Floristic groups and plant communities of southeastern Santa Fe,Argentina

This paper is a survey of the vegetation of the southeastern departments in the Province of Santa Fe (Argentina). The vegetation was analyzed following Braun-Blanquet's approach modified by Mueller-Dombois & Ellenberg (1974). The most relevant species of the region were placed in 25 groups according to their requirements or general behaviour. Most of the communities are herbaceous, and apart from the woody and some other miscellaneous ones they were grouped into three ecologically and floristically defined sets. The first set, the Stipa grasslands and related communities, which are characterized by the more or less abundant presence of Stipa hyalina, Stipa neesiana and Stipa papposa, comprises five different communities. The second, the halophilous communities, comprises five communities, the two Spartina ssp. grasslands, the halophilous prairies of Distichlis spicata, the short sedge Scirpus americanus communities and the ‘pela-dales’. The third, the hygrophilous communities, comprises nine communities which are not so well defined as the ones in the other sets. Besides, two further communities have been included, the Paspalum quadrifarium and the Melica macra tall grasslands.     

In vitro modification of Candida albicans invasiveness

Candida albicans produces germ-tubes (GT) when it is incubated in animal or human serum. This dimorphism is responsible for its invasive ability.The purpose of the present paper is (1) to evaluate the ability of rat peritoneal macrophages to inhibit GT production of ingested Candida albicans, obtained from immunized rats and then activated in vitro with Candida-induced lymphokines; (2) to determinate any possible alteration of phagocytic and candidacidal activities.The phagocytes were obtained from rats immunized with viable C. albicans. Some of them were exposed to Candida-induced lymphokines in order to activate the macrophages in vitro. The monolayers of activated, immune and normal macrophages were infected with a C. albicans suspension during 4 hr.Activated macrophages presented not only the highest phagocytic and candidacidal activities but a noticeable inhibition of GT formation and incremented candidacidal activity.     

Computer-aided three-dimensional reconstructions of the arrangement of primary spermatocytes in human seminiferous tubules

Summary With the use of a digital image-processing method three-dimensional reconstructions of the arrangement of spermatocytes in human seminiferous tubules were performed. With this method it was possible to investigate the cellular distribution in the tubule in nearly any given perspective and projection. In addition, by means of simple mathematical procedures, such as by transformation of Cartesian coordinates into cylindrical coordinates, it was possible to vary the shape of a reconstruction, i.e., to convert the cylindrical image of a tubular portion into a right-angled r--z-representation.The present work not only confirms the existence of a complex helical plan of organization of the human seminiferous epithelium but also provides further aspects of the phenomenon of physiological germ-cell loss and its integration into the kinetics of spermatogenesis.Dedicated to Prof. E.C. Roosen-Runge, Seattle, on the occasion of his 75th birthday     

The importance of the Escherichia coli ribosomal protein L16 for the reconstitution of the peptidyl-tRNA hydrolysis activity of peptide chain termination

The incubation of the 50 S ribosomal subunit of Escherichia coli with 1.5 M LiCl yields 1.5c core particles inactive in the peptidyl-tRNA hydrolysis activity of in vitro termination. The omission of L16 alone from reconstitutions of the proteins into the core results in inactive ribosomes. The single omission of a number of other proteins, in particular L7/L12, L10, L25, L27, and L15, gives ribosomes with intermediate activity. L16 alone is unable to restore significant activity to 1.5c cores, but together L16 and the above "stimulating" proteins produce particles as active as those reconstituted with the full complement of proteins. The ribosomal proteins important for the expression of peptidyl-tRNA hydrolysis and peptidyl transferase activities are very similar. However, ribosomes lacking both L11 and L16, but not L16 alone, surprisingly can catalyze codon- and release factor 2-dependent peptidyl-tRNA hydrolysis. The addition of L16 dramatically increases the activity. L16 is, therefore, important but not essential for the expression of the release factor 2-dependent peptidyl-tRNA hydrolysis.     

Effect of Deseeding on the Indole-3-acetic Acid Content of Shoots and Roots of Zea mays Seedlings

We wished to determine the effect of endosperm removal on the amounts of free and esterified indole-3-acetic acid (IAA) in young Zea mays seedlings. The increases of IAA derived from endosperm and from biosynthesis, but without correction for catabolic losses, were 0.9 picomole of free IAA per shoot per hour, and 1.1 picomoles per shoot per hour of ester IAA. After deseeding, free IAA in the shoot declines by 40% following kernel removal and total (free + ester) IAA declines at a rate of about 1 picomole per shoot per hour. A slight, but insignificant increase of ester IAA occurs following endosperm removal. In the primary roots, the decreases of free IAA and total (free + ester) IAA are accelerated by seed removal. Thus, the endosperm appears to be a major source of IAA for the shoot and root.     

Ultrastructural localization of nucleoside phosphatase activity in the thymocytes of rats

A comparative electron histochemical investigation was made of ATPase and 5'-nucleotidase activities in isolated cells and in cryostate sections of the rat thymus after various pretreatment. A most optimal demonstration of intracellular ATPase and 5'-nucleotidase activities was possible in non-fixed isolated cells whose cytoplasm was partially or completely destroyed in the process of homogenization. ATPase and 5'-nucleotidase activities were revealed in the nuclear chromatin and in interchromatin ribonucleoproteins, perinuclear space, endoplasmic reticulum and Golgi complex. ATPase activity on the plasma membrane was revealed in the best way in isolated cells after glutaraldehyde prefixation.     

Protein kinase from Mucor rouxii

Summary Cyclic AMP binding to Mucor rouxii protein kinase holoenzyme and free regulatory subunit was measured by the classical membrane filtration technique and by equilibrium dialysis. The results obtained demonstrate that the filtration method can be used without loss of any cyclic AMP binding site. Both methods unambiguously demonstrate that the number of molecules of cyclic AMP bound to the holoenzyme are half of those bound to the regulatory subunit. This result suggests that unshielding of new cyclic AMP binding sites occurs upon dissociation of the ternary complex holoenzyme-cyclic AMP.     

Regulation of idiotope expression. IV. Genetic linkage of two D region-dependent T15 idiotopes to the IgH allotype

The idiotopic (Id) repertoire of antibody response to phosphocholine was studied in mouse strains with different IgH allotypes. The T15 idiotype-bearing (T15+) serum antibody and antibody plaque-forming cells (PFC) were characterized with four monoclonal anti-Id that recognize distinct Id determinants on T15+ antibody encoded by VH-1 (of the S107 gene family), DH FL16.1, JH-1 and Vk22 germ-line genes. We have previously shown that expression of the Id designated AB1-2 and B36-82 depends on the third hypervariable loop (D region), whereas the other Id, MaId5-4 and B24-44, are influenced by VH structures outside of the D region. All four Id were expressed in the PC-response of all mouse strains tested, except the Ighj strains (C3H/HeJ, CBA/H-T6, PL/j), where the D region-dependent Id, AB1-2 and B36-82, were absent. The other Id, however, were normally expressed on individual PFC as well as the serum antibody of the Ighj strains. Expression of AB1-2 and B36-82 on 50% of PFC occurred in (BALB/c-Igha x C3H/HeJ-Ighj)F1 mice. The absence of Id correlated with a unique RFLP of the S107 gene family in Ighj strains. Finally, Id expression segregated with the appropriate RFLP pattern in individual (BALB/c x C3H/HeJ)F2 mice. These data demonstrate a selective genetic linkage of discrete T15 Id determinants, AB1-2 and B36-82 with the Igh allotype. By comparing these results with the available Ig sequences, we suggest that the Ighj allotype may be associated with an allelic form of the DH-FL16.1 segment which with VH-1, JH-1, and the Vk 22 code for the phosphocholine-specific antibody in the mouse.