Ultrastructural changes in chloroplasts of mesophyll cells of chlorotic and prematurely yellowed leaves of Betula pendula Rothr

The ultrastructure of chloroplasts was studied in mesophyll cells of the leaves of silver birch (Betula pendula) showing interveinal chlorosis or premature yellowing, in comparison with leaves without symptoms or exhibiting symptoms of natural senescence. The leaves were collected between May 26 to June 7 and additionally in the September 10-12 from the upper part of the crown, from increments of the past four years. No major difference in ultrastructure of chloroplasts was found between spongy and palisade mesophyll cells. The following senescencerelated changes were observed in chloroplasts of prematurely yellowed leaves and showing inteveinal chlorosis: reduced chloroplast size, degeneration of the membrane systems of thylakoids and increased electron density of plastoglobuli. The most electron dark globules (lipid droplets) were found together with starch grains in cells of spongy mesophyll of leaves showing interveinal chlorosis. Abnormal, spherical and rounded chloroplasts with electron-dark inside of thylakoids or the electron-dark stroma between thylakoids were found only in yellowed and chlorotic leaves in spring

The ultrastructure of anther wall and pollen of Hordeum vulgare at the microspore stage

The ultrastructure of anther wall and pollen of Hordeum vulgare was de-scribed at the microspore stage. In future studies this stage will constitute an initial material in experiments for the inducement of androgenesis

Fine structure ot the protonema in the moss Ceratodon purpureus and its response to a cytokinin

Fine structure of the protonema is described, with a special attention to its differentiation depending on the position of cells in the protanemal filament, as well as in response to a cytokinin treatment. Complexes of micro-filaments with osmiophilic globules represented structures of particular interest. They appeared temporarily, almost exclusively in apical cells. The cytokinin treatment resulted in the apical cells in an increased number of cytokinetic figures and in structural changes indicating increased metabolic activity. In the intercalary cells, changes in response to the cytokinin were much smaller and mostly concerned an augmented development of the thylakoid system in chloroplasts. After a prolonged (5 days) treatment, degeneration symptoms developed in all cells, particularly in nuclei and chloroplasts, whereas the structure of mitochondria was relatively stable. The results are compared with the observations concerning the cytokinin-induced gametophore buds and with the data of biochemical and physiological investigations of the protonema

Cell wall formation in multinucleate pollen grains of Hordeum vulgare anthers cultured in vitro

Cell wall formation in several-nucleate pollen grains of Hordeum vulgare anthers cultured in vitro was initiated at the intine. The walls grew centripetally and branched, dividing pollen protoplast into a several-celled embryoid

Fine structure ot the protonema in the moss Ceratodon purpureus and its response to a cytokinin

Fine structure of the protonema is described, with a special attention to its differentiation depending on the position of cells in the protanemal filament, as well as in response to a cytokinin treatment. Complexes of micro-filaments with osmiophilic globules represented structures of particular interest. They appeared temporarily, almost exclusively in apical cells. The cytokinin treatment resulted in the apical cells in an increased number of cytokinetic figures and in structural changes indicating increased metabolic activity. In the intercalary cells, changes in response to the cytokinin were much smaller and mostly concerned an augmented development of the thylakoid system in chloroplasts. After a prolonged (5 days) treatment, degeneration symptoms developed in all cells, particularly in nuclei and chloroplasts, whereas the structure of mitochondria was relatively stable. The results are compared with the observations concerning the cytokinin-induced gametophore buds and with the data of biochemical and physiological investigations of the protonema

Cell wall formation in multinucleate pollen grains of Hordeum vulgare anthers cultured in vitro

Cell wall formation in several-nucleate pollen grains of Hordeum vulgare anthers cultured in vitro was initiated at the intine. The walls grew centripetally and branched, dividing pollen protoplast into a several-celled embryoid

Ultrastructural aspects of chromatin elimination in hybrid embryos of Hordeum

Chromatin elimination was observed in hybrid embryos of Hordeum as incorporation of single chromosomes into tiny vacuoles-lysomes and as fragmentation of interphase nuclei: The latter process led mostly to the formation of micronuclei which underwent gradual degradation

Morphological differentiation of Primula veris L. pollen from natural and cultivated populations

Micromorphological characterisation and the comparative statistical analysis of the size of Primula veris L. pollen grains collected in three natural and three cultivated populations were done. Observations were carried out with SEM. The obtained measurements were analysed with the use of one-way ANOVA, Kruskal-Wallis Test and the Student-t Test. Pollen grains from long-styled ('pin') flower-morphs were mainly 6 colpate and from shortstyled ('thrum') flower-morphs 8 colpate. Colpi of some grains from 'thrum' flowers were 'sinuous' and 'circular', and they incised into the apocolpium zone. Ornamentation of 'pin' pollen grains was microreticulate, with lumina up to 0.8 μm wide, and for pollen grains from 'thrum' flowers was reticulate and eureticulate with lumina 1.1-1.7 μm wide. In lumina of mesocolpium area some free columellae were observed. Pollen grains from 'thrum' flower-morphs were more variable in size, both in natural and in cultivated populations, than grains from 'pin' flower-morphs. The differences in mean length (P) and breadth (E) of pollen grains from 'thrum' flowers collected in cultivated populations were statistically important (FP = 3.154 for the critical F005 = 3.098; K-We = 7.469 for the critical Test value α=005 = 5.991). Pollen grains from 'thrum' flowers were bigger when coming from plants growing in natural populations (tE = 2.784 for the critical Test value α=005 = 2.001)

Pollen dimorphism and androgenesis in Hordeum vulgare

Dimorphism of binucleate pollen grains of Hordeum vulgare has been confirmed. It is considered, however, in contrast to the accepted opinions, that some of the large pollen grains with dense cytoplasm lying close to the tapetum are the outset forms for embryoids, and not the small pollen grains with scarce cytoplasm lying in the pollen sac centre