The Crassulaceae family mainly comprises herbaceous leaf succulents, some of which are used as ornamentals. The development of the embryo suspensor in Sedum reflexum L. was investigated using cytochemical methods, light and electron microscopy. The full development and functioning of the suspensor occurs during the late globular and heart-stage embryos. The suspensor consists of a large basal cell and a single row of 6-10 chalazal cells. The basal cell produces a branched haustorium which invades ovular tissues. The walls of the haustorium and the micropylar part of the basal cell form the wall ingrowths that are typical for transfer cells. The dense cytoplasm filling the basal cell is rich in profiles of endoplasmic reticulum, active dictyosomes, mitochondria, plastids, microtubules, bundles of microfilaments, microbodies and lipid droplets. The present work reveals that the suspensor structure in S. reflexum markedly differs from that found in other representatives of Crassulaceae. Ultrastructural analysis and cytochemical tests (including proteins, insoluble polysaccharides and lipids) indicate that in S. reflexum the embryo suspensor is involved mainly in absorption and transport of metabolites from the ovular tissues to the developing embryo proper via the chalazal suspensor cells.

Plant viruses create many changes in the morphology of the plant cell once the infection process has begun. This paper describes and compares the ultrastructural changes induced in maize cells by two isolates of Maize dwarfmosaic virus (MDMV), Spanish (MDMV-Sp) and Polish (MDMV-P), and one isolate of Sugarcane mosaic virus (SCMV) at 10 and 42 days post-inoculation: the concentration and arrangement of virus particles, inclusion bodies associated with infection, and other cytological alterations. The most important difference between maize cells infected with MDMV isolates and with SCMV-P1 was in the form of cytoplasmic cylindrical inclusions. In cells infected with MDMV only typical inclusions such as pinwheels and scrolls were observed, but laminar aggregates were also present in SCMV-infected cells. No virus particles were found in plant cell organelles. Specific virion arrangements occurred in cells infected with MDMV-Sp and SCMV. The most interesting new finding was of specific amorphous inclusions in the cytoplasm of MDMV-Sp-infected cells, which clearly differentiated the two MDMV isolates studied.

The arbuscules of mycorrhizae develop within apoplastic compartments of the host plant, as they are separated from the cell protoplast by an interfacial matrix continuous with the plant cell wall. Expansins are proteins that allow cell wall loosening and extension. Using fluorescence and electron microscopy we located the NtEXPA5 epitopes recognized by polyclonal antibody anti-NtEXPA5 in mycorrhizal tobacco roots. The expansin protein was localized mainly within the interfacial matrix of intracellular hyphae, arbuscule trunk and main branches. NtEXPA5 proteins were detected neither within the interface of collapsing arbuscule branches nor in non-colonized cortex cells. In plant cell walls, expansin protein was detected only at the penetration point and in the parts of cell walls that adhered firmly to fungal hyphae growing intracellularly. For the first time, NtEXPA5 protein was localized ultrastructurally in hyphae growing intracellularly at the interface of the hypha tip and sites of bending. The novel localization of NtEXPA5 protein suggests that this protein may be involved in the process of arbuscule formation: that is, in promoting apical hyphal growth and arbuscule ramification, as well as in controlling the dynamic of arbuscule mycorrhiza development.

The paper describes anatomical and physiological features of photobionts and mycobionts in Bryoria forsteri Olech & Bystrek, Caloplaca regalis (Vain.) Zahlbr., Cetraria aculeata (Schreb.) Fr., Ramalina terebrata Hook f. & Taylor, Sphaerophorus globosus (Huds.) Vain. and Usnea antarctica Du Rietz, collected in the Antarctic under varied weather conditions. Green algae from the genera Lobosphaera and Trebouxia were gathered in depressions of the cortex under the more resistant mycobiont hyphae. In photobiont cells a large amount of highly osmiophilic electron-dense PAS-negative material, lipid-like in character, was of particular interest. Similar material also filled certain areas of the aerial apoplast. A star-shaped chromatophore with central and lateral pyrenoids encompassed most of the photobiont protoplast in all the studied species. Regularly arranged thylakoids with evenly widened lumina along their entire length and osmiophilic lipid droplets adhering to their outer surfaces were visible within the pyrenoid. Inside the chloroplast, large protein inclusions tightly joined with the thylakoids were observed. The mycobionts were closely attached to each other another and with the photobionts by means of an outer osmiophilic wall layer, and formed intramural haustoria. Their protoplasts were filled with PAS-positive polysaccharides and a large amount of lipid-like substances. The photobionts were physiologically active and produced a large amount of electron-dense osmiophilic material, and PAS-positive starch grains were visible around their pyrenoids in the thalli collected in different weather conditions. The permanent reserves of nutritive materials deposited in the thalli enable these organisms to quickly begin and continue indispensable physiological processes in the extreme Antarctic conditions.