The Fructose Transport Mechanism in Microsomal Membrane Vesicles from Rye Roots

In a fructose-containing medium in which rye root-microsomal membrane vesicles had reached the equilibrium of uptake of fructose, the presence of both Mg²⁺ and ATP caused the efflux of fructose from the vesicles. Among nucleotides examined, ATP caused the largest efflux of fructose. The efflux of fructose dependent on Mg²⁺ and ATP was quite insensitive to a protonophore, carbonylcyanide m-chlorophenylhydrazone (CCCP), which actually abolished MgATP-dependent proton accumulation in the vesicles, while it was largely inhibited by vanadate, which inhibits ATP-binding cassette transporters (ABCTs). The Michaelis-Menten constant (Km) of the efflux of fructose was 0.4 mM. It was observed that fructose stimulated the ATPase activity of the vesicles and that vanadate markedly decreased the fructose-stimulated ATPase activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interaction between alpha-2 macroglobulin and trypsin with synthetic trypsin inhibitors]

The complex formed between trypsin (Tn) and alpha 2 Macroglobulin (alpha 2 M) retains the whole hydrolytic activity of the enzyme for synthetic substrates. Moreover synthetic inhibitors of low molecular weight stiel inhibit this activity. A comparative study of three inhibitors (Benzylamine, Butylamine, Benzamidine) has been carried out and shows that their behavior is similar. These inhibitors bind trypsin when it is bound to alpha 2 M and reciprocally alpha 2 M can bind Tn-inhibitor complex. Nevertheless the dissociation constant of the enzyme-inhibitor complex (Ki) is increased by alpha 2 M. In the case of Benzamidine the value of Ki is 2.22.10(-5) M for native enzyme and 13.4.10(-5) M for Tn-alpha 2 M and in the case of Butylamine this value increases from 0.5.10(-3) M to 2.95.10(-3) M. These variations of the Ki values are due to the modification of the accessibility of the inhibitor to the active site. Unpublished results show that the alpha 2 M molecule undergoes a deep structural modification in the course of the complex formation, which must lead to an increase of the value of Ki. This structural modification is probably irreversible so that the alpha 2 M complex has never been dissociated without altering the alpha 2 M molecule. The increase of the values of Ki cannot therefore result in an effective decrease of the association constant of the Tn-alpha 2 M complex.     

The photosynthetic characteristics of differently shaped leaves in Populus euphratica Olivier

There is a distinct leaf shape polymorphism within a single plant of P. euphratica Olivier. The anatomical structure, carbon isotope discrimination (Δ¹³C), and stomatal and photosynthetic behaviour were investigated in broad-ovate (BOL) and lanceolate (LL) leaves, located at the top and bottom in crown, respectively, of a mature Euphrates poplar growing in its native habitat. Both types of leaves had a non-Kranz anatomy and low Δ¹³C values. However, Δ¹³C of a LL was in average 3.2‰ larger than that of a BOL. In comparison with the LL, the BOL had a smaller stomatal conductance, causing subsequent decreases in transpiration rate and ratio of CO₂ concentrations in intercellular spaces to air. Carbon assimilation rate and water use efficiency were higher in the BOLs than in the LLs. The BOL exhibited C₄-like enzymological features, the activity of glycollate oxidase, and the ratio of activities of ribulose-1,5-bisphosphate carboxylase (RuBPC) to phosphoenolpyruvate carboxylase (PEPC) was lower in BOL than in LL throughout the whole growing season. The lowered ratio of RuBPC/PEPC in BOL was mainly associated with a marked decline in the activity of RuBPC, and only a slight increase in the activity of PEPC. These differences might contribute to microclimate adaptation in both types of leaves. This revised version was published online in June 2006 with corrections to the Cover Date.     

毛萼田菁茎瘤菌(Azorhizobium caulinodans)吸氢活性缺陷株的筛选及特性

利用转座子Tn5随机插入突变法,从毛萼田菁茎瘤菌（Azorhizobiumcaulinodans）中筛选得到两株吸氢活性缺陷突变株（Hup-）R－49和R－309,其固氮酶活性也大大降低,约为野生型固氮酶活性的6％～8％。以带有Bradyrhizobiumjaponicum的5．9kb的hup基因的质粒pHR11为探针与A．caulinodansORS571和B.japonicum122DES（Hup＋）的总DNA进行分子杂交,放射自显影表明,A．coulinodans基因组含有与B.japonicum的hup基因同源的DNA片段,将携带B．japonicumhup基因的嵌合质粒pHR11与A.caulinodansHup-突变株进行体内遗传互补,接合转移子吸氢酶活性可以恢复至野生型的60％,同时固氮酶的活性亦有所提高。     

Genetic complementation of rhizobial nod mutants with Frankia DNA: artifact or reality?

Two divergent reports have been published on the genetic complementation of rhizobial nod mutants using Frankia DNA. In 1991 putative Frankia cosmid library clones were reported to restore normal nodulation properties to Rhizobium leguminosarum biovar viciaenodD::Tn5, but no supporting sequence data were published. In 1992 a second group reported a failure to find any evidence of functional complementation of various rhizobial nod mutants by Frankia DNA (nodA, nodB and nodC). Complementation tests of nine Nod⁻ R. leguminosarum bv. viciae or Sinorhizobium meliloti Tn5 mutants (nodA ⁻ , nodB ⁻ , nodC ⁻ , nodD ⁻ , nodF  ⁻ , nodL ⁻ , nodH ⁻ ) were thus performed using a Frankia gene library in pLAFR3 to clarify this situation. Rhizobial transconjugants obtained by tri-parental matings were screened for restoration of the nodulation phenotype on their host plants, Vicia sativa subsp. nigra or Medicago sativa. Nodulation was observed on plants inoculated with transconjugants of the R. leguminosarum bv. viciaenodC::Tn5 mutant. The Nod⁺ rhizobial transconjugants were isolated and analysed. The Nod⁺ phenotype of these transconjugants was found to be due to Tn5 excision/transposition. No functional complementation was found with any of the mutants used, suggesting that rhizobial complementation of nod mutants with Frankia DNA is unlikely to occur. Received: 17 April 1998 / Accepted: 22 July 1998     

Proline accumulation induced by excess nickel in detached rice leaves

The regulation of proline accumulation in detached rice leaves exposed to excess NiSO₄ was investigated. NiSO₄ treatment increased proline and Ni contents but had no effect on relative water content, indicating that proline accumulation in Ni-exposed detached rice leaves was due to Ni uptake per se, rather than to water stress. Proline accumulation caused by NiSO₄ was related to protein hydrolysis, a decrease in proline dehydrogenase activity, and a decrease in proline utilization. It seems that an increase in the content of ammonia and an increase in the activities of Δ¹-pyrroline-5-carboxylate reductase and ornithine-δ-aminotransferase play minor if any role in Ni-induced proline accumulation in detached rice leaves.     

转座子Tn5096对刺孢吸水链霉菌北京变种RF220转座的诱变

用大肠杆菌/链霉菌穿梭质粒pCZA168(bla,tsr,Tn5096,ColEI rep,Strep repts)多次转化农抗120产生菌刺孢吸水链霉菌北京变种(S.Streptomyces hygrospinocus var. beijingensis)RF220的原生质体,均未得到转化子。来自吸水链霉菌应城变种(S.Streptomyces hygroscopicus var.)10-22突变株的链霉菌质粒pIJ702(tsr mel+)可以转化RF220,但转化频率只有数十个转化子/μgDNA。用来自RF220本身的pIJ702对消除pIJ702后的RF220的原生质体进行了再转化,转化率没有明显的提高。用氨苄青霉素和甘氨酸协同处理RF220的菌丝体,并经-70℃冷冻原生质体再转化,得到了4个pCZA168的转化子。质粒提取、酶切、抗性测定表明：4个转化子中pCZA168中大肠杆菌DNA部分均被切除,成为大小约50～60kb的小质粒,命名为pWZH102(tsr,Tn5096,strep repts)。用pWZH102上的转座子Tn5096对RF220进行转座实验,在168个转座个体中,有2株可能为抗生素生物合成阻断变株,另有产生抗生素水平各异的变株,说明Tn5096的转座可以引起表型的不同变化。     

Isolation and Characterization of NH+4-Excreting Mutants of Enterobacter gergoviae

NH4+-excreting mutants were isolated from Enterobacter gergoviae 57–7 wild type as methylamine resistant strains which were obtained by mutagenesis with a transposable element Tn5. The MG 61 mutants excreted 2 mmol/L of ammonium during a diazotrophic growth. The growth of MG 61 mutants were slower than the growth of wild types because of its excreting ammonium. MG 61 mutants expressed up to 86% of the fully depressed nitrogenase activity when grown in a medium containing 20 mmol/L ammonium. By contrast the ammonium grown cultures of wild type had no nitrogenase activity. In the presence of 5 mmol/L or 30 mmol/L of ammonium in the medium, the growth of MG 61 mutants was as same as CK and much slower than that of the wild types which means that the mutants could not utilize amonium very well in the medium. But MG 61 mutants could utilize glutamate as a sole nitrogen source. In the presence of nitrate (10 mmol/L) in the medium, MG 61 mutants grew slowly but excreted 7.8 mmol/L of ammonium.