Disturbed nitrogen metabolism associated with the hyperhydric status of fully habituated callus of sugarbeet

The content of polyamines and proline was much lower in a normal (N) callus of Beta vulgaris L. than in a fully habituated hyperhydric (H) callus. The H callus also contained more glutamate and had a higher glutamate dehydrogenase activity. The excess of glutamate, in this chlorophyll-deficient callus, was linked to accumulation of proline and polyamines. Experiments with α-difluoromethylornithine (DFMO) and α-difluoromethylarginine (DFMA) showed that both ornithine decarboxylase and arginine decarboxylase participated in the synthesis of polyamines (especially spermidine and putrescine) and removal of ammonia. It is hypothesized that the H callus was subjected to ammonia stress from the start of the culture. Experiments with gabaculine, an inhibitor of ornithine aminotransferase, showed that this enzyme linked proline degradation to polyamine synthesis through the production of ornithine. This disturbed nitrogen metabolism appeared to be characteristic of the fully habituated callus and might explain the low growth of this hyperhydric tissue.     

The Response to Exercise with Constant Energy Intake in Identical Twins

Seven pairs of young adult male identical twins completed a negative energy balance protocol during which they exercised on cycle ergometers twice a day, 9 out of 10 days, over a period of 93 days while being kept on a constant daily energy and nutrient intake. The total energy deficit caused by exercise above the estimated energy cost of body weight maintenance reached 244 ± 9.8 MJ (Mean ± SEM). Baseline energy intake was estimated over a period of 17 days preceding the negative energy balance protocol. Mean body weight loss was 5.0 kg (SEM = 0.6) (p <0.001) and it was entirely accounted for by the loss of fat mass (p <0.001). Fat-free mass was unchanged. Body energy losses reached 191 MJ (SEM = 24) (p <0.001) which represented about 78% of the estimated energy deficit. Subcutaneous fat loss was slightly more pronounced on the trunk than on the limbs as estimated from skinfolds, circumferences, and computed tomography (CT). The reduction in CT-assessed abdominal visceral fat was quite striking, from 81 cm² (SEM = 5) to 52 cm² (SEM = 6) (p <0.001). At the same submaximal power output level, subjects oxidized more lipids than carbohydrates after the program as indicated by the changes in the respiratory exchange ratio (p <0.05). Intrapair resemblance was observed for the changes in body weight (p <0.05), fat mass (P <0.01), percent fat (p <0.01), body energy content (p <0.01), sum of 10 skinfolds (p <0.01), abdominal visceral fat (p <0.01), fasting plasma triglycerides (p <0.05) and cholesterol (p <0.05), maximal oxygen uptake (p <0.05), and respiratory exchange ratio during submaximal work (p <0.01). We conclude that even though there were large individual differences in response to the negative energy balance and exercise protocol, subjects with the same genotype were more alike in responses than subjects with different genotypes particularly for body fat, body energy, and abdominal visceral fat changes. High lipid oxidizers and low lipid oxidizers during sub-maximal exercise were also seen despite the fact that all subjects had experienced the same exercise and nutritional conditions for about three months.     

Differential localization of two isoforms of the regulatory subunit RIIα of cAMP-dependent protein kinase in human sperm: Biochemical and cytochemical study

In the present study, immunogold labeling of ultrathin sections of ejaculated sperm was used to obtain insight into the ultrastructural localization and presumable function of type II cAMP-dependent protein kinase in sperm motion. In the flagellum, a human-specific isoform of the RIIα subunit was located on the axonemal microtubule wall, whereas a different isoform of broader specificity was present in the cytoplasm at the periphery of the coarse fibers and fibrous sheath. This isoform was also found in the mitochondria. The human-specific RIIα subunit is likely linked to microtubules by a unique binding protein of M_r 72kD. These findings are in agreement with the concept of a concerted mechanism involving phosphorylation of both the axonemal microtubules and the fibrous structures for the regulation of mammalian sperm motion. © 1994 Wiley-Liss, Inc.     

Amplified somatic embryogenesis from male flowers of triploid banana and plantain cultivars (Musa spp.)

Summary Somatic embryogenesis and plant regeneration of banana and plantain cultivars (Musa spp.) were obtained by culturing young male flowers. Multiplication and maintenance of embryogenic cultures were achieved by culturing somatic embryos in a temporary immersion system (SIT). A multiplication rate of 40 allowed us to obtain more than 6000 somatic embryos after 6 mo. of subculture. Plant recovery frequencies were 60 to 70%. This method was expanded to different banana and plantain genomic groups.     

Benthic invertebrates of some saline lakes of the Sud Lipez region,Bolivia

The benthic invertebrates fauna of most of the saline lakes of the Sud Lipez region (Bolivia, Altiplano) has been until now quite unstudied. Samples collected during an extensive survey of 12 lakes and two small inflow rivers allow a first list of the main macroinvertebrates living in these biotopes.The heterogeneous nature of these saline lakes with their freshwater springs and phreatic inflows offers a variety of habitats to macroinvertebrates. The benthic fauna in lakes with salinities > 10 g l^–1 is not so low in density but includes few species and is dominated by Orthocladiinae and Podonominae larvae. In contrast, the freshwater springs and inflows are colonized by a diverse fauna, with a mixture of both freshwater and saline taxa, but dominated by Elmidae and Amphipoda. The lakes are quite isolated and, apart from some cosmopolitan organisms, their fauna can be quite distinctive.     

Heterogeneous Na+ Sensitivity of Na+,K+-ATPase Isoenzymes in Whole Brain Membranes

Abstract: The Na⁺ sensitivity of whole brain membrane Na⁺,K⁺-ATPase isoenzymes was studied using the differential inhibitory effect of ouabain (α1, low affinity for ouabain; α2, high affinity; and α3, very high affinity). At 100 m M Na⁺, we found that the proportion of isoforms with low, high, and very high ouabain affinity was 21, 38, and 41%, respectively. Using two ouabain concentrations (10⁻⁵ and 10⁻⁷ M ), we were able to discriminate Na⁺ sensitivity of Na⁺, K⁺-ATPase isoenzymes using nonlinear regression. The ouabain low-affinity isoform, α1, exhibited high Na⁺ sensitivity [ K _a of 3.88 ± 0.25 m M Na⁺ and a Hill coefficient ( n ) of 1.98 ± 0.13]; the ouabain high-affinity isoform, α2, had two Na⁺ sensitivities, a high ( K _a of 4.98 ± 0.2 m M Na⁺ and n of 1.34 ± 0.10) and a low ( K _a of 28 ± 0.5 m M Na⁺ and an n of 1.92 ± 0.18) Na⁺ sensitivity activated above a thresh old (22 ± 0.3 m M Na⁺); and the ouabain very-high-affinity isoform, α3, was resolved by two processes and appears to have two Na⁺ sensitivities (apparent K _a values of 3.5 and 20 m M Na⁺). We show that Na⁺ dependence in the absence of ouabain is the result of at least of five Na⁺ reactivities. This molecular functional characteristic of isoenzymes in membranes could explain the diversity of physiological roles attributed to isoenzymes.     

Cellular Quantification of Tyrosine Hydroxylase in the Rat Brain by Immunoautoradiography

Abstract: We developed a rapid and sensitive radioimmunohistochemical method for the quantification of tyrosine hydroxylase (TH) at both the anatomical and cellular level. Coronal tissue sections from fresh-frozen rat brains were incubated in the presence of a TH monoclonal antibody. The reaction was revealed with a ³⁵S-labeled secondary antibody. TH content was quantified in catecholaminergic brain areas by measuring optical density on autoradiographic films or silver grain density on autoradiographic emulsion-coated sections. Regional TH concentrations determined in the locus ceruleus (LC), substantia nigra pars compacta (SNC), and ventral tegmental area (VTA) were significantly increased by 45% after reserpine treatment in the LC but unchanged in the SNC and VTA. Microscopic examination of TH radioimmunolabeling showed a heavy accumulation of silver grains over catecholaminergic cell bodies. In the LC, grain density per cell was heterogeneous and higher in the ventral than in the dorsal part of the structure. After reserpine treatment, TH levels were significantly increased (57%) in the neurons of the LC but not in those of the SNC or VTA. The data support the validity of this radioimmunohistochemical method as a tool for quantifying TH protein at the cellular level and they confirm that TH protein content is differentially regulated in noradrenergic and dopaminergic neurons in response to reserpine.     

Chromosomes of the Antarctic amphipod Waldeckia obesa Chevreux

Mitotic and meiotic chromosomes of the Antarctic lysianassoid amphipod Waldeckia obesa are described. The modal chromosome number is n = 25 and 2n = 50. The potential applications of cytogenetical studies in this group are discussed.     

Sulphate/proton cotransport in plasma-membrane vesicles isolated from roots of Brassica napus L.: increased transport in membranes isolated from sulphur-starved plants

The characteristics of sulphate uptake into right-side-out plasma-membrane vesicles isolated from roots of Brassica napus L., Metzger, cv. Drakkar, and purified by aqueous polymer two-phase partitioning, were investigated. Sulphate uptake into the vesicles was driven by an artificially imposed pH gradient (acid outside), and could be observed for 5–10 min before a plateau was reached and no further net uptake occurred. The uptake was partially inhibited in the presence of depolarizing agents and little uptake was observed in the absence of an imposed pH gradient. Uptake was strongly pH-dependent, being greatest at more acidic pH. After imposition of a pH gradient, the capacity for uptake decreased slowly (t1/2>10 min). The uptake had a high-affinity component which was strongly dependent on the external proton concentration (K _m=10μM at pH 5.0, 64 μM at pH 6.5). The K _m for protons varied from 0.4–1.9 μM as the sulphate concentration was reduced from 33 to 1 μM. A low-affinity component was observed which could be resolved at low temperatures (0 °C). Microsomal membranes that partitioned into the lower phase of the two-phase system gave no indication of high-affinity sulphate transport. Sulphate uptake into plasma-membrane vesicles isolated from sulphur-starved plant material was approximately twofold greater than that observed in those isolated from sulphate-fed plant material. Isolated vesicles therefore mirror the well-known in-vivo response of roots, indicating an increase in the number of transporters to be, at least in part, the underlying cause of derepression.     

Effects of sexual differences of age at maturity and survival on population sex ratio

Summary Five demographical factors influencing the sex ratio of a population are classically considered. The influence of two of them is dependent on the longevity of individuals in the population. The effect of differential age at maturity between males and females is higher for animals with low annual survival, whereas the effect of differential annual survival between males and females is higher for animals with high annual survival. Such a conclusion applied to turtles, which are long life-span animals, allows us to retain differential survival between sexes as a major factor influencing the population sex ratio.