Production of chitinolytic enzymes from a novel species ofAeromonas

A bacterial strain secreting potent chitinolytic activity was isolated from shrimp-pond water by enrichment culture using colloidal crab-shell chitin as the major carbon source. The isolated bacterium, designated asAeromonas sp No. 16 exhibited a rod-like morphology with a polar flagellum. Under optimal culture conditions in 500-ml shaker flasks, it produced a chitinolytic activity of 1.4 U ml^–1. A slightly higher enzymatic activity of 1.5 U ml^–1 was obtained when cultivation was carried out in a 5-liter jar fermentor using a medium containing crystalline chitin as the carbon source. The secretion of the enzyme(s) was stimulated by several organic nitrogenous supplements. Most carbon sources tested (glucose, maltose, N-acetylglucosamine, etc) enhanced cell growth, but they slightly inhibited enzyme secretion. Glucosamine (0.5% w/v) severely inhibited cell growth (16% of the control), but it did not significantly affect enzyme secretion. The production of chitinolytic enzymes was pH sensitive and was enhanced by increasing the concentration of colloidal chitin to 1.5%. The observed chitinolytic activity could be attributed to the presence of -N-acetylglucosaminidase and chitinase. Chitinase was purified by ammonium sulfate fractionation and preparative gel electrophoresis to three major bands on SDS-PAGE. An in-gel enzymatic activity assay indicated that all three bands possessed chitinase activity. Analysis of the enzymatic products indicated that the purified enzyme(s) hydrolyzed colloidal chitin predominantly to N,N-diacetyl-chitobiose and, to a much lesser extent, the mono-, tri, and tetramer of N-acetylglucosamine, suggesting that they are mainly endochitinases.     

A glutamate/glutamine/aspartate/asparagine transport operon in Rhodobacter capsulatus

A mutant of Rhodobacter capsulatus was identified in which an operon encoding a binding-protein-dependent transporter was interrupted by Tn5 transposition. Cloning and sequence analysis of the wild-type operon revealed a four-gene cluster with similarities to genes encoding periplasmic binding proteins (BztA), integral membrane proteins (BztB and BztC), and ATP-binding proteins (BztD). To assess the function of this putative binding-protein-dependent transport system, a mutant was constructed in which most of the bztABCD operon was deleted and replaced by an antibiotic-resistance marker. The deletion mutant grew more slowly than the wild type in NH-free medium supplemented by glutamate, glutamine, aspartate or asparagine; it was resistant to toxic analogues of Glu, Asp, and Asn at concentrations that inhibited growth of the wild type; and it was defective in the uptake of Glu, Gin, and Asp. A complementing plasmid containing the wild-type copy of bztABCD was able to rescue all the mutant phenotypes. Taken together, these results indicate that the proteins encoded by bztABCD are active in the uptake of Glu, Gin, Asp, and Asn. In addition, competition experiments, in which the ability of each of the four amino acids to compete for the transport of one another was examined, demonstrated that all four substrates share at least one component of this transport system.     

玉米种子萌发成苗不同阶段需水阈值的研究

用渗透势不同的聚乙二醇（ＰＥＧ）６０００模拟外界环境水分条件,对玉米不同品种的种子在萌动、萌发及成苗三个阶段需水的量化研究表明,种苗的抗旱性随吸水进程的推进而减弱;种子在萌动、萌发及胚芽伸长至一定长度的时间（ｔ）与外界环境水势（ｗ）之间存在着１／ｔ＝ａ＋ｂｗ的关系,据此推算出不同品种在不同成苗阶段的需水阈值,发现不同品种在同一成苗过程中对环境水分条件的反应不同,它们的抗旱性也不同。     

广西水土保持植物材料试验研究初报

植物措施能有效地防止水土流失。本文根据水土保持植物措施的新思路和新模式,选用和配置水土保持植物材料,研究其生态经济效益。     

北方稻田生态系统研究Ⅱ．稻萍结合系统细绿萍共生固N量研究

对稻萍结合系统细绿萍共生固Ｎ量研究表明,萍的固Ｎ力在整个生长季不同时期有所变化．最高固Ｎ率出现在６月初,萍固Ｎ量随其接种量和水稻行距增加而增加．５０～１０ｃｍ宽窄行交替的水稻行距和１５００ｋｇ·ｈｍ－２的萍接种量的稻萍结合系统的总固Ｎ量为１０７．１ｋｇ·ｈｍ－２,而３０ｃｍ等行距的３２５ｋｇ·ｈｍ－２的萍接种量的稻－萍结合系统的总固Ｎ量仅为３６．０ｋｇ·ｈｍ－２     

Drosophila MCM protein complexes.

MCM genes encode a family of evolutionarily conserved proteins required for DNA replication. In Saccharomyces cerevisiae, where they were first identified, MCM genes interact genetically with each other. Allele specificity in these interactions suggests that MCM proteins physically associate with one another and that this association is essential for function. We describe here an analysis of physical interactions among three Drosophila MCM proteins. Using specific antibodies we detect Drosophila MCMs almost exclusively in 600-kDa protein complexes. Co-immunoprecipitation data demonstrate the existence of at least two distinct types of 600-kDa complexes, one that contains DmCDC46 and one that appears to contain both DmMCM2 and Dpa (a CDC54 homologue). These complexes are stable throughout embryonic division cycles, are resistant to treatments with salt and detergent, and are present during development in tissues undergoing mitotic DNA replication as well as endoreplication. When extracts are prepared under low salt conditions all three MCM proteins co-immunoprecipitate. Consequently, we suggest that the 600-kDa complexes interact in a higher order complex.     

酶法合成天冬甜精中的几个问题

本文从酶、酶的作用底物和合成体系三个方面综述了酶法合成天冬甜精中的几个问题。     

桃花营养元素的分析与开发探讨

桃花含有较高的蛋白质和人体必需的各种氨基酸、维生素和微量元素。由于桃树在我国分布范围广泛,产花量大且需要人工疏花,使桃花的开发利用具有良好的条件。     

The Effects of Cytokinin and Light on Hypocotyl Elongation in Arabidopsis Seedlings Are Independent and Additive

Cytokinin has been reported to mimic some of the effects of light on de-etiolation responses in dark-grown Arabidopsis seedlings. The interaction between cytokinin and light was examined by analyzing cytokinin dose and light fluence effects on hypocotyl elongation in wild-type and mutant Arabidopsis seedlings with defects in light or hormone responses. It was found that (a) cytokinin and light-response systems have independent and additive effects on the inhibition of hypocotyl elongation and (b) either cytokinin or light can saturate the morphogenic responses. As a consequence, cytokinin has no effect on hypocotyl elongation under normal growth conditions because light levels saturate the hypocotyl inhibition response. To determine whether a functional light-response pathway is required for cytokinin responses, light-insensitive long hypocotyl (hy) mutants were tested for cytokinin responses. The hy mutants (hy1 to hy6) had normal cytokinin responses, except phyB-1 (hy3-1), in which hypocotyl elongation was insensitive to cytokinin. Cytokinin insensitivity in phyB-1 was attributed to an indirect effect of the mutation on cytokinin responses. The effects of cytokinin on the inhibition of hypocotyl elongation are largely mediated by ethylene, and blocking the ethylene-response pathway through the action of a cytokinin-resistant, ethylene-insensitive mutant (ckr1/ein2) had no effect on the light inhibition of hypocotyl elongation. These results do not support the idea that cytokinin mediates the action of light on hypocotyl elongation.