Free and conjugated gibberellins in dormancy and germination of apple seeds

Halińska, A. and Lewak, St. 1987. Free and conjugated gibberellins in dormancy and germination of apple seeds.
The presence of gibberellin A₄ (GA₄) was confirmed in partly stratified seeds of apple ( Malus domestica Borb., cv. Antonówka) by mass spectrometry of the methyl ester. Levels of free and conjugated gibberellins A₄₊₇ and A₉ changed during drying of mature seeds, during cold and warm stratification, as well as during germination of dormant and non-dormant embryos. The temporary rise in GA₄₊₇ during cold stratification and during the culture of dormant embryos as well as the lack of it under conditions of warm stratification, allowed us to postulate a role for GA₄₊₇ in the removal of dormancy. In addition, GA₉ was absent in dormant embryos and increased during cold stratification and during the culture of non-dormant embryos. This suggests the involvement of GA₉, in induction of normal development of the seedling. The equivalence between changes in free and conjugated GAs suggests that formation and hydrolysis of conjugates are involved in the control of the physiologically active levels of free GA₄₊₇ and GA₉.     

A new species of the genusLotus (Fabaceae) in North Africa

A new species,Lotus digii, has been found in Morocco growing on the coastal sandy soils. Further localities are from Algeria and Egypt. It should be expected also in Libya.     

Vitamin K-dependent carboxylase: influence of the "propeptide" region on enzyme activity

The liver microsomal vitamin K-dependent carboxylase catalyzes the post-translational conversion of specific glutamyl to gamma-carboxyglutamyl (Gla) residues in precursor forms of a limited number of proteins. These proteins contain an amino-terminal extension (propeptide) that is presumed to serve as an enzyme recognition site to assure their normal processing. The free, noncovalently bound propeptide has also been shown to stimulate the in vitro activity of this enzyme. This peptide has now been shown to lower the app Km of a low-molecular-weight Glu site substrate while having no influence on the app Km of the other substrates, vitamin KH2, O2, and CO2/HCO3-. Propeptide addition was shown to have no influence on the ratio of the two products of the enzyme, Gla and vitamin K-2,3-epoxide. Stimulation of carboxylase activity by the propeptide from human factor X was observed in a number of rat tissues and in the liver of a number of different species. Stability of the enzyme in crude microsomal preparations was greatly enhanced by the presence of propeptide. These observations are consistent with the hypothesis that this region of the protein substrates for the carboxylase not only serves an enzyme recognition or docking function but also modulates the activity of the enzyme by altering the affinity for one of its substrates.     

Expression of HOX homeogenes in human neuroblastoma cell culture lines

Mammalian genes containing a class-I homeobox (HOX genes) are highly expressed in the embryonic nervous system. As a first step towards the molecular analysis of the role these genes play in neural cells, we studied the expression of four human HOX genes in five neuroblastoma (NB) cell lines - SK-N-BE, CHP-134, IMR-32, SK-N-SH and LAN-1 - during the process of differentiation induced by treatment with retinoic acid (RA). The four genes, HOX1D, 2F, 3E and 4B, located at corresponding positions in the four HOX loci, share a high degree of sequence similarity with the Drosophila Deformed homeotic gene and constitute a homology group, group 10. One of these genes, HOX1D, is not expressed in the cells used, whereas the other three are highly expressed in untreated and RA-induced NB cells, even though the expression pattern in the various lines is slightly different for the three genes. Our analysis reveals a complex and specific expression pattern in these lines, paving the way to an identification of different NB-cell populations by means of specific HOX gene expression schemes. On the other hand, in every line studied, morphological maturation toward a neuronal differentiated phenotype appears to be associated with increased HOX gene expression.     

Rhodobacter capsulatus strain BK5 possesses a membrane bound respiratory nitrate reductase rather than the periplasmic enzyme found in other strains

Rhodobacter capsulatus strain BK5 possesses a membrane bound respiratory nitrate reductase rather than the periplasmic enzyme found in other strains. The enzyme in strain BK5 is shown to be both functionally and structurally related to the nitrate reductase of Paracoccus denitrificans and Escherichia coli.Abbreviation TMAO trimethylamine-N-oxide     

Effects of tRNA-intron structure on cleavage of precursor tRNAs by RNase P from Saccharomyces cerevisiae.

RNase P derived from S. cerevisiae nuclei was tested for its ability to cleave a variety of naturally occurring and selectively altered precursor-tRNA molecules to yield matured 5' termini. Precursors were synthesized in vitro in order to test which aspects of substrate structure are crucial to recognition and cleavage by RNase P. Base modifications in the precursor substrates are not required for cleavage by the enzyme, but deletion and substitution mutations affecting any portion of the precursor tertiary structure reduce cleavage. In particular, a number of alterations in the intervening sequence (IVS) reduce the susceptibility of the substrate to cleavage by RNase P. The significance of these results is discussed in reference to the contribution of the IVS to the structure of the precursor-tRNA.     

The altered expression of MHC-class II determinants on monocytes of cancer patients

Summary The expression of MHC class II determinants Ia.7 (detected by cross reactive mouse anti-Ia^k antibody) and HLA-DR on monocytes (MO) of gastric and colorectal cancer patients was examined. An increased proportion of MO bearing the Ia.7 determinant was found, while the number of MO expressing DR was not elevated. In gastric cancer patients the increased expression of the Ia.7 determinant was most pronounced in advanced cancer (stage IVA and IVB). The increased expression of this determinant was related to the presence of the tumour as the number of MO expressing Ia.7 decreased 6 months following surgical resection of the tumour. Further, the increased expression of Ia.7 on MO correlated with the tumour infiltration of the serosa. The Ia.7 determinants were mainly expressed on MO which also expressed the receptor for the Fc part of immunoglobulin. Immunostaining in cellular infiltrates surrounding the tumour revealed that Ia.7⁺ macrophages (MØ) were more numerous than in normal gastric mucosa and severe chronic gastritis and were mostly present in close proximity to tumour cells, while DR⁺ MØ were mainly localized within the stromal tissue of the tumour and their number was not increased in cancer infiltrates. These observations indicate that the Ia.7⁺ subpopulation of MØ may be involved in the anti-tumour response of the host.     

Nyctohemeral Rhythms of Gonadal, Thyroid and Pineal Function in the Hyperprolactinemic Male Rat

In young adult male rats bearing a donor anterior pituitary gland grafted for 3 weeks under a kidney capsule, serum prolactin (PRL) concentrations were elevated and exhibited a rhythm with the highest values in the light phase. Serum PRL in control animals did not exhibit a significant rhythm. Eutopic pituitary PRL content, manifesting a biphasic (12-hr) rhythm with crests during the day and night in controls, exhibited a similar pattern in grafted rats though an overall reduction in pituitary PRL content was seen in the grafted animals. Neither the normal biphasic serum testosterone rhythm nor the normal 24-hr rhythm (nocturnal surge) of pineal N-acetyltransferase activity and melatonin content were altered in the hyperprolactinemic rats. Serum thyroxine (T₄) and triiodothyronine (T₃) and their free indices (FT₄ I, FT₃ I) and serum thyrotropin (TSH) were highest during the day in controls and grafted rats and a 12-hr rhythmic component was detected in data for these variables. In the grafted animals, the 12-hr component was reflected in an additional peak at night detectable by testing of means. The overall serum T₄ FT₄ I, and TSH levels were lower in grafted rats though overall T₃ and FT₃I levels did not differ between grafted and controls. T₃ uptake (T₃ U) values were similar between controls and grafted rats, in both cases exhibiting a fall during the night. Changes in serum thyronines could not be explained by changes in serum binding as assessed by the T₃U₃ and thus may represent changes in thyroidal secretion of T₄. The rhythm in serum PRL of grafted rats suggests the presence of rhythmic circulating factor(s) capable of influencing ectopic lactotrophs. The reduced eutopic pituitary PRL content suggests a role for PRL in influencing eutopic lactotrophs in the pituitary-grafted hyperprolactinemic male rat model. Though circulating testosterone and pineal melatonin synthesis were not altered in this model, thyroid function appeared to be so.