运用致病毒素筛选抗稻瘟病细胞突变体

本文研究报道了抗稻瘟病细胞突变体筛选方法、程序与结果,并对有关问题进行了讨论。毒素对水稻成熟胚愈伤组织的诱导与分化有明显的抑制作用,抑制程度随毒素浓度提高和处理时间延长而加强,但抗感品种之间差异显著。以含毒素的诱导培养基或诱导与分化培养基均含毒素的筛选处理效果较好,而且简便易行。5年来接种筛选了29个品种25000多个外植体,在已鉴定的349个R_1个体中,有183株表现抗病。经多次接种鉴定与选择,已获得12个高抗稻瘟病的株系和1个抗病丰产品系,并对部分抗病突变体的抗性基因进行了遗传分析。     

辣椒疫毒致病毒素

辣椒疫霉（PhytophthoracapsiciLeonian）在培养液中振荡培养时可分泌毒素,这种毒素能引起辣椒叶片形成水渍状褐腐斑,类似病原菌侵染后形成的症状。Plich’s和V8C培养液适于P.capsici的生长和产毒;生长适宜温度和pH范围分别为20～30℃与pH6～7,在25～30℃、pH5～8的条件下培养滤液毒性最强;培养15天产毒达到最高值。滤液先后经85％硫酸铰沉淀、DE52、CM32和SephadexG－75柱层析将毒素纯化。经鉴定该纯毒素为39．8kD酸性糖蛋白,并对80℃以上高温或蛋白酶敏感,而β-D-葡萄糖苷酶处理不影响其毒性,蛋白亚基为毒素的活性中心。毒素处理寄主叶片引致病理性坏死,这一作用与辣椒品种抗病性有关。     

Chickpea wilt: identification and toxicity of 8-O-methyl-fusarubin from Fusarium acutatum

Fusarium acutatum was isolated from wilting chickpea plants in Pakistan. Filtrates from cultures grown on a defined liquid medium caused permanent wilting of chickpea cuttings and killed cells, isolated enzymically from healthy plants, in a bioassay. Toxic activity was retained by a cyano solid phase extraction cartridge and the toxin was isolated by elution from the cartridge in acetonitrile and Si-gel thin layer chromatography of the eluate. Analytical HPLC of the compound on a cyano column with diode array detection gave a single peak with a homogeneous spectrum and lambda(max) at 224 and 281 nm. NMR and mass spectral studies showed that the toxin was 8-O-methyl-fusarubin. The pure compound caused permanent wilting of chickpea cuttings and the LD50 value in the cell bioassay was 327 ng/ml.     

Ecophysiological aspects of allelopathy

Allelochemicals play an important role in explaining plant growth inhibition in interspecies interactions and in structuring the plant community. Five aspects of allelochemicals are discussed from an ecophysiological perspective: (i) biosynthesis, (ii) mode of release, (iii) mode of action, (iv) detoxification and prevention of autotoxicity, and (v) joint action of allelochemicals. A discussion on identifying a compound as an allelochemical is also presented.     

Responses of cells and protoplasts of Coffea arabica genotypes to partially purified culture filtrates produced by Colletotrichum kahawae

Hypocotyl-derived calli of genotypes and segregating populations of Coffea arabica, differing in susceptibility to Colletotrichum kahawae, were used to produce cell suspensions and protoplasts which were exposed to partially purified culture filtrates (PPCFs) prepared from the pathogen. The growth and viability of PPCF-treated cells and protoplasts were measured using packed cell volume, fluorescein diacetate staining and a colorimetric assay involving the tetrazolium salt MTT. Differential responses of cells and protoplasts were influenced by genotype, time of exposure and PPCF concentration. Protoplasts of resistant genotypes responded differentially from more susceptible genotypes as early as 4 h after challenge with the phytotoxin, suggesting that they were more sensitive than cell suspensions to the treatments. Protoplasts exposed to PPCFs from C. kahawae may therefore be used to screen and select genotypes resistant to, or tolerant of, coffee berry disease. Received: 10 April 1996 / Revision received: 25 August 1996 / Accepted: 15 September 1996     

Isolation and identification of a potent allelopathic substance in Bangladesh rice

Aqueous methanol extracts of Bangladesh rice (Oryza sativa L. cv. BR17) inhibited the growth of roots and shoots of cress (Lepidium sativum), lettuce (Lactuca sativa), alfalfa (Medicago sativa), timothy (Phleum pratense), Digitaria sanguinalis, Echinochloa crus-galli and Echinochloa colonum. Increasing the extract concentration increased the inhibition, suggesting that the BR17 may have growth inhibitory substances and possess allelopathic potential. The aqueous methanol extract of the BR17 was purified and a main inhibitory substance was isolated and determined by spectral data as 2,9-dihydroxy-4-megastigmen-3-one. This substance inhibited root and shoot growth of cress and E. crus-galli seedlings at concentrations greater than 0.03 and 3 μM, respectively. The concentrations required for 50% growth inhibition on cress roots and shoots were 0.22 and 0.47 μM, respectively, and on E. crus-galli roots and shoots were 36 and 133 μM, respectively. These results suggest that 2,9-dihydroxy-4-megastigmen-3-one may contribute to the growth inhibitory effect of BR17 and may play an important role in the allelopathy of BR17. Thus, Bangladesh rice BR17 may be potentially useful for weed management in a field setting. An erratum to this article can be found at     

儿茶素诱导的拟南芥根细胞膜脂变化

儿茶素是一种可以短时间内杀死植物细胞的植物毒素,由于具有强的植物毒性,儿茶素是开发除草剂的理想化合物,它可以诱导植物根系统的死亡.为了研究植物根细胞膜脂对化学胁迫的响应规律,我们运用高通量的脂类组学方法检测了拟南芥根中膜脂分子的组成,比较了儿茶素处理下拟南芥野生型(WS)及磷脂酶Dδ缺失突变体( PLDδ-KO)根中膜脂分子的组成情况、膜脂含量、双键指数及碳链长度值.结果发现,儿茶素处理拟南芥根90 min后,二半乳糖基二酰甘油(DGDG)、单半乳糖基二酰甘油(MGDG)、磷脂酰甘油(PG)、磷脂酰胆碱(PC)及磷脂酰肌醇(PI)的总含量在WS与PLDδ-KO植株根中都显著下降,磷脂酰乙醇胺(PE)和磷脂酰丝氨酸(PS)在WS中下降,在PLDδ-KO中上升.儿茶素处理导致PLDδ-KO植株的PC/PE比值显著下降,WS植株PS碳链长度显著增加.上述结果说明儿茶素处理后,磷脂酶Dδ缺失突变体膜不稳定性增加,PLDδ-KO植株对儿茶素胁迫更加敏感.     

The phytotoxic lichen metabolite, usnic acid, is a potent inhibitor of plant p-hydroxyphenylpyruvate dioxygenase

The lichen secondary metabolite usnic acid exists as a (−) and a (+) enantiomer, indicating a or β projection of the methyl group at position 9b, respectively. (−)-Usnic caused a dose-dependent bleaching of the cotyledonary tissues associated with a decrease of both chlorophylls and carotenoids in treated plants whereas no bleaching was observed with the (+) enantiomer. (−)-Usnic acid inhibited protophorphyrinogen oxidase activity (I₅₀=3 μM), but did not lead to protoporphyrin IX accumulation. Bleaching appears to be caused by irreversible inhibition of the enzyme 4-hydroxyphenylpyruvate dioxygenase by (−)-usnic acid (apparent IC₅₀=50 nM).     

Botrydial confers Botrytis cinerea the ability to antagonize soil and phyllospheric bacteria

The role of the sesquiterpene botrydial in the interaction of the phytopathogenic fungus Botrytis cinerea and plant-associated bacteria was analyzed. From a collection of soil and phyllospheric bacteria, nine strains sensitive to growth-inhibition by B. cinerea were identified. B. cinerea mutants unable to produce botrydial caused no bacterial inhibition, thus demonstrating the inhibitory role of botrydial. A taxonomic analysis showed that these bacteria corresponded to different Bacillus species (six strains), Pseudomonas yamanorum (two strains) and Erwinia aphidicola (one strain). Inoculation of WT and botrydial non-producing mutants of B. cinerea along with Bacillus amyloliquefaciens strain MEP₂18 in soil demonstrated that both microorganisms exert reciprocal inhibitory effects; the inhibition caused by B. cinerea being dependent on botrydial production. Moreover, botrydial production was modulated by the presence of B. amyloliquefaciens MEP₂18 in confrontation assays in vitro. Purified botrydial in turn, inhibited growth of Bacillus strains in vitro and cyclic lipopeptide (surfactin) production by B. amyloliquefaciens MEP₂18. As a whole, results demonstrate that botrydial confers B. cinerea the ability to inhibit potential biocontrol bacteria of the genus Bacillus. We propose that resistance to botrydial could be used as an additional criterion for the selection of biocontrol agents of plant diseases caused by B. cinerea.     

Differential expression of defense‐related proteins of rice and sheath blight symptoms in response to active and inactive Rhizoctonia solani toxin

The effects of the phyotoxin from the fungal pathogen Rhizoctonia solani, causing sheath blight on the expression of defense‐related proteins of rice were investigated. The toxin inactivated by chemical treatment and by the toxin‐inactivating enzyme α‐glucosidase produced by Trichoderma viride was used in the study along with the active toxin. Toxin inactivated by T. viride α‐glucosidase and sodium periodate caused significantly less damage and electrolyte leakage to test plants. The active toxin and the pathogen induced chitinase and ß‐1,3‐glucanase synthesis in rice plants, while the inactivated toxin did not have any effect on the expression of these pathogenesis‐related proteins. The toxin was found to suppress the peroxidase activity 72 h after inoculation and the inactivated toxin restored the activity as that of untreated plants. There was no remarkable change in phenylalanine ammonia lyase activity in rice sheath treated with both the forms of the toxin.