紫茎泽兰的光合作用特征及其生态学意义

本文研究了紫茎泽兰(Eupatorium adenophorum Spreng)光合作用强度的变化规律及其与环境主要生态因子的关系,比较了它与某些农作物叶片净光合速率的差异,得到如下结果: 1.紫茎泽兰是一种阳性偏阴的C_3类草本植物,其光合作用的光饱和点约为40000 lx,光补偿点约为700 lx,且具有80 ppm左右的CO_2补偿点。 2.紫茎泽兰的最大净光合速率能达到23毫克CO_2/平方分米·时左右,叶片净光合速率的日变化规律呈双峰曲线型(主峰在10时左右,次峰在16时左右)。在一年中有较长的时间,它的光合速率保持着较高的水平。 3.生长在一般菜园土上的紫茎泽兰,当土壤含水量降至17％左右时,叶片光合速率接近0:而且,受过干旱处理的紫茎泽兰植株,在恢复供水后的第三天,其光合速率只达到原来的53％。 根据以上结果,结合受紫茎泽兰危害地区干湿季分明的特点,提出干季是防除紫茎泽兰的最佳季节。     

兰萼丙素的结构

从北京地区产兰萼香茶菜[Rabdosia japonica (Burm. f.)Hara var.glaucocalyx(Maxim.)Hara]叶中分得三个对映-贝壳杉烯二萜化合物,其中二个为已知物兰萼甲素(2)和乙素(3),另一个为新化合物,命名为兰萼丙素,经光谱和化学方法证明,其结构为对映-7β,14α,15α-三羟基-16-贝壳杉烯-3-酮(1)。     

Hepatic 7 alpha-dehydroxylation of bile acid intermediates, and its significance for the pathogenesis of cerebrotendinous xanthomatosis

The bile acid precursor 7 alpha-hydroxy-4-cholesten-3-one was found to be enzymatically dehydroxylated at a slow rate by liver tissues from the rat, human, and guinea pig. The rat liver enzyme is localized in the microsomal fraction, has a pH optimum of about 8.5, an apparent Km of 0.03-0.04 mM, and a Vmax of 10-15 nmoles.mg protein-1.hr-1. The product from 7 alpha-hydroxy-4-cholesten-3-one was identified as cholesta-4,6-dien-3-one by its chromatographic properties and by mass spectrometry. The reaction proceeded both in air and N2, and pyridine nucleotides were not required as cofactors. In addition to the enzymatic reaction, there was a significant nonenzymatic dehydroxylation of 7 alpha-hydroxy-4-cholesten-3-one, in particular at high pH and with high concentrations of protein. No 7 alpha-dehydroxylation occurred with various 7 alpha-hydroxylated 3 beta-hydroxy-delta 5-steroids. We have previously shown that at least part of the accumulation of cholestanol in cerebrotendinous xanthomatosis (CTX) is due to accelerated 7 alpha-dehydroxylation of bile acid intermediate(s), which are further converted into cholestanol. The capacity to dehydroxylate 7 alpha-hydroxy-4-cholesten-3-one was found to be about the same in homogenates of liver biopsies from two patients with CTX as in preparations from control subjects. It is suggested that increased levels of substrate (7 alpha-hydroxy-4-cholesten-3-one) in the liver, rather than increased amounts of 7 alpha-dehydroxylase is the explanation for the accelerated 7 alpha-dehydroxylation in CTX that leads to increased biosynthesis of cholestanol.     

Diminished oestrogen sensitivity and increased ovulation rate in adult female rats after prepubertal treatment with oestrogen or pimozide

Immature female rats were implanted with oestradiol benzoate or cholesterol in the medial preoptic area at different ages, and the inhibition of the ovariectomy-induced increase of LH secretion by s.c. injected oestradiol was investigated. Medial preoptic oestrogen implants reduced the inhibition of LH secretion in 4-week-old rats, but not in younger animals. Elevation of the circulating oestrogen concentration or suppression of the central nervous dopamine activity by daily injections of oestradiol and pimozide, respectively, from Day 26 to the day of vaginal opening, i.e. during the time when the mechanism of the oestrogen-induced desensitization of the negative oestrogen feedback matures, resulted in considerable diminution of the LH-inhibiting effect of oestradiol in ovariectomized adult females. In intact cyclic rats, both prepubertal treatments led to a significant increase of the average number of eggs per ovulation that was mainly caused by reduction of the number of animals with a low ovulation rate.     

Molecular cloning of three structurally related genes for chicken avidin

The chicken genomic library was screened using the 32P-labelled 3'-end of avidin cDNA as a hybridization probe. A positive clone, lambda gAV12201, containing a 15-16 kb insert, was detected. The EcoRI subclones, pgAV0.4, pgAV1.8, pgAV3.3 and pgAV3.7 from the genomic clone were subjected to hybridization and restriction enzyme mapping analysis. The preliminary results suggest the existence of three structurally related genes for chicken avidin. Whether the natural gene is within the subclones can only be established when sequencing analyses of the subclones have been completed.     

Macrophages, lymphocytes and MHC II antigen in the ram and the rat testis

Macrophages and various subtypes of lymphocytes were identified in the ram and the rat testis by using cytochemical and immunocytochemical techniques. Large and round acid phosphatase-positive cells, notably macrophages, were observed in the rat testis. These cells were absent in the ram testis. Small, elongated cells exhibiting acid phosphatase activity were observed in the testis of both species. The rat testicular interstitium contained 7.7 times as many acid phosphatase-positive cell profiles/surface area unit as did the ram testicular interstitium. T lymphocytes were only occasionally seen in the testis of rat and ram. B lymphocytes were not found in the ram. None of the cell types studies was found in the germinal epithelium.     

Human immune responses to major human cytomegalovirus glycoprotein complexes.

Sera from both human cytomegalovirus (HCMV)-seropositive adults and infants with congenital HCMV infection recognized two major HCMV glycoprotein complexes. However, proliferative responses of peripheral blood mononuclear cells to these complexes varied among seropositive adults and were not detected in any of the infants. Thus, these glycoproteins alone may not be sufficient to develop a subviral HCMV vaccine.     

Mutagenicity of gossypol analyzed by induction of meiotic micronuclei in vitro

Chromosome breakage caused by mutagens in male germ cells can be analyzed by micronucleus induction during meiotic division. This can be followed in vitro by culturing seminiferous tubular segments from stages of the epithelial cycle that contain late pachytene and diakinetic primary spermatocytes. We studied the mutagenic potential of a male contraceptive, gossypol, in this test system using adriamycin (10 ng/ml) as a reference mutagen. A small but significant increase in the frequency of micronuclei was induced with concentrations of 10 and 20 micrograms/ml of gossypol, while cytotoxic effects appeared at concentration of 20 micrograms/ml and were evident at 50 micrograms/ml. Analysis of meiotic micronucleus induction in vitro seems to be a sensitive test system of male germ-cell mutagenesis, but further studies on the possible mutagenic effects of gossypol are needed.     

Directed synthesis of 2',5'-oligoadenylates with increased stability towards phosphodiesterases

Phosphodiesterase stability of synthetic analogs of 2',5'-oligoadenylates, the mediators of antiviral and antiproliferative action of interferons was analysed. The analogs with a 3'-terminal acyclic nucleoside residue were prepared. These analogs were treated with NIH3T3 cell lysate, mice liver homogenate and snake venom phosphodiesterase. All analogs have demonstrated a high stability as compared with the natural 2',5'-oligoadenylate and its 3'-deoxyderivative. The possible biological activity of these stable analogs of 2',5'-oligoadenylates is discussed.     

Attachment of trivaline changes the specificity of binding of netropsin analogs with DNA

In the present communication, synthesis and DNA binding activities of three analogs of the antibiotic netropsin are reported. Each analog contains two N-propylpyrrolecarboxamide units linked covalently to either Dns-Gly-Val-Val-Val-Gly-Gly- (I), Val-Val-Val-Gly-Gly (II) or Gly-Gly (III). It is shown that analogs I and II can self-associate in aqueous solution and methanol as revealed from the fact that UV absorbance and circular dichroism spectra obtained for these analogs are concentration-dependent. By contrast, analogs III exists as a monomer, even at concentration levels of the order of 1.10(-3) M. Determination of the apparent sizes of intramolecular aggregates by gel-filtration shows that analog I in aqueous solution at concentration levels of the order of 1.10(-3) M forms a series of aggregates containing from 2 to 12 monomers. Analog II exhibits a lower tendency to form intermolecular aggregates as compared with that of analog I. Dimerization constants are determined for analogs I and II in aqueous solution and methanol. The binding of N-propylpyrrolecarboxamide units and peptide fragments of analog I to DNA can be independently monitored by circular dichroism and fluorescence methods. If self-associated species of analog I (or II) are present in solution, the ligand exhibits a markedly different order of base pair sequence preferencies as compared with that of analog III. The results obtained are consistent with the inference that analogs I and II in a beta-associated form recognizes base pair sequences containing two runs of 3 AT pairs separated by two GC pairs.