Molecular cloning of genes related to aflatoxin biosynthesis by differential screening.

A differential hybridization strategy was used to clone genes associated with aflatoxin biosynthesis. A genomic library, formed between nuclear DNA and the pUC19 plasmid, was screened with three different cDNA probes by the colony hybridization procedure. Nineteen clones were selected; all were positively correlated with and presumably enriched with genes associated with aflatoxin production. Some of these clones were further characterized by using them as probes in Northern (RNA blot) hybridizations. Five clones hybridized strongly with some polyadenylated RNAs formed during the transition to or during idiophase when aflatoxin was produced. However, little or no corresponding hybridization occurred with polyadenylated RNAs formed in early and mid-log growth phase. Two of the clones were further used as probes to hybridize with polyadenylated RNAs formed under aflatoxin-permissive and nonpermissive temperatures. Hybridization occurred with RNA species formed under the permissive temperature only.     

Common denominators in the etiology and pathology of visceral lesions of cystic fibrosis and Keshan disease

The common denominator of a unique disseminated multi-focal milliary myocardial hyaline necrosis and fibrosis in Keshan disease (KSD) and cystic fibrosis (CF) and a commonality of the affected age groups of fetuses and preschool children led to the review of existing KSD autopsy material to search for pancreatic and hepatic lesions considered pathognomonic for CF. Pancreatic lesions considered pathognomonic for CF were found in 595, or 35% of 1700 documented cases of KSD. The pancreatic lesions were limited to tissues of fetuses and preschool children. Adults dying of KSD had diagnostic lesions limited to the cardiovascular system, liver, and skeletal muscle. Varying degrees of focal biliary cirrhosis were identified in 850, or 50% of the KSD autopsies, and 85, or 5% developed severe lobular cirrhosis. The common denominator in CF and KSD appears to be a primary or induced secondary selenium deficiency in age-susceptable humans, prenatally at or around 22 wk of fetal life, during early postnatal life, or during the rapid-growth preschool years. The basic difference between the natural history of CF and KSD is that the selenium deficiency is totally environmental in KSD and appears to be the result of a maternal malabsorptive syndrome or an abnormality of selenium transfer in CF.     

背联体贻贝棘尾虫的形态,形态发生及其调节现象

背联体贻贝棘尾虫的每一虫腹面含有相当于正常棘尾虫的腹面纤毛系统,背联两虫任意一侧属于一虫的背面有4列背触毛,它们的排列分布相似于正常棘昆虫的第1—4列背触毛,另一虫背面打2列背触毛,它们相似于正常棘尾虫的第5、6列背触毛。结果表明,背联体棘尾虫是其中两虫各以背面第4列和第5列背触毛之间的皮层区相联接形成的。也有的背联体中背部皮层联接区有变化。无性分裂中背联两虫皮层纤毛结构的形态发生相似于正常棘尾虫,并且两者其皮层纤毛器如口围带、额腹横棘毛、左、右缘棘毛和背触毛等相应结构的发育是同步进行的,推测背联两虫的皮层发育既是相对独立的,又有某种机制控制着相互间的协调。背联体棘昆虫在无性生殖周期中总是经历着一个调节成单体的过程,认为这于背联两虫都具有一套结构功能正常的运动胞器(特别是口围带),而产生向不同方向运动的“不协调”的力有关。     

家兔脊髓蛛网膜下腔注射乙酰胆碱对血压和心率的影响

将乙酰胆碱(ACh)注入麻醉家兔脊髓蛛网膜下腔,观察其对心血管活动的影响。结果表明:(1)脊髓蛛网膜下腔注射50～100μg ACh可使血压下降,心率减慢;(2)预先由脊髓蛛网膜下腔注射阿托品,可阻断ACh引起的降压和降心率作用;(3)脊髓蛛网膜下腔注射六甲双铵、酚妥拉明或心得安均不能阻断上述ACh的心血管反应;(4)切断两侧颈部迷走神经,ACh不再使心率减慢,但其降低血压的作用不受到任何影响。 脊髓中ACh水平升高可通过激活胆碱能M-受体引起血压下降和心率减慢。ACh的这种降压作用既没有中枢肾上腺素能受体活动参与,也不是通过迷走神经实现的,可能是由于脊髓交感血管中枢紧张性降低所造成的。     

急性缺氧性缺氧时心脏功能的改变

F_(IO_2)(吸入气氧浓度)为12.35、9.87及7.7l％,分别吸入10、8及5min时,心功能呈代偿性增强改变。F_(IO_2)为9.37％、吸入20min时心功能的变化趋势与9.87％8min时仍基本相同。继发性缺二氧化碳对缺氧引起的心功能代偿性增强,在一定程度上起抵消作用。F_(IO_2)为9.87％时的缺氧程度约相当于18km高空加压供氧总压值为15.3kPa(115mmHg)时的缺氧。单纯从缺氧因素考虑,将总压值由常用的17.3kPa(130mmHg)降低为15.3kPa是可允许的。     

大田玉米、高粱、芝麻、豇豆叶片水势、蒸腾速率、气孔阻力对环境因素的反应

本文研究了田间生长的玉米、高梁、芝麻、豇豆在不同土壤供水条件下,叶水势、气孔阻力、蒸腾速率日变化及其与环境因素的关系。结果表明,四种作物气孔开闭与光强密切相关:夜间气孔关闭,rs高;白天气孔开放,rs低。ψ_(WL)、TR与环境因素(气温、RH、ψ_(WV)、光强等)密切相关,它们之间的相关系数(在0.05和0.01水平)显著。四种作物ψ_(WL)日节奏为“正弦曲线”状,13:00—15:00小时ψ_(WL)最低,黎明前最高。中午ψ_(WV)和土壤含水量愈低。ψ_(ML)愈低。四种作物TR在早晨逐斩增高,13:00—15:00小时最强;傍晚前又降低;夜间TR最低。干旱植株ψ_(WL)、TR低于灌水植株,而rs高于灌水植株。     

Survival of genetically engineered Escherichia coli in natural soil and river water

Twelve derivatives of Escherichia coli strain HB101 which contained different sizes of plasmids ranging from 3.9 Kb to 48 Kb and encoding resistance to various antibiotics were used. When these organisms were introduced into natural river water, the population declined rapidly and by day 3, the majority (i.e. more than 99.9%) of them could no longer be detected on antibiotic-amended culture plates. If the river water was filter sterilized first, the added organisms maintained their population for up to 7 d without any significant decrease in numbers. Similar results were also observed in sterilized tap water or distilled water. This indicated that the disappearance of these organisms in the aquatic environment was caused mainly by biotic factor(s). The loss of the ability to grow in the presence of antibiotics by some of the E. coli was not observed unless they were allowed to grow in the antibiotic-free environment first. When the test organisms were added to natural silt loam, a large portion of the original population still remained viable after 16 d. There was no relationship between the percentage survival of E. coli in natural river water and the sizes of plasmid harboured. On the other hand, when these bacteria were added to natural soil, survival appeared to increase as plasmid size increased. and accepted 19 August 1989     

PHA激活的脐血T细胞条件培养液对人骨髓CFU-c的抑制

本文研究了PHA刺激18小时收获的脐血T细胞条件培养液(PHA-TCM)对正常人骨髓CFU-c的影响。结果显示PHA-TCM能够显著抑制CFU-c的生长,这种抑制与PHA-TCM浓度有关。并发现经PHA-TCM作用后M型集落比例明显降低。PHA-TCM中未检出IFN和IL-2活性。进一步研究证实,PHA-TCM中CFU-c抑制活性是一种对酸碱敏感对热相对不敏感的蛋白质,其分子量大于10,000道尔顿。