Induction of Crassulacean Acid Metabolism in the Facultative Halophyte Mesembryanthemum crystallinum by Abscisic Acid

The facultative halophyte, Mesembryanthemum crystallinum, shifts its mode of carbon assimilation from the C₃ pathway to Crassulacean acid metabolism (CAM) in response to water stress. In this study, exogenously applied abscisic acid (ABA), at micromolar concentrations, could partially substitute for water stress in induction of CAM in this species. ABA at concentrations of 5 to 10 micromolar, when applied to leaves or to the roots in hydroponic culture or in soil, induced the expression of CAM within days (as indicated by the nocturnal accumulation of total titratable acidity and malate). After applying ABA there was also an increase in phosphoenolpyruvate carboxylase and NADP-malic enzyme activities. The degree and time course of induction by ABA were comparable to those induced by salt and water stress. Electrophoretic analyses of leaf soluble protein indicate that the increases in phosphoenolpyruvate carboxylase activity during the induction by ABA, salt, and water stress are due to an increase in the quantity of the enzyme protein. ABA may be a factor in the stress-induced expression of CAM in M. crystallinum, serving as a functional link between stress and biochemical adaptation.     

Sucrose synthase in rice plants : growth-associated changes in tissue specific distributions

Different parts of the rice (Oryza sativa L.) plant at different growth stages were analyzed for sucrose synthase (SS) by enzyme activity assay and enzyme-linked immunosorbent assay directly on the extracts or on the eluates from a gel filtration column. On a dry matter basis, the amount of soluble protein and SS activity decreased significantly, but the amount of enzyme protein changed little in growing leaves. In the grain, the SS activity was the highest at the early ripening stage and decreased later, but the amount of SS protein increased with the increase in maturity. In the root, a low activity of SS was detectable only in the tillering but not in other stages. Immunoblotting of SS protein extracted from different parts of rice showed two bands. Elution patterns of crude extracts from a gel filtration column showed the presence of several types of SS protein. Among them, two to three types with larger elution volumes had the SS activity but others with smaller elution volumes (considered as the aggregated forms) had no activity. The SS purified from different parts of the plant showed similar but distinctly different electrophoretic mobilities in a native gel. It has been concluded that different isozymes are expressed in different tissues at different growth stages.     

Gibberellin structure and florigenic activity in Lolium temulentum,a long-day plant

Structural requirements for florigenic activity among gibberellins (GAs) and GA derivatives, including several new ones, applied once to leaves of Lolium temulentum, were examined. The compounds were applied to plants kept either in non-inductive short days (SD) or exposed to one inductive long day (LD). Inflorescence initiation and stem-elongation responses were assessed three weeks later. Among the GAs used, the range in effective dose for inflorescence initiation was more than 1000-fold, but substantially less for stem elongation. Some GAs promoted both stem elongation and inflorescence initiation, some promoted one without the other, and some affected neither. The structural features enhancing florigenic activity were often different from those enhancing stem elongation. Except in the case of 2,2-dimethyl GA₄, a double bond in the A ring at either C-1,2 or C-2,3 was essential for high florigenic activity, though not for stem elongation. A free carboxy group was needed for both. Inflorescence initiation in Lolium was enhanced by hydroxylation at C-12, ?13 and ?15, whereas hydroxylation at C-3 reduced the effect on inflorescence initiation but increased that on stem elongation. A 12β-hydroxyl was more effective than the α epimer for inflorescence initiation whereas the reverse was true for stem elongation. Although such differential effectiveness of GAs for inflorescence initiation and for stem elongation could reflect differences in uptake, transport or metabolism, we suggest that it is indicative of specific structural requirements for inflorescence initiation.     

Drugs of abuse--opiates.

Treating opiate-dependent patients can be difficult for many physicians because the patients'' life-styles, values, and beliefs differ from those of the physicians. Primary care physicians, however, are often involved in the treatment of the medical complications of opiate abuse, and physicians must often manage a patient''s opiate dependence until appropriate referral to a drug abuse treatment program can be arranged. Treatment is guided by an understanding of the patient''s addictive disease, for which there are specific diagnostic criteria, and an understanding of the pharmacology of opiates of abuse and the medications used in treating opiate dependence. The opiate agonist, methadone, is useful for both detoxification and maintenance. The opiate antagonist, naloxone, is the treatment of choice for opiate overdose, and naltrexone, also an opiate antagonist, is a useful adjunct in subgroups of opiate-dependent patients for preventing relapse. New medications for the treatment of opiate dependence are being developed.     

Purification and characterization of a novel nucleoside phosphorylase from a Klebsiella sp. and its use in the enzymatic production of adenine arabinoside

An adenosine-assimilating bacterium, Klebsiella sp. strain LF1202, inducibly formed a novel nucleoside phosphorylase which acted on both purine and pyrimidine nucleosides when the cells were cultured in medium containing adenosine as a sole source of carbon and nitrogen. The enzyme was purified (approximately 83-fold, with a 17% activity yield) to the homogeneous state by polyacrylamide gel electrophoresis. The molecular weight of the purified enzyme was calculated to be 125,000 by gel filtration of Sephadex G-200 column chromatography, although the enzyme migrated as a single protein band with a molecular weight of 25,000 on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis; thus, it was thought to consist of five identical subunits. Besides purine nucleosides (adenosine, inosine, and guanosine), the purified enzyme also acted on pyrimidine nucleosides such as uridine, 2'-deoxyuridine, and thymidine. The purified enzyme catalyzed the synthesis of adenine arabinoside, a selective antiviral pharmaceutic agent, from uridine arabinoside and adenine.     

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.     

Comparison of DMO and flow cytometric methods for measuring intracellular pH and the effect of hyperthermia on the transmembrane pH gradient

Intracellular pH (pHi) was measured in both unheated and heated cells by the distribution of the weak acid, 5,5-dimethyl-2,4-oxazolidinedione-2-14C (14C-DMO), and by the fluorescence intensity ratio (I530/I630) of the pH sensitive fluorescent dye, 2',7'-bis(carboxyethyl)-5,6-carboxy-fluorescein (BCECF), analyzed by flow cytometry (FCM). BCECF-loaded Chinese hamster ovary (CHO) cells were analyzed by FCM after they had incubated in fresh medium at 37 degrees C for 90 min, during which time a decrease in fluorescence ratio stabilized. After stabilization, the pHi determined for CHO cells by the FCM method at pHe values of 6.0-8.1 agreed-within 0.1 pH units with that determined by the 14C-DMO method. There is a pH gradient across the plasma membrane that is not affected by heat. In CHO cells, the gradient, determined by DMO and FCM, is less or greater than pHe by 0.30 and 0.15 pH units at pHe 7.4 and 6.3, respectively, and in NG108-15 cells, the gradient determined by DMO increases to 0.50 pH units at pHe 6.3. Both cells maintained their pH gradients for at least 4 h after heating, although 99.9% of the cells were reproductively dead (survival of 10(-3)) after heating at 45.5 degrees C either at the normal pHe of 7.4 or at a low pHe of 6.4-6.7.     

条鳅亚科鱼类一新属新种

本文描述了云南省条鳅亚科鱼类一新属和一新种。根据形态特征并结合区系间的相互关系,探讨了属的分类地位。     

西双版纳热带季节雨林植物种类多样性的一种研究方法

一、方法1.样地的选择样地分别选取热带干性季节雨林的典型代表——以箭毒木(Antiaris toxicaria)、龙果(Pouteria grandifolia)为标志的群落,以千果榄仁(Terminalia myriocarpa)、番龙眼     

Genetic analysis of two tomato mutants affected in the regulation of iron metabolism

Iron is one of the most important micronutrients for plants. Like other organisms, plants have developed active mechanisms for the acquisition of sufficient iron from the soil. Nevertheless, very little is known about the genetic mechanisms that control the active uptake. In tomato, two spontaneously derived mutants are available, which are defective in key steps that control this process. The recessive mutationchloronerva (chln) affects a gene which controls the synthesis of the non-protein amino acid nicotianamine (NA), a key component in the iron physiology of plants. The root system of the recessive mutantfer is unable to induce any of the characteristic responses to iron deficiency and iron uptake is thus completely blocked. We present a characterization of the double mutant, showing that thefer gene is epistatic over thechln gene and thus very likely to be one of the major genetic elements controlling iron physiology in tomato. In order to gain access to these two genes at the molecular level, both mutants were precisely mapped onto the high density RFLP map of tomato. Thechln gene is located on chromosome 1 and thefer gene is on chromosome 6 of tomato. Using this high-resolution map, a chromosome walk has been started to isolate thefer gene by map-based cloning. The isolation of thefer gene will provide new insights into the molecular mechanisms of iron uptake control in plants.