Heidemarie Halbritter

Preparing Living Pollen Material for Scanning Electron Microscopy Using 2, 2-Dimethoxypropane (DMP) and Critical-Point Drying

A simple, quick, and inexpensive method for preparing any type of pollen material is described. Fresh, mature pollen grains without previous chemical fixation are dehydrated in acidified 2, 2-dimethoxypropane (DMP) followed by critical-point drying in CO2. This method helps preserve size, shape and surface details of both fragile pollen grains and pollen grains that are heavily covered with pollenkitt. Handling of already opened anthers and avoiding loss of pollen grains during the preparation steps are also described. With the DMP direct method, many morphologically and functionally important details that may be lost by conventional methods are well preserved without shrinkage, distortion, or dissolution. The DMP direct method is performed with pollen grains and the results are compared with two other frequently used methods, acetolysis and critical-point drying of chemically fixed material.

Principal modes of infoldings in tricolp(or)ate Angiosperm pollen

Angiosperm pollen grains can absorb or release water quickly. The respective degree of hydration has great influence upon the actual pollen grain shape and is, to a certain extent, reversible (harmomegathic effect). In the hydrated condition the majority of pollen grains are usually spherical, but in the dry condition they are infolded in a highly variable manner. This paper demonstrates many kinds of infolding within dicotyledonous tricolp(or)ate pollen from several angiosperm families. In most cases the foldings are directionally oriented, but it is only possible to predict the final form in dry condition to a limited degree.

Morphologie und systematische Bedeutung des Pollens der Bromeliaceae

Abstract Der Pollen von 338 Arten aus 31 Gattungen der Familie der Bromeliaceae wurde untersucht und mit der systematischen Stellung der Arten in Verbindung gebracht. Der uberwiegende Teil der Bromeliaceen besitzt sulcaten, ein kleinerer Teil poraten oder inaperturaten Pollen mit reticulater, foveolater oder glatter Oberflache. Die Form und Ausbildung des Sulcus — es lassen sich 6 verschiedene Typen unterscheiden — kann in manchen Fallen als systematisches Merkmal dienen. Insgesamt spiegelt die Pollenmorphologie die Verwandtschaftsbeziehungen in der Familie wider. Gut abgegrenzte Sippen sind auch pollenmorphologisch einheitlich, umgekehrt sind systematisch problematische Sippen auch im Pollenbau heterogen. The pollen morphology of 31 genera (338 species) of the Bromeliaceae was investigated. The pollen grains are mostly reticulate, but also foveolate or rarely smooth. 3 main aperture types occur: porate pollen (restricted to subfamily Bromelioideae), inaperturate pollen, and (predominantly) sulcate pollen...

The Basic Pollen Wall Types in Araceae

An ultrastructural investigation of 60 species, representing 47 genera, of Araceae showed two basic pollen wall types, each with two subtypes. The two main types are distinguished by presence (type 1) or absence (type 2) of an acetolysis‐resistant ektexine. The subtypes are differentiated by a structured (type 1a) or unstructured (type 1b) ektexine, respectively, and the presence (type 2a) or absence (type 2b) of polysaccharidic wall ornamentations. A characteristic of all types is a spongy endexine, which is electron dense after thiocarbohydrazide–silver proteinate staining and is only partially resistant to acetolysis.

THE SPINY POLLEN WALL IN SAUROMATUM (ARACEAE)-WITH SPECIAL REFERENCE TO THE ENDEXINE

Pollen grains of Sauromatum are inaperturate with a microechinate exine ornamentation. The outer pollen wall is formed by the spongious endexine and spines. An acetolysis-resistant ektexine is missing. The endexine appears electron dense after TCH-Sp staining and electron translucent after the Thiéry-test. The spines are polysaccharidic in nature. Acetolysis leads to a considerable increase in pollen size and destroys the spines. PAS-positive Ubisch body-like structures are found within the anther loculus. The tapetum is of the amoeboid type. Spines as well as Ubisch bodylike structures are formed by the tapetum at the stage of first pollen mitosis

Thread-forming structures in angiosperm anthers: their diverse role in pollination ecology

This paper reviews the origin, nature, systematic distribution, and the respective function of the highly variable and diverse thread-forming structures in angiosperm anthers (including somewhat similar, rare features in ferns and gymnosperms). On one hand, such threads may function as pollen-connecting vectors in forming pollen dispersal units, as sporopollenin threads (viscin threads), e.g. in Onagraceae, or sporopollenin-less threads in surprisingly many other angiosperm families. On the other hand, as is known from theImpatiens — “pollen basket”, threads or ropes may be involved in pollen presentation. In addition, for the first time two new examples of “pollen baskets” in Boraginaceae and Scrophulariaceae are reported. InEchium the basket is formed by cellular elements from the modified septal regions, whereas inEsterhazya a similar effect is achieved in an analogous manner by trichomes of the epidermal layer of the thecal wall. There is obviously a different function of these seemingly very similar baskets: inEchium the feature acts preferably as a pollen presentation agent, whereas inEsterhazya the primary function is to prevent all the pollen from being dispersed too soon.

Palynology of the perigoniate Aroideae: Zamioculcas, Gonatopus and Stylochaeton (Araceae)

The pollen of the perigoniate Aroideae sensu Mayo et al. (1997) ( Zamioculcas Schott, Gonatopus Hook. f. ex Engl. and Stylochaeton Lepr.) differs ultrastructurally from that of the aperigoniate Aroideae in several important exine and aperture characters. The almost identical zona-aperturate pollen of Zamioculcas and Gonatopus has outside the aperture an elaborated, thick ectexine, while the aperture consists of a thin, but continuous ectexine and a thick, lamellate endexine. In contrast, the omniaperturate pollen of Stylochaeton has a thin, not clearly stratified ectexine and a thin, heterogeneous endexine below. However, the zona-aperturate pollen of Zamioculcas and Gonatopus deviates significantly from the superficially similar zona-aperturate pollen of the unrelated Monstereae (e. g., Monstera Adans., Amydrium Schott): in the apertures of Monstera or Amydrium both the thin, but continuous ectexine and the lamellate endexine, which are typical features for Zamioculcas and Gonatopus , are absent. The palynological data underline not only the present classification of Zamioculcas , Gonatopus and of Stylochaeton into two tribes (Zamioculcadeae and Stylochaetoneae) and the differences of both tribes from the other Aroideae, but show also significant deviations in the respective zona-aperturate condition in Monstereae (Monsteroideae) and Zamioculcadeae (Aroideae).

Pollen walls of Araceae, with special reference to their fossilization potential

Araceae, a basal monocot family, has a very poor fossil record, especially with regard to pollen grains. An ultrastructural study of Araceae pollen walls was undertaken to answer the questions: which pollen is resistant to decay and will appear in the fossil record? and which pollen has a smaller fossilization potential and why? The wall strata of Araceae pollen differ in morphology and chemical composition. Only a minority of all Araceae pollen grains has the ?conventional? type of exine architecture consisting of an acetolysis-resistant ektexine upon a generally thin, but ratherspongy endexine. Pollen grains with this type of exine have a high fossilization potential and should be found unmodified in the fossil record. In contrast, the majority of Araceae pollen has a strikingly different, newly discovered exine architecture: a thick, spongy, acetolysis-resistant endexine is covered by an outer stratum, which either may or may not be resistant to acetolysis. We conclude from these features that the pote...

The convergent evolution of exine shields in angiosperm pollen

Abstract The appearance of the pollen grains (or tetrads) of some taxa of only distantly related angiosperm families Berberidaceae (Mahonia), Bignoniaceae (Catalpa), Euphorbiaceae (Phyllanthus), Iridaceae (Iris sect. Juno), Malpighiaceae (Malpighia, Banisteriopsis, Heteropteris) and Martyniaceae (Ibicella, Proboscidea) is very similar. For this pollen type we propose the term “clypeate” (= covered with shields), i.e. “pollen grains with large, isolated, polygonal or circular (s)exinous shields, separated by grooves”. Despite their similar appearance both their aperture condition and wall stratification are different. Phyllanthus x elongatus and the Malpighia species investigated have (panto-) porate pollen grains, and local intine thickenings are present beneath the pores, which are located between the exine shields in a regular (Phyllanthus) or more irregular manner (Malpighia). This pantoporate condition differs markedly from the aperture condition which is present in all of the other taxa investigated ...

Pollen‐connecting threads in Gymnocalycium (Cactaceae): Their origin, function, and systematic relevance

In dehisced anthers of all Gymnocalycium species (Cactaceae, subfam. Cactoideae, tribe Trichocereae) investigated so far, a small percentage of pollen grains are aggregated by only a few threads. These threads are located at the margin of the dehiscing zone of stomium and septum. They are not part of the pollen grain wall, and they are not resistant to acetolysis, thus indicating the absence of sporopollenin. The threads originate in part from modified stomium/septum cells (split cell walls, cytoplasmic remnants and lipid droplets) and in part from pollenkitt produced by the—now desintegrated—tapetal cells. This highly viscous, gum‐like substance along the modified stomium and septum cell walls may assume an irregular thread‐like habit before or during dehiscence. Pollen aggregates may be formed frequently by different sticky or non‐sticky agents. A detailed conspectus on origin, nature, significance and function of various types of pollen‐connecting agents forming threads is presented. Pollen‐connecting ...