Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 8

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych:  gymnosperm
help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
The authors investigated zoosporic fungi developing on the pollen grains of 36 taxons of gymnosperm plants in three bodies of water of various trophic state. A total of 83 zoosporic fungus species were noted, with predominance by the Peronosporales (39) and Chytridiales species (29). Twelve fungus species were recorded for the first time in Polish waters.
ThepsbA-trnH intergenic region is among the most variable regions in the gymnosperm chloroplast genome. It is proposed as suitable for DNA barcodmg studies and is useful in phylogenetics at the species level. This region consists of two parts differing in their evolutionary characteristics: 1) the psbA 3'UTR (untranslated region) and 2) the psbA-trnH intergenic spacer. We compared the sequence and RNA secondary structure of the psbA 3'UTR across gymnosperms and found consensus motifs corresponding to the stem portions of the RNA stem-loop structures and a consensus TGGATTGTTATGT box. The psbA-trnH spacer is highly variable in length and composition. Tandem repeats that form stem-loop structures were detected in both the psbA 3' UTR and the psbA-trnH spacer. The presence of promoters and stem-loop structures in the psbA-trnH spacer and high sequence variation in this region suggest that psbA and trnH in some gymnosperms are independently transcribed. A comparison of chloroplast UTRs across gymnosperms offer clues to the identity of putative regulatory elements and information on selective constraints imposed on the chloroplast non-coding regions. The present study should inspire researchers to explore the full potential of the psbA-trnH non-coding sequence and to further stimulate its application in a broader spectrum of studies, not limited to phylogenetics and DNA barcoding.
The aim of the present study was to analyse the occurrence of monoecious individuals in selected populations of Taxus baccata in Poland and Ukraine. The investigation showed the monoecy in Taxus baccata to be extremely rare phenomenon. Only four cosexual individuals were found in three by seven populations examines and the frequency of monoecy was 0.13% on average among 2986 trees verified. Isolated seeds were found on individuals with large number of male flowers. Only one tree was found with numerous macro- and microstrobiles.
Pollen grains of Pinus wallichiana, P. mugo, P. ponderosa and Ephedra distachya germinated at various intensities on in vitro cultured placentas of 32 angiosperm species. Pollen of the same gymnosperms did not form tubes on stigmas of pistils cultured under the same conditions as the placentas. Pollen of several angiosperms germinated on semi in vitro cultured opened ovules of Larix decidua and nucelli of Taxus baccata. Angiosperm pollen did not germinate in vivo in the pollination drop secreted by ovules of T. baccata. This report shows that (1) gymnosperm pollen produces fully formed tubes on ovules of angiosperms but do not germinate on their stigma, and (2) pollen representing angiosperms is able to germinate and form tubes on ovules of gymnosperms.
Cycads are an ancient lineage of plants that originated in the Permian, which are vital to the interpretation of plant ecology. The evidence in the fossil records indicates that the morphological and anatomical features of cycads are remarkably similar to the extant taxa, which has been instrumental in our understanding the connections between the early origins of seed plants and their present-day counterparts. The cycad ecosystem is an important vegetation type throughout geological time. Research on the ecological function of the cycad plays a significant role in the study of evolutionary ecology. In this study, we investigated the biomass, productivity and total carbon storage (total of vegetation, litter, and soil carbon) of cycad (Cycas panzhihuaensis L. Zhou et S.Y. Yang) ecosystems in the National C. panzhihuaensis Reserve of China (latitude 26°37′, longitude 101°35′, at 1635 m altitude) by applying the site-standard tree sampling harvest.Cycads are considered to be rare and endangered species, and are in the list of key protected wild plants in the world. The National C. panzhihuaensis Reserve is in Southwestern China, which area approximately 1358 ha, growing approximately 20 000 C. panzhihuaensis individuals. 20 sample plots, each 5 × 5 m were established in the spring of 2006. The mean height of cycads within the stand was 0.44 m and the mean basal diameter was 23.2 cm. The biomass and productivity data for other communities was compiled from references published over the past 20 years throughout China. The biomass and productivity of cycad ecosystems (8.102 ± 6.880 t C ha⁻¹ and 1.183 ± 0.975 t C ha⁻¹ yr⁻¹, respectively) are smaller than tree fern (Alsophila spinulosa (Wall. ex Hook.) R. M. Tryon) or gymnosperm (Pinaceae, Cupressaceae or Taxodiaceae for representative) ecosystems. The community biomass of Pinaceae-, Cupressaceae- or Taxodiaceae-dominated ecosystems are 6.8, 5.4, and 5.3 times larger than the cycad ecosystem, respectively. The productivity of each is 2.3, 2.8 and 3.8 times larger than the cycad ecosystem. Cycad is an ancient dioecious plant. However, the results show that the differences between the biomass of male and female cycads, as well as the productivity, are not significant.
In vitro placental pollination can be employed to overcome barriers of self-incompatibility and cross-incompatibility. Pollen grains of self-incompatible plants are capable of germinating directly on ovules, and the whole process of sexual reproduction can be accomplished. In some combinations of crosses, direct pollination of ovules enables prezygotic incompatibility barriers to be overcome. As a result, hybrid embryos or even hybrid plants can develop, depending on the partners crossed. Pollen grains germinate abundantly on immature ovules irrespective of the stage of megasporogenesis or megagametogenesis, and their tubes can penetrate the integuments and the nucellus cells. Preliminary investigations revealed that pollen grains of seven selected species of gymnosperms germinated on ovules of various species of Angiospermae. Embryological analysis of ovules of Melandrium album fixed 3 days after pollination with pollen of Pinus wallihiana revealed the presence of remnants of pollen tubes and 2-celled embryos in the embryo sacs. Those preliminary observations have not been described heretofore.
W pracy przedstawiono syntetyczny przegląd roślin naczyniowych prawnie chronionych oraz rzadkich i interesujących z punktu widzenia naukowego i biogeograficznego, zanotowanych na obszarze projektowanego Boreckiego Parku Krajobrazowego.
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.