Links between morphology and function of the pollen wall: an experimental approach

The wall of pollen grains exhibits morphological variation in many features including apertures, ornamentation and thickness, but the function of these characters remains to be clarified. It has been suggested that they are involved in the accommodation of volume changes (harmomegathy). To investigate this further, we developed a protocol that induces a controlled hydration of the pollen without affecting its metabolism and we applied it to six species differing in their pollen wall morphology. The entry of water caused pollen swelling and volume increase leading to breakage of the wall and/or of the plasma membrane, such that the per cent of intact grains was negatively correlated with the level of hydration. Qualitative and quantitative differences were observed between the species. Breakage of the exine was observed only in pollen lacking apertures and with thin exine. Variation in the exine ornamentation and thickness could explain the interspecific differences observed for the rates of breakage of the plasma membrane. Our results suggest that pollen wall morphology matters for survival and maintenance of pollen integrity further to volume increase due to hydration. We propose a rationale for future studies that should allow disentangling the contribution of different pollen morphological and physiological features to harmomegathy.     

Entwicklungsgeschichte und Ultrastruktur von Pollenkitt und Exine bei nahe verwandten entomophilen und anemophilen Angiospermensippen derAlismataceae,Liliaceae, Juncaceae,Cyperaceae, Poaceae undAraceae

Some closely related members of the monocotyledonous familiesAlismataceae, Liliaceae, Juncaceae, Cyperaceae, Poaceae andAraceae with variable modes of pollination (insect- and wind-pollination) were studied in relation to the ultrastructure of pollenkitt and exine (amount, consistency and distribution of pollenkitt on the surface of pollen grains). The character syndromes of pollen cementing in entomophilous, anemophilous and intermediate (ambophilous or amphiphilous) monocotyledons are the same in principal as in dicotyledons. Comparing present with former results one can summarize: 1) The pollenkitt is always produced in the same manner by the anther tapetum in all angiosperm sub-classes. 2) The variable stickiness of entomophilous and anemophilous pollen always depends on the particular distribution and consistency of the pollenkitt, but not its amount on the pollen surface. 3) The mostly dry and powdery pollen of anemophilous plants always contains a variable amount of inactive pollenkitt in its exine cavities. 4) A step-by step change of the pollen cementing syndrome can be observed from entomophily towards anemophily. 5) From the omnipresence of pollenkitt in all wind-pollinated angiosperms studied one can conclude that the ancestors of anemophilous angiosperms probably have been zoophilous (i.e. entomophilous) throughout.

     

Correlations between pollen exine sculpturing and angiosperm self-incompatibility systems — a reply

The exine morphology and pore size of pollen from diverse angiosperm taxa with homomorphic gametophytic, homomorphic sporophytic, and heteromorphic self-incompatibility have been studied. The results indicate that correlations alleged to exist between the type of self-incompatibility system and the nature of the pollen wall morphology should be treated with considerable caution.     

Colloidal crystal-like structure of sporopollenin in the megaspore walls of Recent Selaginella and similar fossil spores

HEMSLEY, A. R., COLLINSON, M. E. & BRAIN, A. P. R., 1992. Colloidal crystal-like structure of sporopollenin in the megaspore walls of Recent Selaginella and similar fossil spores. TEM and SEM studies of iridescent fossil Erlansonisporites and Recent Selaginella spores reveal a wall composed of three regions. The central region consists of close-packed particles in a semi-crystalline arrangement. This organization is compared with that of aggregated Iridoviridae, prolamellar bodies, lipid micelles and precious opal. Our observations suggest that the structure of this wall region (and that of the remaining regions) can be explained by derivation from colloidal mixtures. It is concluded that colloids and their precursors may play a far more significant part in spore and pollen wall structure than was previously believed.     

Pollen morphology of the genus Cornukaempferia （Zingiberaceae） in Thailand

Cornukaempferia is a recently described genus of Zingiberaceae which only occurs in Thailand as a rare genus with limited geographical distribution. Only three species have been described so far, including a recently described new species, C. larsenii. These three species are morphologically very similar and additional data on other biological aspects are useful for the elucidation of their relationship. Pollen morphology of all three species of genus Cornukaempferia has been studied by light microscopy and scanning electron microscopy. The pollen grains are monad, spherical, inaperturate. The exine sculpture is echinate with psilate between the spines for C. aurantiflora and C. longipetiolata, or echinate with regulate between the spines for C. larsenii. This observation helps support the taxonomic status of C. larsenii.     

Palynological characters of Glycyrrhiza,Glycyrrhizopsis,and Meristotropis(Leguminosae),with special reference to their taxonomic significance

Li X-Y.1992.Studies on germplasm of Glycyrrhiza by using different taxonomic methods.Advances in Plant Taxonomy in Northwest China 1:7-24.

Li X-Y.1993.A study of the system and new taxa of genus Glycyrrhiza L.Bulletin of Botanical Research 13(1):14-43.

Turrill WB.1937.Glycyrrhizopsis syriaca Turrill.Bulletin of Miscellaneous Information 2:79.

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Pollen Morphology and Generic Phylogenetic Relationships in Ophiopogonoideae (Liliaceae)

In the present work, pollen grains of 3 species of Liriope, 24 species of Ophiopogon and 2 species of Peliosanthes were examined under scanning electron microscope, Among them 4 species were also observed under transmission electron microscope. The observation (Table 3)shows that Liriope and Ophiopogon distinctly differ from Peliosanthes in the exine ornamentation and structure, They may be divided into two types: 1. Rugulate-perforate, ektexine with perforate tectum in Liriope and Ophiopogon. 2. Verrucate, Verracae unequal in size, ektexine intectate in Peliosanthes. Pollen morphology shows the close affinity between Liriope and Ophiopogon, but they are very far from Peliosanthes. The correlation between pollen and gross morphology in Liriope, Ophiopogon and Peliosanthes are stated and their evolutionaly trends are discussed in this paper. The pollen characters support the placement of Liriope and Ophiopogon in one tribe—Ophiopogoneae, and Peliosanthes in another tribe—Peliosantheae. Peliosanthes is more advancedthan Liriope and Ophiopogon.