水稻中央细胞发育期间超微结构变化的观察

本文通过透射电镜对水稻受精前胚囊中央细胞发育过程中超微结构的变化进行观察。结果表明,八核胚囊形成后很快就进行细胞化形成7个细胞,其中刚形成的中央细胞由1个大液泡、2个极核（珠孔端和合点端各1个）和一些含有丰富细胞器的胞质组成。中央细胞以后的发育主要是极核的发育和极核周围胞质的变化。极核发育经历以下过程：a．2个核都膨大呈“椭圆”形。核周围胞质呈不对称分布。b．2个核分别向胚囊中央移动并相互靠近。之后2个极核调整排列方式,由纵排（即与胚囊纵轴平行）变成横排。此时期有细胞质“桥”联结珠孔端卵器、2个极核和合点端反足细胞器。c．横排的极核移向卵器,并排列于卵细胞之上。此时胚囊未明显膨大,但极核相靠近的两边核膜有许多处已形成“融合桥”,核周围的胞质也起较大的变化,如质体内淀粉消失和光面内质网增加等。极核进一步发育直至胚囊成熟期间,极核排列方式及其周围胞质组成未观察到明显的变化,但胚囊体积明显增大。     

Characteristics of the inward-rectifying potassium current in mouse ventricular myocytes and its relation to early after-depolarization

The properties of the inward-rectifying potassium current (IK1) were studied in the single myocytes isolated from adult mouse ventricles by the whole-cell patch-damp technique for the first time. Most of the properties of IK1 including channel conductances, activation, inactivation, rectification and external K sensitivity in mouse ventricular myocyte were similar to those in other species, but the current-voltage (1-V) curve of mouse ventricular myocyte showed no negative slope, i.e the slope in the range of membrane potential 50 mV positive to the reversal potential (VRev) was virtually flat and remained at a low current level ((59±39) pA). Under the superfusion of Tyrode's solution with 3mmol/L K and 3mmol/L Cs , IK1 in the above region nearly decreased to zero, and then the early after-depolarization (EAD) occurred. The results suggest that this distinctive characteristic of IK1 in mouse ventricular myocyte may relate to the high susceptibility to EA0 in mouse myocardium. The inhibition of IK1 se     

Divalent cation channels activated by phenothiazines in membrane of rat ventricular myocytes

Phenothiazines (PTZ) such as chlorpromazine (CPZ) or trifluoperazine (TPZ) induced a sustained divalent cation-permeable channel activity when applied on either side of inside-out patches or on external side of cell-attached patches of adult rat ventricular myocytes. The percentage of active patches was 20%. In the case of CPZ, the K _dof the dose-response curve was 160 m. CPZ-activated channels were potential-independent in the physiological range of membrane potential and were permeable to several divalent ions (Ba²⁺, Ca²⁺, Mg²⁺, Mn²⁺). At least three levels of currents were usually detected with conductances of 23, 50 and 80 pS in symmetrical 96 mm Ba²⁺ solution and 17, 36 and 61 pS in symmetrical 96 mm Ca²⁺ solution. Saturation curves corresponding to the three main conductances determined in Ba²⁺ symmetrical solutions (tonicity compensated with choline-Cl) gave maximum conductances of 36, 81 and 116 pS (with corresponding half-saturating concentration constants of 31.5, 38 and 34.5 mm). The corresponding conductance values were estimated to 1.7, 3.3 and 5.2 pS in symmetrical 1.8 mm Ba²⁺ and to 1.1, 2.4 and 3.7 pS in symmetrical 1.8 mm Ca²⁺ (the value in normal Tyrode solution). Channels were poorly permeable to monovalent cations, such as Na, with a P _Ba/P _Na ratio of 10. A PTZ-induced channel activity similar to that described in cardiac cells was also observed in cultured rat aortic smooth muscle cells but not in cultured neuroblastoma cells.PTZ-activated channels described in cardiac cells appear very similar to the sporadically active divalent ion permeable channels described in a previous paper (Coulombe et al., 1989). Surprisingly, when 100 m CPZ were applied to myocytes studied in the whole-cell configuration, and maintained at a holding potential of –80 mV in the presence of 24 mm external Ca²⁺ or Ba²⁺, no detectable macroscopic inward current could be observed, whereas the L-type Ca²⁺ current triggered by depolarizing pulses was markedly and reversibly reduced. The possible reasons are discussed.     

A homologue of the MAP/ERK family of protein kinase genes is expressed in vegetative and in female reproductive organs of Petunia hybrida

The mitogen activated protein (MAP) kinase pathway of eukaryotes is stimulated by many growth factors and is required for the integration of multiple cellular signals. In order to study the function of MAP kinases during plant ovule development we have synthesized a Petunia hybrida ovule-specific cDNA library and screened for MAP protein kinase-related sequences using a DNA probe obtained by PCR. A full-length cDNA clone was identified (PMEK for Petunia hybrida MAP/ERK-related protein kinase) and shown to encode a protein related to the family of MAP/ERK protein kinases. Southern blot analysis showed that PMEK is a member of a small multigene family in P. hybrida. The cDNA codes for a protein (PMEK1) of 44.4 kDa with an overall sequence identity of 44% to the products of the mammalian ERK/MAP kinase gene, and the budding yeast KSS1 and FUS3 genes. PMEK1 displays 96 and 80% identity respectively with the tobacco NTF3 and Arabidopsis ATMPK1 kinases, and only 50% to the more distantly related plant MAP kinase MsERK1 from alfalfa. The two phosphorylation sites found in the loop between subdomain VII and VIII in all the other MAP kinases are also present in PMEK1. RNA gel blot and RT-PCR analyses demonstrated that PMEK1 is expressed in vegetative organs and preferentially accumulated in female reproductive organs of P. hybrida. In situ hybridization experiments showed that in the reproductive organs PMEK1 is expressed only in the ovary and not in the stamen.     

The development of female gametophyte and antipodal embryo formation in Sedum fabaria

In Sedum fabaria, the ovule is anantropus, bitegmic and crassinucellate. The development of the nucellus conforms to the Sedum type. The development of the embryo sac is of the Allium type. The antipodal cells in unfertilized embryo sac occasionally divide and one of them forms four-celled structures resembling embryos and remaining once elongate in the form of haustoria. The entry of the pollen tube is porogamous. After division the primary endosperm nucleus forms two cells: the apical one develops into cellular endosperm according to the Acre type and the basal one acts as the endosperm haustorium of the Sempervivum type. The embryogeny corresponds to the Caryophyllad type. This revised version was published online in July 2006 with corrections to the Cover Date.     

Activation of inwardly rectifying potassium channels by muscarinic receptor-linked G protein in isolated human ventricular myocytes

Muscarinic receptor-linked G protein, G _i , can directely activate the specific K⁺ channel (I _K(ACh)) in the atrium and in pacemaker tissues in the heart. Coupling of G _i to the K⁺ channel in the ventricle has not been well defined. G protein regulation of K⁺ channels in isolated human ventricular myocytes was examined using the patch-clamp technique. Bath application of 1 μm acetylcholine (ACh) reversibly shortened the action potential duration to 74.4 ± 12.1% of control (at 90% repolarization, mean ±sd, n= 8) and increased the whole-cell membrane current conductance without prior β-adrenergic stimulation in human ventricular myocytes. The ACh effect was reversed by atropine (1 μm). In excised inside-out patch configurations, application of GTPγS (100 μm) to the bath solution (internal surface) caused activation of I _K(ACh) and/or the background inwardly-rectifying K⁺ channel (I _K1) in ventricular cell membranes. I _K(ACh) exhibited rapid gating behavior with a slope conductance of 44 ± 2 pS (n= 25) and a mean open lifetime of 1.8 ± 0.3 msec (n= 21). Single channel activity of GTPγS-activated I _K1 demonstrated long-lasting bursts with a slope conductance of 30 ± 2 pS (n= 16) and a mean open lifetime of 36.4 ± 4.1 msec (n= 12). Unlike I _K(ACh), G protein-activated I _K1 did not require GTP to maintain channel activity, suggesting that these two channels may be controlled by G proteins with different underlying mechanisms. The concentration of GTP at half-maximal channel activation was 0.22 μm in I _K(ACh) and 1.2 μm in I _K1. Myocytes pretreated with pertussis toxin (PTX) prevented GTP from activating these channels, indicating that muscarinic receptor-linked PTX-sensitive G protein, G _i , is essential for activation of both channels. G protein-activated channel characteristics from patients with terminal heart failure did not differ from those without heart failure or guinea pig. These results suggest that ACh can shorten the action potential by activating I _K(ACh) and I _K1 via muscarinic receptor-linked G _i proteins in human ventricular myocytes. Received: 23 September 1996/Revised: 18 December 1996     

水稻PDER品系的特点和二倍体孢子生殖胚囊的形成和发育

对水稻（ＯｒｙｚａｓａｔｉｖａＬ．）早发生胚ＰＤＥＲ（ｐｒｅ－ｄｅｖｅｌｏｐｅｄｅｍｂｒｙｏｏｆｒｉｃｅ）品系的特点和细胞胚胎学研究表明,ＰＤＥＲ是二倍体植物２ｎ＝２４,约有５０％胚囊的卵细胞未经受精能自行发育形成胚,成熟种子的萌发和生长速度较常规正常水稻快。ＰＤＥＲ的大孢子母细胞经有丝分裂产生未减数的胚囊,即无融合生殖中的二倍体孢子生殖类型。在胚囊形成和发育过程中有如下几个特点：（１）孢原细胞至大孢子母细胞分裂前的过渡期持续时间较长,孢原细胞和大孢子母细胞的细胞质比周围的珠心细胞质稀淡。（２）大孢子母细胞经二次有丝分裂后形成直线排列的三个细胞（三分体）,珠孔端的两个解体,合点端的一个发育为功能细胞,有少数胚囊的三个细胞全部解体形成败育胚囊。（３）功能细胞经三次连续核分裂形成具八核七个细胞的成熟胚囊,它的结构与常规正常水稻基本相同,但助细胞呈长形而没有回抱着卵细胞。     

巯甲丙脯酸降低缺血再灌注心律失常的发生率

本工作用放射免疫法、荧光组织化学等方法探讨心肌儿茶酚胺和前列环素在大鼠缺血再灌注心律失律失常发生中的作用。结扎左冠状动脉造成局部心肌缺血然后再灌注。在缺血再灌注组,缺血再灌注引起的心室纤颤发生率为７８％;在巯甲丙脯酸组,巯甲丙脯酸预处理可使缺血再灌注心室纤颤发生率下降了６５．５％;与缺血再灌注组相比,巯甲丙脯酸组的心肌儿茶酚胺含量、心肌６－酮－ＰＧＦ１ａ（６－Ｋｅｔｏ－ＰＧＦ１ａ）的含量明显升高（     

急性低氧对大鼠血粘度,红细胞变形能力和左心室功能的影响

健康ＳＤ雄性大鼠,体重２５０—３００ｇ,麻醉、气管插管,用人工呼吸机经气袋供气,自发吸入氧浓度为９％的氧氮混合气,用ＳＭＵＰ－ＰＣ生物信号处理系统处理左心室功能。结果：（１）急性低氧经动脉血气分析可见ＰａＯ２下降（Ｐ＜０．０１）,ｐＨ值升高（Ｐ＜０．０５）,ＰａＣＯ２稍下降（Ｐ＞０．０５）,左心室功能各指标如ＬＶＰ,ＨＲ,Ｖｍｐ,±ｄｐ／ｄｔｍａｘ,Ｖｃｅ４０,Ｖｍａｘ,Ｌ０、等均下降;血液流变学指标如全血粘度（高、低切值及其还原值）升高,红细胞滤过指数（ＩＦ）升高;复氧后上述各指标恢复正常。（２）静脉注射心得安（０．５ｍｇ／Ｋｇ）后,使急性低氧诱发的左心室功能各指标更加明显下降,而血液流变学各值不再明显上升;静脉注射酚妥拉明（３ｍｇ／Ｋｇ）后,使急性低氧诱发的血液流变学各值上升不明显。（３）石炭酸破坏双侧颈动脉窦区后也可致低氧诱发的左心室功能各指标进一步下降,而血液流变学指标也不再明显上升。结果提示：急性低氧可引起左心室功能下降和全血粘度升高,红细胞变形能力降低,复氧后可恢复;交感神经活动及颈动脉窦区化学感受性反射可能对抗低氧诱发的左心室功能的下降,促进血粘度的升高。     

Ultrastructural characterization of apospory in Panicum maximum

The nucellar ultrastructure of apomictic Panicum maximum was analyzed during the meiocytic stage and during aposporous embryo sac formation. At pachytene the megameiocyte shows a random cell organelle distribution and sometimes only an incomplete micropylar callose wall. The chalazal nucellar cells are meristematic until the tetrad stage. They can turn into initial cells of aposporous embryo sacs. The aposporous initials can be recognized by their increased cell size, large nucleus, and the presence of many vesicles. The cell wall is thin with few plasmodesmata. If only a sexual embryo sac is formed, the nucellar cells retain their meristematic character. The aposporous initial cell is somewhat comparable to a vacuolated functional megaspore. It shows large vacuoles around the central nucleus and is surrounded by a thick cell wall without plasmodesmata. In the mature aposporous embryo sac the structure of the cells of the egg apparatus is similar to each other. In the chalazal part of the egg apparatus the cell walls are thin and do not hamper the transfer of sperm cells. Structural and functional aspects of nucellar cell differentiation and aposporous and sexual embryo sac development are discussed.