Vacuolar efflux of malate and its influence of nitrate accumulation in Catharanthus roseus cells

Catharanthus roseus cell suspension cultures may accumulate large quantities of malate in the vacuolar space. Upon transfer into a fresh medium malate moves out of the vacuole. This compound is then oxidized and its assimilatory products (CO₂ + HCO₃^?) are excreted into the medium. The malate concentration decreases concurrently with an intracellular accumulation of nitrate. The opposite time course changes in malate and nitrate concentrations can be slowed down by treatment with synthetic auxins and fusicoccin which increase the HCO₃^? concentration in the cytoplasm. A line of evidence is presented which shows that malate consumption is causally related with the uptake of nitrate. The involvement of a HCO₃^?/NO₃^? antiport is proposed.     

White Ibis integument color during the breeding season

ABSTRACT.   Many birds undergo bare part color changes during the breeding season. Most investigators have focused on color as a signal of individual quality. An alternative, but not exclusive, function of bare part color may be signaling readiness to breed, especially in colonial, asynchronous breeders. White Ibises ( Eudocimus albus ) are colonial waterbirds that show vivid bare part colors on their bills and legs during reproduction. We quantified bill and leg colors to describe color changes and their possible relationship to reproductive status during the breeding season of White Ibises in the Florida Everglades from 1998 to 2001. We also examined the correlation between bare part colors and circulating concentrations of sex steroids to understand the factors that regulate bare part colors. During the display stage, male and female ibises developed dark pink bills and scarlet legs. As the breeding season progressed, bills and legs faded and developed a muted pink hue. The bare part colors of female ibises were correlated with testosterone concentrations, but those of male ibises were not correlated with any hormones. A discriminant function analysis based on principal component scores (representing variation in saturation and hue) and the amount of black on the bill successfully classified ibis reproductive stage 94% of the time. The use of bare part colors to determine reproductive status may be useful for studying reproduction in colonially nesting birds, where access to breeding sites can be difficult and potential for researcher disturbance is high.     

SECONDARY-FRUIT ONTOGENY IN NAVEL ORANGE

Ontogeny of the secondary fruit of navel orange (Citrus sinensis [L.] Osbeck) was studied using flower buds and fruit from groves in north central Florida. The secondary fruit, or navel, develops as a whorl of secondary-carpel primordia within the primary-carpel whorl when the flower bud is 1.5 to 2.0 mm in length. A complete secondary gynoecium with fused ovary but separate styles and stigmas develops within the primary gynoecium before anthesis. The stigma and style of secondary carpels are not as distinct as those of primary carpels. Three types of tissue protrusions from the secondary fruit into primary-fruit locules were abnormal placentae, free secondary carpels, and secondary-carpel outgrowths, the last being the most common. An abscission layer is present in the central axis of the primary fruit near the base of the secondary ovary. This layer is indistinguishable from adjacent tissues prior to commencement of secondary fruit abscission. Parenchyma cells in the abscission layer, however, contain large numbers of starch grains during abscission. Secondary and primary fruit have similar sigmoid growth patterns; however, onset of the cell-enlargement stage is approximately 2 wk later in secondary fruit.     

Test of the principle of initial value in rat genetic models of exercise capacity

An inverse relationship between initial level of physical capacity and the magnitude of response to training is termed the principle of initial value. We tested the operation of this principle under experimental conditions of minimal genetic and environmental variation. Inbred rat strains previously identified as genetic models of low [Copenhagen (COP)] and high [Dark Agouti (DA)] intrinsic (untrained) exercise capacity were trained for 8 wk on a treadmill using two disparate protocols: 1) a relative mode where each rat exercised daily according to its initial capacity, and 2) an absolute mode where both strains received the same amount of training independent of initial capacity. Response to exercise was the change in running capacity as estimated by meters run to exhaustion before and after training. When trained with the relative mode, COP rats gained 88 m (+21%; NS) whereas DA rats increased distance run by 228 m (+36%; P < 0.001). When each strain trained with the same absolute amount of training, the COP strain showed essentially no change (-6 m, -2%) and the DA strain gained 325 m (+49%; P < 0.009). Differences in response to exercise between the COP and DA could not be explained by body mass differences, oxidative enzyme activity (citrate synthase or ATP), or spontaneous behavioral activity. Our data demonstrate that genetic factors causative of high response to exercise are not uniquely associated with genetic factors for low intrinsic capacity and thus are not in accord with the principle of initial value.     

Discovering functional relationships: biochemistry versus genetics

Biochemists and geneticists, represented by Doug and Bill in classic essays, have long debated the merits of their methods. We revisited this issue using genomic data from the budding yeast, Saccharomyces cerevisiae, and found that genetic interactions outperformed protein interactions in predicting functional relationships between genes. However, when combined, these interaction types yielded superior performance, convincing Doug and Bill to call a truce.     

Maintenance of quantal size and immediately releasable granules in rat chromaffin cells by glucocorticoid

Glucocorticoid is reported to regulate catecholamine synthesis and storage. However, it is not clear whether the actual amount of catecholamine released from individual granules (quantal size, Q) in mature chromaffin cells is affected by glucocorticoid. Using carbon fiber amperometry, we found that dexamethasone did not affect mean cellular Q or the proportional release from different populations of granules in rat chromaffin cells cultured for 1 day in a serum-free defined medium. After two extra days of culture in the defined medium, there was a rundown in mean cellular Q, and it was associated with a shift in the proportional release from the different granule populations. This phenomenon could not be rescued by serum supplementation but could be prevented by dexamethasone via an action that was independent of changes in voltage-gated Ca²⁺ channel (VGCC) density. Using simultaneous measurements of membrane capacitance and cytosolic Ca²⁺ concentration, we found that for cells cultured in defined medium dexamethasone enhanced the exocytotic response triggered by a brief depolarization (50 ms) without affecting the VGCC density or the fast exocytotic response triggered via flash photolysis of caged Ca²⁺. Thus glucocorticoid may regulate the number of immediately releasable granules that are in close proximity to a subset of VGCC. Because chromaffin cells in vivo are exposed to high concentrations of glucocorticoid, our findings suggest that the paracrine actions of glucocorticoid maintain the mean catecholamine content in chromaffin cell granules as well as the colocalization of releasable granules with VGCCs. catecholamines; paracrine action; exocytosis; calcium channels     

Minimally invasive method for murine brain fixation

Complete brain fixation can be achieved with transthoracic cardiac infusion without thoracotomy. Light and electron microscopy tissue sections reveal preservation of cytoplasmic and nuclear structure at all magnification levels. Punched samples were obtained from the fixed tissue specimens in precisely localized areas for study using electron microscopy. This perfusion fixation technique provides both faster tissue harvesting capability and higher quality tissue preservation, without the artifacts of brain swelling and ventricular dilation observed in direct cardiac perfusion. Acute, discrete change in brain tissue can be studied.     

Genetic diversity and the evolutionary history of plant immunity genes in two species of Zea

Plant pathogenesis-related genes (PR genes) code for enzymes, enzyme inhibitors, and other peptides that confer resistance to pathogens and herbivores. Although several PR genes have been the subject of molecular population genetic analyses, a general understanding of their long-term evolutionary dynamics remains incomplete. Here we analyze sequence data from 17 PR genes from two closely related teosinte species of central Mexico. In addition to testing whether patterns of diversity at individual loci depart from expectations under a neutral model, we compared patterns of diversity at defense genes, as a class, to nondefense genes. In Zea diploperennis, the majority of defense genes have patterns of diversity consistent with neutral expectations while at least two genes showed evidence of recent positive selection consistent with arms-race models of antagonistic coevolution. In Zea mays ssp. parviglumis, by contrast, analyses of both defense and nondefense genes revealed strong and consistent departures from the neutral model, suggestive of nonequilibrium population dynamics or population structure. Nevertheless, we found a significant excess of replacement polymorphism in defense genes compared to nondefense genes. Although we cannot exclude relaxed selective constraint as an explanation, our results are consistent with temporally variable (transient or episodic) selection or geographically variable selection acting on parviglumis defense genes. The different patterns of diversity found in the two Zea species may be explained by parviglumis' greater distribution and population structure together with geographic variation in selection.