金边卫矛抗寒性研究初探

比较观察了金边卫矛在自然越冬及人工冷驯化期间叶片组织结构及胞内淀粉的变化,并测定了未经冷驯化和经冷驯化的金边卫矛幼苗叶片的光响应曲线及两种处理苗在低温胁迫下的光合速率。结果表明：自然越冬及人工冷驯化期间叶片栅栏细胞出现的液泡分割现象以及胞内淀粉在低温驯化前累积、驯化后降解并在脱锻炼后重新积累,均表现出与植物抗寒性发育高度的一致性;与未驯化苗相比,驯化苗叶片的光合速率和光补偿点下降,光饱和点增大。低温胁迫72h后,驯化苗仍能维持一定的光合作用,而未驯化苗已无光合作用,表明冷驯化提高了幼苗在低温胁迫下光合作用的稳定性。亦对上述适应性变化与抗寒性的关系作了探讨。     

Interactive cytogenetic effects on rat bone-marrow due to chronic ingestion of 2,5,2',5' and 3,4,3',4' PCBs.

Rats who were fed low doses of single PCBs, either 2,5,2',5' or 3,4,3',4', did not demonstrate any chromosome breakage or mitotic changes in their bone marrow cells. However, there was a significant increase in chromosome damage observed in bone marrow cells of rats ingesting 10 ppm 2,5,2',5' plus 0.1 ppm 3,3,3',4' in combination. It is suggested that this PCB combination, previously found to cause superadditive chromosome damage in vitro, is also capable of causing chromosome damage in vivo, but these effects do not compromise cell proliferation because the mitotic index is not depressed.     

Radioimmunoassay of cytidine 3',5' monophosphate (cCMP). I. Development of the assay.

A method is presented for the production of reagents for a radioimmunoassay for cCMP. cCMP was succinylated at the 2′0 position with [1,4 ¹⁴C] succinic anhydride, and the monosuccinyl cCMP coupled to Keyhole limpet hemocyanin and injected into rabbits. Antibodies to cCMP were produced that showed minimal crossreactivity with other cyclic nucleotides. Monosuccinyl cCMP was coupled to tyrosine methyl ester, then labeled with ¹²⁵I, and used as the radiolabeled ligand in the immunoassay of cCMP. By use of this assay, the concentration of cCMP in various tissues of rat and guinea pig have been determined.     

Rapid detection of Salmonella from poultry meat products using the '1. 2. Test®'

The 1.2 Test® is a new method of Salmonella detection and it was tested in naturally contaminated poultry meat products. The method, first tested on 48 samples using only previous pre-enrichment phase (experiment 1). gave 30% sensitivity and 91% specificity compared with a classical method. A second study was conducted using the 1.2 Test® following three different cultural procedures ((i) pre-enrichment, (ii) enrichment, and (iii) a combination of pre-enrichment and enrichment) (experiment 2). The three cultural procedures, before inoculation of the 1.2 Test®, gave 73, 73, and 93% sensitivity respectively and all of them were 100% specific. Moreover, the 1.2 Test® gave results very similar to those obtained with the 'enrichment serology' of Sperber and Deibel. It appears that both the preenrichment and enrichment steps are necessary in order to obtain reliable results from the 1.2 Test®, even with raw and 'highly' contaminated products.     

Evidence for a 5' leads to 3' direction of hydrolysis by a 5' mononucleotide-producing exoribonuclease from Saccharomyces cerevisiae.

[³H]rRNA labeled at the 5′ terminus with ³²P and [³H]rRNA labeled at the 3′ end with [¹⁴C] (pA)_n have been degraded at 0° with a highly purified exoribonuclease from $\text{Saccharomyces cerevisiae}$. The results show that with the [³²P, ³H] substrate, the ³²P label is rendered acid-soluble at a much faster rate than the ³H label. Both acid-soluble labels are found in 5′ mononucleotide. With the [¹⁴C, ³H]rRNA, the ³H label is hydrolyzed at a faster rate than the ¹⁴C label. The exoribonuclease hydrolyzes in the 5′ → 3′ direction.     

The interaction of 3,3',4',5-tetrachlorosalicylanilide with phosphatidylcholine bilayers.

1. The interaction of the germicide 3,3',4',5-tetrachlorosalicylanilide (T4CS) with vesicles and dispersions of egg phosphatidylcholine has been studied by gel permeation chromatography, electron microscopy, electron spin resonance spin labelling and ion permeability measurements. 2. Incorporation of T4CS into vesicles of egg phosphatidylcholine gives rise to a large increase in the permeability rate of the paramagnetic cation N,N-dimethyl-N-(1'-oxyl-2',2',6',6'-tetramethyl-4'-piperidyl)-2-hydroxyethylammonium chloride through the lipid bilayer but has no significant effect on the vesicle sizes as measured by gel permeation chromatography or electron microscopy. 3. ESR studies using a spin-labelled fatty acid have demonstrated the presence of two different environments for the spin label when T4CS is incorporated into phosphatidylcholine bilayers. These two environments are identified as (a) highly ordered areas of the bilayer, rich in T4CS and (b) areas with very similar ordering to that in pure egg phosphatidylcholine. 4. The effectiveness of very low concentrations of the germicide in increasing vesicle permeability is explained in terms of its clustering to give rigid patches, rich in T4CS, rather than being evenly distributed throughout the bilayer. It is proposed that the increased ion permeability arises from leakage at the interfaces between the rigid and flexible regions of the lipid bilayer. 5. Comparisons between the effective levels of T4CS in phosphatidylcholine vesicles and its minimum inhibitory concentration with a Gram-positive bacterium confirm the validity of phospholipid vesicles as a model for studies of germicidal activity.     

Distribution of both lengths and 5' terminal nucleotides of mammalian pre-tRNA 3' trailers reflects properties of 3' processing endoribonuclease.

Mammalian tRNA 3'processing endoribonuclease (3'tRNase) removes 3'extra nucleotides after the discriminator from tRNA precursors. Here I examined how the length of a 3'trailer and the nucleotides on each side of the cleavage site affected 3'processing efficiency. I performed in vitro 3'processing reactions of pre-tRNAArgs with various 3'trailers or various discriminator nucleotides using 3'tRNase purified from mouse FM3A cells or pig liver. On the whole, the efficiency of pre- tRNAArg3'processing by mammalian 3'tRNase decreased as the 3'trailer became longer, except in the case of a 3'trailer composed of CC, CCA or CCA plus 1 or 2 nucleotides, which was not able to be removed at all. The distribution of 3'trailer lengths deduced from mammalian nuclear tRNA genomic sequences reflects this property of 3'tRNase. The cleavage efficiency of pre-tRNAArgs varied depending on the 5'end nucleotide of a 3'trailer in the order G approximately A > U > C. This effect of the 5'end nucleotide was independent of the discriminator nucleotides. The distribution of the 5'end nucleotides of mammalian pre-tRNA 3'trailers reflects this differential 3'processing efficiency.