被子植物系统发育研究的现状与展望

为植物界最大的类群—被子植物建立一个能真正反映植物的进化历史和系统发育（phylogeny）的分类系统一直是许多植物系统学家和进化学家所向往的。到目前为止,已经提出的被子植物分类系统至少有二十多个。问题在于这样的分类系统能否说已符合于系统发育的要求？要回答这个问题,首先必须弄清系统发育的真正含义是什么。     

Long-term superfusion of rat pituitary cells: interaction of 17 beta-estradiol with pulses of gonadotropin-releasing hormone on luteinizing hormone release

In a series of four experiments, the temporal development of acute inhibitory and delayed stimulatory effects of 17 beta-estradiol (E) on luteinizing hormone (LH) release by superfused rat anterior pituitary cells pulsed with gonadotropin-releasing hormone (GnRH) was studied. Dispersed anterior pituitary cells from ovariectomized rats were cultured on Bio-Beads for 3 days and then placed in columns and superfused for up to 24 hr. During superfusion, the cells were exposed to GnRH pulses (3 X 10(-9) M, one 6-min pulse/hr). Cells treated with E (3 X 10(-10) M) either before (only 24 hr prior to superfusion) or before and during superfusion released significantly (P less than 0.05) more LH in response to the first few pulses of GnRH than cells treated with diluent. In contrast, cells treated with E only during superfusion initially released less GnRH-induced LH than cells treated with diluent. In a subsequent experiment, the inhibitory effect of E reached a maximum by 1.5 hr (P less than 0.01), and then gradually disappeared after 4.5 hr. Cells superfused simultaneously with E and fixed "low"-dose GnRH (5 X 10(-10) M) pulses did not exhibit enhanced LH responses with time to that dose of GnRH. However, E-superfused cells responded more than diluent-superfused cells to subsequent stimulation with a higher-dose GnRH pulse. Superfusion of cells with E for 16.5 hr in the absence of GnRH pulses also did not increase release of LH to low-dose (5 X 10(-10) M) pulses of GnRH, yet did cause a transitory increase to subsequent high-dose (10(-8) M) GnRH pulses. In conclusion, these results demonstrate the direct biphasic inhibitory then stimulatory effects of E on GnRH-induced LH release by superfused rat anterior pituitary cells. Expression of the stimulatory effect of E is related to the dose of GnRH.     

中国下泥盆统脊椎动物化石组合层序

本文综合了滇、黔、川、桂等地的一些早泥盆世地层剖面中的脊椎动物化石的出露情况,粗略地描绘出了早期脊椎动物演化的一般特征,归纳成三个发展阶段。并以此为依据,讨论了下泥盆统的分层与对比。     

Identification, characterization, and quantitative measurement of cyclic AMP receptor proteins in cytosol of various tissues using a photoaffinity ligand.

Two protein bands, present in cytosol fractions from each of seven rat tissues examined, specifically incorporated 32P-labeled 8-azidoadenosine 3':5'-monophosphate (8-N3-[32P]cAMP), a photoaffinity label for cAMP-binding sites. These proteins had apparent molecular weights of 47,000 and 54,000 on a sodium dodecyl sulfate-polyacrylamide gel electrophoresis system. These two proteins were characterized in three of the tissues, namely, heart, uterus, and liver, by the total amount of 8-N3-[32P]cAMP incorporation, by the dissociation constant (Kd) for 8-N3-[32P]cAMP, and by the nucleotide specific inhibition of 8-N3-[32P]cAMP incorporation. Several lines of evidence were obtained that the protein with an apparent molecular weight of 47,000 represents the regulatory subunit of a type I cAMP-dependent protein kinase, while the protein with an apparent molecular weight of 54,000 represents the regulatory subunit of a type II cAMP-dependent protein kinase. Almost all of the cAMP receptor protein found in the cytosol of these tissues, as measured by 8-N3-[32P]cAMP incorporation, was associated with these two protein kinases, in agreement with the idea that most effects of cAMP are mediated through protein kinases. The photoaffinity labeling with 8-N3-[32P]cAMP can be used to estimate quantitatively the amounts of regulatory subunit of type I and type II cAMP-dependent protein kinases in various tissues.     

Yeast mutants deficient in heme biosynthesis and a heme mutant additionally blocked in cyclization of 2,3-oxidosqualene.

Mutants of Saccharomyces cerevisiae were isolated which were blocked in heme biosynthesis and required heme for growth on a nonfermentable carbon source. They were rho+, and grew fermentatively on ergosterol or cholesterol and Tween 80, as a source of oleic acid. Cells grown on ergosterol and Tween 80 lacked cytochromes and catalase which were restored by growth on heme. The mutants comprised five nonoverlapping complementation groups. Tetrad analysis showed that the pleiotropic properties of each of the mutants resulted from a single mutation in one of five unlinked loci (hem1 to hem5) affecting heme biosynthesis. Biochemical studies confirmed that each mutation resulted in loss of a single enzyme activity. hem1 mutants grew on delta-aminolevulinate and lacked delta-aminolevulinate synthase activity, hem2 mutants lacked delta-aminolevulinate dehydratase, and hem3 mutants uroporphyrin I synthase. Mutants in hem1, hem2, and hem3 had an additional requirement for methionine on synthetic medium supplemented with either heme or ergosterol and Tween 80, owing to a lack of sulfite reductase which contains siroheme, a modified uroporphyrin III. Since hem4 and hem5 mutants have sulfite reductase activity under all growth conditions, they are blocked after uroporphyrin III. Cell extracts of a hem4 mutant incubated with delta-aminolevulinate accumulated coproporphyrin III suggesting a block in coproporphyrinogenase, the enzyme which converts coproporphyrinogen III to protoporphyrinogen. Cells and extracts of a hem5 mutant accumulated protoporphyrin IX. Since it was the only mutant that grew on heme but not on protoporphyrin IX, a block in ferrochelatase was suggested for this strain. Mutant strains grown on heme had the sterol composition of wild type cells, whereas without heme only squalene, small amounts of lanosterol, and added sterol was observed. A heme product therefore participates in the transformation of lanosterol to ergosterol. A hem3 mutant was isolated which was also blocked between 2,3-oxidosqualene and lanosterol (erg12). When grown on lanosterol or ergosterol (with Tween 80) it accumulated a compound which was identified as 2,3-oxidosqualene by comparison with the synthetic compound in thin layer and gas-liquid chromatography, and by proton magnetic resonance and mass spectroscopy. Supplementation with heme did not remove the requirement for sterol, but it enabled the mutant to convert lanosterol to ergosterol.     

Calcium dependent action potentials in skeletal muscle fibres of a beetle larva, Xylotrupes dichotomus

The ionic requirement for generating action potentials in ventral longitudinal muscle fibers dissected from beetle larvae was examined by conventional electrophysiological techniques. Muscle fibers that generated only graded responses in physiological saline were able to generate an all-or-none action potential when the potassium permeability of the membrane was inhibited by tetraethylammonium⁺ added to the saline. The peak of the action potential thus elicited was intimately related to the external Ca⁺⁺ concentration. The action potential was blocked by Co⁺⁺ which is known as a competitive inhibitor of Ca-spikes. Neither tetrodotoxin (3 μM) nor a Na-free condition effectively blocked the generation of the action potential. Mg⁺⁺ induced a shift in the peak of the action potential; this was, however, due to the stabilizing action of Mg⁺⁺ but not due to the penetration of Mg⁺⁺ through the muscle membrane. No action potential was elicited in the muscle fiber when immersed in a Ca-free, EGTA saline even when a high concentration of either Mg⁺⁺, Na⁺, or tetraethylammonium⁺ was present. The action potential of the larval muscle fiber was thus concluded to be a Ca-spike, through the channel of which Na⁺ or Mg⁺⁺ did not penetrate.     

Novel topologically knotted DNA from bacteriophage P4 capsids: studies with DNA topoisomerases.

DNA molecules isolated from bacteriophage P4 are mostly linear with cohesive ends capable of forming circular and concatemeric structures. In contrast, almost all DNA molecules isolated form P4 tailless capsids (heads) are monomeric DNA circles with their cohesive ends hydrogen-bonded. Different form simple DNA circles, such P4 head DNA circles contain topological knots. Gel electrophoretic and electronmicroscopic analyses of P4 head DNA indicate that the topological knots are highly complex and heterogeneous. Resolution of such complex knots has been studied with various DNA topoisomerases. The conversion of highly knotted P4 DNA to its simple circular form is demonstrated by type II DNA topoisomerases which catalyze the topological passing of two crossing double-stranded DNA segments [Liu, L. F., Liu, C. C. & Alberts, B. M. (1980) Cell, 19, 697-707]. The knotted P4 head DNA can be used in a sensitive assay for the detection of a type II DNA topoisomerase even in the presence of excess type I DNA topoisomerases.     

Iatrogenic hyponatraemia of the newborn due to maternal fluid overload: a prospective study.

Over five weeks 136 out of 246 deliveries were studied. Maternal plasma sodium concentrations were normal at admission. At delivery no significant difference was found between maternal and infant cord plasma sodium concentrations. Twenty-four of the 41 mothers who had received only oral fluids during labour had infants whose cord plasma sodium concentrations were normal. Of the 95 mothers who had been given intravenous fluids, however, only 14 infants with normal plasma sodium concentrations, 31 had a concentrations of 130 mmol (mEq)/1 or less and nine of these had a concentration of 125 mmol/1 or less. There was a highly significant inverse relation between cord plasma sodium concentration and rate of fluid administration, suggesting that hyponatraemia was due to intravenous treatment with predominantly sodium-free solutions. Endogenous antidiuretic activity probably increases during labour, and synthetic oxytocin in large doses has been shown to have an antidiuretic effect. The dose used in this study did not appear to have such an effect. Glucose solutions are often used as a vehicle for oxytocin; 83% of all fluid intake in this study was 5% or 10% glucose in water. Fluid balance in labour should be supervised closely, and oxytocin should be given in a more concentrated solution.