水稻幼穗组培及白化苗的电镜观察

木文报道了五份水稻材料的幼穗组培的诱导率和分化率,对继代８次后的幼穗愈伤分化出的白苗和绿苗及其各自的愈伤进行电镜扫描,发现白苗的质体结构不完整,不能正常合成叶绿素。     

外源钙调蛋白对植物细胞分裂增殖作用的研究

外源钙调蛋白（Ｃａｌｍｏｄｕｌｉｎ,ＣａＭ）对胡萝卜悬浮细胞增殖具明显促进作用,不同浓度ＣａＭ的促进程度不同,７ｕｇ／ｍｌ时促进作用最大。ＣａＭ抑制剂ＴＦＰ（Ｔｒｉｆｌｕｏｐｅｒ－ａｚｉｎｅ）则明显抑制该悬浮细胞的增殖,ＴＦＰ浓度越高则抑制作用越强。另外,外源ＣａＭ可以加快珍珠梅花粉第二次有丝分裂,改变生殖细胞有丝分裂各期花粉管的比例,说明外源ＣａＭ对植物体细胞和性细胞的增殖和分裂均有促进作用。     

乳链菌肽的分离纯化和部分生物学性质

用乳酸链球菌ＳＭ５２６进行乳链菌肽的发酵生产,产量为４０～５０ｍｇ／ｌ．经中空纤维超滤器超滤,非极性大孔吸附树脂ＸＡＤ－２层析,ＣＭ－ＳｅｐｈａｄｅｘＣ－２５层析和ＳｅｐｈａｄｅｘＧ－５０层析纯化了该肽。ＳＤＳ－ＰＡＧＥ表明达均一,ＲＰ－ＨＰＬＣ表明其纯度不低于９５％。ＳＤＳ－ＰＡＧＥ测其Ｍｒ约为３６００,用ＩＥＦ测其等电点为９．５．酸性条件下稳定且抗热;对胰蛋白酶、胃蛋白酶和木瓜蛋白酶不敏感,但对α－胰凝乳酶和蛋白酶Ｋ敏感。乳链菌肽对多种革兰氏阳性菌有强烈的抑制作用;以枯草杆菌和金黄色葡萄球菌为指示菌,其作用方式是杀菌。     

The zygote and proembryo of alfalfa: quantitative,three-dimensional analysis and implications for biparental plastid inheritance

Summary Genetic studies have demonstrated biparental inheritance of plastids in alfalfa. The ratio of paternal to maternal plastids in the progeny varies according to the genotypes of the parents, which can be classified as strong or weak transmitters of plastids. Previous cytological investigations of generative cells and male gametes have provided no consistent explanation for plastid inheritance patterns among genotypes. However, plastids in the mature egg cells of a strong female genotype (6–4) were found to be more numerous and larger than in mature eggs of a weak female genotype (CUF-B), and the plastids in 6–4 eggs are positioned equally around the nucleus. In CUF-B, the majority of plastids are positioned below (toward the micropyle) the mid level of the nucleus, which is the future division plane of the zygote. Since only the apical portion of the zygote produces the embryo proper, plastids in the basal portion were predicted to become included in the suspensor cells and not be inherited. In the present study, we examined zygotes and a two-celled proembryo from a cross between CUF-B and a strong male genotype (301), a cross that results in over 90% of the progeny possessing paternal plastids only. Our results indicate that the distribution of plastids observed in the CUF-B egg cell is maintained through the first division of the zygote. Further, paternal plastids are similarly distributed; however, within the apical portion of the zygote and in the apical cell of the two-celled proembryo, the number of paternal plastids is typically much greater than the number of maternal plastids. These findings suggest that maternal and paternal plastid distribution within the zygote is a significant factor determining the inheritance of maternal and paternal plastids in alfalfa.     

Iodothyronine deiodinase activity in methionine-deficient rats fed selenium-deficient or selenium-sufficient diets

We examined the effect of methionine deficiency on iodothyronine 5’-deiodinase activity in selenium-deficient rats or selenium-sufficient rats fed sodium selenate or selenomethionine. Forty-two weanling male Wistar rats were divided into six groups and pair fed the respective purifiedl-amino acid-based diets for 4 wk.l-methionine concentrations in the diet were 8.0 g/kg for sufficient rats, and 2.0 g/kg for deficient rats. Selenium concentrations in the diet were 0.5 mg/kg (as sodium selenate or selenomethionine) for selenium-sufficient rats and less than 0.005 mg/kg for selenium-deficient rats. Type I 5’-deiodinase activities were significantly lower in liver and higher in kidney of methionine-deficient rats than in those of methionine-sufficient rats fed either the selenium-sufficient or the selenium-deficient diets. The type I 5’-deiodinase activity in brain was significantly lower in the methionine-deficient rats than in the methionine-sufficient rats fed the selenium-deficient diet. Type II 5’-deiodinase activity in brain was significantly higher in the methionine-deficient rats than in the methionine-sufficient rats fed selenium-sufficient diet as sodium selenate. Both thyroxine and 3,3’,5-triiodothyronine concentrations in plasma were significantly higher in the methionine-deficient rats than in the methionine-sufficient rats. It is suggested that the methionine deficiency affects the 5’-deiodinase activity and thyroid hormones level in the rats.     

Sequence diversity of V1 and V2 domains of gp120 from human immunodeficiency virus type 1: lack of correlation with viral phenotype.

We analyzed by PCR and direct sequencing 57 viral sequences from 47 individuals infected with human immunodeficiency virus type 1, focussing on the V1 and V2 regions of gp120. There was extensive length polymorphism in the V1 region, which rendered sequence alignment difficult. The V2 hypervariable locus also displayed considerable length variations, whereas flanking regions were relatively conserved. Two-thirds of the amino acid residues in these flanking regions were highly conserved (> 80%), presumably reflecting their critical contribution to V2 structure or function. We also characterized the syncytium-inducing properties of the isolates from which we derived sequence information. There was no correlation between V1 or V2 sequences and the viral phenotype, contrary to a previous report (M. Groenink, R. A. M. Fouchier, S. Broersen, C. H. Baker, M. Koot, A. B. van't Wout, H. G. Huisman, F. Miedema, M. Tersmette, and H. Schuitemaker, Science 260:1513-1516, 1993). The sequence heterogeneity described in this study provides information to suggest that it would be most difficult to exploit the V1 and V2 domains for vaccine development.     

Genomic organization and evolution of the soybean SB92 satellite sequence

Repetitive DNA sequences comprise a large percentage of plant genomes, and their characterization provides information about both species and genome evolution. We have isolated a recombinant clone containing a highly repeated DNA element (SB92) that is homologous to ca. 0.9% of the soybean genome or about 10⁵ copies. This repeated sequence is tandemly arranged and is found in four or five major genomic locations. FISH analysis of metaphase chromosomes suggests that two of these locations are centromeric. We have determined the sequence of two cloned repeats and performed genomic sequencing to obtain a consensus sequence. The consensus repeat size was 92 bp and exhibited an average of 10% nucleotide substitution relative to the two cloned repeats. This high level of sequence diversity suggests an ancient origin but is inconsistent with the limited phylogenetic distribution of SB92, which is found an high copy number only in the annual soybeans. It therefore seems likely that this sequence is undergoing very rapid evolution.