for floral evolution, adaptation to pollinator fit and phenotypic diversity in specialized systems.