The secretory apparatus of Xerophyta viscosa (Velloziaceae): Epidermis anatomy and chemical composition of the secretory product

In this study, secretory activity on the adaxial surface of the leaves of the desiccation tolerant plant, Xerophyta viscosa Baker was investigated, using light, scanning and transmission electron microscopy. Glandular activity was associated with sunken cavities which appear to be modifications of infolded epidermal cells. The secretory cavity consisted of a globose lumen surrounded by two layers of cells. The cells of the outer layer were flattened with thickened walls, while those of the inner layer (epithelium), exhibited ultrastructural features of intense metabolic activity. Epithelial cells were larger with a large nucleus, numerous vacuoles, and a dense cytoplasm with abundant mitochondria, endoplasmic reticulum (ER), plastids and a few dictysomes. Lipophilic droplets were abundant in the cytoplasm, mitochondria, ER, plastids and in infolding sites of the plasmalemma outside the protoplast. ER appeared to be involved in the synthesis and transport of lipophilic substances. The mechanism of secretion in X. viscosa appeared to be granulocrine. The chemical composition of hexane and methanol extracts of the leaves, analysed by gas chromatography coupled with mass spectrometry (GC–MS), revealed the presence of diterpenes, phenolic compounds and fatty acids. Compounds in the hexane fraction included velloziolone, manoyl oxide, asperdiol and an unknown substance. Compounds in the methanol fraction included 5-(hydroxymethyl)-2-furancarboxaldehyde, 2,6-dimethoxyphenol, 4-(3-hydroxy-1-propenyl)-2-methoxyphenol and stearic acid.     

Phthalides produced by Coccomyces strobi (Rhytismataceae,Rhytismatales) isolated from needles of Pinus strobus

As part of a broad survey of the metabolites produced by foliar endophytes of conifers, a strain was isolated from surface-sterilized needles collected from eastern white pine on the north shore of Lake Huron, Ontario. The isolate was sterile in culture. Species identity was not resolved by ITS sequence because of the absence of corresponding sequences in public sequence databases, however the strain was placed in Rhytismataceae (Rhytismatales). Field collections targeting Rhytismataceae species on Pinus strobus were conducted enabling the isolate to be identified as Coccomyces strobi. An extract of the culture filtrate demonstrated moderate antifungal activity. Two new phthalides, (±)-strobides A-B (1-2) and the known phytotoxin cyclopaldic acid (3) were characterized from C. strobi DAOMC 251937. This is the first record of the occurrence of this species as a foliar endophyte. Previous reports have suggested that it is a cambium endophyte associated with small cankers on branches. The production of the phytotoxin cyclopaldic acid suggests that C. strobi is a weak opportunistic pathogen, switching from an endophytic to a pathogenic phase when the host tissue becomes weakened.     

Secondary metabolite profile and phytotoxic activity of genetically distinct forms of Colletotrichum gloeosporioides from yam (Dioscorea spp.)

Highly virulent, slow-growing grey (SGG); moderately virulent, fast-growing salmon (FGS); and avirulent/weakly virulent, fast-growing grey (FGG) forms of Colletotrichum gloeosporioides have been described from yam (Dioscorea spp.), but little is known about their chemodiversity or the role of toxins in their pathogenesis. Secondary metabolite profiles in high performance tlc (hptlc) showed that the pathogenic SGG and FGS forms have a chemotype (A or B) that is distinct from the non-pathogenic FGG form (chemotype C). Crude extracts of 35-d-old Czapek-Dox yeast broth cultures of FGS and SGG isolates caused tissue necrosis on treated yam leaves but not those of FGG isolates. Extracts from uninoculated broth cultures showed no phytotoxic activity. Toxicity of the culture filtrate was not host specific and toxic substances were thermostable. Dioscorea genotypes with varying levels of resistance to anthracnose differed in their sensitivity to crude toxin extract of FGS (Cg33) and SGG (Cg25) isolates, indicating that these extracts may be useful in evaluating host resistance to anthracnose in vitro. Analysis of two toxin fractions unique to the pathogenic FGS and SGG forms using hlpc, mass spectrometry and nuclear magnetic resonance suggested the presence of a low molecular weight amide peptide. However, possibly due to low yield and the presence of impurities, the chemical structure of the compound(s) could not be fully elucidated.     

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90min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。     

Effect of carbohydrates on the production of thaxtomin A by <Emphasis Type="Italic">Streptomyces acidiscabies</Emphasis>

Several Streptomyces species cause plant diseases, including S. scabies, S. acidiscabies and S. turgidiscabies, which produce common scab of potato and similar diseases of root crops. These species produce thaxtomins, dipeptide phytotoxins that are responsible for disease symptoms. Thaxtomins are produced in vivo on diseased potato tissue and in vitro in oat-based culture media, but the regulation of thaxtomin biosynthesis is not understood. S. acidiscabies was grown in a variety of media to assess the impact of medium components on thaxtomin A (ThxA) production. ThxA biosynthesis was not correlated with bacterial biomass, nor was it stimulated by α-solanine or α-chaconine, the two most prevalent potato glycoalkaloids. ThxA production was stimulated by oat bran broth, even after exhaustive extraction, suggesting that specific carbohydrates may influence ThxA biosynthesis. Oat bran contains high levels of xylans and glucans, and both of these carbohydrates, as well as xylans from wheat and tamarind, stimulated ThxA production, but not to the same extent as oat bran. Starches and simple sugars did not induce ThxA production. The data indicate that complex carbohydrates may act as environmental signals to plant pathogenic Streptomyces, allowing production of thaxtomin and enabling bacteria to colonize its host.     

In vitro screening of rice germplasm for resistance to brown spot disease using phytotoxin

Summary Two R₁ IR₈ plants derived from somatic cells cultured in 25% Helminthosporium oryzae toxin-medium, and one IR₅₄ plant derived from a control (toxin free medium) were found to have mutated resistance to brown spot disease of rice. In the second generation (R₂, the offspring of the R₁ generation) of the three resistant populations, the segregation of resistance and susceptibility to the disease was observed. This is the first report about a disease resistant mutation obtained successfully in rice by tissue culture and in vitro screening with phytotoxin.This research was conducted at the IRRI, Manila     

Characterization of the metabolite produced by Mycosphaerella pinodes, the causal agent of mycosphaerella blight on field peas (Pisum sativum L.)

The metabolite produced by Mycosphaerella pinodes, the causal agent of mycosphaerella blight on field peas, was detected by thin layer chromatography (TLC) and was analyzed for its chemical and pathogenic characteristics. One blue dot was detected using 254nm UV light on TLC plate, and a spray of rho-anisaldehyde (110 degrees C, 30 min) also produced a blue dot. The solvent systems used for TLC analysis were ethyl acetate/water/acetone (5/2/5), chloroform/methanol/glacial acetic acid (19/10/2), toluene/ethyl acetate/90% formic acid (6/3/1), diethylether/methanol/water/90% formic acid (95/4/1/1), and bezene/methanol/acetic acid (24/2/1), with R(f) values (min-max) of 0.09-0.18, 0.88-0.95, 0.06-0.15, 0.39-0.47 and 0.05-0.12, respectively. The recovered metabolite from the TLC plate displayed UV absorption peaks at 212, 244, 250, 256 and 261 nm. The proposed formula of the main component of the metabolite was C16H12N3O6. The TLC-purified metabolite induced symptom of discoloration on detached pea leaves.     

Nature,nurture, and vegetation management: Studies with sheep and goats

Diet selection and preference by grazing animals are determined by genetic and environmental factors (i.e., nature and nurture) that interact and affect their efficacy for managing vegetation as targeted grazers. The effect of rearing environment on the consumption of leafy spurge by sheep and goats was investigated. We hypothesized that although rearing environment will affect the preference for chemically defended plants ultimately, the inherent ability to detoxify or eliminate phytotoxins will limit an animal’s preference for them. The objective of this study was to determine if sheep would consume more of the invasive weed leafy spurge (Euphorbia esula) if they were raised by goat compared to sheep raised by sheep and goat raised by goat. Sheep were raised on leafy spurge-infested pastures by either their ewe (S) or a goat doe (FS) on which they were fostered within 24 hours of birth and parturition of lamb and doe, respectively. Does that fostered lambs also raised their own goat offspring (G) such that the same doe raised the FS and G animals. The rearing environment’s effect on leafy spurge consumption was tested the following growing season by simultaneously grazing all animals on the same leafy spurge-infested rangeland and estimating percentage leafy spurge in their diet with either fecal near-infrared spectroscopy (f.NIR) or bite count. Goats consumed more leafy spurge as determined by either f.NIR (62.8%, P < 0.06) or bite count (71.9%, P < 0.01) than FS (35.2 % f.NIR, 39.3% bite count) or S (10.1 % f.NIR, 18.2% bite count). The FS consumed over twice as much leafy spurge as S and were numerically intermediate to G and S for leafy spurge consumption but not significantly different from the S sheep, most likely because one FS sheep did not eat leafy spurge during the evaluation period. Because leafy spurge is aversive to sheep but not goats, higher leafy spurge consumption by FS sheep is hypothesized to result from inoculation of their rumen microbes with microbes from the does capable of denaturing aversive phytotoxins in leafy spurge. The higher consumption of leafy spurge by G compared to FS shows that genetically determined physiological differences influence an animal’s ability to ameliorate phytotoxins and determine the upper limit of an animal’s preference for a chemically defended plant. It also indicated that in addition to the animal’s genome, the genome of an animal’s microbiome, which the mother may influence, can play an important role in diet selection.     

Phytotoxin production by Pseudomonas syringae pv. syringae: Syringopeptin production by syr mutants defective in biosynthesis or secretion of syringomycin

Abstract Syringomycin and syringopeptin are lipodepsipeptide phytotoxins produced by Pseudomonas syringae pv. syringae . Four syr genes were identified previously and hypothesized to be involved in the regulation ( syrA ), biosynthesis ( syrB and syrC ), or export ( syrD ) of syringomycin. This study determines the influence of syr mutations on the composition of phytotoxic metabolites produced by P. syringae pv. syringae strain B301D-R. Levels of syringomycin and syringopeptin produced in liquid cultures were estimated by reverse phase HPLC analyses and differential antimicrobial assays. Significant quantities of syringopeptin were produced by both syrB and syrC mutants despite their inability to produce syringomycin. Only trace quantities of both lipodepsipeptides were produced by syrA and syrD mutants of P. syringae pv. syringae . These results indicate that syringomycin and syringopeptin are synthesized by separate pathways, but may share common mechanisms for secretion and regulation.