Silvia Ulrich

The endexine: a frequently overlooked pollen wall layer and a simple method for detection

Abstract For the detection of pollen wall layers, the use of different staining methods for one and the same species is highly recommended. The usage of standard transmission electron microscopy (TEM) staining methods showed that the ektexine-layers have always the same contrast behaviour, while the endexine changes its electron opaqueness depending on the method used. However, the endexine can often not be discriminated from the other wall layers. A simple method to detect the endexine is the use of potassium permanganate, which stains the layer electron dense, producing a distinct contrast.

Amorphophallus: New insights into pollen morphology and the chemical nature of the pollen wall

Abstract In pollen characters, Amorphophallus is one of the most diverse genera in the Araceae. The present work is a critical survey of contradicting reports on the impact of acetolysis treatment on Amorphophallus pollen, on the chemical nature of the outer pollen wall layer and of electron-dense (dark) granules found within it. Furthermore, we wanted to clarify the pollen polarity and to test conclusions based on different preparation techniques. Pollen morphology of 25 species is investigated by light microscopy, scanning electron microscopy and transmission electron microscopy. Our results show that Amorphophallus pollen is not resistant to acetolysis treatment. The use of different transmission electron microscopy staining methods proved the polysaccharide nature of the outer pollen wall layer and of the granules within it. Moreover, an additional thin surface layer was found in all investigated species. Microspores in early and late tetrad stages show that the less convex side of the microspore is the proximal face and the more convex side the distal face. The extrusion of pollen in strands is illustrated for the first time by light microscopy and scanning electron microscopy. Furthermore, observations of pollen in water showed that in some of the investigated species the pollen wall is shed immediately before pollen tube formation.

Calla palustris (Araceae): New palynological insights with special regard to its controversial systematic position and to closely related genera

Almost all systematic treatments agree that Calla is a puzzling case, being a highly autapomorphic taxon with obscure relationships. In molecular-based classifications the variable placements of Calla within Aroideae conflict strongly with those in morphologically and anatomically based systematic classifications, which treat the genus as a subfamily (Calloideae) of its own. We studied the pollen morphology and ultrastructure of Calla by light and electron microscopy, and mapped the relevant pollen characters as well as some flower characters to the proposed placements of Calla within the Araceae as indicated in the various molecular phylogenies. Calla pollen is extraordinary within the entire Araceae. Pollen grains are small, and basically disulcate or with a ring-like aperture. The ornamentation is psilate to perforate, and the pollen wall consists of a sporopolleninous tectate-columellate exine. These pollen characters are shared with those of several earlier-diverging aroid taxa, especially with those of subfamily Zamioculcadoideae, whereas pollen characters in members of subfamily Aroideae deviate significantly. These findings are in accordance with other floral characters. Therefore, we propose that Calla is best placed in a transition zone between either subfamily Zamioculcadoideae (Stylochaeton clade) and subfamily Aroideae (Aroideae clade) or between subfamily Zamioculcadoideae (Stylochaeton clade) and subfamily Lasioideae.

PalDat 3.0 – second revision of the database, including a free online publication tool

Abstract PalDat is the world’s most comprehensive pollen database. At present, the database provides about 22 000 pollen pictures from more than 2500 plant species. Each dataset includes a detailed description of the pollen grain, light- and electron-microscopy images of the pollen grain, images of the plant/inflorescence/flower and relevant literature. Founded in 1997, PalDat had a major revision in 2015. The database contains tools for pollen identification and online publication. Online access to the database and data submission (www.paldat.org) are free of charge.

Forensic Palynology: How Pollen in Dry Grass Can Link to a Crime Scene

This chapter describes a homicide case of a baby and the forensic potential of pollen in dry grass. Dry grass is a good source for pollen. Pollen analysis gave a very characteristic pollen assemblage, dominated by grass pollen and a fungal spore. The dry grass in which the baby’s corpse was embedded could be traced back to the crime scene. An accompanying investigation of various dry grass samples showed that each one had a unique pollen assemblage. This case reintroduced Forensic Palynology to Austria.

Adaptations for insect‐trapping in brood‐site pollinated Colocasia (Araceae)

The Araceae include both taxa with rewarding and deceptive trap pollination systems. Here we report on a genus in which rewarding and imprisonment of the pollinators co-occur. We studied the pollination of four species of Colocasia in Southwest China and investigated the morpho-anatomical adaptations of the spathe related to the attraction and capture of pollinators. All four species were pollinated by drosophilid flies of the genus Colocasiomyia. The flies are temporally arrested within the inflorescence and departure is only possible after pollen release. Trapping of the flies is accomplished by the closure of the spathe during anthesis. Moreover, in two species the spathe is covered with papillate epidermal cells known to form slippery surfaces in deceptive traps of Araceae. However, in Colocasia the papillae proved not slippery for the flies. The morpho-anatomical properties of the spathe epidermis indicate that it is an elaborate osmophore and serves for the emission of odours only. Despite its similarity to deceptive traps of other aroids, Colocasia and Colocasiomyia have a close symbiotic relationship, as the attracted flies use the inflorescence as a site for mating and breeding. The trap mechanism has presumably evolved independently in Colocasia and is supposed to facilitate more efficient pollen export.

Pollen Morphology and Ultrastructure

The study of pollen should encompass all structural and ornamental aspects of the grain. Pollen morphology is studied using LM and SEM and is important to visualize the general features of a pollen grain, including, e.g., symmetry, shape, size, aperture number and location, as well as ornamentation. TEM investigations are used to highlight the stratification and the uniqueness of pollen wall layers as well as cytoplasmic features. The following sections explain the most important structural and sculptural pollen features a palynologist should observe.

Misinterpretations in Palynology

The description of pollen ornamentation depends on three major parameters (1) the interpretations of the palynologist (which are subjective), (2) the pollen terminology applied, and (3) the magnification, resolution, and methods used.

Palynology: History and Systematic Aspects

Palynology is the science of palynomorphs, a general term for all entities found in palynological preparations (e.g., pollen, spores, cysts, diatoms). A dominating object of the palynomorph spectrum is the pollen grain. The term palynology was coined by Hyde and Williams (1955; Fig. 1). It is a combination of the Greek verb paluno (пαλύνω, “I strew or sprinkle”), palunein (пαλύνeιν, “to strew or sprinkle”), the Greek noun pale (пαλƞ, in the sense of “dust, fine meal,” and very close to the Latin word pollen, meaning “fine flour, dust”), and the Greek noun logos (λογος, “word, speech”).

Methods in Palynology

Multiple methods and techniques should be used when investigating pollen grains in order to provide comprehensive and accurate information about pollen morphology and ultrastructure (see also “Misinterpretations in Palynology”). The preparation methods used depend on the material to be studied, if the pollen grains are to be obtained from recent flower material (herbarium sheets, newly collected) or from various sedimentary rocks, sediments or soils (fossil to subfossil pollen). Recent and fossil pollen grains are easily studied using both LM and SEM, but recent pollen grains are also more often studied using TEM.