Aluminum hyperaccumulation in angiosperms: A review of its phylogenetic significance

Aluminum phytotoxicity and genetically based aluminum resistance has been studied intensively during recent decades because aluminum toxicity is often the primary factor limiting crop productivity on acid soils. Plants that grow on soils with high aluminum concentrations employ three basic strategies to deal with aluminum stress. While excluders effectively prevent aluminum from entering their aerial parts over a broad range of aluminum concentration in the soil, hyperaccumulators take up aluminum in their aboveground tissues in quantities above 1000 ppm; that is, far exceeding those present in the soil or in the nonaccumulating species growing nearby. In between these two extremes are indicator species, representing intermediate responses. A list of aluminum hyperaccumulators in angiosperms is compiled on the basis of data in the literature. Aluminum hyperaccumulators include mainly woody, perennial taxa from tropical regions. Recent molecular phylogenies are used to evaluate the systematic and phylogenetic implications of the character. As was hypothesized earlier, our preliminary conclusions support the primitive status of aluminum hyperaccumulation. According to the APG classification system, this phytochemical character is found in approximately 45 families, which belong largely to the eudicots. Aluminum hyperaccumulators are particularly common in basal branches of fairly advanced groups such as rosids (Myrtales, Malpighiales, Oxalidales) and asterids (Cornales, Ericales, Gentianales, Aquifoliales), but the character has probably been lost in the most derived taxa. The feature is suggested to characterize approximately 18 families (e.g., Anisophylleaceae, Cunoniaceae, Diapensiaceae, Memecylaceae, Monimiaceae, Rapateaceae, Siparunaceae, Vochysiaceae, and several monogeneric families). In 27 other families, aluminum hyperaccumulation is restricted to subfamilies, tribes, or genera. Further analyses of a broader range of taxa are needed to examine the origin and taxonomic significance of aluminum hyperaccumulation in several clades. Aluminum hyperaccumulation provides an evolutionary model system for the integration of different biological disciplines, such as systematics, ecology, biogeography, physiology, and biochemistry. Therefore, multidisciplinary approaches are needed to make further progress in understanding the biology of aluminum hyperaccumulators.     

Wood anatomy of Rauvolfioideae (Apocynaceae): a search for meaningful non-DNA characters at the tribal level

Wood anatomical studies in the economically important Apocynaceae or dogbane family are fragmentary. This study represents a first attempt to unravel the phylogenetic significance and major evolutionary trends in the wood of the family, using existing and new microscopic wood observations within the large subfamily Rauvolfioideae. On the basis of LM and SEM observations of 91 species representing all 10 currently recognized tribes, we found that most of the tribes are characterized by a unique combination of wood characters, such as vessel grouping, vessel element length, fiber type, frequency of uniseriate rays, and fused multiseriate rays. Climbing rauvolfioid taxa can generally be distinguished from erect species by their wider vessels, tendency to form paratracheal axial parenchyma, presence of tracheids, and occurrence of laticifers in rays. With respect to the entire family, there is a general phylogenetic trend toward shorter vessel elements, a higher proportion of vessels in multiples and more vessels per multiple, higher tracheid abundance, more paratracheal parenchyma, and fewer cells per axial parenchyma strand in the more derived Apocynaceae. Most of these evolutionary trends are likely to be triggered by drier environmental conditions and/or shifts from an erect to a climbing habit.     

A critical comparison of extant batch respirometric and substrate depletion assays for estimation of nitrification biokinetics

Estimation of nitrification biokinetics has been conducted using different batch techniques via measurement of nitrogen species or surrogates such as oxygen (respirometry). However, there are no reports that specifically compare kinetic parameters estimated from respirometry with those from direct nitrogen species measurements. In this study, we evaluated the ability of parameter estimates from isolated and optimally designed complete extant respirometric assays to describe concurrently obtained ammonia and nitrite depletion profiles. Additionally, we mapped the different parameter sets to steady-state bioreactor performance. Using multivariate analysis of variance, we found that estimates from respirometric and substrate depletion assays were predominantly statistically different at the 95% confidence level. The sensitivity of predicted stead-state nitrifying reactor performance to differences in parameter estimates was highest close to the limiting solids retention time (SRT). However, at characteristic nitrifying SRTs the predicted reactor performance using parameter estimates from respirometry and substrate depletion assays were in very close correspondence. Therefore, parameters estimated from extant respirometric assays can be used to adequately predict nitrifying reactor performance.     

Floral and inflorescence morphology and ontogeny in Beta vulgaris, with special emphasis on the ovary position

Background and Aims

In spite of recent phylogenetic analyses for the Chenopodiaceae–Amaranthaceae complex, some morphological characters are not unambiguously interpreted, which raises homology questions. Therefore, ontogenetic investigations, emphasizing on ‘bracteoles’ in Atripliceae and flowers in Chenopodioideae, were conducted. This first paper presents original ontogenetic observations in Beta vulgaris, which was chosen as a reference species for further comparative investigation because of its unclarified phylogenetic position and its flowers with a (semi-)inferior ovary, whereas all other Chenopodiaceae–Amaranthaceae have hypogynous flowers.

Methods

Inflorescences and flowers were examined using scanning electron microscopy and light microscopy.

Key Results

Floral development starts from an inflorescence unit primordium subtended by a lateral bract. This primordium develops into a determinate axis on which two opposite lateral flowers originate, each subtended by a bracteole. On a flower primordium, first five tepal primordia appear, followed by five opposite stamen primordia. Simultaneously, a convex floral apex appears, which differentiates into an annular ovary primordium with three stigma primordia, surrounding a central, single ovule. A floral tube, which raises the outer floral whorls, envelops the ovary, resulting in a semi-inferior ovary at mature stage. Similarly, a stamen tube is formed, raising the insertion points of the stamens, and forming a staminal ring, which does not contain stomata. During floral development, the calyces of the terminal flower and of one of the lateral flowers often fuse, forming a compound fruit structure.

Conclusions

In Beta vulgaris, the inflorescence is compound, consisting of an indeterminate main axis with many elementary dichasia as inflorescence units, of which the terminal flower and one lateral flower fuse at a later stage. Floral parts develop starting from the outer whorl towards the gynoecium. Because of the formation of an epigynous hypanthium, the ovary becomes semi-inferior in the course of floral development.Key words: Beta vulgaris, Chenopodiaceae, floral ontogeny, gynoecial development, epigynous hypanthium, semi-inferior ovary, inflorescence ontogeny, LM, SEM     

Staminodes: Their morphological and evolutionary significance

Different approaches to circumscribe staminodial structures in the angiosperms are reviewed. The need for a morphological distinction between “true staminodes” (derived from stamens or homologous to stamens) and “pseudostaminodes” (nonhomologous to stamens) is emphasized. In phylogenetic studies the term “staminode” is often used uncritically, without knowledge of the true homology of these structures. Staminodes are either whole organs (outer tiers or whorls, namely petals, intermediate tiers, or organs within a tier), or partial organs. This article aims to discuss the shortcomings of the past and current approach of staminodes and proposes definitions of staminode types for use as characters in phylogenetic analyses. Staminodial structures should be classified according to their position and function in the flower. Both aspects are intricately linked and make the identification of staminodes sometimes problematic. Shifts in time (heterochrony) and space (heterotopy or homeosis) make that a regressing organ either aborts completely or becomes remodeled into something new. Petals are included in the definition of staminodes as they combine function and heterotopy. A hierarchical ordering of staminodial types is given and discussed. Three interdependent but possibly complementary functions are attached to the occurrence of staminodes: an attractive, nutritional, and structural function. The importance of staminodes for the evolution of the androecium and flower is demonstrated. The difficulty in unmasking pseudostaminodes, comprising receptacular disks, is demonstrated. The value and shortcomings of molecular-based interpretations of staminodes are discussed. It is shown that the decision to recognize a staminode from receptacular emergences often relies on unstable grounds and remains largely dependent on the acceptance of a given phylogenetic background.     

Morphology, anatomy, and taxonomic position of Pagameopsis (Rubiaceae-Rubioideae)

Morphological and anatomical features (including wood anatomy and pollen morphology) of the small neotropical genusPagameopsis (Rubiaceae-Rubioideae) are discussed and illustrated. The fused ovaries, fenestrate corolla tube, basally attached anther filaments, and absence of raphides are especially noteworthy.Pagameopsis is definitely not a member of the Psychotrieae because of significant differences in wood anatomy and gynoecial and fruit structure. A close affinity with Gaertnereae seems doubtful for similar reasons. The taxonomic affinities ofPagameopsis remain obscure. The genus shows similarities with several taxa of the Rubioideae, such as Coccocypseleae, Morindeae, Hedyotideae, andMetabolos. The absence of raphides, on the other hand, makes a position in the Rubioideae doubtful.     

Modern pollen studies in the territory of Sagalassos (Southwest Turkey) and their use in the interpretation of a Late Holocene pollen diagram

Modern pollen precipitation studies were carried out on a regional scale in the territory of the classical city of Sagalassos (Southwest Turkey). 57 moss cushions and 7 soil samples from different vegetation types were analysed palynologically. The resulting pollen spectra were grouped into 14 vegetation groups, which were examined using discriminant analysis and principal components analysis. These numerical procedures are applied to display the structure in the data set in a comprehensive way. Some of the modern spectra groups seem to be well-defined, whereas others are difficult to distinguish from each other. After the relationships between the modern pollen spectra had been analysed, the fossil data from a core from the marsh of Gravgaz were added to the data set so that any similarities between fossil and modern spectra could be seen. A joint principal components analysis of the modern and fossil pollen spectra revealed that the pollen spectra from the earliest (ca. 2600-2500 BP; Cal. 830-590 BC till 790-520 BC) and the latest (starting at ca. 1300 BP; Cal. 660-780 AD) pollen assemblage zones have modern counterparts. On the other hand, the pollen spectra from the pollen assemblage zone dominated by Artemisia (ca. 2500-2300 BP; Cal. 790-520 BC till 410-210 BC) and from the pollen assemblage zone that indicated the practice of arboriculture (ca. 2300-1300 BP; Cal. 410-210 BC till 660-780 AD) have no close modern analogues, although individual tabulated pollen percentages revealed some similarities with some modern spectra groups.     

A floral ontogenetic study on the sister group relationship between the genus Samolus (Primulaceae) and the Theophrastaceae

The former Primulales used to be subdivided into the woody Theophrastaceae and Myrsinaceae, from the tropics and subtropics, and the herbaceous Primulaceae, which are mainly found in the temperate regions of the northern hemisphere. Recent analyses based on morphological as well as molecular data revealed a close relationship between the genus Samolus L. of Primulaceae and the monophyletic family Theophrastaceae. We studied the floral development of six species from four different genera of Theophrastaceae and compared it to floral ontogenetical data of Samolus valerandi L. to find support for a close relationship. Samolus and the members of Theophrastaceae share the presence of staminodes and a similar development of the placenta and the ovules. Apart from the different habit and distribution, however, we also observed some major differences between both lineages, such as the absence of common primordia in Theophrastaceae, the development of a gynoecial cap in Samolus, and the difference in development, shape, and structure of the staminodes. Therefore, we propose to keep Samolus separated from the genera of the Theophrastaceae, and we suggest that it be raised to family level.