Oat Roots Research Articles

Isolation, Characterization, and Sensitivity to 2,4-Diacetylphloroglucinol of Isolates of Phialophora spp. from Washington Wheat Fields

Dark pigmented fungi of the Gaeumannomyces-Phialophora complex were isolated from the roots of wheat grown in fields in eastern Washington State. These fungi were identified as Phialophora spp. on the basis of morphological and genetic characteristics. The isolates produced lobed hyphopodia on wheat coleoptiles, phialides, and hyaline phialospores. Sequence comparison of internal transcribed spacer regions indicated that the Phialophora isolates were clearly separated from other Gaeumannomyces spp. Primers AV1 and AV3 amplified 1.3-kb portions of an avenacinase-like gene in the Phialophora isolates. Phylogenetic trees of the avenacinase-like gene in the Phialophora spp. also clearly separated them from other Gaeumannomyces spp. The Phialophora isolates were moderately virulent on wheat and barley and produced confined black lesions on the roots of wild oat and two oat cultivars. Among isolates tested for their sensitivity to 2,4-diacetylphloroglucinol (2,4-DAPG), the 90% effective dose values were 11.9 to 48.2 microg ml(-1). A representative Phialophora isolate reduced the severity of take-all on wheat caused by two different isolates of Gaeumannomyces graminis var. tritici. To our knowledge, this study provides the first report of an avenacinase-like gene in Phialophora spp. and demonstrated that the fungus is significantly less sensitive to 2,4-DAPG than G. graminis var. tritici.

Geographical and plant genotype effects on the formation of arbuscular mycorrhiza in Avena sativa and Avena nuda at different soil depths

We have examined the influence of host plant genotype and geographical characters on the vertical distribution pattern of arbuscular mycorrhiza associated with Avena. The degree of colonization of oat roots at different soil depths (0–10, 10–20, 20–30, 30–40, 40–50 cm) was compared among three habitats from lower to higher altitude and six different cultivars in one specific habitat. Altitude had no impact on the percentage of root length colonized by mycorrhiza. However, oats growing at the higher altitudes formed more abundant arbuscules and vesicles within their roots. Plant genotype showed a significant influence on the percentage of root length colonized and abundance of arbuscules and vesicles, and there was much greater colonization of naked oat than of husk oat (common oat). The vertical distribution pattern of mycorrhizal root length was similar in terms of geographical and genotypic aspects, with the most extensive root colonization occurring in the topsoil and decreasing with increasing soil depth. However, the percentage of root length colonized by arbuscular mycorrhizal fungi (AMF) remained at about 20% colonization at a depth of 40–50 cm. Intraradical structures also showed a decreasing trend with increasing soil depth. The results suggest that an AMF “gene bank” may persist in the subsoil, and this may facilitate the ecological restoration of degraded agricultural areas.

Evolution of serine carboxypeptidase-like acyltransferases in the monocots

The serine carboxypeptidases are a large family of proteases. In higher plants some members of this family have diversified and adopted new functions as acyltransferases required for the synthesis of natural products. We recently reported the first serine carboxypeptidase-like (SCPL) acyltransferase enzyme to be characterised from monocotyledonous plants.1 This enzyme, AsSCPL1, is required for acylation of antimicrobial terpenes (avenacins) that are produced in the roots of oat (Avena spp.) and that provide protection against soil-borne pathogens. The SCPL enzyme family has undergone substantial expansion following the divergence of monocots and dicots. Here we discuss the evolution of the SCPL enzyme family in monocots, their contribution to metabolic diversity, and the roles of these enzymes in biotic and abiotic stress tolerance.

The Problem of Root and Stem Base Health of Oat (Avena Sativa L.) Cultivated in Mixture with Spring Rye (Secale Cereale L.)

Field experiments were carried out at Mochelek (17°51’E, 53°13’N). The health status of roots and stem bases of oat cultiEvated in pure stand and in mixture with spring rye was evaluated. A low intensity of root-rot was observed. Eyespot and Fusarium foot rot were observed on stem bases. Oat was infected with Fusarium spp. in higher degree when it was grown in mixture with spring rye. The pathogenic fungi occurring on oat roots were mostly represented by Fusarium spp., especially F. solani and F. equiseti. Stem bases showed the occurrence of F. culmorum, F. equiseti and F. avenaceum. Cultivation of oat in mixture did not affect the composition of fungal species occurring on roots and stem bases.

Localized Search Cues in Corn Roots for Western Corn Rootworm (Coleoptera: Chrysomelidae) Larvae

Cues that elicit a characteristic localized search behavior by neonate larvae of the western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), were extracted from living corn, Zea mays L., roots with acetone. Larvae were exposed to corn roots or to an acetone extract of corn roots and then transferred into a bioassay arena where their movements were tracked and recorded. After a 5-min exposure to live corn roots, larvae produced highly convoluted tracks that were indicative of a localized search behavior, and these distinctive tracks were also produced by larvae exposed to an acetone extract of corn roots. Larvae exposed to a filter paper control moved in relatively straight paths that were indicative of ranging behavior. Larval tracks were recorded by means of a videocamera and tracking software, and four parameters of movement were used to quantify the tracks: mean turn angle, mean meander, total distance, and maximum distance from origin. For every parameter measured, tracks resulting from exposure to the control were significantly different from tracks resulting from exposure to live corn roots and to all doses of the corn root extract. In a separate experiment, larvae exposed to corn root pieces or corn root juice exhibited the localized search behavior, but larvae exposed to oat root pieces and oat root juice (nonhost) exhibited ranging behavior.

Activation of Plant Plasma Membrane H+-ATPase by 14-3-3 Proteins Is Negatively Controlled by Two Phosphorylation Sites within the H+-ATPase C-terminal Region

The proton pump ATPase (H(+)-ATPase) of the plant plasma membrane is regulated by an autoinhibitory C-terminal domain, which can be displaced by phosphorylation of the penultimate Thr residue and the subsequent binding of 14-3-3 proteins. We performed a mass spectrometric analysis of PMA2 (plasma membrane H(+)-ATPase isoform 2) isolated from Nicotiana tabacum suspension cells and identified two new phosphorylated residues in the enzyme 14-3-3 protein binding site: Thr(931) and Ser(938). When PMA2 was expressed in Saccharomyces cerevisiae, mutagenesis of each of these two residues into Asp prevented growth of a yeast strain devoid of its own H(+)-ATPases. When the Asp mutations were individually introduced in a constitutively activated mutant of PMA2 (E14D), they still allowed yeast growth but at a reduced rate. Purification of His-tagged PMA2 showed that the T931D or S938D mutation prevented 14-3-3 protein binding, although the penultimate Thr(955) was still phosphorylated, indicating that Thr(955) phosphorylation is not sufficient for full enzyme activation. Expression of PMA2 in an N. tabacum cell line also showed an absence of 14-3-3 protein binding resulting from the T931D or S938D mutation. Together, the data show that activation of H(+)-ATPase by the binding of 14-3-3 proteins is negatively controlled by phosphorylation of two residues in the H(+)-ATPase 14-3-3 protein binding site. The data also show that phosphorylation of the penultimate Thr and 14-3-3 binding each contribute in part to H(+)-ATPase activation.

Selective progressive response of soil microbial community to wild oat roots

Roots moving through soil induce physical and chemical changes that differentiate rhizosphere from bulk soil, and the effects of these changes on soil microorganisms have long been a topic of interest. The use of a high-density 16S rRNA microarray (PhyloChip) for bacterial and archaeal community analysis has allowed definition of the populations that respond to the root within the complex grassland soil community; this research accompanies compositional changes reported earlier, including increases in chitinase- and protease-specific activity, cell numbers and quorum sensing signal. PhyloChip results showed a significant change compared with bulk soil in relative abundance for 7% of the total rhizosphere microbial community (147 of 1917 taxa); the 7% response value was confirmed by16S rRNA terminal restriction fragment length polymorphism analysis. This PhyloChip-defined dynamic subset was comprised of taxa in 17 of the 44 phyla detected in all soil samples. Expected rhizosphere-competent phyla, such as Proteobacteria and Firmicutes, were well represented, as were less-well-documented rhizosphere colonizers including Actinobacteria, Verrucomicrobia and Nitrospira. Richness of Bacteroidetes and Actinobacteria decreased in soil near the root tip compared with bulk soil, but then increased in older root zones. Quantitative PCR revealed rhizosphere abundance of beta-Proteobacteria and Actinobacteria at about 10(8) copies of 16S rRNA genes per g soil, with Nitrospira having about 10(5) copies per g soil. This report demonstrates that changes in a relatively small subset of the soil microbial community are sufficient to produce substantial changes in functions observed earlier in progressively more mature rhizosphere zones.

Membrane phospholipids as a phosphate reserve: the dynamic nature of phospholipid‐to‐digalactosyl diacylglycerol exchange in higher plants

It is well established that phosphate deficiency induces the replacement of membrane phospholipid with non-phosphorous lipids in extra-plastidial membranes (e.g. plasma membrane, tonoplast, mitochondria). The predominant replacement lipid is digalactosyl diacylglycerol (DGDG). This paper reports that the phospholipid-to-DGDG replacement is reversible, and that when oat seedlings are re-supplied with radio-labelled phosphate, it is initially recovered primarily in phosphatidylcholine (PC). Within 2 d, the shoot contains more than half of the lipid-associated radiolabel, reflecting phosphate translocation. Oat was also cultivated in different concentrations of phosphate and the DGDG/PC ratio in roots and phospholipase activities in isolated plasma membranes was assayed after different times of cultivation. The DGDG/PC ratio in root tissue correlated more closely with plasma membrane-localized phospholipase D, yielding phosphatidic acid (PA), than with plasma membrane-localized PA phosphatase, the activity that results in a decreased proportion of phospolipids. The lipid degradation data did not reflect a significant involvement of phospholipase C, although a putative phospholipase C analogue, non-specific phospholipase C4 (NPC4), was present in oat roots. The correlation between increased phospholipase D activity and DGDG/PC ratio is consistent with a model where phospholipid-to-DGDG replacement involves formation of PA that readily is removed from the plasma membrane for further degradation elsewhere.

Host range and mycotoxin production by Fusarium equiseti isolates originating from ginseng fields1

Fusarium equiseti is prevalent in soil and straw mulch in ginseng (Panax ginseng) fields in British Columbia and causes a reddish brown discolouration on ginseng roots. The pathogenicity of two isolates of F. equiseti from ginseng fields to other plant species belonging to different families was evaluated. Mycelial plugs and spore suspensions were used to inoculate seeds and roots in laboratory, growth room, and greenhouse experiments. Seed decay and reddish brown to black lesions were observed on hypocotyls and roots of kidney bean (Phaseolus vulgaris), bush bean (Phaseolus lunatus), broad bean (Vicia faba), chickpea (Cicer arietinum), and pea (Pisum sativum). A brownish discolouration and water-soaking symptoms developed on roots of alfalfa (Medicago sativa), canola (Brassica napus), wheat (Triticum aestivum), barley (Hordeum vulgare), and oat (Avena sativa) seedlings. Tomato (Lycopersicon esculentum), pepper (Capsicum annum), carrot (Daucus carota), and cucumber (Cucumis sativus) plants did not exhibit any visible symptoms. Diseased tissues from several affected plant species contained the mycotoxins nivalenol and (or) zearalenone at concentrations ranging from 0.3 to 11 ppm. This study shows that the host range of F. equiseti includes several members of the Leguminoseae, in addition to some cereals. The fungus may be one of the potential causes of damping-off and root rot on these plant species.

Sad3 and sad4 are required for saponin biosynthesis and root development in oat.

Avenacins are antimicrobial triterpene glycosides that are produced by oat (Avena) roots. These compounds confer broad-spectrum resistance to soil pathogens. Avenacin A-1, the major avenacin produced by oats, is strongly UV fluorescent and accumulates in root epidermal cells. We previously defined nine loci required for avenacin synthesis, eight of which are clustered. Mutants affected at seven of these (including Saponin-deficient1 [Sad1], the gene for the first committed enzyme in the pathway) have normal root morphology but reduced root fluorescence. In this study, we focus on mutations at the other two loci, Sad3 (also within the gene cluster) and Sad4 (unlinked), which result in stunted root growth, membrane trafficking defects in the root epidermis, and root hair deficiency. While sad3 and sad4 mutants both accumulate the same intermediate, monodeglucosyl avenacin A-1, the effect on avenacin A-1 glucosylation in sad4 mutants is only partial. sad1/sad1 sad3/sad3 and sad1/sad1 sad4/sad4 double mutants have normal root morphology, implying that the accumulation of incompletely glucosylated avenacin A-1 disrupts membrane trafficking and causes degeneration of the epidermis, with consequential effects on root hair formation. Various lines of evidence indicate that these effects are dosage-dependent. The significance of these data for the evolution and maintenance of the avenacin gene cluster is discussed.

Suppression of root-knot nematode damage to succeeding sweet potato by summer-sown cultivation of an oat variety, "Tachiibuki"

Reproduction of four populations of Meloidogyne incognita on ten oat varieties was examined in a greenhouse. Eggmass numbers produced on oat roots inoculated with 500 J2 were counted. Eggmasses of all nematode populations were present on all oat varieties but“Tachiibuki”had the lowest number (1.8 - 11.8 eggmasses / root system). Summersown cultivation of four early forage oat varieties sown in September and a fallow treatment were examined in a field infested with M. incognita and M. arenaria. The final / initial population density of J2 (Pf / Pi) in December for varieties “Haeibuki”,“Super Hayate Hayabusa”, “Tachiakane”,“Tachiibuki”and the fallow were 36.5, 34.7, 23.9, 1.9 and 0.2, respectively. Yield of succeeding sweet potato planted in May of the next year and harvested in September was highest in the plot that was previously cropped with the variety “Tachiibuki”, and in the “Tachiakane” plot which also received a nematicide treatment (1.5% a.i. fosthiazate, 20 kg / 10 a) before planting. Sweet potato storage roots from the “Haeibuki”, “Super Hayate Hayabusa” and fallow plots were significantly damaged by root-knot nematode with similar low yields. Damage to storage roots caused by the nematode was significantly reduced by the preceding “Tachiibuki” cropping to an extent similar to the nematicide treatment.

Release of C and N from roots of peas and oats and their availability to soil microorganisms

Nutrient mobilisation in the rhizosphere is driven by soil microorganisms and controlled by the release of available C compounds from roots. It is not known how the quality of release influences this process in situ. Therefore, the present study was conducted to investigate the amount and turnover of rhizodeposition, in this study defined as root-derived C or N present in the soil after removal of roots and root fragments, released at different growth stages of peas ( Pisum sativum L.) and oats ( Avena sativa L.). Plants were grown in soil columns placed in a raised bed under outdoor conditions and simultaneously pulse labelled in situ with a 13C-glucose- 15N-urea solution using a stem feeding method. After harvest, 13C and 15N was recovered in plant parts and soil pools, including the microbial biomass. Net rhizodeposition of C and N as a percentage of total plant C and N was higher in peas than in oats. Moreover, the C-to-N ratio of the rhizodeposits was lower in peas, and a higher proportion of the microbial biomass and inorganic N was derived from rhizodeposition. These results suggest a positive plant–soil feedback shaping nutrient mobilisation. This process is driven by the C and N supply of roots, which has a higher availability in peas than in oats.

The effect of ground cover or initial organic carbon on soil fungi, aggregation, moisture and organic carbon in one season with oat ( Avena sativa) plots

The unique capacity of fungi to efficiently sequester carbon in aerobic conditions, presents a way to maximize OC gain in agricultural systems. Oat ( Avena sativa) was planted in the temperate climate of southern Ontario, Canada to study factors affecting soil organic carbon (OC). The plots varied with initial OC from 25 to 68 g kg −1 or with ground cover of differing decomposability (alfalfa ( Medicago sativa) growing from seed, dried oat straw, dried hay and compost) on high OC soil (60–70 g kg −1). The soil was analysed for correlation of changes in soil aggregation, moisture, OC, fungal hyphal number and length and distribution of organic matter by mass and OC in density fractions within the growing season. At harvest, soil OC and moisture were increased only in plots with ground cover. Total hyphal length was not significantly different with ground cover treatment at harvest, and did not correlate with soil aggregation and soil OC. However, the number of hyphae with >5 μm diameter (primarily mycorrhizal fungi) correlated with % OC in ground cover plots while the number of hyphae <5 μm (primarily saprophytic fungi) correlated with % OC without ground cover in the gradient of initial soil OC. Mycorrhizal hyphae may be important to the increases in soil OC from surface treatment, although there was no treatment effect of mycorrhizal occurrence on the oat roots. This microcosm study, with growing and dried ground cover, suggests surface management may a simple and inexpensive means in agriculture to increase soil moisture and OC that benefits farmers as well as reducing atmospheric CO 2.

Tillage systems affect trifluralin bioavailability in soil

Trifluralin is widely used for control of rigid ryegrass in no-till grain crops in southern Australia. Trifluralin must be incorporated into soil to be effective. Several field studies were conducted to evaluate the effect of different tillage systems on vertical seed distribution and efficacy and rate of loss of bioavailable trifluralin. Experiments were conducted during the growing seasons of 2004 and 2005 at two sites in South Australia: on the Roseworthy Campus farm of the University of Adelaide and near Minlaton on the Yorke Peninsula. The tillage systems at the Roseworthy Campus were minimum tillage (MinTill) and no-till using narrow points, whereas four direct-drill-seeding systems were used at Minlaton. Plastic beads were spread on the soil surface to simulate weed seeds. MinTill sowing buried more plastic beads than no-till, indicating that greater soil disturbance was caused by the MinTill system. Trifluralin efficacy was lower under no-till as compared to MinTill. A bioassay, based on response of oat roots, was used to quantify the concentrations of bioavailable trifluralin under different tillage systems. In both years at the Roseworthy Campus, loss of bioavailable trifluralin was greater under no-till than under MinTill; however, the rate of loss under both systems was much faster in 2004 than in 2005. In 2004, bioavailable trifluralin at 12 d after sowing under MinTill and no-till was 55 and 33% of the initial concentration, respectively. In 2005, bioavailable trifluralin remaining at 23 d after sowing was 86% under MinTill and 54% under no-till. At Minlaton in both years, bioavailable trifluralin was greater under tillage systems that provided the highest level of soil disturbance. These results demonstrate that reduced bioavailability of trifluralin occurs in no-till seeding systems, which could result in reduced weed control.

Evidence of Chemical Interactions on Germination and Seedling Growth in Annual Forage Species

Poor establishment of forage legumes may result when they are sown with annual grasses in mixtures. Our objective was to determine the importance of allelopathy as a mechanism of interference between seed germination and seedling growth. Laboratory studies were conducted using two grasses (donor plants): oat (Avena sativa L.) and Italian ryegrass (Lolium multiflorum Lam.) and five annual legumes (target plants)-burr medic (Medicago polymorpha L.), berseem (Trifolium alexandrinum L.), crimson clover (Trifolium incarnatum L.), squarrosum clover (Trifolium squarrosum L.), and common vetch (Vicia sativa L.). The technique used legumes seeded into 7-day-old grass plants in a Petri dish with perlite, where they grow together for 10 d under controlled conditions. Measurements were taken to determine the effect of root exudates on root and shoot lengths, total germination, rate of germination, and seedling vigor. The root was found to be the most sensitive plant organ for inhibition by grass root exudates. The legume species studied differed in their response to the root exudates of oat and ryegrass. Berseem clover, squarrosum clover, and common vetch were more inhibited than the other legume species. Total percent germination and rate of germination (82.6 and 8.5% on average, respectively) were not significantly lower than the control. Inhibition of germination was not a good measure of phytotoxicity since seedling growth was inhibited even when germination was not. By contrast, seedling vigor was significantly lower for several legume species: squarrosum clover showed a marked reduction in early seedling vigor (-54%) in the presence of oat root exudates. Generally, responses of berseem clover were similar to that of squarrosum clover. These results suggested that grass exudates might affect seedling growth and development of some legume species owing to the inhibitory effects of allelochemicals found in grass live roots. However, further research is necessary to verify our laboratory results under field conditions.

Promotion of the seed germination and seedling growth of cabbage by root-colonizing fungi isolated from oat and Eucalyptus roots

(Jpn. J. Soil Sci.Plant Nutr., 77, 265–272, 2006) We isolated fungi colonizing oat (Avena sativa L.) and eucalyptus (Eucalyptus camaldulensis Dehnh) roots to select the strains that promote the seed germination and seedling growth of cabbage. Twenty-nine strains were inoculated into the soil which grows cabbage seedlings. This inoculation test was repeated three times. From the results of the test, we found that MT0011 and EU0013 strains promoted seed germination. In the first inoculation test, seven strains increased the dry weight of cabbage seedling significantly compared with the control. In the second test with the strains that promoted cabbage growth, MT0008 and EU0013 strains significantly increased the dry weight of seedlings. In the third test, only EU0013 significantly increased seedling growth. The ITS region for DNA (ITS1-5·8SrDNA-ITS2) of 28 isolated strains were sequenced to examine the molecular phylogeny. Isolates were classified into two divisions, Zygomycota and Ascomycota. Nine strains showed the highest similarities with same accession number AF504832 (Uncultured fungus clone D50). MT0011 was clustered with fungi belonging to Drechela sp. from the sequence data on the rDNA ITS region. EU0013 was identified as Penicillium sp. from the morphological feature conidiophore and the sequence of the ITS region.

A phosphatidylserine decarboxylase activity in root cells of oat ( Avena sativa) is involved in altering membrane phospholipid composition during drought stress acclimation

During acclimation to drought stress, the lipid composition of oat root cell membranes is altered. The level of phosphatidylethanolamine (PE), a non-bilayer forming lipid, is increased relative to the bilayer-forming lipid phosphatidylcholine (PC). These changes are believed to increase stress tolerance by increasing the flexibility of the membranes. To elucidate if de novo lipid synthesis is involved in altering membrane lipid composition, oat plants, acclimated or non-acclimated, were incubated in vivo with radioactively labelled lipid precursors. The labelling pattern indicated that de novo synthesis, at least partly, is causing the alterations. In plants, phospholipids can be synthesized by the Kennedy pathway, with addition of activated head groups to diacylglycerol (DAG) or, alternatively, via the CDP-DAG pathway, where phospahtidylserine (PS) is decarboxylated to form PE. To reveal the importance of the respective pathways during acclimation, we studied the effect of a decarboxylase inhibitor and the relative incorporation of [ 3H]-serine and [ 14C]-ethanolamine in vivo. Activities of CTP:ethanolaminephosphate cytidyltransferase (EC 2.7.7.14), phosphatidylserine decarboxylase (EC 4.1.1.65) and phosphatidylserine synthase; CDP-DAG: l-serine o-phosphatidyltransferase (EC 2.7.8.8) were measured and additionally, the presence of a PS decarboxylase (PSD1) in oat was confirmed by immunoblotting. The results suggest that PE synthesis via the Kennedy pathway is downregulated during acclimation and that synthesis by PS decarboxylation, via the CDP-DAG pathway, is increased, mainly through an increased activity of PS synthase.

Avenacin Production in Creeping Bentgrass (Agrostis stolonifera) and Its Influence on the Host Range of Gaeumannomyces graminis

Avenacinase activity has been shown to be a key factor determining the host range of Gaeumannomyces graminis on oats (Avena sativa). G. graminis var. avenae produces avenacinase, which detoxifies the oat root saponin avenacin, enabling it to infect oats. G. graminis var. tritici does not produce avenacinase and is unable to infect oats. G. graminis var. avenae is also reported to incite take-all patch on creeping bentgrass (Agrostis stolonifera). It is unknown whether creeping bentgrass produces avenacin and if the avenacin-avenacinase interaction influences G. graminis pathogenicity on creeping bentgrass. The root extracts of six creeping bentgrass cultivars were analyzed by fluorimetry, thin-layer chromatography, and high performance liquid chromatography for avenacin content. Avenacin was not detected in any creeping bentgrass cultivars, and pathogenicity assays confirmed that both G. graminis var. avenae and G. graminis var. tritici can infect creeping bentgrass and wheat (Triticum aestivum), but only G. graminis var. avenae incited disease on oats. These results are consistent with the root analyses and confirm that avenacinase activity is not required for creeping bentgrass infection by G. graminis.

CeHMT-1, a Putative Phytochelatin Transporter, Is Required for Cadmium Tolerance in Caenorhabditis elegans

Phytochelatins (PCs), (gamma-Glu-Cys)n Gly polymers that were formerly considered to be restricted to plants and some fungal systems, are now known to play a critical role in heavy metal (notably Cd2+) detoxification in Caenorhabditis elegans. In view of the functional equivalence of the gene encoding C. elegans PC synthase 1, ce-pcs-1, to its homologs from plant and fungal sources, we have gone on to explore processes downstream of PC fabrication in this organism. Here we describe the identification of a half-molecule ATP-binding cassette transporter, CeHMT-1, from C. elegans with an equivalent topology to that of the putative PC transporter SpHMT-1 from Schizosaccharomyces pombe. At one level, CeHMT-1 satisfies the requirements of a Cd2+ tolerance factor involved in the sequestration and/or elimination of Cd x PC complexes. Heterologous expression of cehmt-1 in S. pombe alleviates the Cd2+-hypersensitivity of hmt- mutants concomitant with the localization of CeHMT-1 to the vacuolar membrane. Suppression of the expression of ce-hmt-1 in intact worms by RNA interference (RNAi) confers a Cd2+-hypersensitive phenotype similar to but more pronounced than that exhibited by ce-pcs-1 RNAi worms. At another level, it is evident from comparisons of the cell morphology of ce-hmt-1 and cepcs-1 single and double RNAi mutants that CeHMT-1 also contributes to Cd2+ tolerance in other ways. Whereas the intestinal epithelial cells of ce-pcs-1 RNAi worms undergo necrosis upon exposure to toxic levels of Cd2+, the corresponding cells of ce-hmt-1 RNAi worms instead elaborate punctate refractive inclusions within the vicinity of the nucleus. Moreover, a deficiency in CeHMT-1 does not interfere with the phenotype associated with CePCS-1 deficiency and vice versa. Double ce-hmt-1; ce-pcs-1 RNAi mutants exhibit both cell morphologies when exposed to Cd2+. These results and those from our previous investigations of the requirement for PC synthase for heavy metal tolerance in C. elegans demonstrate PC-dependent, HMT-1-mediated heavy metal detoxification not only in S. pombe but also in some invertebrates while at the same time indicating that the action of CeHMT-1 does not depend exclusively on PC synthesis.

Plant-growth inhibitory activity of heliannuol derivatives

In addition to (+)-, (−)- and (±)-heliannuol E, growth-inhibitory activities of five synthetic chromans and four tetrahydrobenzo[b]oxepins were examined against oat and cress. All heliannuol E isomers exhibited similar biological activities against cress, whereas when tested against oat roots, the unnatural optical isomer (+) showed no inhibitory activity. Four brominated chromans and two tetrahydrobenzo[b]oxepin derivatives also showed apparent inhibition against both cress and oat.