Zur Pollenmorphologie der Gattung Waltheria L. (Sterculiaceae)

The pollen grains of 69 specimens representing 44 species or supposed species of the genus Waltheria L. have been studied. Based mainly on differences in exine characters 2 pollen types, a spinulose and a suprareticulate one were pointed out. Both types show ± parallel trends in the development of the aperture system to an increase of aperture number, to a shortening of the colpi and to more distinct bounds and nexine thickenings of the ora. They exemplify important steps of aperture evolution, which in the spinulose type leads from zonocolporate by way of zonopororate to pantopororate and in the suprareticulate type from zonocolporate to pantocolporate grains. The tendencies of sporoderm evolution concern a more distinct morphological and partially also a regional differentiation of the exine elements (bacula, spinulae), which prove to be close correlated with the evolution levels of the apertures. According to the pollen morphological point of view the species of the genus Waltheria are to be arranged in two groups, which may be regarded as two related, but relative independent phyletic entities. These evidences speak in favour of a taxonomic     

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Pollen and Tapetum Development in Male Fertile Rosmarinus Officinalis L. (Lamiaceae)

The development of microspores/pollen grains and tapetum was studied in fertile Rosmarinus officinalis L. (Lamiaceae). Most parts of the cell walls of the secretory anther tapetum undergo modifications before and during meiosis: the inner tangential and radial cell walls, and often also the outer tangential and radial wall, acquire a fibrous appearance; these walls become later transformed into a thin poly-saccharidic film, which is finally dissolved after microspore mitosis. Electron opaque granules found within the fibrous/lamellated tapetal walls consist of sporopollenin-like material, but cannot be interpreted as Ubisch bodies. The middle lamella and the primary wall of the outer tangential and radial tapetal walls remain unmodified, but get covered by an electron opaque, sporopollenin-like layer. Pollenkitt is formed only by lipid droplets from the ground plasma and/or ER profiles, the plastids do not form pollenkitt precursor lipids. Tapetum maturation (“degeneration”) does not take place before late vacuolate stage.

The apertures are determined during meiosis by vesicles or membrane stacks on the surface of the plasma membrane. The procolumellae are conical, but at maturity the columellae are more cylindrical in shape. The columellar bases often fuse, but a genuine foot layer is lacking. The formation of the endexine starts with sporopollenin-accumulating white lines adjacent to the columellar bases. Later, the endexine grows more irregularly by the accumulation of sporopollenin globules. In mature pollen the intine is clearly bilayered.

Generative cells (GCs) and sperm cells contain a comparatively large amount of cytoplasm, and organelles like mitochondria, dictyosomes, ER, and multi-vesicular bodies, but no plastids; GCs and sperms are separated from the vegetative cell only by two plasma membranes.     

Pollenmorphologie und Chromosomenzahlen der Poaceen-Subtribus Deschampsiinae Holub

Pollen morphology and ultrastructure of twenty-seven European species of the subtribe Deschampsiinae Holub were investigated by light, phase contrast and scanning electron microscopy. Genera are characterized by pollen size, development of the anuli and pollen surface. Comparison of the data with the known chromosome numbers and some karyotypes confirms the important influence of karyology on the size and fine structure of pollen.     

Osservazioni sul primo sviluppo dell'apparato Radicale dell'asparago (Asparagus Officinalis L.)

Summary

In order to determine how long the primary root of Asparagus officinalis L. keeps living, the writer has periodically observed plants of this species grown on two soils differing in texture an pH; so he could ascertain that in the coarse-textured and less acid soil the primary root disappears in some individual already 45 days after germination, being quite lost in all of them 75 days after germination; while in the fine-textured and more acid soil such terms are respectively antedated at the 40th and 70th day after germination. The writer also relates on early development of the first order and second order lateral rootlets, and of the first and second secondary asparagus roots.     

Exine ontogeny in Borago officinalis pollen

The primexine matrix is finely granulo-fibrillar up to callose digestion; it becomes distinctly fibrillar at the free microspore stage. The columellae and the tectum are initiated at the middle tetrad stage, the foot layer and the endexine are initiated when the callose wall digestion begins. The columellae are initiated by the deposition of spiral elements around a clear central zone. This hollow aspect of columella disappears when thickening. The foot layer and the endexine are built by the expansion of plasmalemma derived components. The foot layer appears first at the poles, then at the interapertural levels and at last at the apertures while the endexine appears first at the mesoapertures, then it spreads laterally towards the interapertural levels and, at last, at the poles. The gemmae are formed at the free microspore stage over all the tectum. The thickening of the exine takes place essentially during the free microspore stage and continues during the vacuolate microspore one. Apertures are entirely formed before the complete digestion of the callose wall. The ectoapertures are determined by the lacking of the columellae; the sites of the pericolpal cavities and the mesoapertures result from the plasmalemma retraction even before the setting up of the foot layer and the endexine by which they will be delimited respectively afterwards. The endoapertures are determined by the lacking of compact endexine at their level, and merge into a continuous equatorial belt.     

Geitonogamy: a mechanism responsible for high selfing rates in borage (Borago officinalis L.)

Borage, a species traditionaly defined as allogamous, has revealed a high selfing rate although a mechanism of protandry has been confirmed in this plant. Studies investigating flower behaviour showed that several flowers open every day and that others are also receptive at the same time within a plant. Moreover, pollinator behaviour, mainly by bees, contributes to the selfing rate because it is demonstrated that these insects visit several flowers in a given plant before flying to other plants. The ecological studies reported here reveal the contribution of geitonogamous pollination to the high selfing rate detected in Borago officinalis L. Received: 23 March 2000 / Accepted: 26 May 2000     

Quantitatively determined self-incompatibility. IV. Pollination and seed set in Borago officinalis

Summary The outcomes of sequential double pollination, mixed double pollination and single pollination are compared. Single pollination leads to lower seed set than double pollination. Systematic differences between female genotypes are shown to be possible. It is also shown that failure to set seed is generally due to pre-zygotic maternal factors.     

Growth and Fatty Acid Composition of Borage (Borago officinalis L.) Leaves and Seeds Cultivated in Saline Medium

The effects of salinity on growth and fatty acid composition of borage (Borago officinalis L.) leaves and seeds grown in hydroponic medium were investigated. Three different levels of NaCl (25, 50, and 75 mM) were applied. The first results showed that salinity significantly reduced plant growth by 56.5 % at 75 mM compared with the control, suppressed seed yield at 50 and 75 mM, and increased lipid peroxidation. Raising NaCl concentrations led to an important decrease in total fatty acid (TFA) content by 77 % at 75 mM NaCl. Moreover, the polyunsaturated fatty acid (PUFA) content decreased, whereas the saturated fatty acids increased with respect to increasing salinity. The 25 mM NaCl level did not modify the fatty acid composition of seeds and their contents.     

Von Zittwitz. Nachruf

Ohne Zusammenfassung