Characterization of two class II chitinase genes from peanut and expression studies in transgenic tobacco plants

Two different genes encoding class II chitinases from peanut (Arachis hypogaea L. cv. NC4), A.h.Chi2;1 and A.h.Chi2;2, have been cloned. In peanut cell suspension cultures, mRNA levels of A.h.Chi2;2 increased after ethylene or salicylate treatment and in the presence of conidia from Botrytis cinerea. The second gene, A.h.Chi2;1, was only expressed after treatment with the fungal spores. Transgenic tobacco plants containing the complete peanut A.h.Chi2;1 gene exhibited essentially the same expression pattern in leaves as observed in peanut cell cultures. Expression characteristics of transgenic tobacco carrying a promoter-GUS fusion of A.h.Chi2;1 are described.     

Genotypic variation in zinc efficiency and resistance to crown rot disease (Fusarium graminearum Schw. Group 1) in wheat

A crown rot disease in wheat caused by the fungusFusarium graminearum Schw. Group 1 is a widespread problem in chronically Zn-deficient Australian soils. A link between crown rot and Zn deficiency was established by Sparrow and Graham (1988). This paper reports a test of a further hypothesis, that wheat genotypes more efficient at extracting zinc from low-zinc soils are more resistant to infection by this pathogen. Three wheat cultivars (Excalibur, Songlen and Durati) of differential Zn efficiency were tested at three zinc levels (0.05, 0.5 and 2.0 mg Zn kg⁻¹ of soil) and three levels ofF. graminearum S. Group 1 inoculum (0.1 g and 0.3 g kg⁻¹ live chaff-inoculum and control having 0.1 g kg⁻¹ dead chaff inoculum). Six weeks after sowing dry matter production of shoots and roots was decreased byFusarium inoculation at 0.05 mg and 0.5 mg kg⁻¹ applied Zn.Fusarium inoculum at 0.1 g was as effective as 0.3 g kg⁻¹ for infection and decreasing dry matter. The infection at the basal part of culm decreased significantly by increasing the rate of Zn application. Excalibur, a Zn-efficient cultivar (tolerant to Zn deficiency) produced significantly more shoot and root dry matter, and showed less disease infection compared with Zn-inefficient cultivars (Durati and Songlen) at low (0.05 mg Zn kg⁻¹ soil) and medium (0.5 mg Zn kg⁻¹ soil) Zn fertilization rates. Higher rate of Zn fertilization (2.0 mg Zn kg⁻¹ soil) reduced the disease level in Durati to the level of Excalibur but the disease level of Songlen was still high, indicating its high Zn requirement and or sensitivity to crown rot. The data on Zn uptake show that Excalibur, being Zn-efficient, was able to scavenge enough Zn from Zn-deficient soil, we suggest that besides sustaining growth Excalibur was able to build and maintain resistance to the pathogen; inefficient cultivars needed extra Zn fertilization to achieve performance comparable to that of Excalibur. The present study indicates that growing Zn-efficient cultivars of wheat along with judicious use of Zn fertilizer in Zn-deficient areas where crown rot is a problem may sustain wheat production by reducing the severity of the disease as well as by increasing the plant vigour through improved Zn nutrition. ei]Section editor: R Rodriques-Kalana     

Suppression of fungal β-glucan-induced plant defence in soybean (Glycine max L.) by cyclic 1,3-1,6-β-glucans from the symbiont Bradyrhizobium japonicum

The production of antimicrobial phytoalexins is one of the best-known inducible defence responses following microbial infection of plants or treatment with elicitors. In the legume soybean (Glycine max L.), 1,3-1,6--glucans derived from the fungal pathogen Phytophthora sojae have been identified as potent elicitors of the synthesis of the phytoalexin, glyceollin. Recently it has been reported that during symbiotic interaction between soybean and the nitrogen-fixing bacterium Bradyrhizobium japonicum USDA 110 the bacteria synthesize cyclic 1,3-1,6--glucans. Here we demonstrate that both the fungal and the bacterial -glucans are ligands of -glucan-binding sites which are putative receptors for the elicitor signal compounds in soybean roots. Whereas the fungal -glucans stimulate phytoalexin synthesis at low concentrations, the bacterial cyclic 1,3-1,6--glucans appear to be inactive even at relatively high concentrations. Competition studies indicate that increasing concentrations of the bacterial 1,3-1,6--glucans progressively inhibit stimulation of phytoalexin synthesis in a bioassay induced by the fungal 1,3-1,6--glucans. Another type of cyclic -glucan, a 1,2--glucan from Rhizobium meliloti, that does not nodulate on soybean, seems to be inactive as elicitor and as ligand of the -glucan-binding sites. These results may indicate a novel mechanism for a successful plant-symbiont interaction by suppressing the plant's defence response.Abbreviations HG-APEA 1-[2-(4-aminophenyl)ethyl]amino-l-[hexaglucosyl]deoxyglucitol - HG-AzPEA l-[2-(4-azidophenyl)-ethyl]amino-l-[hexaglucosyl]deoxyglucitol - IC₅₀ concentration for half-maximal displacement We thank Ines Arlt for excellent technical assistance. This work was supported by the Deutsche Forschungsgemeinschaft (SFB 369), the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie, Fonds der Chemischen Industrie (J.E.), and USDA CSRS NRI Competitive Research grant 93373059233 (A.A.B.).     

Paracoccidioides brasiliensis antigen batches from the same isolate show immunological and biochemical differences

We investigated the occurrence of antigenic and biochemical variability among Paracoccidioides brasiliensis antigen batches prepared according to the same protocol. Initially (experiment #1), we analyzed two antigen lots of two human isolates (Bt1 & Bt2), cultured in two media (PYG: bactopeptone, yeast extract, glucose; MMM: McVeigh & Morton medium) in SDS-PAGE and in two immunological tests (imunodiffusion-ID and footpad swelling test-FPT). Afterwards (experiment #2), we compared the antigenic profile of three antigen batches from three human isolates (Bt1, Bt2 & Bt3) by two-dimensional immunoelectrophoresis (2 D-IEP) against a reference system for P. brasiliensis antigens. In experiment #1, there were important intra- and inter-strain antigenic differences between batches of the fungal isolates cultured on both media. The block titration of the antigen batches for the immunological tests revealed correlation between protein concentration and biological activity in ID and no correlation in FPT. In experiment #2, the reference system for P. brasiliensis showed 26 antigen peaks. There were important differences between batches prepared from the same isolate and between batches from different isolates. Our data suggested the occurrence of instability in the synthesis of antigenic components by a same P. brasiliensis isolate, under controlled incubation conditions.     

Ultrastructure of the parasitic interface ofPucciniastrum,Thekopsora, Naohidemyces,andCalyptospora (Uredinales,Pucciniastraceae) in the dikaryotic stage

The ultrastructure of dikaryotic haustoria of sevenPucciniastrum species,Thekopsora galii, Naohidemyces vaccinii, andCalyptospora goeppertiana was investigated.Pucciniastrum actinidiae, P. agrimoniae, P. pyrolae, andCalyptospora goeppertiana revealed haustoria whose necks were wrapped by a fold of the extrahaustorial matrix. The matrix-fold ofCalyptospora goeppertiana was characteristically shaped.Pucciniastrum circaeae, P. epilobii, P. hikosanense, P. styracinum, Thekopsora galii, andNaohidemyces vaccinii showed typical haustorial necks which were not sheathed by a matrix-fold. Haustorial necks which were wrapped by a fold of the extrahaustorial matrix were designated velopedunculate, and those which were naked gymnopedunculate. The application of haustorial ultrastructure as a character for use in systematics is discussed.Part 112 of the series Studies in Heterobasidiomycetes.     

Fungal succession in the early decomposition process of pine cones on the floor ofPinus densiflora forests

The fungal succession on pine cones on the floor ofPinus densiflora forest was investigated in the early decomposition process (within ca. 30% decrease in dry weight). The fungal flora was examined by both washing and surface-sterilization methods on artificially placed cones and naturally fallen cones. The decomposition rates of artificially placed cones were 0.081–0.082 yr^–1. On withered cones still attached to the tree,Pestalotiopsis spp. were dominant. These fungi also occurred with higher frequencies after cones had lain on the floor and on cones in the L and FH horizons.Xylaria sp. andPhomopsis sp., which seem to colonize the interior of the tissue, occurred with higher frequencies on the cones on the tree, but their occurrence frequencies decreased after cones had lain on the forest floor. Conversely,Mortierella spp. andTrichoderma spp. newly occurred or their occurrence frequencies increased on lying cones. Of these,Trichoderma koningii increased rapidly and showed high occurrence frequencies.Thysanophora penicillioides, which prefers coniferous substrates, showed higher occurrence frequencies in the early stages of lying on the forest floor. On cones lying on the floor, the fungal flora did not significantly change during the investigation period.     

A clarification of two congeners,Pseudodiaptomus lobipes and P. binghami (Calanoida,Pseudodiaptomidae) from India,with description of P. mixtus sp.n. from Bangladesh

Two closely related and often confused species of Pseudodiaptomus from the Lobus-species group, P. lobipes and P. binghami are redescribed from various locations along the east coast of India. These species predominately occur in freshwater though they can survive temporary periods of increased salinity. The distinctive features of the species are found on: female caudal ramal setae, female and male urosome 1–2 spinulation patterns, and fifth legs. A new species P. mixtus from Bangladesh is described.     

The systematics and ecology of snakeheads (Pisces: Channidae) in Peninsular Malaysia and Singapore

Seven species of snakeheads (Channidae) are known from Peninsular Malaysia and Singapore, viz. Channa bankanensis, C. gachua, C. lucius, C. marulioides, C. melasoma, C. micropeltes and C. striata. Up-to-date distribution maps of each species are presented, including new records. Their systematics is reviewed and partially revised. The taxonomic status of C. marulioides and C. melanoptera is clarified. Specimens from Peninsular Malaysia identified as C. melanoptera sensu Weber & de Beaufort, 1922, proved to be the adult form of C. marulioides s.str. The real C. melanoptera appears to be restricted to Borneo and possibly Sumatra. The life history of a blackwater species C. bankanensis is also documented, with regards to the morphological and colour-pattern changes associated with growth. An updated key to the seven species based on morphometric measurements and meristic counts is presented.     

Cladistics and the comparative morphology of linyphiid spiders and their relatives (Araneae, Araneoidea, Linyphiidae)

This paper provides the first quantitative cladistic analysis of linyphiid morphology. Classical and novel homology hypotheses for a variety of character systems (male and female genitalia, somatic morphology, spinneret silk spigot morphology, etc.) are critically examined and studied within a phylogenetic context. Critical characters have been illustrated. A sample of linyphiid taxa (nine genera in four subfamilies), five species of Pimoa (Pimoidae), and two other araneoid families (Tetragnathidae and Araneidae, represented by Tetragnatha and Zygiella , respectively) were used to study the implications of the phylogeny of Pimoidae for the systematics of linyphiids. The phylogenetic relationships of these 16 exemplar taxa, as coded for the 47 characters studied, were analysed using numerical cladistic methods. In the preferred cladogram Pimoidae and Linyphiidae are sister groups, Stemonyphantinae are sister group to the remaining linyphiids, and Mynogleninae are sister group to the clade composed of Erigoninae plus Linyphiinae. These results agree with the relationships recently proposed by Wunderlich, except by finding erigonines as the sister group to linyphiines rather than to mynoglenines.