Tapetum Type Research Articles

Review on tapetal ultrastructure in angiosperms

The appearance of new cellular structures and characteristics in the tapetum suggests that there is still much to discover that would help to better understand the tapetum functions. The ultrastructure of the tapetum provides important information for the understanding of the functions performed by this tissue. Since there are no reviews on the subject, we aim to collect all the detailed information about the tapetum ultrastructure present until this moment in order to lay the foundations for future research. Detailed information on the tapetal ultrastructure of 80 species from 45 different families: 2 species with invasive non-syncytial tapetum, 11 with plasmodial and 67 with a secretory tapetum was collected. These studies allowed to establish (a) the most usual cytological characteristics of this tissue, (b) unique characteristics and/or cellular structures in tapetum cells, (c) the ultrastructural changes that occur in different types of tapetum, during the progress of microsporogenesis and microgametogenesis, and (d) the most recognized ultrastructural traits of the tapetum that cause androsterility. The structure of these cells is related to their function in each developmental stage. Since most species present their particular ultrastructure and may sometimes, share some traits within families, there is not a model plant on tapetum ultrastructure. However, knowing the general cytological aspect of the tapetum may help distinguish between patterns of cytoplasmic disorganization due to tapetum degeneration from technical failures of the preparation. Moreover, as the amount of species analyzed increases, unknown tapetal organelles or traits may be identified that might be associated to particular functions of this tissue. On the other hand, different ultrastructural changes may be related to the metabolisms and the regulation of normal/abnormal tapetum development.

Tapetum Types and Forms in Angiosperms

Abstract Based on the analysis of literature and our own data, we have suggested a new version of the typification of types and forms of the tapetum. It is proposed to distinguish two types of tapetum: parietal and periplasmodial. Parietal tapetum lines the locule of microsporangium and this position is maintained throughout the development. A periplasmodial tapetum is characterised by the formation of a coenocyte as a result of the fusion of protoplasts, while the cytoplasm and nucleus are located not only between the developing microspores and pollen grains, but also come into contact with the inner layers of the cavity. The differences between tapetum types relate to the peculiarities of structural and temporal reorganisation in anther development. The protoplasts that form after the disappearance of the cell walls (usually at the stage of microspore tetrad, or after their disaggregation), gradually break down (form 1 – typical parietal tapetum), or they form protrusions inside the microsporangium cavity (form 2 – amoeboid tapetum). The protoplasts in the periplasmodial tapetum are formed before or during meiosis. They fuse resulting in a symplast. It is possible to distinguish two forms of periplasmodial tapetum: combining and invasing of protoplasts into the locule of microsporangium (form 1 – typical periplasmodial tapetum), and almost or partly fusion of protoplasts, which do not organise the invasions and maintain the initial position (form 2 – bordering symplast). Data on the diversity and structure of the tapetum, like any other characters, are used to clarify the position of taxa on the phylogenetic tree.

Does Moonlight Increase Predation Risk for Elusive Mammals in Costa Rica?

An increasing body of evidence indicates that moonlight influences the nocturnal activity patterns of tropical mammals, both predators and prey. One explanation is that brighter moonlight is associated with increased risk of predation (Predation Risk hypothesis), but it has also been proposed that nocturnal activity may be influenced by the sensory ecology of a species, with species that rely on visual detection of food and danger predicted to increase their activity during bright moonlight, while species relying on non-visual senses should decrease activity (Visual Acuity hypothesis). Lack of an objective measure of “visual acuity” has made this second hypothesis difficult to test, therefore we employed a novel approach to better understand the role of lunar illumination in driving activity patterns by using the tapetum lucidum as a proxy for “night vision” acuity. To test the alternative predictions, we analyzed a large dataset from our long-term camera trap study in Costa Rica using activity overlap, relative abundance, and circular statistical techniques. Mixed models explored the influence of illumination factors (moonrise/set, cloud cover, season) and night vision acuity (tapetum type) on nocturnal and lunar phase-related activity patterns. Our results support the underlying assumptions of the predation risk and visual acuity models, but indicate that neither can fully predict lunar-related activity patterns. With diurnal human “super predators” forcing a global increase in activity during the night by mammals, our findings can contribute to a better understanding of nocturnal activity patterns and the development of conservation approaches to mitigate forced temporal niche shifts.

Developmental and ultrastructural characters of the pollen grains and tapetum in species of Nymphaea subgenus Hydrocallis

Variations in pollen characters and tapetum behavior were recently acknowledged in the early-divergent family Nymphaeaceae and even within the genus Nymphaea, which probably is not monophyletic; some traits such as infratectum and tapetum type are also a matter of different interpretations. In this study, developmental characters of the pollen grains and tapetum in Nymphaea subgenus Hydrocallis are provided for the first time. Observations were made in N. amazonum, N. gardneriana, and N. prolifera using light, scanning, and transmission electron microscopy. Tapetum is of the secretory type and produces orbicules. At microspore and pollen grain stages, the distal and proximal walls differ considerably. This result supports the operculate condition of the aperture in Hydrocallis, and such aperture might be plesiomorphic for Nymphaeoideae. The infratectum is intermediate, composed of inter-columellae granular elements, robust columellae consisting of agglomerated granules, complete columellae, and fused columellae. Narrow microchannels are present and persist until the mature pollen grain stage. The membranous granular layer is often present in the pollen grains of Nymphaeaceae. In N. gardneriana, this layer is most probably a component of the intine because it is lost after acetolysis. Orbicules in the Nymphaeaceae are characterized as spherical or subspherical, with a smooth sporopolleninic wall that surrounds an electron-lucent core and with individual orbicules that usually merge to give irregular aggregations. The aperture, pollen wall ultrastructure, and the tapetum of the studied species are discussed in an evolutionary and systematic context, and these characters are also compared with those of other angiosperm lineages.

Pollen structure and development in Nymphaeales: insights into character evolution in an ancient angiosperm lineage.

A knowledge of pollen characters in early-diverging angiosperm lineages is essential for understanding pollen evolution and the role of pollen in angiosperm diversification. In this paper, we report and synthesize data on mature pollen and pollen ontogeny from all genera of Nymphaeales within a comparative, phylogenetic context and consider pollen evolution in this early-diverging angiosperm lineage. We describe mature pollen characters for Euryale, Barclaya, and Nymphaea ondinea, taxa for which little to no structural data exist. We studied mature pollen for all nymphaealean genera using light, scanning electron, and transmission electron microscopy. We reviewed published reports of nymphaealean pollen to provide a comprehensive discussion of pollen characters in water lilies. Nymphaeales exhibit diversity in key pollen characters, including dispersal unit size, ornamentation, aperture morphology, and tapetum type. All Nymphaeales pollen are tectate-columellate, exhibiting one of two distinct patterns of infratectal ultrastructure-a thick infratectal space with robust columellae or a thin infratectal space with thin columellae. All genera have pollen with a lamellate endexine that becomes compressed in the proximal, but not distal wall. This endexine ultrastructure supports the operculate hypothesis for aperture origin. Nymphaeaceae pollen exhibit a membranous granular layer, which is a synapomorphy of the family. Variation in pollen characters indicates that significant potential for lability in pollen development was present in Nymphaeales at the time of its divergence from the rest of angiosperms. Structural and ontogenetic data are essential for interpreting pollen characters, such as infratectum and endexine ultrastructure in Nymphaeales.

Exine and tapetum development in Symphytum officinale (Boraginaceae). Exine substructure and its interpretation

After detailing the exine ontogeny, our purpose was to find out whether the sequence of sporoderm developmental events corresponds to self-assembling micellar mesophases, initiated by genomically determined physicochemical parameters and induced by surfactant glycoproteins at increasing concentrations. Indeed, a scaffolding of the future exine, i.e., the glycocalyx, initiates with scattered clots, which then appear as clusters of spherical and worm-like micelles, derived from surface-active glycoproteins. At the middle tetrad stage, a continuous layer of the glycocalyx emerges, consisting of parallel, tightly packed cylinder-like units, which we interpret as a layer of cylindrical micelles, the so-called middle mesophase. These units bear dark-contrasted particles, arranged in strings or columns. These sites of the glycocalyx units–micelles accumulate initial sporopollenin, hence the term “sporopollenin acceptor particles” (SAPs). This process leads to the appearance of procolumellae at the late tetrad stage. The glycocalyx units are rooted into callose and into the microspore cytoplasm. After formation of the tectum and the foot layer, the endexine initiates as a thin layer, and the latter develops into a very thick layer in the post-tetrad period. When callose disintegrates, “bouquets” of SAPs become evident on the tectum, which were evidently hidden inside the callose layer; these structures self-assemble into supratectal gemmae. An unusual, “hybrid” type of tapetum was observed. What is observed in Symphytum exine development allows us to obtain more evidence for the hypothesis of the participation of micellar self-assembly in sporoderm development and to bring together the concepts of micelles and of SAPs.

Relationships between Tapetum, Loculus, and Pollen during Development

Various parts of the anther (walls, tapetum, locular fluid, meiocytes, microspores) cooperate for correct pollen development. To show the different types of relationships possible between these parts, we considered the following characteristics, alone and in combination: types of tapetum, types of pollen‐dispersing unit, form of loculus, amount of locular space and fluid, number of pollen grains in transverse sections of the anther and in the loculus, and hydration status of pollen at dispersal. The different relationships between pollen, loculus, and tapetum should enable uniform nourishment of grains in the loculus and ensure a high percentage of viable grains. Two opposite modes were identified: direct and indirect nourishment of grains, the latter occurring when locular fluid is more or less abundant between the tapetum and the grains. The amount of space between developing grains determines different manners of grain nourishment and modes of pollen presentation for dispersal. Cyclosis, which is presu...

A Review of the Distribution of Plasmodial and Invasive Tapeta in Eudicots

The tapetum, a nutritive tissue necessary for microspore development, is of two basic types in angiosperms: secretory and plasmodial. A third type, invasive nonsyncytial, is possibly intermediate. Secretory tapeta are plesiomorphic in angiosperms, and plasmodial and invasive tapeta are derived types that have evolved several times in early‐divergent angiosperms and particularly in monocots. Many eudicots have secretory tapeta. In this article, records based on new observations for plasmodial and invasive tapeta in eudicots are presented, together with a literature survey. The data indicate that these tapetal types have evolved independently several times in eudicots, particularly in later‐branching lineages. They are rare in early‐divergent eudicots, where they occur only in Berberis and Mahonia (Berberidaceae: Ranunculales). They are recorded in some Amaranthaceae s.l. (Caryophyllales) and in some rosids. Plasmodial and invasive tapeta are more frequent in asterids, where they occur in several families, together with the secretory type. Plasmodial tapeta predominate in Asteraceae (Asterales) and Caprifoliaceae s.l. (Dipsacales). In eudicots, tapetum type is often variable within families or even genera, unlike in early‐divergent angiosperms and especially monocots, where a single tapetum type usually characterizes families or orders. In eudicots, the plasmodium usually forms after the microspores are released from the tetrads, unlike in monocots, where it forms earlier, surrounding the tetrads.

Pollen and anther characters in monocot systematics

Pollen and anther characters are potentially informative in higher-level systematics of monocotyledons. Several characters of monocot pollen and anthers (tapetum type, microsporogenesis type and inaperturate pollen) are reviewed here in relation to recent phylogenetic concepts of the group, and new data are presented for some critical taxa. The first-branching monocotyledon, Acorus , has a secretory tapetum but most other early branching taxa (i.e., most Alismatales, except Tofieldia ) are plasmodial. The lilioid orders, Pandanales, Dioscoreales, Liliales and Asparagales are almost uniformly secretory. The tapetum is more diverse within the commelinoid clade. Successive microsporogenesis predominates in the monocotyledons although the simultaneous type is of systematic significance within some orders, such as Dioscoreales,Asparagales and Poales. Inaperturate pollen (either "functionally monoaperturate" or "omniaperturate") occurs in every major monocot group. It predominates in Alismatales and Zingiberales, and is a synapomorphy for some Liliales and Asparagales.

Systematic Position ofXyris: Flower and Seed Anatomy

Flower anatomy, embryology, and seed anatomy are described for some Brazilian species of Xyris section Nematopus and reviewed with respect to the systematic position of Xyris and allied taxa in Commelinanae. Apart from tenuinucellate ovules (shared with Poales, Mayaca, and Eriocaulaceae), Xyris lacks some of the synapomorphies of other genera that are sometimes included in Xyridaceae (Aratitiyopea, Achlyphila, Abolboda, and Orectanthe), such as inaperturate spinulate pollen; Xyris has monosulcate reticulate pollen. There is an unusual degree of variation among different genera of Xyridaceae for characters such as tapetum type, indicating that the monophyly of the family requires testing. However, while several characters indicate two generic groups, there is much missing critical information for embryological and seed coat characters in other Xyridaceae.

Inaperturate Pollen in Monocotyledons

Inaperturate pollen is widespread in the monocotyledons, includes a diverse range of forms, and has arisen independently numerous times. Evidence for this comes from the phylogenetic distribution of inaperturate pollen and also from developmental and structural differences. There is no correlation between the production of inaperturate grains and either microsporogenesis type or tapetum type. Inaperturate pollen has phylogenetic significance within some groups, e.g., in Zingiberales, Liliales, and some Asparagales. Character states for inaperturate pollen are presented. It can broadly be divided into two types, “omniaperturate” and “functionally monoaperturate,” based on the thickening of the intine. The characters of omniaperturate pollen are adaptations that potentially increase the germination efficiency of the pollen. Both types sometimes occur in environments where pollen is not subject to desiccation and, thus, may remain viable with reduced exines.

Structure and systematics of Hanguana, a monocotyledon of uncertain affinity

Floral anatomy and some aspects of leaf and root anatomy of Hanguana are described for the first time and reviewed with respect to its systematic position in monocotyledons. Several characters support its placement in the commelinoid clade, including cell wall ferulates, silica bodies and tetracytic stomata with non-oblique cell divisions. Analysis of morphological data indicates that Hanguana is the sister taxon to Zingiberales. Characters supporting this association include spinulate inaperturate pollen, plasmodial tapetum type, mucilage-secreting intra-ovarian trichomes and modified septal nectaries. Gynoecial nectaries were present in male flowers (probably modified septal nectaries, as in some Zingiberales) and staminodial nectaries in female flowers examined.

Orbicules in angiosperms: Morphology, function, distribution, and relation with tapetum types

Orbicules, or Ubisch bodies, are sporopollenin particles lining the inner tangential and sometimes also the radial tapetal cell walls. They occur only in species with a secretory tapetum. The surface ornamentation of orbicules and pollen of the same species is often strikingly similar. Although orbicules were discovered more than a century ago, these structures remain enigmatic since their function is still obscure. Proposed hypotheses about their possible function are discussed. We also deal here with topics such as the possible allergenicity of orbicules and their representation in the fossil record. The use of orbicule characters for systematics is reviewed. The distribution of orbicules throughout the angiosperms, based on a literature review from the first report until today, is shown in a list with 314 species from 72 families. Those species found in the literature without orbicules are presented together with their tapetum type. We plotted this information on a dahlgrenogram to visualize the distribution of orbicules. Orbicules occur in all subclasses of the angiosperms. Their occurrence is not correlated with certain modes of pollination or habitats.

The tapetum and systematics in monocotyledons

This paper critically reviews the homologies and distribution of tapetum types in monocotyledons, in relation to their systematics. Two main types of tapetum are widely recognised: secretory and plasmodial, although intermediate types occur, such as the “invasive” tapetum described inCanna. In secretory tapeta, a layer of cells remains intact around the anther locule, whereas in the plasmodial type a multinucleate tapetal plasmodium is formed in the anther locule by fusion of tapetal protoplasts. In invasive tapeta, the cell walls break down and tapetal protoplasts invade the locule without fusing to form a plasmodium. When examining tapetum type, it is often necessary to dissect several developmental stages of the anthers. Secretory and plasmodial tapeta are both widely distributed in monocotyledons and have probably evolved several times, although there may be some systematic significance within certain groups. Among early branching taxa,Acorus andTofieldia have secretory tapeta, whereas Araceae and Alismatales are uniformly plasmodial. The tapetum is most diverse within Commelinanae, with both secretory and plasmodial types, and some Zingiberales have an invasive tapetum. Lilianae (Dioscoreales, Liliales, and Asparagales) are almost uniformly secretory.

Tapetum character states: analytical keys for tapetum types and activities

The different types of tapetum found in the spermatophyta are described, along with associated characters. The characters (taken singly, pairwise, or in multiple combinations) are (i) tapetum types; (ii) cell walls, tapetum types, and loculus; (iii) tapetal cells individually, tapetum types, and loculus; (iv) number of pollen grains enveloped by tapetal cells and type of pollen dispersing unit; (v) cell types and tapetum types; (vi) number of nuclei per cell and tapetum type; (vii) cycles of hyperactivity; (viii) exine formation; (ix) orbicles; (x) peritapetal membrane; (xi) plastid differentiation; (xii) stage of pollen development in which tapetal cells degenerate and type of pollen coat; (xiii) storage vacuoles; (xiv) sporophytic proteins; and (xv) devices of tapetal origin responsible for compound pollen formation and pollination. Examples are given and an analytical key of structural and functional diversity is provided as a helpful approach to the study of the tapetum. Key words: tapetum types, activities, pollen dispersing units.

Development of Tapet urn and Microspores in Canna L.: an Example of an Invasive but Non-syncytial Tapetum

An investigation of microsporogenesis in Canna L. revealed that the tapetum is invasive but non-plasmodial. Tapetai cell protoplasts are released as individuals. In the loculus they are at first more or less spherical but can produce amoeboid processes in late stages of microsporogenesis. They do not fuse with one another. Meiosis is normal and cytokinesis is successive. The implications of the novel type of tapetum are discussed.

THE CYTOLOGY OF POLLEN ABORTION IN C‐CYTOPLASMIC MALE‐STERILE CORN ANTHERS

Anther development of the C‐cytoplasmic male‐sterile (cms C) and the normal cytoplasm version (N) in the W182BN corn inbred was studied by light and electron microscopy. Deviation from normal pollen development was first observed in the tapetal cells at the tetrad stage of development. Two types of tapetal abnormalities were observed in plants with C cytoplasm. The first behaved like the N anther until the tetrad stage, when numerous small vacuoles appeared in the tapetal cells. Inner and radial tapetal cell walls broke down normally, but irregular Ubisch body deposition was observed, and exine development was inhibited and delayed. The tapetum and microspores disintegrated at the intermediate microspore stage. The second type of tapetum was highly vacuolated at the early tetrad stage, with dense inner and radial cell walls that remained intact and enlarged when the tetrads aborted. No organellar abnormalities, such as the mitochondrial changes observed in cms T, were observed in C anthers.

Embryological Studies in Phaseolus aconitifolius Jacq. Obs.

The life history of Phaseolus aconitifolius Jacq Obs. is described in detail. The male archesporium is unicellular. The anther wall is made up of five layers of cells. The secretory type of tapetum consists of uninucleate cells Some of the sporogenous cells remain sterile and divide the anther locule into many chambers. The pollen grains are two celled at anthesis. The mature ovule is campylotropous, bitegmic, and crassinucellate The nucellus persists for long time at the chalazal end of the embryo sac. The female archesporium is unicellular The parietal tissue consists of three to four layers of cells The megaspore tetrad is linear. The monosporic embryo sac conforms to the Polygonum type. Fertilization is porogamous. Syngamy and triple fusion occur almost simultaneously Endosperm ab initio is free nuclear. However, part of it later becomes cellular. The free nuclear portion functions as an haustorium The mature seed is nonendospermic. The embryo follows the Onagrad type of development. The mature seed c...

A NOTE ON THE EVOLUTIONARY STATUS OF TAPETAL TYPES IN DICOTYLEDONS

SUMMARYThe glandular type of tapetum in dicotyledons is shown statistically to be correlated with four primitive characters. It is concluded, therefore, that this kind of tapetum is primitive, while the amoeboid type is advanced.