Krystyna Idzikowska

Late steps of egg cell differentiation are accelerated by pollination in Zea mays L.

Abstract. Egg cells were analysed cytologically during the female receptivity period in maize (Zea mays L., line A 188). Three classes of egg cell were distinguished: type A – small, non-vacuolated cells with a central nucleus; type B – larger cells with small vacuoles surrounding the perinuclear cytoplasm located in the middle of the cell; type C – big cells with a large apical vacuole and the mid-basal perinuclear cytoplasm. The less-dense cytoplasm of the vacuolated egg cells usually contained numerous cup- or bell-shaped mitochondria. The three egg types appear to correspond to three late stages of egg cell differentiation. The frequencies of each of the three egg types were monitored in developing maize ears before and after pollination. In young ears, with the silks just extending out of the husks, small A-type cells were found in about 86% of ovules. Their frequency decreased to about 58% at the optimum silk length, remained unchanged in non-pollinated ears, and fell to 16% at the end of the female receptivity period. However, after pollination and before fertilisation the frequency of these cells decreased to about 33%, and the larger vacuolated egg cells (types B and C) prevailed. At various stages of the receptivity period, pollination accelerated changes in the egg population, increasing the number of ovules bearing larger, vacuolated egg cells. Experiments with silk removal demonstrated that putative pollination signals act immediately after pollen deposition and are not species-specific.

Behaviour of the hyphae of Laccaria laccata in the presence of Trichoderma harzianum in vitro

The growth rate and the behaviour of Laccaria laccata and Trichoderma harzianum hyphae in co-culture and in the rhizosphere of 3-month-old Pinus sylvestris seedlings grown in vitro were investigated. In the interaction zone, hyphae of L. laccata became more pigmented and formed short branches growing towards the hyphae of the saprobic fungus, coiled around them and penetrated sporadically. Vacuolated hyphae of T. harzianum showed protoplasm granulation and breaks in walls followed by release of protoplasts. In the rhizosphere, the mantle hyphae of L. laccata showed a tendency to surround conidia of T. harzianum. No obvious penetration of the conidial walls by the hyphae of the mycorrhizal fungus was observed by scanning electron microscopy. Instead, in rare cases, the hyphae of L. laccata showed marked wrinkles, and a partial degradation of a mucilaginous material covering the mantle appeared to occur.

Ultrastructural and cytochemical aspects of the interaction between the ectomycorrhizal fungus Laccaria laccata and the saprotrophic fungi, Trichoderma harzianum and T. virens

Abstract Different interactions between soil fungi competing in the rhizosphere with each other are necessary to understand their influence on plant growth and health. The interactions between the ectomycorrhizal (ECM) fungus Laccaria laccata and soil saprotrophic fungi (T. harzianum, T. virens) were studied by transmission electron microscopy, and by gold cytochemistry to assess the potential role of cell wall lytic enzymes in mycoparasitism. Anti-β-1,3-glucan antibody, WGA/ovomucoid–gold complex and PATAg test were used to localize β-1,3-glucan, chitin and polysaccharides. Cytoplasm disorganisation of the saprotrophic fungi occurred concurrently with dissolution of β-1,3-glucan in walls of hyphae and conidia of the saprotrophic fungi. Then digestion of polysaccharides and chitin of colonised fungal structures occurred. The studies suggest sequential contribution of cell wall lytic enzymes and importance of disturbing the hosts cell integrity during mycoparasitism. We conclude that the ECM fungus can parasitise on the saprotrophic fungi not only in dual culture on artificial medium but also in the rhizosphere of Scots pine.

The ultrastructural aspects of the cytokinin-induced bud formation inCeratodon purpureus

SummaryThe fine structure of gametophore buds developing in response to a cytokinin treatment is described and compared with the results of biochemical and physiological investigations. In the early period of growth, the buds followed a regular pattern of development, with the differentiation of a tetrahedral apical cell at the 3-cell stage of the bud. After 6 and 48 hours of the cytokinin treatment, structural changes indicating an increased metabolic activity were found in the developing buds. Treatment for 5-days resulted in signs of degeneration in most of the bud cells. Nuclei and chloroplasts were the organelles most sensitive to the cytokinin. Among the structures described, complexes of minute, strongly osmiophilic globules, arranged in parallel rows between microfilaments were of particular interest. They seemed to appear temporarily in cells and they may constitute storage material for building structures at an appropriate stage of cell development.

The First Stages of Microspore Division in Anthers of Hordeum vulgare Cultured in vitro

Summary The first mitosis of Hordeum vulgare -microspores cultured in vitro is described. The ultrastructure of the following two possible routes of androgenesis was observed: a) equal division of the nucleus of the microspore; b) division of the nucleus of the vegetative cell.