Biological and taxonomical investigations of some oak species
Hermaphroditic flowers blooming unseasonably on an oak tree (»the green oak«) of uncertain hybrid origin prompted a detailed investigation into the biology of the flowering, and the morphology of various traits of the tree, which is growing in an urban area near Zadar, northern Dalmatia, Croatia. Hermaphroditic flowers were also detected on one holm oak tree from Weihenstephan, Germany. Since the first oak tree was described as a hybrid between Q. cerris f. austriaca Q. ilex, scanning electron microscope investigations of pollen and hairs on the leaves of three species were made, on: Q. ilex L., Q. cerris L. and the »green oak«. Oak pollen is of elliptical shape and tricolpate. The ornamentation of the pollen grains of Q. cerris and the »green oak« were similar concerning the ornamentation of the exine – warty and rough and with small rounded protrusions – as well as the size of the pollen grain. Q. ilex pollen was much smaller and the surface lacked the small irregularly shaped protrusions typical of the other oaks. Within samples of holm oak pollen, significant difference in the surface structures was observed. Concerning the different types and number of hairs on the leaf surfaces, Q. ilex revealed a much greater number of stellate hairs on the upper leaf side as compared to Q. cerris and the »green oak«. Simple uniseriate hairs and simple unicellular hairs were missing on the leaves of Q. ilex, but were present on both the other oaks. To sum up the results, the »green oak« and Q. cerris reveal some similarities whereas Q. ilex does not.
Contribution to Discussions on the Origin of the Green Oak Growing in Northern Dalmatia
The "green oak" growing in Ravni Kotari, near Zadar, Croatia was described as a hybrid Q. x viridis Trinajsti};, hybr. nov., hybrid between Quercus cerris f. austriaca and Q. ilex. It is unlikely to find a hybridization between two species where acorns mature in the second year (Q. cerris L.) and in the first year (Q. ilex L.). Therefore we visited "green oak" repeatedly and described diagnostic features in details. The composition of leaf volatiles of the "green oak" with gas chromatography and gas chromatography/mass spectrometry was analyzed too. Same method was used for investigation of leaf volatiles in leaf samples of supposed parent species Q. cerris and Q. ilex. The volatile fraction obtained by steam distillation of leaves averaged to 0.05 % fresh weight. In total 206 compounds were isolated from all three investigated specimens of which 141 were identified. 128 components were separated in "green oak", 126 in Q. ilex, and 100 in Q. cerris. Cluster analysis of the patterns of volatiles in leaves of the "green oak", Quercus ilex and Q. cerris did not support the assumption that the "green oak" is a hybrid between Quercus ilex and Q. cerris. The opinion is given that the "green oak" could be a progeny of back-crossed hybrid between Q. cerris and Q. suber or a variety of Q. cerris restricted to a small area of distribution in Ravni Kotari, Croatia.
Mode of action of bredinin with guanylic acid on L5178Y mouse leukemia cells.
Moderate concentrations of bredinin (1.2 X 10(-5) M) strongly inhibited growth of L5178Y cells, with the effect being reversed by guanylic acid (GMP). However, at higher concentrations of breeding the inhibition was not reversed completely by GMP added in excess. Bredinin was cytocidal at concentrations above 2 X 10(-5) M, but 5 X 10(-5) M bredinin in the presence of excess GMP, bredinin was cytostatic. Bredinin inhibited nucleic acid synthesis of L5178Y cells, but bredinin itself was not incorporated into the nucleic acid. Inhibition of nucleic acid synthesis was clearly reversed by GMP. Similarly chromosomal aberrations in L5178Y cells caused by bredinin were reversed by GMP. In contrast, the effect of ahigh concentration of bredinin on cell multiplication was not reversed by GMP. The modal volume of L5178Y cells increased during incubation in the presence of bredinin and GMP for 24 hours, 5 X 10(-5) M bredinin with GMP causing a 70% increase in cell volume. This increase in cell volume was mainly due to an increase in the protein content of the cells. The cytostatic effect of bredinin with GMP was reversed completely by adenosine-3',5'-cyclic monophosphate (cyclic AMP). Other cyclic nucleotides and nucleotides were ineffective. The reversing effect of cyclic AMP on cell survival depended upon the concentration of GMP, and was not seen in the absence of GMP. It was concluded that cyclic AMP influences the secondary cytostatic effect of bredinin, and not the primary cytotoxic effect reversed by GMP.