Oxygen stable isotope ratios of tree-ring cellulose: the next phase of understanding

Analysis of the oxygen isotope ratio of tree-ring cellulose is a valuable tool that can be used as a paleoclimate proxy. Our ability to use this tool has gone through different phases. The first began in the 1970s with the demonstration of empirical relationships between the oxygen isotope ratio of tree-ring cellulose and climate. These empirical relationships, however, did not provide us with the confidence that they are robust through time, across taxa and across geographical locations. The second phase began with a rudimentary understanding of the physiological and biochemical mechanisms responsible for the oxygen isotope ratios of cellulose, which is necessary to increase the power of this tool. This phase culminated in a mechanistic tree-ring model integrating concepts of physiology and biochemistry in a whole-plant system. This model made several assumptions about leaf water isotopic enrichment and biochemistry which, in the nascent third phase, are now being challenged, with surprising results. These third-phase results suggest that, contrary to the model assumption, leaf temperature across a large latitudinal gradient is remarkably constant and does not follow ambient temperature. Recent findings also indicate that the biochemistry responsible for the incorporation of the cellulose oxygen isotopic signature is not as simple as has been assumed. Interestingly, the results of these challenges have strengthened the tree-ring model. There are several other assumptions that can be investigated which will improve the utility of the tree-ring model.     

Biogenesis of the ciliary roots: participation of the dictyosomes of Golgi's complex.

In this study, the hypothesis of a possible biogenesis of the ciliary roots is suggested, after observing the cilia neurons under the electron microscope, which were found as an exception in the periaqueductal nucleus of the mesencephalon in the domestic cat, conserving the potential to differentiate the cilia, basal bodies and ciliary roots. The dictyosomes of Golgi's complex and Golgi's vesicles participated in this biogenesis. Vesicles of approximately 71.6 nm in diameter had become separated from the periphery of the flattened discoid cisterns of the dictyosome and were aligned normally, in tangential contact with each other, forming rows of vesicles or 'ringed chains', whose points of contact formed the beginning of the 'periodic striation' of a thin ciliary root. Later, the lateral walls of the vesicles and the molecules of the intracisternal proteins gave rise to the interperiodic microfilaments, when the carrier proteins were transformed into structural proteins of the ciliary roots. The parallel apposition of several ringed chains or thin ciliary roots, with their rings joined at the same level (or transversal striations), gave rise to thicker striated roots. This hypothesis of an ultrastructural biogenesis of the striated ciliary roots involves the following six stages: stage I = separation of Golgi's vesicles from the periphery of the flattened disk of dictyosomes near the basal body, with a diameter of over 71.6 nm; stage II = reinforcement of the membrane of the vesicles at the two opposite polar ends of its larger diameter; stage III = alignment of vesicles to form ringed chains, due to the tangential contact between their reinforced points; initiation of the 71.6-nm striation period, roots ringed linearly; stage IV = formation of joining microfilaments between periods (69.2 nm) with the lateral walls of the vesicles and the molecules of the proteins in their content; stage V = lengthening of the thin ciliary roots due to the coupling of new Golgi's vesicles at their ends so that their length increases as a result of the addition of terminal vesicles; stage VI = increase in thickness of the thin ciliary roots, due to the parallel apposition of several ringed chains or thin ringed ciliary roots, at the point where their transversal striation points coincide.     

Curculionid beetles in aborted flower buds and immature fruits of <Emphasis Type="Italic">Ceiba</Emphasis><Emphasis Type="Italic">pentandra</Emphasis> (Bombacaceae)

We determined the incidence of curculionid beetles of the genus Lonchophorus on aborted and not aborted flower buds and developing fruits of the tree Ceiba pentandra in southeastern Costa Rica. Beetle larvae were found in reproductive parts of all trees sampled trees. The frequency of beetle larvae was greater in aborted buds and immature fruits. A positive correlation between larvae development and flower bud development indicates that female oviposition occurred in an early flower developmental stage and time until bud abortion is variable. Weevil herbivory could be considered as one of the main factors that cause flower bud and fruit abortion in C. pentandra.

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Resumen Determinamos la incidencia de curculiónidos del género Lonchophorus en botones florales y frutos inmaduros tanto abortados como no abortados en el árbol Ceiba pentandra en el SE de Costa Rica. Las larvas de curculiónidos fueron encontradas en todos los árboles muestreados. La frecuencia de larvas fue mayor en botones y frutos abortados. Una correlación positiva entre el desarrollo larval y el desarrollo del botón indica que la oviposición ocurre en una fase temprana de este y que el tiempo hasta el aborto es variable. La herbivoría por larvas de curculiónidos puede ser uno de los factores más importantes en el aborto de botones y frutos inmaduros en C. pentandra.

     

Localization of eukaryotic initiation factor 2 in neuron primary cultures and established cell lines

Eukaryotic initiation factor 2 (eIF-2) is a heterotrimeric protein with subunits α, β and γ that forms a ternary complex with Met-tRNA and GTP. It promotes the binding of Met-tRNA to ribosomes and controls translational rates via phosphorylation/dephosphorylation mechanisms. By means of immunofluorescence and post-embedding immunocytochemistry of intact cells and quantitative immunoblotting of cell extracts, the cellular distribution of the initiation factor has been examined in primary neuronal cultures as well as in two established cell lines: PC12 phaeochromocytoma cells and rat pituitary GH4C1 cells. Our results indicated that the initiation factor is located not only in the cytoplasm but also in the nuclei of the cultured neurons and cell lines. In the cytoplasm, immunocytochemical studies reveal that the factor is present mainly in those areas that are rich in ribosomes. In the nucleus, the immunolabelling of eukaryotic initiation factor 2 verified the presence of gold particles in both nucleolar and extranucleolar areas. The specific distribution of this factor on both sides of the nuclear envelope suggests that it might have some nuclear-related function(s) besides its already known role in the control of translation     

Contrasting effects of sn-1,2-dioctanoyl glycerol as compared to other protein kinase C activators in adrenal glomerulosa cells

Angiotensin II acts on adrenal glomerulosa cells to induce the phospholipase C-mediated generation of inositol trisphosphate and sn-1,2-diacylglycerol as the major products of inositol phospholipid breakdown. This last product is known to activate protein kinase C, but its role in the action of angiotensin II on steroidogenesis has not been defined. We report herein that, in bovine adrenal glomerulosa cells, protein kinase C activators, such as phorbol 12,13-dibutyrate, 12-O-tetradecanoylphorbol-13-acetate, mezerein and sn 1,2 oleoyl acetoylglycerol, each failed to increase steroidogenesis. These results contrast with our recent report on the enhancement of aldosterone output by sn-1,2-dioctanoylglycerol (DiC8) [J. Steroid Biochem. 35 (1990) 19-33]. In addition, the difference between DiC8 and the other protein kinase activators was also observed in the pattern of 86Rb efflux from preloaded glomerulosa cells; only DiC8 mimicked the effect of angiotensin II on ion fluxes. Furthermore, staurosporine, a potent inhibitor of protein kinase C, was capable of amplifying the aldosterone output induced by a maximally effective concentration of DiC8 or angiotensin II. These data suggest that the effect of the cell permeant DiC8 on aldosterone biosynthesis either is not mediated by protein kinase C activation, or is mediated by a phorbol ester-insensitive isoenzyme of protein kinase C.