STUDIES ON THE REGULATION OF GABA SYNTHESIS: THE INTERACTION OF ADENINE NUCLEOTIDES AND GLUTAMATE WITH BRAIN GLUTAMATE DECARBOXYLASE

The effects of adenine nucleotides and glutamate on glutamate decarboxylase were studied in a dialyzed, high-speed supernatant of rat brain. When incubated with 10 μm -pyridoxal-P the enzyme was strongly inhibited by ATP, ADP and their Mg²⁺ complexes at concentrations which were well below tissue levels. The enzyme was not significantly inhibited by 15 mm -AMP or by 100 μM-3′-5’cyclic AMP or 3′-5’cyclic GMP. Inhibition by the nucleotides cannot be described in conventional steady-state kinetic terms. Addition of ATP in the presence of pyridoxal-P resulted in a slow, progressive decrease in the reaction rate which was similar to the inactivation observed when the enzyme was incubated in the absence of pyridoxal-P. The progressive inactivation in the presence of ATP was minimal at concentrations of glutamate which were well below K_m and became much more pronounced at higher glutamate concentrations. Addition of suprasaturating amounts of pyridoxal-P late in the incubation when the enzyme was almost completely inactivated resulted in an immediate and complete reactivation of the enzyme. Inhibition by ATP could be prevented by addition of saturating amounts of pyridoxal-P at the start of the reaction and was also relieved by addition of potassium phosphate buffer. The results suggest that inhibition by the nucleotides involves the prior formation of the inactive apoenzyme which results from the glutamate-promoted dissociation of pyridoxal-P. In the absence of the nucleotides, the enzyme is normally reactivated by the added pyridoxal-P. The nucleotides act to block this reassociation of pyridoxal-P with the apoenzyme thereby producing a progressive inactivation of the enzyme. The implications of these results for the regulation of GABA synthesis are discussed.     

THE SYNTHESIS OF GLUTAMATE BY RAT BRAIN MITOCHONDRIA

The synthesis of glutamate from 2-oxoglutarate generated by the citric acid cycle and ammonium acetate has been studied in brain mitochondria of synaptic or non synaptic origin. Non synaptic brain mitochondria synthesise glutamate at twice the rate (1.3 nmol. min^?1. mg protein^?1) of synaptic mitochondria (0.65 nmol. min^?1. mg protein^?1) when pyruvate is the precursor for 2-oxoglutarate, but at a similar rate (0.9 and 0.7 nmol. min^?1, mg protein^?1) when 3 hydroxybutyrate is the precursor. Glutamate synthesis from ammonium acetate and extramitochondrially addcd 2-oxoglutarate (5 mM) by both synaptic and nonsynaptic mitochondria was 5-fold higher (5-6nmol. min^?1. mg protein^?1) than glutamate synthesis from endogenously produced 2-oxoglutarate. In the uncoupled state (or un-coupler + oligomycin) the rate was reduced by half. (2.5-3 nmol. min^?1. mg protein^?1) as compared to mitochondria synthesising glutamate in states 3 or 4 (± oligomycin). The changes in brain mitochondrial nicotinamide nucleotide redox state have been monitored by fluorimetric, spectrophotometric and enzymatic techniques during glutamate synthesis and compared with liver mitochondria under similar conditions. On the instigation of glutamate synthesis by NH⁺₄ addition a significant NAD(P)H oxidation occurs with liver mitochondria but no detectable change occurs with brain mitochondria. Leucine (2 mM) causes a doubling of glutamate synthesis by both synaptic and non synaptic brain mitochondria with no detectable change in the NAD(P)H redox state. The results are discussed with respect to the control of glutamate synthesis by mitochondrial redox potential and the possible intramitochondrial compartmentation of this process.     

紫茎泽兰种群年龄结构动态及对控制的指示意义

外来入侵植物紫茎泽兰 (Eupatoriumadenophorum) 给我国西南地区的经济、社会和环境造成了严重的危害。为了阐明紫茎泽兰种群的年龄结构和未来发展趋势, 为今后的防治工作提供科学依据, 在攀枝花地区设置了 2 0个样地 (10m× 10m), 对 4种不同生境种群的年龄结构、静态生命表和时间序列预测进行了分析。这 4个种群是该地区有代表性类型中紫茎泽兰的种群 :路旁荒地、云南松 (Pinusyunnanensis) 林、阔叶林和阔叶林的林缘。种群年龄结构分析表明, 目前 (几个类型总和 ) 个体数量比重分别为 :幼年期占 92.32 %, 青年期占 6.4 0 %, 成熟期占 2.2 0 %, 衰老期占 0.18%, 个体数量主要集中于幼年期。紫茎泽兰不同种群生命表和存活曲线的分析显示, 紫茎泽兰对 4个种群的入侵过程是路旁荒地→阔叶林林缘→阔叶林→云南松林, 尽管所处的生境差异较大, 但基本属于DeeveyⅢ型, 一年生幼苗死亡率高达 97.30 %, 种群偏离典型曲线的程度与群落受干扰程度强弱有关, 一般由幼年期到青年期和由成熟期到衰老期死亡率较高 (分别为 93.0 7%和 92.0 0 % ) 。时间序列分析表明, 在未来的 3~ 5年中, 紫茎泽兰种群仍然是以青年期和成熟期个体占绝对优势。     

THE PERMEABILITY OF CELLS FOR OXYGEN AND ITS SIGNIFICANCE FOR THE THEORY OF STIMULATION

It can be demonstrated by an indicator method that living cells are as freely permeable to oxygen as dead cells, and that sudden admission of oxygen to the cell cannot account for increased oxidation as a result of stimulation. Oxygen penetrates as readily as carbon dioxide among the acids and ammonia among the alkalies. Exposure of living plant cells to high oxygen pressures does not initiate certain oxidations (except after some hours), which proceed readily in dead plant cells in the air. In the light of the preceding statement, about the permeability of cells for oxygen, this is interpreted to mean that more oxygen enters the cell at high pressure, but that the reacting substances (chromogen and oxidase) are kept apart by some phase boundary as long as the cell is alive. Increased oxygen concentration eventually produces injury to the cell.     

A METHOD FOR THE ISOLATION AND ESTIMATION OF GABA, GLUTAMATE AND GLUTAMINE FROM COMPLEX MIXTURES BY A COMBINATION OF ENZYMIC INTERCONVERSION AND FORMATION OF 1-DIMETHYLAMINONAPHTHALENE-5-SULPHONYLBUTYROLACTAM

Abstract— A method is presented which allows the isolation and estimation of GABA, glutamate and glutamine in extracts of nervous tissue. It depends on the enzymic conversion of the last two compounds to GABA, before isolating the GABA as DNS-γ-butyrolactam. The low polarity of this compound makes this possible without the use of chromatography. Furthermore, the specific radioactivities of these 3 compounds in a complex mixture may be found without elaborate separation procedures. Details are given of optimum reaction conditions, and comparisons made with other methods of estimation of these amino acids.     

糖皮质激素对谷氨酸和DGABA受体的电生理反应的快速调制作用

在大鼠下丘脑薄片和豚鼠腹腔神经节上,分别用玻璃微电极细胞外和细胞内记录方法,观察了１０－６ｍｏｌ／Ｌ糖皮质激素（ＧＣ）对谷氨酸和ＧＡＢＡ受体介导效应的快速调制作用。结果表明,ＧＣ灌流后５ｍｉｎ,对谷氨酸受体介导的效应起抑制作用,而对ＧＡＢＡ受体介导的效应起增强作用。撤除ＧＣ后,神经元对谷氨酸和ＧＡＢＡ的反应恢复到对照水平。低钙高镁灌流液不能取消ＧＣ的调制作用。结果提示,ＧＣ在不需要突触环路条件下,可能通过非基因组途径影响谷氨酸和ＧＡＢＡ受体介导的效应。     

LIGHT ABSORPTION BY PLANTS AND ITS IMPLICATIONS FOR PHOTOSYNTHESIS

The preceding account has attempted to examine the interactions between light absorption and photosynthesis, with reference to both unicellular and multicellular terrestrial and aquatic plants. There are, however, some notable plant groups to which no direct reference has been made, e.g. mosses, liverworts and lichens. Although many have similar optical properties to terrestrial vascular plants (Gates, 1980) and apparently similar photosynthetic responses (see Green & Snelgar, 1982; Kershaw, 1984) they may possess subtle, as yet unknown differences. For instance, the lichen thallus has a high surface reflectance although the transmittance is virtually zero (Gates, 1980; Osborne, unpublished results). It is envisaged, however, that differences in optical properties between species will reflect differences in degree not kind. Although not all variation in photosynthesis is due to differences in light absorption a number of accounts suggest that this is a contributing factor. Variations in leaf absorptance have been found to account for most of the variation in leaf photosynthesis at low J_is (see Ehleringer & Björkman, 1978a; Osborne & Garrett, 1983). There is, however, little direct experimental evidence on light absorption and photosynthesis in either microalgal species or aquatic macrophytes. We also do not know over what range of incident photon flux densities photosynthesis is determined largely by changes in light absorption. Plants growing under natural conditions also experience large diurnal and seasonal fluctuations in J_i, unlike species grown under laboratory conditions. The occurrence of transitory peaks in J_i tends to overshadow the fact that the average J_i is often lower than the J₁ required to saturate photosynthesis, i.e. 1500–2000 μmol m^-2 s^-1, depending on the growth treatment. Using the data of Monteith (1977) and I W m²= 5 μmol m^-2 s^-1, and with photosynthetically active radiation 50% of total solar radiation, the daily mean value for Britain is approximately 450 μmol m^-2 s^-1, with a maximum in June of 1000μmol m^-2 s^-1 and a minimum during the winter of 75 μmol m^-2 s^-1. Such values could be even lower on shaded understory leaves and considerably lower for aquatic species. Based on average values of net photosynthesis for a terrestrial plant leaf, light saturation would only be expected in June while for most of the year the average values would lie largely on the light-limited portion of the photosynthesis light response curve. Although the daily average values in tropical climates may be higher during the winter months, they are remarkably similar throughout the world for the respective summers in the northern and southern hemispheres, because the increased daylength at high latitudes compensates for the lower J_is. The expected lower dark respiration rates during the winter may also partially offset the effects of a lower light level. There is therefore a trade-off between high J_is for a short period of time against a lower J_i for a longer period of time. We might expect different photosynthetic responses to these two very different conditions. Importantly, a low J_i with a long daylength may enable a plant to photosynthesize at or near its maximum photon efficiency for most of the day. Although the response of the plant to fluctuations in J_i is complicated because it is affected by the previous environmental conditions, this may indicate that light absorption has a much greater significance under natural conditions, particularly for perennial species. The bias in many laboratories towards research on terrestrial vascular plants also tends to ignore the fact that a number of multicellular and unicellular aquatic species survive in very low light environments. Furthermore, the direct extrapolation of photosynthetic responses from measurements on single leaves to those of whole plants is clearly erroneous. Although this is obvious, many physiological ecologists have attributed all manner of things to the photosynthetic responses of ‘primary’ leaves. Most researchers have ignored problems associated with composite plant tissues and internal light gradients. Clearly caution is required in interpreting the photosynthesis light-response curve of multicellular tissues based on biochemical features alone. Also, the importance of cell structure on light absorption and photosynthesis has generally been ignored and attributed solely to the effects of structural features on CO₂ diffusion. In doing so the work of two or three generations of plant physiologists has been ignored. Haberlandt (1914) at the turn of the century probably first implicated the role of cell structure in leaf optics, and Heath (1970) stressed that in order to completely understand the role of light in photosynthesis we need to know the flux incident on the chloroplast itself. Even this suggestion may need modification because of the capacity of the internal chloroplast membranes for scattering light. It is worth emphasizing the importance of light gradients within tissues and their role in regulating photosynthesis, particularly at light saturation. Measurements of light gradients are fraught with problems because of experimental difficulties and the majority (few) are based on reflectance and transmittance measurements. Seyfried & Fukshansky (1983) have shown that light incident on the lower surface of a Cucurbita cotyledon produced a larger light gradient than light incident from above, indicating the importance of the spatial arrangement of the tissues with respect to the light source. Also, light incident on the lower surface of leaves of Picea sitchensis was less ‘effective’ in photosynthesis than light from above (Leverenz & Jarvis, 1979). Clearly, two tissues could have the same gross absorptance but different photosynthetic rates because of differences in the internal light environment. Fisher & Fisher (1983) have recently found asymmetries in the light distribution within leaves, which they related to asymmetries in photosynthetic products due to differences in solar elevation. Such modifications in light distribution could be important for a number of solar-tracking species. Changes in light absorption are brought about by a whole gamut of physiological, morphological and behavioural responses which serve to optimize the amount of light absorbed. Perhaps the simplest way of regulating the amount of light absorbed is by restricting growth either to particular times of the year or to conditions when the light climate is favourable. We are still largely ignorant of many details of these modifications. In particular, differences in tissue structure such as the size and number of vacuoles or the effects of organelles on the scattering component of the internal light environment of photosynthetic tissues are not understood. A better understanding of the interaction of light with plants in aquatic systems is also required. It is unfortunate that light-absorptance measurements are not routinely made in photosynthetic studies, and this is quite clearly a neglected area of study. That these measurements are not made is even more surprising, since techniques have been available for over sixty years (Ulbricht, 1920). Absorptance measurements are of particular importance in the photosynthetic adaptation of microalgae, where only a small proportion of the incident photon flux density is absorbed. For multicellular species more detailed information is required on internal light gradients and their variability. Light-absorptance measurements are also important in any study relating kinetic data on CO₂ fixation to in vivo photosynthesis, especially when there are large variations in the morphology and structure of the photosynthetic organ.     

THE STIMULATION OF ARGININE PHOSPHOKINASE IN LOBSTER AXONS BY GABA

GABA at physiological concentrations has been shown to stimulate the synthesis of arginine phosphate in lobster walking nerves. This effect can be observed both in intact axons and in axonal homogenates. The stimulatory activity of GABA on the synthesis of arginine phosphate appears to be on the V_max of arginine phosphokinase whereas in the reverse reaction the effect is referable to the K_m of ADP.     

褪黑素对谷氨酸致痫大鼠海马内谷氨酸、GABA及其受体水平的影响

目的探讨褪黑素(melatonin,MT)对谷氨酸(glutamate,Glu)致痫大鼠海马内Glu及GluR2、γ-氨基丁酸(γ-aminobutyric-acid,GABA)及其受体GABRA1水平的影响,进而研究褪黑素的抑痫作用机制。方法随机将健康SD雄性大鼠40只分为A、B、C、D组,每组10只。A组:生理盐水组;B组:MT Glu组;C组:Glu致痫组;D组:Luzidole MT Glu组。观察并记录行为学变化,采用免疫组化法进行Glu、GluR2、GABA和GABRA1免疫组化染色和图像分析。结果行为学观察结果显示,C组和D组大鼠均有不同程度的癫痫发作,B组大鼠癫痫发作不明显,A组无发作;免疫组化结果显示,C组和D组海马内CA1-CA3区和齿状回Glu阳性反应较A组增强(P<0.05),GluR2、GABA和GABRA1均较A组减弱(P<0.05),B组Glu较C组和D组阳性反应有显著性减弱(P<0.05),GluR2、GABA和GABRA1阳性反应均较C组和D组有显著性增强(P<0.05),而B组与A组无明显差异性。结论MT通过增加GABA及其受体GABRA1和GluR2的作用和抑制Glu作用对Glu致痫大鼠癫痫发作发挥抑制作用。     

STUDY ON THE INHIBITION OF BRAIN GLUTAMATE DECARBOXYLASE BY PYRIDOXAL PHOSPHATE OXIME-O-ACETIC ACID

The kinetics of the inhibition of mouse brain glutamate decarboxylase by pyri-doxaI-5′-phosphate oxime-O-acetic acid (PLPOAA) was studied. The inhibition was noncompetitive with regard to glutamic acid; it could be partially reversed by pyridoxal phosphate, but only when the concentration of the latter in the incubation medium was higher than that of pyridoxal-5′-phosphate oxime-O-acetic acid. The inhibition produced by aminooxyacetic acid, which is remarkably greater than that produced by PLPOAA, was also partially reversed only when an excess of pyridoxal phosphate was added. Both in the presence and in the absence of a saturating concentration of pyridoxal phosphate, the activity of the enzyme was decreased by PLPOAA at a 10^?4m concentration to a value of about 50 per cent of the control value obtained without added coenzyme. This activity could not be further reduced even when PLPOAA concentration was increased to 5 × 10^?3m . This same minimal activity of glutamate decarboxylase was obtained after dialysis of the enzymic preparation, or after incubation with glutamic acid in the cold followed by filtration through Sephadex G-25. The addition of pyridoxal phosphate to the dialysed or glutamic acid-treated enzyme restored the activity to almost the control values. PLPOAA did not affect the activity of glutamate decarboxylase from E. coli or that of DOPA decarboxylase and GABA transaminase from mouse brain. To account for the results obtained it is postulated that brain glutamate decarboxylase has two types of active site, one with firmly bound, non-dialysable pyridoxal phosphate and the other with loosely bound, dialysable coenzyme; PLPOAA behaves as a weak inhibitor probably because it can combine mainly with the loosely bound coenzyme site, while aminooxyacetic acid is a potent inhibitor probably because it can block both the ‘loosely bound coenzyme’ and the ‘firmly bound coenzyme’ sites.     

THE INFESTATION OF WINTER LETTUCE BY APHIDS AND ITS CONTROL

Observations have been made on the infestation by aphids of winter lettuce at Imperial College Field Station, Slough, for the seasons 1947–8 and 1949–54. The effects of transplanting and of the use of insecticides have been studied.
Plants drilled in September where they were to mature were ready for cutting a little earlier than those transplanted in November, but in years when aphids were numerous the drilled lettuces were heavily infested and very few of them hearted.
The infestation of young crops varied from year to year; in some winters it fell to a low level, in others it increased rapidly and persisted with serious effect on the crop. In some years lettuce mosaic virus was also prevalent. The dominant aphid species was Nusonovia ribis-nigri (Mosley).
An early and persistent attack, even in the absence of virus disease, much reduced the number of hearted plants and their average weight. A late attack by winged aphids in early spring sometimes spoilt fully hearted lettuces.
Dipping the plants in nicotine solution at the time of transplanting in November reduced aphid infestation; dusting with benzene hexachloride proved more effective.
If transplanting was delayed until February or March a relatively clean crop could be produced by insecticide treatment, but losses from fungal disease were usually high.     

PHOSPHATE UPTAKE UNDER NITRATE LIMITATION BY SCENEDESMUS SP. AND ITS ECOLOGICAL IMPLICATIONS1

Under nitrogen limitation the phosphate content of Scenedesmus sp. shows little variation regardless of growth rate and the N/P atomic ratio of the medium. P uptake therefore can be calculated as the product of P content and N-dependent growth rate. The maximum rate of P uptake in N limitation is lower by a factor of about 8 than the rate in P limitation. As reported earlier, P uptake by this alga under P limitation is described by the kinetics resembling non-competitive enzyme inhibition, with one or several intracellular P fractions as inhibitors. These fractions include surplus P (water extractable) and inorganic polyphosphate fractions A (acid soluble) and B, C, and D (acid insoluble). In N limitation, the ratios of fractions A, B, C, and D are quite different from the ratios of P limitation at comparable growth rates. The concentrations of polyphosphate fraction A in N-limited cells are much, higher than the levels in P-limited cells, and this fraction becomes more predominant at low growth rates in N limitation. This fraction, if introduced as the inhibitor into the noncompetitive scheme, explains the uptake kinetics in both N- and P-limited cells and the low maximum uptake rate in N limitation. This finding may have two significant ecological implications: (1) A nutrient imbalance which brings about changes in the internal, level or the metabolism, of fraction A would affect P uptake. (2) Nitrogen sufficiency would cause a competitive advantage in P uptake. This advantage would be shared by N₂ fixers and algae with low optimum N/P ratios. In Scenedesmus sp. P limitation switches to N limitation and vice versa when the cell N/P atomic ratio is about 30.     

THE SYNTHESIS OF ACETYLCHOLINE FROM ACETYL-CoA, ACETYL-DEPHOSPHO-CoA AND ACETYLPANTETHEINE PHOSPHATE BY CHOLINE ACETYLTRANSFERASE

Abstract— The synthesis of ACh by choline acetyltransferase (ChAc) has been examined using acetyl-CoA, acetyl-dephospho-CoA and acetylpantetheine phosphate. At pH 7.5 K_m values of 25.7 μ m for acetyl-CoA, 54.8 μ m for acetyl-dephospho-CoA and 382 μ m for acetylpantetheine phosphate were obtained and are similar to those at pH 6.0. This indicates that the 3-phosphate may not be required for binding the substrate to the enzyme unlike carnitine acetyltransferase.
Inhibitor constants ( K_i ) for CoA, dephospho-CoA and pantetheine phosphate were also measured and when considered with the K_m values obtained for the acetyl derivatives it is concluded that acetyl-dephospho-CoA could be a successful acetyl donor in the synthesis of ACh.
Acetyl-dephospho-CoA was found to be less satisfactory as a substrate for citrate synthase.     

ANOMALOUS STIMULATION OF PROTEIN SYNTHESIS: EVIDENCE FOR TRANSLATIONAL CONTROL IN PRIMARY CELLS

Chick cells in primary culture synthesize protein at an accelerated rate following recovery from prolonged (2-12 hr) inhibition of protein synthesis. This 'overshoot' is followed by a return to the normal rate of synthesis.
Both actinomycin and fluorophenylalanine provided during the recovery period enhance the 'overshoot' and prevent the return to normal.
The results are consistent with the proposal that protein synthesis is restricted by an inhibitor or 'governor', itself a protein of relatively short half life.
Neither L nor HeLa cells demonstrate an 'overshoot' during the recovery phase.     

STIMULATION OF BRAIN DOPAMINE SYNTHESIS BY GAMMA-HYDROXYBUTYRATE

Abstract— Gamma-hydroxybutyrate administration produces a marked selective increase of brain dopamine in different animal species. Following γ -hydroxybutyrate administration, dopamine accumulated in the basal ganglia of the rat and in the caudate nucleus of the rabbit at a rate which greatly exceeded the normal synthesis rate of the amine in these species. Dopamine accumulation was prevented by α -methyltyrosine. These data indicate that γ -hydroxybutyrate stimulates dopamine synthesis. In addition, γ -hydroxybutyrate increased the homovanillic acid level in the rat basal ganglia to a maximum of about 300 per cent of the normal level indicating that γ -hydroxybutyrate inhibits neither monoamine oxidase nor catechol O -methyltransferase in vivo. The possible mechanisms of dopamine accumulation following γ -hydroxybutyrate administration are discussed.     

小麦叶片依赖于铁氧还蛋白的谷氨酸合成酶的纯化、特性和调节

经硫酸铵分级沉淀和DEAE-纤维素柱层析,小麦叶片Fd-GOGAT被纯化了19.1倍。其分子量为 330 000,最适反应pH为 7.4,在pH 7.5 下最稳定,在粗提液中较纯化后稳定。该酶对 L-Gln、α-KG和Fd专一,K_m值分别为1350、625、和3μmol/L。还原型 MV可以作为该酶的电子供体,而NADH则不能。 植物无机氮素同化的四个酶 NR、NiR.GS和 GOGAT的活力对光、激素和无机氮源等因素表现出一致的反应。用钨酸钠和MSO分别将NR或GS活力完全抑制后,其它三个酶的活力都大大降低。四者间可能有某种共同的调节机制。     

膜翅目寄生蜂的互补性别决定机制及其在生防上的意义(英文)

在膜翅目中 ,未受精卵形成单倍体的雄蜂 ,而在大多数情况下受精卵将产生双倍体的雌蜂。但是 ,因互补性别决定机制 (CSD)的作用 ,受精卵有时也会产生双倍体雄蜂。这种性别决定机制包括单位点的CSD和多位点的CSD。在单位点的CSD作用下 ,唯一的一个性位点上的多个等位基因决定后代个体的性别。性位点上杂合的个体将是雌性 ,半合或同型结合的个体将分别形成单倍体或双倍体的雄性。在多位点的CSD作用下 ,两个或两个以上的性位点控制后代的性别 ,每个性位点上包含两个或两个以上的等位基因。如果一个或一个以上的性位点是杂合的 ,形成的双倍体后代都是雌性的 ,但若是所有的性位点都为同型合子 ,则将产生双倍体的雄蜂。在膜翅目中 ,目前已知 4 3种具有双倍体雄蜂 ,其中 2 2种发现存在单位点的CSD ,但是多位点的CSD还有待于确认。双倍体的雄性个体或者不能存活 ,或者不育 ,这样的个体形成将对寄生蜂种群的增长带来一定的遗传负担。在生物防治上 ,保护寄生蜂种群的性等位基因的多样性及减少其遗传多异性的损失极其重要。如果利用具有单位点CSD的种类 ,采取一定的措施将可避免由于双倍体雄性的形成所带来的负面影响。     

COMPLEMENTARY SEX DETERMINATION IN HYMENOPTERAN PARASITOIDS AND ITS IMPLICATIONS FOR BIOLOGICAL CONTROL

In haplodiploid Hymenoptera, unfertilized eggs produce haploid males while fertilized eggs lead to diploid females under most circumstances. Diploid males can also be produced from fertilization under a system of sex determination known as complementary sex determination (CSD). Under single-locus CSD, sex is determined by multiple alleles at a single sex locus. Individuals heterozygous at the sex locus are female while hemizygous and homozygous individuals develop as haploid and diploid males, respectively. In multiple-locus CSD, two or more loci, each with two or more alleles, determine sex. Diploid individuals are female if one or more sex loci are het-erozygous, while a diploid is male only if homozygous at all sex loci. Diploid males are known to occur in 43 hym-enopteran species and single-locus CSD has been demonstrated in 22 of these species. Diploid males are either developmentally inviable or sterile, so their production constitutes a genetic load. Because diploid male production is more likely under inbreeding, CSD is a form of inbreeding depression. It is crucial to preserve the diversity of sex alleles and reduce the loss of genetic variation in biological control. In the parasitoid species with single-locus CSD, certain precautionary procedures can prevent negative effects of single-locus CSD on biological control.     

COMPLEMENTARY SEX DETERMINATION IN HYMENOPTERAN PARASITOIDS AND ITS IMPLICATIONS FOR BIOLOGICAL CONTROL

Abstract In haplodiploid Hymenoptera, unfertilized eggs produce haploid males while fertilized eggs lead to diploid females under most circumstances. Diploid males can also be produced from fertilization under a system of sex determination known as complementary sex determination (CSD). Under single-locus CSD, sex is determined by multiple alleles at a single sex locus. Individuals heterozygous at the sex locus are female while hemizygous and homozygous individuals develop as haploid and diploid males, respectively. In multiple-locus CSD, two or more loci, each with two or more alleles, determine sex. Diploid individuals are female if one or more sex loci are heterozygous, while a diploid is male only if homozygous at all sex loci. Diploid males are known to occur in 43 hymenopteran species and single-locus CSD has been demonstrated in 22 of these species. Diploid males are either developmentally inviable or sterile, so their production constitutes a genetic load. Because diploid male production is more likely under inbreeding, CSD is a form of inbreeding depression. It is crucial to preserve the diversity of sex alleles and reduce the loss of genetic variation in biological control. In the parasitoid species with single-locus CSD, certain precautionary procedures can prevent negative effects of single-locus CSD on biological control.