Cloning and Characterization of a Novel Endo-Type Metal-Independent Alginate Lyase from the Marine Bacteria Vibrio sp. Ni1

The applications of alginate lyase are diverse, but efficient commercial enzymes are still unavailable. In this study, a novel alginate lyase with high activity was obtained from the marine bacteria Vibrio sp. Ni1. The ORF of the algB gene has 1824 bp, encoding 607 amino acids. Homology analysis shows that AlgB belongs to the PL7 family. There are two catalytic domains with the typical region of QIH found in AlgB. The purified recombinant enzyme of AlgB shows highest activity at 35 °C, pH 8.0, and 50 mmol/L Tris-HCl without any metal ions. Only K⁺ slightly enhances the activity, while Fe²⁺ and Cu²⁺ strongly inhibit the activity. The AlgB preferred polyM as substrate. The end products of enzymatic mixture are DP2 and DP3, without any metal ion to assist them. This enzyme has good industrial application prospects.     

Protection against bacterial soft rot by olive extracts is related to general defence induction in potato tubers

Controlling bacterial plant diseases remains a challenge, as direct chemical control is usually not possible. Obtaining new biocontrol methods, in particular efficient biomolecules able to boost defence reactions and limit infection or symptom development, is therefore of major importance. This study screened extracts from leaves of two Mediterranean plants rich in bioactive phenolic compounds, olive and carob, for their ability to reduce soft rot severity and to trigger phenylalanine ammonia‐lyase (PAL) activity in potato tuber slices. Extracts from olive leaves significantly reduced disease severity caused by Pectobacterium atrosepticum or Pectobacterium carotovorum, whereas carob leaf extracts significantly increased it. Olive extracts and its main phenolic components, oleuropein and hydroxytyrosol, also significantly increased PAL activity 7.5 h after application. None of the extracts or purified molecules reduced bacterial growth in vitro. Furthermore, the effect of these extracts varied according to potato cultivars. These data therefore open new ways for the biological control of soft rot bacteria, but stress the importance of understanding the causes of response difference in different potato varieties in order to obtain optimal efficacy.     

Local and systemic effects of oxylipins on powdery mildew infection in barley

Treatment of the first leaves of barley seedlings with the oxylipin colneleic acid, or the two trihydroxy oxylipins 9,12,13-trihydroxy-11(E)-octadecenoic acid and 9,12,13-trihydroxy-10(E)-octadecenoic acid, reduced infection of that leaf by the powdery mildew fungus Blumeria graminis Speer f sp hordei Marchal. When applied to first leaves, etheroleic acid and colneleic acid, as well as the trihydroxy oxylipin 9,12,13-trihydroxy-10(E),15(Z)-octadecadienoic acid, also reduced mildew infection in second leaves. In all cases where local and systemic effects against mildew were observed, activity of the defence-related enzyme phenylalanine ammonia lyase (PAL) was increased, but only following challenge inoculation with powdery mildew. Peroxidase activity was not affected by oxylipin treatment or mildew inoculation. Whether the effects observed were due to the oxylipins or to breakdown products is not known, since no information is available on the stability of these particular oxylipins on leaf surfaces. Nevertheless, these data represent the first report of systemic effects against pathogen infection following pre-treatment with oxylipins.     

Reinforcement of cell wall in roots of Lycopersicon esculentum through induction of phenolic compounds and lignin by elicitors

Changes in phenolic metabolism and lignin deposition have been studied in roots of tomato plants after elicitation with four elicitors which are Fusarium mycelium extract (FME), chitosan (CHT), Fusarium culture filtrate (FCF) and Trichoderma mycelium extract (TME). Most profound effect of elicitors was observed on ferulic acid among the phenolic compounds. After 24 h elicitation, the increase in ferulic acid content of root cell wall was 3.71 and 3.30 times by FME and CHT, respectively. The increase of 4-hydroxybenzoic acid was 2.71 and 2.16 times by these two elicitors. The level of 4-coumaric acid was little more than double by these two elicitors after 24 h elicitation. Most pronounced increase in lignin synthesis was also effected by FME followed by CHT. Lignin deposition in the root cell wall was increased 3.6, 5.4 and 7.1 times by FME during 12, 24 and 36 h after elicitation, respectively. Similarly, CHT increased lignin deposition by 2.8, 5.1 and 6.8 times at 12, 24 and 36 h after elicitation, respectively. FCF and TME also increased lignin deposition significantly in the cell walls of tomato roots during the above time periods of elicitation. Activity of phenylalanine ammonia lyase reached highest level at 24 h post elicitation under the influence of the elicitors. Peroxidase activity registered a sharp increase at 24 h post elicitation. Markedly increased level of polyphenol oxidase activity was found at 12 h post elicitation. Cinnamyl alcohol dehydrogenase activity was observed to reach highest level at 48 h post elicitation. Cell wall strengthening, through the deposition of lignin, preceded by the induction of the synthesizing enzymes appears to play an important role in the defense response of Lycopersicon esculentum in reaction to elicitors, including one derived from Fusarium oxysporum f. sp. lycopersici, the causal organism of Fusarium wilt of tomato.     

Note: Phenylalanine ammonia lyase activity in tomato seedlings and its relationship to bacterial canker disease resistance

Phenylalanine ammonia lyase (PAL) activity was studied in different genotypes of tomato with varying degrees of resistance and susceptibility to bacterial canker disease after inoculation withClavibacter michiganensis ssp.michiganensis. In resistant genotypes the enzyme activity increased significantly 21 h after bacterial inoculation, whereas in the susceptible genotypes the activity decreased. The increase or decrease in PAL activity correlated well with the degree of host resistance along with total phenol contents. The role of PAL in imparting resistance to tomato against bacterial canker disease is discussed. http://www.phytoparasitica.org posting Nov. 14, 2005.     

花椒叶锈病的抗性研究

以6个花椒品种为对象，利用Coleosporium xanthoxyli在温室定量接种和田间人工诱发病害流行条件下，测定了不同品种对叶锈病的抗性程度，并通过组分分析确定正路椒、清椒、金阳椒为快锈品种，而竹叶椒、大红袍、高脚黄为慢锈品种，其慢锈性表现在流行学特征上为侵染率低、病菌扩展慢、繁殖力低、发病率和严重度上升慢。在此基础上测定的苯丙氨酸解氨酶表明，其活性变化与花椒品种有关，快锈品种酶活变化同程关系不大，慢锈品种酶活变化随病害发展而逐渐增加，酶活性变化与叶锈病流行学特征值有相关性。因此该酶可作为鉴定花椒抗锈性的生化指标，而能否作为划分快锈或慢锈品种的定量指标，尚需进一步研究。     

苜蓿斑蚜为害对5种苜蓿品种(系)PAL、POD、PPO酶活性的影响

在室内将苜蓿斑蚜人工接种在不同抗性级别的苜蓿品种（系）幼苗上,苜蓿斑蚜为害后的3、7、10 d分别测定了5个品种（系）叶片中苯丙氨酸解氨酶（PAL）、多酚氧化酶(PPO)、过氧化物酶（POD）3种酶活性。结果表明,在试验期内,所有品种（系）叶片中的PAL活性在接虫后随着时间的增加而升高; PPO活性随天数增加呈下降趋势; POD与PAL酶的情况相同,随着为害时间的延长不断升高。HA 3感蚜后3种酶活性明显高于其他品种。     

桃果胶裂解酶编码基因PpPL1的鉴定及其在果实成熟软化过程中的表达

为了深入了解桃果胶裂解酶(PL)家族编码基因的功能,本研究利用生物信息学方法对桃基因组中的PL基因进行鉴定,并对这些基因在硬质型桃和溶质型桃果实成熟软化过程中的表达差异进行分析。结果表明,从桃基因组中共鉴定出20个PL基因,所有的PpPL蛋白都含有Pec-Lyase-C结构域,但其中只有4个PpPL(PpPL7、PpPL8、PpPL12、PpPL17)包含Pec-Lyase-N结构域。Pec-Lyase-N的保守性表明其可能是执行果胶裂解功能所必须的功能团。聚类分析表明,桃PL基因可以分为5类:这与模式植物拟南芥和番茄PL基因的聚类模式一致。基因表达分析表明,6个PL基因在桃果实成熟过程中高表达,其中PpPL1基因在有名硬质型桃成熟过程中表达量很低,而在黄金蜜3号溶质型桃成熟阶段高表达。序列比对和聚类分析发现,PpPL1基因与果实软化相关的番茄SLPL高度同源。以溶质型桃湖景蜜露和硬质型桃夏之梦为试材,检测采后软化过程中PpPL1的表达,结果表明PpPL1基因是与桃果实的成熟软化相关的主要基因。本研究结果为进一步探究PL基因家族在桃果实软化中作用的分子机理奠定了基础。