广东种子植物区系地理成分研究

广东种子植物区系共有２１９科１４３４属４９８６种。其中：①热带区系成分占有较大的比例,约占非世界属的６２．３％,表明广东区系受到热带区系的强烈渗透,次之为亚热带（至亚热带山地）成分约占３２．２％,及中国特有分布占５．６％;②以单型属（７２属）,单种属（５８５属）和寡种属（５６２属）占绝对优势,共占８５．０％,充分显示了广东区系的古老性和过渡性特点;③从区系组成和植被结构的特征成分来看,以华夏植物区系成分为主,包括：亚热带分布,亚热带山地分布,中国特有分布,东亚—北美间断分布,及一些亚洲热带分布中以亚热带为主的属：④在这些属中有东亚特有属１３２属,中国特有属７５属以及华南—西南—中南半岛特有属６８属等;这些属的存在毫无疑问地说明,广东区系是华夏植物区系的核心地区之一,同时也显示了热带区系与亚热带区系有着不可分隔的统一性。     

油梨果实的生长和内含物变化的观察

本文报道对油梨果实的生长及内含物的变化的观察结果．果实生长发育过程中,以６—７份生长最快,干物质及脂肪含量由低到高变化,以１１月份增加最快,蛋白质含量由高到低递诚．１１月份后含量相对稳定,总糖和维生素Ｃ含量随果实的发育程度而下降。     

水库对投饵网箱养鱼的负荷力

本文用１８个１４．３ｍ￣３的围隔组成的围隔群,以鲤为材料,研究了水库对投饵网箱养鱼的负荷力。实验中观测了水温、透明度、ｐＨ值、溶氧、化学耗氧量、生化需氧量与非离子氨等环境因素的变化。结束时将这些变化与我国渔业水质标准相比较,查明该负荷力约为３０００ｋｇ·ｈａ￣（－１）,建议增加２５－３５％的安全储备,以最大载鱼量１８００－２３００ｋｇ·ｈａ￣（－１）作为推荐值。     

Gain control in a proprioceptive feedback loop as a prerequisite for working close to instability

In the artificially closed femur-tibia control system of stick insects oscillations were induced in 3 different ways: Increasing the phase-shift by introducing an electronic delay, afference sign reversal and coupling the tibia to an inert mass. In all 3 cases the oscillations stopped after some time. The gain of the open-loop system was significantly smaller after the oscillations. Afference sign reversal by surgically crossing of the receptor apodeme of the femoral chordotonal organ for 25–85 days does not lead to altered characteristics of the control loop. When sinusoidal passive movements are forced upon the intact femur-tibia joint the forces resisting these movements do not decrease with time. In contrast to direct stimulation of the femoral chordotonal organ, these passive movements also influence the contralateral leg. The experiments show that the gain-control system of the femur-tibia control loop of stick insects consists of at least two components: A sensitization system (with inputs from many kinds of stimuli indicating some kind of disturbance) increases the gain of all reflex loops. A specific habituation-like system decreases the gain with repetitive stimulation only of one control system.Abbreviations fCO femoral chordotonal organ - SETi slow extensor tibiae motor neuron     

Oviposition substrate affects adult mortality, independent of reproduction, in the seed beetle Callosobruchus maculatus

Abstract.

• 1 Seed beetles (Coleoptera: Bruchidae) are commonly used to study the influence of reproduction on life-span and senescence. To study the physiological trade-off between reproduction and mortality, many experiments rely on manipulating access to oviposition substrates to manipulate the reproductive rate of females.
• 2 The presence of host seeds, independent of reproduction, results in increased mortality of female Cullosobruchus muculutus. This influence on mortality varies between two host seed species, suggesting a role of either allelochemicals or energetic costs associated with behaviour on hosts.
• 3 The influence of host seeds on survivorship, independent of reproduction, confounds the interpretation of cost-of-reproduction studies with seed beetles. This complication must thus be considered in the design and interpretation of life-history studies of seed beetles and other insects.

     

Regulation of calmodulin content in synaptic plasma membranes by glucocorticoids

Synaptic plasma membranes (SPM) from the brain are known to have specific binding sites for several steroid hormones, but the mechanisms of membrane transduction of steroid signals is not understood. In this study, corticosterone was found to prevent temperature-dependent dissociation of endogenous calmodlin (CaM) from highly purified SPM from rat cerebral cortex. The steroid stabilizes Ca²⁺-dependent membrane binding of endogenous CaM (78% of total CaM), whereas Ca²⁺-independent binding of CaM (the other 22%) is not affected. The stabilization of membrane binding of endogenous CaM by corticosterone is concentration-dependent, with the maximal effect occurring at steroid concentration of 1 M. The EC₅₀ is estimated as 130 nM, which is almost identical to the K_d of specific binding of the steroid to SPM (120 nM) reported previously. The effect in stabilizing membrane binding of CaM is specific to corticosterone and other glucocorticoids (cortisol, dexamethasone and triamcinolone); gonadal steroids (17-estradiol, progesterone and testosterone) are ineffective. Furthermore, corticosterone administration in vivo (2 mg/kg, i.p.) produced a rapid increase of CaM content in SPM, occurring within 5 min after steroid injection and persisting for at least 20 min. Since CaM mediates a variety of biochemical processes in synaptic membranes, we hypothesize that the effect of glucocorticoids in promoting membrane binding of CaM may lead to a cascade of consequences in synaptic membrane function.Special issue dedicated to Dr. Sidney Ochs.     

Effects of Ca(II) ions on Mn(II) dynamics in chick glia and rat astrocytes: Potential regulation of glutamine synthetase

Previous studies have demonstrated that in glia and astrocytes Mn(II) is distributed with ca. 30–40% in the cytoplasm, 60–70% in mitochondria. Ca(II) ions were observed to alter both the flux rates and distribution of Mn(II) ions in primary cultues of chick glia and rat astrocytes. External (influxing) Ca(II) ions had the greatest effect on Mn(II) uptake and efflux, compared to internal (effluxing) or internal-external equilibrated Ca(II) ions. External (influxing) Ca(II) ions inhibited the net rate and extent of Mn(II) uptake but enhanced Mn(II) efflux from mitochondria. These observations differ from Ca(II)–Mn(II) effects previously reported with brain (neuronal) mitochondria. Overall, increased cytoplasmic Ca(II) acts to block Mn(II) uptake and enhance Mn(II) release by mitochondria, which serve to increase the cytoplasmic concentration of free Mn(II). A hypothesis is presented involving external L-glutamate acting through membrane receptors to mobilize cell Ca(II), which in turn causes mitochondrial Mn(II) to be released. Because the concentration of free cytoplasmic Mn(II) is poised near the K_d for Mn(II) with glutamine synthetase, a slight increase in cytoplasmic Mn(II) will directly enhance the activity of glutamine synthetase, which catalyzes removal of neurotoxic glutamate and ammonia.     

Incorporation of [3H]ethanolamine into acetylcholine by a human cholinergic neuroblastoma clone

Human neuroblastoma cholinergic LA-N-2 cells were used as an experimental model to test the possibility that the methylation of phosphoethanolamine (PEtn) to phosphocholine (PCho) and free choline (Cho) (Andriamampandry et al. 1989) could contribute to acetylcholine (AcCho) synthesis. LA-N-2 cells were incubated with [³H]Cho for 90 min and 22.7% of the radioactivity was present in PCho, 18.5% in free Cho and 4.8% as AcCho. The ratio of Cho/AcCho, however, was of about 1 after 16 hours of incubation. The incorporation of 10M [³H]ethanolamine (Etn) into MeEtn, PMeEtn, PMe₂Etn and their corresponding phospholipids was reduced in cells incubated in medium containing 7.2M choline as compared to cells incubated in medium devoid of choline indicating that the lack of Cho from the incubation medium stimulated the conversion of PEtn to Cho water soluble derivatives. Incubation of LA-N-2 cells with [³H]Etn led to the labelling of [³H]AcCho. Cultures incubated in parallel with [³H]Cho showed that roughly 10% of [³H]AcCho obtained after 16 hrs of incubation with the Cho label derived from [³H]Etn. The synthesis of Cho and AcCho from Etn may be enhanced after cellular differentiation induced by the growth of the cells in the presence of retinoic acid (RA). The results indicate that the methylation of [³H]Etn and/or of [³H]PEtn may be used by cholinergic neurons as precursor for AcCho.Abbreviations Etn ethanolamine - MeEtn monomethylethanolamine - Me₂Etn dimethylethanolamine - P- phosphoryl - AcCho acetylcholine - Ptd phosphatidyl - LPtd lysophosphatidyl - RA retinoic acid     

Spawning ofConger oceanicus andConger triporiceps (Congridae) in the Sargasso Sea and subsequent distribution of leptocephali

Synopsis Distribution of leptocephali ofConger in the Western North Atlantic Ocean was studied using specimens from our collections, specimens from other collections, and various existing collection records. The presence of leptocephali ofConger oceanicus andConger triporiceps < 30 mm long over deep water in the southwestern Sargasso Sea in autumn and winter implies a protracted spawning period there. The subtropical convergence zone, meandering east-west across the Sargasso Sea, is probably the northern limit of spawning of both species. Spawning may also occur close to the Bahamas and Antilles.C. triporiceps may spawn also in the Caribbean Sea judging by the capture of small leptocephali in the western Caribbean and of the more southerly continental distribution of its juveniles. The claim of Johannes Schmidt in 1931 that the EuropeanC. conger spawns across the North Atlantic into the western Sargasso Sea is probably incorrect, because leptocephali ofConger are rare in the eastern Sargasso Sea and becauseC. triporiceps, with myomere numbers overlapping those ofC. conger, was recently described in the western North Atlantic. With increasing size, leptocephali ofC. oceanicus and a portion ofC. triporiceps spread westward and northward in the Florida Current and Gulf Stream, but larger leptocephali especially ofC. triporiceps are found also in the Caribbean and Gulf of Mexico. Spawning ofC. oceanicus in the Sargasso Sea indicates that adults cross the Florida Current-Gulf Stream, and successful leptocephali cross the current in the opposite direction to colonize juvenile habitat on the continental shelf, a migratory pattern similar to that of the American eelAnguilla rostrata (Anguillidae).