Root respiration in citrus acclimates to temperature and slows during drought

Citrus seedlings were grown in soil columns in which the root system was hydraulically separated into two equal layers; this enabled us to maintain roots in the upper layer without water for 110 d. The columns were placed into waterbaths modified so that soil temperatures in the top layer could be maintained at 25°C or at 35°C, while temperature in the bottom layer was maintained at 25°C. We hypothesized that, if citrus plants were grown in dry soil for an extended period, root mortality would increase if the cost of maintaining the roots was increased by elevating the soil temperature. However, during the drought period we did not observe any root mortality, even at the higher soil temperature. Moreover, we did not find that root respiration was increased by prolonged exposure to drought and higher soil temperature. We did find that root respiration rates slowed in dry soil. Furthermore, when the soil columns were switched from one temperature treatment to another, root respiration rates in wet soil rapidly increased when moved to a higher temperature or rapidly decreased when moved to a lower temperature. But after only 4 d, respiration rates returned to their original level; root respiration in dry soil was not affected by either short-or long-term shifts in soil temperature. Root respiration in citrus appears to acclimate rapidly to changes in soil temperature.     

Plum Pox Virus in Japanese Plum from Argentina: Serological Detection and Molecular Characterization of an Isolate from cv. Red Beauty

A Plum pox virus (PPV) isolate detected in a Japanese plum orchard in Pocito (San Juan, Argentina) was transmitted mechanically to Prunus tomentosa and Nicotiana benthamiana. DAS‐ELISA and DASI‐ELISA indicated the virus presence and serological relationship with D‐strain isolates; IC‐RT‐PCR amplified a 1.2‐kb fragment of the virus genome encoding the CP‐3′ nc region. The analysis of the sequence showed the presence of the DAG motif at the 5′ end of the capsid protein and the Rsa I and Alu I sites at the 3′ end. The phylogenetic relationships and multiple alignment with PPV isolates from NCBI database indicated greatest (+98%) homology with the D strain and close identity with MNAT1 ( AF360579 ) USA peach isolate. The sequence analysed showed two amino acid mutations towards the 5′ N‐terminus of CP (the most variable region) with respect to a consensus of PPV D‐strain isolates. This is the first molecular characterization of 3′terminal genome region of PPV isolate to confirm D strain in a Japanese plum from Argentina.     

Variation of Intergeneric Somatic Hybrids Between Citrus sinensis cv. Valencia and Fortunella crassifolia cv. Meiwa

Intergeneric somatic hybrid plants derived from protoplast fusion between Citrus sinensis (L.) Osbeck cv. Valencia and Fortunella crassifolia Swingle cv. Meiwa have been grown in the fields for 6 years. The plants grew less vigorously with uneven canopy size and some shoots frequently died. Chromosome count showed that the plants, containing non-tetraploid cells besides amphidiploid, were chimeras. Most somatic hybrid plants exhibited a new band of EST isozyme. RAPD analysis verified that several plants lacked some of the parents' markers. The results indicated that the intergeneric somatic hybrids were genetically unstable.     

福建省经济作物寄生线虫的研究——Ⅳ.福建根结线虫的扫描电镜观察

南靖柑桔的福建根结线虫(Meloidogyne fnjianensis)经扫描电镜观察显示它跟四种常见的根结线虫有明显区别,最明显的区别在于其雌虫的头部结构——唇盘呈“X”状,唇盘和中唇之间有沟隔开。此外,雄虫头区无环纹、幼虫唇盘和中唇呈短哑铃状,也有别于其近似种南方根结线虫和花生根结线虫,而其幼虫头区平滑或偶具一条短环纹也有别于前者。     

Genetic transformation of lime (Citrus aurantifolia Swing.): factors affecting transformation and regeneration

We have previously developed procedures for the efficient production of sweet orange (Citrus sinensis L. Osbeck) and Carrizo citrange (C. sinensis L. Osbeck×Poncirus trifoliata L. Raf.) transgenic plants using an Agrobacterium tumefaciens-mediated transformation and shoot tip grafting in vitro regeneration system. We now report on the optimization of the cocultivation, regeneration and selection conditions for efficient and reliable production of transgenic lime (C. aurantifolia Swing.) plants. Improved transformation frequencies were obtained by cocultivating the explants with Agrobacterium on feeder plates. Optimum regeneration of transgenic shoots was obtained by exposing the explants to darkness for 2 weeks and by using kanamycin at 100 mg/l as selective agent. Attempts to use geneticin as selection antibiotic were not successful. Shoot tip grafting of regenerated shoots on Troyer citrange seedlings resulted in 100% successful production of transgenic plants. The presence and expression of the transferred genes in the regenerated plants was verified by β-glucuronidase histochemical and fluorimetric assays, neomycin phosphotransferase ELISA assays, PCR and Southern analyses. Received: 10 December 1996 / Revision received: 10 February 1997 / Accepted: 25 February 1997     

苹果金属硫蛋白基因MdFjMT2克隆及生物信息学分析

以红富士苹果（Malus domestica CV Red Fuji）浓红型芽变和其条红母株为试材,构建抑制性差减杂交（Suppression Subtractive Hybridization,SSH）文库,差异筛选SSH-cDNA文库,经过大量测序构建成红富士苹果ESTs序列本地数据库,对本地数据库进行Blastn检索,得到42条金属硫蛋白基因MdFjMT2 cDNA片段,通过序列拼接和?逆转录PCR（RT-PCR）方法,获得了红富士苹果金属硫蛋白基因MdFjMT2全长cDNA序列（Genbank登录号为HQ730757）,该基因全长684 bp,其中5′ 非翻译区97 bp,3′ 非翻译区347 bp,开放阅读框（ORF）为240 bp,编码79个氨基酸,推测蛋白分子量为7.7938 kDa,理论等电点为4.75。该基因具有金属硫蛋白基因的典型结构域特征,编码的氨基酸序列中含有14个半胱氨酸残基Cys（C）,Cys 残基的排列特征是以CC、CXC和CXXC集中分布在肽链的N端和C端。系统进化分析表明MdFjMT2与砂梨（Pyrus pyrifolia）、苹果（Malus domestica）和小金海棠（M. xiaojinensis）等植物金属硫蛋白保持了较近的亲缘关系,与扁桃（Prunus dulcis）、旱柳（Salix matsudana）、美味猕猴桃（Actinidia deliciosa）等植物的亲缘关系较远。生物信息学分析结果表明,MdFjMT2主要位于叶绿体中,没有信号肽,是非跨膜亲水性蛋白,其蛋白质二级结构的主要元件是无规则卷曲,没有功能结构域。这些结果为MdFjMT2的结构与功能挖掘提供一定的参考。本研究结果有助于研究该基因在苹果着色中的作用,阐明苹果着色的分子机制。     

Nuclear DNA content of somatic and zygotic embryos ofVitis vinifera cv. Grenache noir at the torpedo stage

Summary A flow cytometric analysis and an in situ DNA microspectrophotometric study were made concomitantly to establish why somatic grapevine (Vitis viniferacv. Grenache noir) embryos showed a low level of conversion into plantlets. In somatic embryos at the torpedo stage and in zygotic embryos at the same stage of development, ploidy level, DNA content per 2 C nucleus, and the cell-cycle state of the shoot apical meristem were examined. The frequency distribution histograms of nuclear DNA values were similar in the two types of embryos. At the torpedo stage both types of embryos had a majority of nuclei with 2 C DNA content equal to 1.6pg. In the shoot apices of somatic and zygotic embryos, DNA microspectrophotometry showed preferential blockage of the cell cycle at the G_0–1 stage; however, 20% of somatic embryo shoot apices were blocked at the G_0–2 stage. Analogies between somatic embryos and their zygotic homologues were shown. The genetical and environmental causes of the low level of conversion of grapevine somatic embryos into plantlets are discussed. Our work suggests that the in vitro culture conditions which were used could be incompatible with normal morphogenesis from the torpedo stage.     

Generation and properties of ascorbic acid-deficient transgenic tobacco cells expressing antisense RNA for L-galactono-1,4-lactone dehydrogenase

In higher plants, the terminal step of L-ascorbic acid (AsA) biosynthesis is catalyzed by the enzyme L-galactono-1,4-lactone dehydrogenase (EC 1.3.2.3, GalLDH). We generated AsA-deficient transgenic tobacco BY-2 cell lines by antisense expression of the GalLDH cDNA that was amplified from BY-2 cells using PCR. Two transgenic cell-lines, AS1-1 and AS2-2, having a marked expression of antisense RNA were analyzed. Antisense suppression of GalLDH mRNA led to a significant decline in the GalLDH activity. The AsA levels in the transgenic cell lines were found to be 30% lower than the wild-type BY-2 cells. In synchronous cultures, division of AS1-1 and AS2-2 cells was restrained with a concomitant decrease in mitotic index that was probably due to a decline in AsA levels. The rate of cell growth was also found to be less than that of the wild-type cells. Interestingly, there was a significant phenotypic difference between the transgenic and wild-type cells. The calli of AS1-1 and AS2-2 appeared to be sticky and soft. Back extrusion method also showed that AsA-deficient BY-2 callus was rheologically soft. Furthermore, microscopic analysis revealed that AS1-1 and AS2-2 cells were abnormally slender, suggesting a potential for a significant and a uni-axial elongation. Thus, we observed that decline in the AsA levels has an adverse effect on the division, growth and structure of a plant cell.     

Ca2+对冷胁迫柑橘离体叶片的相关生理生化指标的影响

研究了不同浓度的外源Ca^2＋对柑橘离体叶片抗寒性的影响。结果表明：10-20mmol／L Ca^2＋处理能够增加柑橘可溶性糖和可溶性蛋白质的含量,提高SOD和POD的活性,同时减少膜质过氧化物丙二醛（MDA）的积累,从而提高柑橘的抗寒性。     

根癌农杆菌介导的雪莲冷诱导蛋白基因对薰衣草遗传转化的初步研究

预培养6d的薰衣草下胚轴在添加100μmol·L-1乙酰丁香酮(AS)的根癌农杆菌重悬液中浸染10min后共培养2～3d,再经过7～10d的恢复培养之后用包含10mg·L-1潮霉素B和200mg·L-1头孢霉素的筛选培养基进行筛选是较为理想的遗传转化条件。通过GFP观察和GUS染色以及对筛选得到的抗性芽的PCR检测证明,外源目的基因()莲冷诱导蛋白基因scp)已整合到薰衣草基因组中,阳性率为40%。