Physiological basis for antagonism of clethodim by imazapic on goosegrass (Eleusine indica (L.) Gaertn.)

Greenhouse and laboratory experiments were conducted to determine the effect of imazapic on the herbicidal activity of clethodim on goosegrass. Imazapic did not affect absorption of [¹⁴C]clethodim by goosegrass. Averaged across the two treatments of clethodim alone and clethodim plus imazapic, absorption was 36 and 89% of applied [¹⁴C]clethodim at 0.5 and 96 h, respectively. The majority of [¹⁴C]clethodim (79% of applied) was absorbed by 24 h. Translocation of ¹⁴C was not affected by imazapic, and 3.6% of applied ¹⁴C had translocated into the portion of the shoot below the treated leaf at 96 h after treatment. Metabolism of clethodim was not affected by the presence of imazapic. Three major metabolites of clethodim were detected in treated tissue at all harvest intervals. The majority (58%) of [¹⁴C]clethodim was converted to a relative polar metabolite form 96 h after treatment, whether clethodim was applied alone or in the presence of imazapic. One day after treatment, the photosynthetic rate in plants treated with imazapic decreased below the rate in the non-treated check, and was less for 8 days, the duration of the study. These data suggest that the antagonism of clethodim by imazapic may be caused by imazapic reducing the photosynthetic rate of goosegrass and therefore the sensitivity of ACCase to clethodim.     

不同品种辣椒幼苗光合特性及弱光耐受性的差异

 在不同弱光处理条件下, 利用L I26400型便携式光合仪研究了弱光对4个辣椒品种幼苗光响应曲线、CO₂ 响应曲线等光合特性的影响, 结果表明弱光下辣椒的光补偿点(LCP) 、光饱和点(LSP) 、光饱和光合速率、CO₂ 补偿点(CCP) 、CO₂ 饱和点(CSP) 、暗呼吸速率(Rd ) 、羧化效率(CE) 、RuBP羧化酶活性、RuBP最大再生速率均下降, 表观量子效率(AQY) 上升, 并且弱光下辣椒净光合速率( Pn)的下降是RuBP羧化限制和再生限制的共同结果。另外随光照的减弱, 辣椒叶片叶绿素(Chl. ) 含量上升,叶绿素a /b比值(Chl. a /b) 和比叶重( SLM) 下降。弱光下LCP和Rd 相对较低、AQY和CE较高的辣椒品种可能具有耐弱光的优势。     

A Diclofop-methyl-Resistant Avena sterilis Biotype with a Herbicide-Resistant Acetyl-coenzyme A Carboxylase and Enhanced Metabolism of Diclofop-methyl

An Avena sterilis biotype was found to be highly resistant to aryloxyphenoxypropionate (APP) herbicides, especially diclofop-methyl. At the enzyme level, this biotype contained a modified acetyl-coenzyme A carboxylase (ACCase) with six-fold resistance to diclofop acid. Absorption and translocation of [¹⁴C]diclofop-methyl applied to the leaf axil of the two-leaf stage plants were similar in both susceptible and resistant biotypes. However, the rate of metabolism of [¹⁴C]diclofop was increased 1·5-fold in this resistant biotype compared to the susceptible. Experiments with tetcyclacis, a cytochrome P450 monooxygenase inhibitor, indicated that inhibition of this enhanced diclofop metabolism increased diclofop-methyl phytotoxicity in this biotype. Studies with ten individual families of the resistant biotype indicated that both mechanisms of resistance, an altered target site and enhanced metabolism, are present in each individual of the population. Hence, it is likely that these two mechanisms of resistance both contribute to resistance in this biotype. © 1997 SCI.     

玉米磷酸烯醇式丙酮酸羧化酶基因高效表达载体构建及其导入小麦的研究

为获得具有C4光合特征的高光效转基因小麦材料,利用从玉米中克隆的磷酸烯醇式丙酮酸羧化酶(PEPC)基因(pepc,GenBank接受号为FJ415327)构建高效双元表达载体,通过基因枪介导法将其导入小麦品种(系)中,利用Real-time PCR方法分析外源基因在转基因植株中的拷贝数.PCR和双酶切鉴定表明,玉米PEPC cDNA序列已插入双元表达载体pCAMBIA3301中,命名为p3301-pepc;对获得的抗性再生植株进行PCR扩增,其中有342株扩增出目的条带;在选取的15株转基因植株中7株拷贝数为1,3株拷贝数为2,2株拷贝数为3,拷贝数为5、8和17的分别为1株.初步证明玉米pepc基因已整合到小麦基因组中,且外源基因在转基因植株中既有单拷贝插入,也有多拷贝插入,这为进一步研究该基因在小麦基因组中的功能表达提供了试验材料.     

Biotin in practical fish-meal based diet for Atlantic salmon Salmo salar L. fry

Groups of Atlantic salmon fry (0.19 g initial weight) were fed a fish-meal based starter diet with different supplements of biotin (0, 0.5, 1.0 and 1.5 mg biotin kg^–1) in triplicate tanks for 18 weeks. The basal diet contained 0.3 mg total biotin kg^–1. The experimental design included a negative control diet made by replacing 10% of the fish-meal with spray-dried raw hen's egg white.
Throughout the experimental period the fish grew to about 5 g and there were no significant differences in growth and mortality among the groups of fish fed the fish-meal diets. At the end of the experiment there were no significant differences in biotin level in the liver, while whole-body biotin concentrations correlated significantly with the dietary biotin concentrations. No significant increase in pyruvate carboxylase (PC) activity was found in livers from fish given different dietary levels of biotin. The control diet with egg white resulted in severe growth reduction and increased mortality compared with the other dietary groups. The concentrations of biotin in liver and whole body were decreased in fish fed egg white. Increased levels of glycogen and reduced PC activity in the liver were observed in this group after 18 weeks.
Histology of the gills showed no differences in appearance when fish were fed fish-meal based diets while the addition of egg white resulted in hypertrophy and hyperplasia of the gill tissue and extensive fusions of the secondary gill lamellae.
The results show that there is no need for supplemental biotin in practical fish-meal based diets for Atlantic salmon fry to achieve optimal growth, survival and maximal liver PC activity.     

ARTP Mutagenesis of Schizochytrium sp. PKU#Mn4 and Clethodim-Based Mutant Screening for Enhanced Docosahexaenoic Acid Accumulation

Schizochytrium species are one of the best oleaginous thraustochytrids for high-yield production of docosahexaenoic acid (DHA, 22:6). However, the DHA yields from most wild-type (WT) strains of Schizochytrium are unsatisfactory for large-scale production. In this study, we applied the atmospheric and room-temperature plasma (ARTP) tool to obtain the mutant library of a previously isolated strain of Schizochytrium (i.e., PKU#Mn4). Two rounds of ARTP mutagenesis coupled with the acetyl-CoA carboxylase (ACCase) inhibitor (clethodim)-based screening yielded the mutant A78 that not only displayed better growth, glucose uptake and ACCase activity, but also increased (54.1%) DHA content than that of the WT strain. Subsequent optimization of medium components and supplementation improved the DHA content by 75.5 and 37.2%, respectively, compared with that of mutant A78 cultivated in the unoptimized medium. Interestingly, the ACCase activity of mutant A78 in a medium supplemented with biotin, citric acid or sodium citrate was significantly greater than that in a medium without supplementation. This study provides an effective bioengineering approach for improving the DHA accumulation in oleaginous microbes.     

谷子PEPC基因的鉴定及其对非生物逆境的响应特性

磷酸烯醇式丙酮酸羧化酶(phosphoenolpyruvate carboxylase,PEPC)是C4植物光合作用关键酶,并在植物多种代谢途径及逆境信号应答过程中起重要作用。本研究通过序列比对,从谷子基因组中筛选出6个SiPEPC候选基因。SiPEPC蛋白特征参数相似度很高,序列非常保守,都含有PEPC基因特征功能域PEPcase Motif。SiPEPC成员主要被定位在细胞质、细胞核和线粒体。在SiPEPC成员启动子序列中含大量有光、激素、逆境以及其他生长调控相关的顺式应答元件。苗期逆境qRT-PCR表达谱分析表明,5个SiPEPC基因(SiPEPC1、SiPEPC2、SiPEPC3、SiPEPC5、SiPEPC6)不同程度受ABA、PEG、高盐和低温诱导表达,表明其参与了苗期对非生物逆境的响应。5个SiPEPC基因表达量在正常生长条件下随着谷子的生长呈增强趋势,且在不同生育时期干旱胁迫下明显增加,表明其参与了拔节、抽穗、灌浆期的干旱胁迫应答。拔节期弱光可诱导5个SiPEPC基因的表达,而在拔节期中等强度光照以及抽穗期和灌浆期的中等光照和弱光照下表达量均急剧降低,揭示光照强度严重影响SiPEPC基因的表达。     

小麦田大穗看麦娘对精噁唑禾草灵的抗性

为明确小麦田大穗看麦娘对精噁唑禾草灵的抗性水平及产生抗性的机理,采用整株法测定了河南省小麦田大穗看麦娘种群对精噁唑禾草灵的抗性水平,以及细胞色素P450s抑制剂胡椒基丁醚(PBO)对精噁唑禾草灵的增效作用,并通过基因测序技术研究了其靶标ACCase基因的突变位点。结果显示:与敏感种群HN-06相比,抗性种群HN-05对精噁唑禾草灵的抗性倍数为52.2,其ACCase基因存在Ile-2041-Asn和Gly-2096-Ala位点突变;喷施PBO后,精噁唑禾草灵对大穗看麦娘的GR50值(有效成分)为5.4 g/hm^2,表现出明显的增效作用,与未喷施PBO处理的差异倍数为161.3。研究表明,抗性种群HN-05对精噁唑禾草灵已产生高水平抗性,该抗性的产生可能是由于其靶标基因突变和P450s介导的代谢增强同时导致的,即表现出了靶标抗性和非靶标抗性共存的现象。