Metabolism of ethylene in olive leaves

Olive tree tissues are able to metabolize ethylene. This metabolism is inhibited by heat killing and carbon disulfide. Rubber stoppers usually employed to close the incubation vials release carbon disulfide, thereby modifying the values obtained for ethylene. The ethylene consumption rate has been found to be 9 nl/h.g, an intermediate value among the different plant tissues so far examined.     

Saccharopine from tobacco leaves

5-Acetoamino-2-hydroxyvaleric acid, (5-AHV) was metabolized to δ-acetylornithine in tobacco leaves. On the other hand, δ-acetylornithine fed to tobacco leaves was metabolized into at least 5 components, one major component being 5-AHV. These results show that tobacco plant has a reversible metabolic pathway between 5-AHV and δ-acetylornithine.     

Impact of two different types of heat stress on chloroplast movement and fluorescence signal of tobacco leaves

Although the chloroplast movement can be strongly affected by ambient temperature, the information about chloroplast movement especially related to high temperatures is scarce. For detailed investigation of the effects of heat stress (HS) on tobacco leaves (Nicotiana tabacum L. cv. Samsun), we used two different HS treatments in dark with wide range of elevated temperatures (25–45°C). The leaf segments were either linearly heated in water bath at heating rate of 2°C min⁻¹ from room temperature up to maximal temperature (T _m) and then linearly cooled down to 25°C or incubated for 5 min in water bath at the same T _m followed by 5 min incubation at 25°C (T-jump). The changes in light-induced chloroplast movement caused by the HS pretreatment were detected after the particular heating regime at 25°C using a method of time-dependent collimated transmittance (CT) and compared with the chlorophyll O–J–I–P fluorescence rise (FLR) measurements. The inhibition of chloroplast movement started at about 40°C while the fluorescence parameters responded generally at higher T _m. This difference in sensitivity of CT and FLR was higher for the T-jump than for the linear HS indicating importance of applied heating regime. A possible influence of chloroplast movement on the FLR measurement and a physiological role of the HS-impaired chloroplast movement are discussed.     

烟草中多酚氧化酶(PPO)的特征

烟草中的多酚氧化酶介导的褐变会影响烟叶和烟丝的色泽和内在质量,因此对其特性的研究,以及活性的控制成为多年来的研究热点。本文从其生物发生模型、分子结构、生物化学和光谱学特征与植物抗病和机械损伤的关系,多酚氧化酶的抑制、多酚氧化酶的应用等方面着手,对近几年来烟草中PPO研究的最新成果进行总结和回顾,对一些有争议的问题进行了探讨,并对未来PPO研究的方向和领域进行了展望。     

Polysomes from expanded tobacco leaves

The isolation of intact polysomes from leaves of tobacco (Nicotiana tabacum L.) is dependent on the age and state of development of leaves. Undegraded polysomes from young leaves in the early stages of expansion can be isolated easily by extracting the leaves in ice-cold extraction buffer (200 mM tris(hydroxymethyl)aminomethylmethane(Tris)-HCl, pH 9.0; 400 mM KCl; 200 mM sucrose; 35 mM MgCl₂). Medium-size leaves give best yields of undegraded polysomes when extractions are carried out in the above buffer and in the presence of ethyleneglycol-bis-(β-amino-ethyl ether)-N,N′-tetracetic acid (EGTA) and mercaptoethanol. Isolation of polysomes from large, nearly fully expanded (mature) leaves requires all of the above plus diethyldithiocarbamate (DIECA) in the extraction medium. An extraction medium consisting of 25 mM EGTA, 0.01 M mercaptoethanol, 25 mM DIECA and 0.5% of the nonionic detergent, Nonidet-P40 (NP 40) was found to be very suitable for extraction of polysomes from all developmental stages of leaves. The polysomes extracted in the above medium showed active translation of protein in the wheat-germ in-vitro protein-synthesizing system. The translational products were similar when translations were carried out directly with polysomes or polysomal RNA, or polysomal poly(A)⁺ RNA from tobacco leaves. Poly(A)^? polysomal RNA was a poor template in the in-vitro wheat-germ system.     

Cytokinin-induced ethylene biosynthesis in nonsenescing cotton leaves

The influence of cytokinins on ethylene production was examined using cotton leaf tissues. Treatment of intact cotton (Gossypium hirsutum L. cv LG 102) seedlings with both natural and synthetic cytokinins resulted in an increase in ethylene production by excised leaves. The effectiveness of the cytokinins tested was as follows: thidiazuron BA isopentyladenine ≥ zeatin kinetin. Using 100 micromolar thidiazuron (TDZ), an initial increase in ethylene production was observed 7 to 8 hours post-treatment, reached a maximum by 24 hours and then declined. Inhibitors of 1-aminocyclopropane-1-carboxylic acid (ACC) synthesis and its oxidation to ethylene reduced ethylene production 24 hours post-treatment; however, by 48 hours only inhibitors of ACC oxidation were effective. The increase in ethylene production was accompanied by a massive accumulation of ACC and its acid-labile conjugate. TDZ treatment resulted in a significant increase in the capacity of tissues to oxidize ACC to ethylene. Endogenous levels of methionine remained constant following TDZ treatment. It was concluded that the stimulation of ethylene production in cotton leaves following cytokinin treatment was the result of an increase in both the formation and oxidation of ACC.     

Role of ethylene in senescence of watercress leaves

Detached watercress leaves showed a rapid senescence rate as compared with other herbs. It was therefore of interest to investigate the role of ethylene in the rapid senescence of watercress leaves, and So estimate the efficacy of various inhibitors of elhylene synthesis (aminoethoxyvinylglycine, AVG) and action (CO₂, Ag⁺) in retarding senescence processes. The progress of senescence in watercress bunches (leaves attached to cut stems) and in detached leaves was estimated by measuring the rate of chlorophyll (Chl) loss, proteolysis and lipid oxidation. Evidence is presented showing that application of 11% CO₂ to watercress bunches in a flow-through system had a long-lasting effect on senescence, exhibited by highly efficient retardation of all the senescence processes tested. On the other hand, application of AVG (O.1 m M ) or Ag-(30 μ M ) to detached leaves affected Chl loss much more than prciteolysis. These results suggest that the senescence-retarding activity of CO₂ cannot be attributed solely to its action as an anli-ethylene agent and that not all senescence-associated processes are regulated by ethylene.     

Photosynthetic electron transport in tobacco leaves infected with tobacco mosaic virus

Tobacco ( Nicotiana tabacum L. cv. Samsun) plants inoculated with different strains of tobacco mosaic virus (TMV) inducing mosaic symptoms of widely varying severity were studied with in vivo chlorophyll fluorescence. This method was used to deduce photosynthetic electron transport efficiency in relation to symptom expression. The quantum yields of photosystem II (PS II) electron transport rate were significantly diminished in virus strains inducing loss of chlorophyll. The reduction in young mosaic-diseased leaves appeared to be due in part to a reduction in the fraction of open reaction centers, whereas in older leaves exhibiting less pronounced symptoms the reduction was mainly caused by a reduced efficiency of capture of excitation energy of open PS II reaction centers. Upon infection with any of the five virus strains PS II seemed to be irreversibly damaged in the inoculated leaves and the ones directly above, indicative of a possible increased susceptibility to photoinhibition in these leaves (Somersalo and Krause 1989) even when no symptoms were apparent. Symptom expression did not appear to be related to the influence of the virus on PS II activity, because the severest effects occurred in the inoculated leaves, which either remained symptomless or developed slight yellowing only. This study demonstrates the usefulness or modulated chlorophyll fluorescence measurements for the investigation of plant-virus interactions. It is particularly important when visual symptoms are absent.     

Polyribosomes in protoplasts isolated from tobacco leaves

Polyribosomes (polysomes), active in an amino acid incorporation system in vitro, were isolated from tobacco leaf protoplasts. A comparison of polysome profiles indicated that the polysome/monosome ratio is greatly decreased in isolated protoplasts as compared to the intact leaf. In isolated protoplasts, a marked accumulation of ribosomal subunits was also found. The division of protoplasts, as investigated in the 8-cell and callus stages, was associated with a(n) (at least) partial regeneration of polysome profiles characteristic for leaves. Plasmolysis of leaves attached to the plant had no great effect on the polysome profile. However, leaf excision per se resulted in a dramatic loss of polysomes, even when the leaf tissue was floated on water. It is concluded that the isolation of the cell from its normal environment, and not the osmotic stress and associated increase in RNase activity, is the most important factor responsible for the loss of polysomes in isolated protoplasts.Abbreviations EGTA ethylene glycol bis (2-aminoethyl ether)-tetraacetic acid - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - mRNA messenger ribonucleic acid - RNase ribonuclease - Tris tris(hydroxymethyl)aminomethane - TCA trichloroacetic acid     

Enhancement by ethylene of cellulysin-induced ethylene production by tobacco leaf discs

Cellulysin-induced ethylene production in tobacco (Nicotiana tabacum L.) leaf discs was enhanced several-fold by prior exposure of the leaf tissue to ethylene. This enhancement in the response of the tissue to Cellulysin increased rapidly during 4 and 8 hours of pretreatment with ethylene and resulted from greater conversion of methionine to ethylene. On treatment with Cellulysin, the content of 1-aminocyclopropane-1-carboxylic acid (ACC) in leaf discs not pretreated with ethylene markedly increased while that of the ethylene-pretreated tissue was only slightly higher than in the tissue incubated in the absence of Cellulysin. Ethylene-treated tissue, however, converted ACC to ethylene at a faster rate than air controls. These data indicate that ethylene stimulates Cellulysin-induced ethylene production by stimulating the conversion of ACC to ethylene. Data are also presented on a possible relation of this phenomenon to ethylene produced by the tobacco leaf upon interaction with its pathogen, Alternaria alternata.     

烟草对烟粉虱的抗性与烟草化学成分的相关性

为探明烟草对烟粉虱Bemisia tabaci(Gennadius)的抗性机制,分别测定了不同烟草品种的叶绿素相对含量、鲜烟叶及烤后烟叶的化学成分含量,并分析了烟草抗虫性与烟草化学成分的关系.结果表明,中部叶片叶绿素含量与烟粉虱数量呈负相关,相关系数达到了显著水平;鲜烟叶化学成分钾氯比、糖碱比、氮碱比、还原糖、烟碱、蛋...     

Peroxidases and ethylene formation in olive tree leaves

The loss of intercellular peroxidases from olive tree leaf sections subjected to isoelectric focusing correlates well with the capacity of the referred sections to convert 1-aminocyclopropane-1-carboxylic acid (ACC) into ethylene. Both activities are compared in leaves of different ages (according to their position on the branch) and it is found that they follow a parallel course. The inhibition of the capacity to convert ACC into ethylene in homogenized olive tree leaves is due to inhibitors release. The results, in relation to other authors' reports, are discussed.     

烤后不同霉变程度烟叶际真菌群落组成与多样性分析

【目的】为了解烤后不同霉变程度烟叶真菌群落组成与多样性。【方法】基于IlluminaMiSeq高通量测序平台对烤后烟叶叶柄和叶片叶际样品的真菌群落组成进行了分析。【结果】霉变重烟叶叶片(BQ)、霉变重烟叶叶柄(BZ)、霉变轻烟叶叶片(JQ)、霉变轻烟叶叶柄(JZ) 4类样品真菌分布于子囊菌门(Ascomycota)、担子菌门(Basidiomycota)、接合菌门(Zygomycota)等7个菌门、27个纲、58个目、104个科、171个属的360个真菌分类单元(OTUs)。不同霉变程度烟叶叶际真菌群落组成、分类单元的相对丰度及优势分类单元皆存在不同程度差异。在属的水平上,霉变重烟叶叶片(BQ)的优势菌属为Aspergillus (89.64%)、Myrothecium (2.54%)、Rhodotorula (2.48%)、Gibberella (1.49%);霉变重烟叶叶柄(BZ)的优势菌属为Aspergillus(96.93%)和Alternaria(1.92%);霉变轻烟叶叶片(JQ)的优势菌属为Aspergillus(40.13%)、Rhodotorula(31.81%)、Alternaria(16.75%);霉变轻烟叶叶柄(JZ)的优势菌属为Aspergillus (62.77%)、Alternaria (9.74%)、Rhodotorula (5.20%)。【结论】霉变轻烟叶叶片样品真菌群落的多样性最高,霉变轻烟叶叶柄的真菌群落丰富度最高。霉变重烟叶样品的叶片部位的真菌群落丰富度和多样性均高于叶柄。烟叶霉烂为烤房常见病害,其病原真菌种类多样,且广泛分布于烟叶和环境中。该研究结果为烤房烟叶霉烂病的防治可根据不同发病程度的不同部位的真菌群落构成特征,制定相应的防治方案提供了参考依据。