Relative parasitic fitness of isolates of Pyricularia oryzae Cav. with different sensitivities to fungicides

The relative parasitic fitness of isolates of Pyricularia oryzae with different sensitivities to isoprothiolane (di-isopropyl 1,3-dithiolan-2-ylidenemalonate) and IBP (S-benzyl O, O-di-isopropyl phosphorothioate) was studied in the absence of fungicides. Four field isolates (S-1,S-2,MR-1 and MR-2) and two in-vitro mutants (Rvt-1 and Rvt-2) were used for disease epidemics. S-l and S-2 were wild types; MR-1 and MR-2 were sensitive to isoprothiolane and moderately resistant to IBP, and Rvt-1 and Rvt-2 were resistant to both fungicides. Twelve epidemics were made by inoculating rice seedlings with mixed conidial suspensions of two isolates or mutants. The value of relative parasitic fitness (W = 0-1.0) was calculated for each isolate and epidemic. S-l and S-2 were stronger (W = 1.0) than MR-2, Rvt-1 and Rvt-2; but weaker (W = 0.75, 0.73, respectively) than MR-1. MR-1 was strongest among all isolates and mutants used. MR-2 was slightly weaker (W = 0.9-1.0) than S-l and S-2, but stronger than Rvt-1 and Rvt-2. Rvt-1 and Rvt-2 had smaller values of W, ranging from 0.25-0.58, in the epidemics with each field isolate. These results suggest that the proportions of in-vitro mutants do not increase unless intensive selection pressure is given, and would be expected to decrease rapidly after the selection pressure is removed. Isolates moderately resistant to IBP, such as MR-1 and MR-2, however, had high values of W, suggesting that they would increase or would not decrease rapidly in the absence of selection pressure. These results may well explain why isolates highly resistant to isoprothiolane and IBP have seldom been found, and why a large number of isolates moderately resistant to IBP but sensitive to isoprothiolane have been observed in the field.     

Specialized inhibitory synaptic actions between nearby neocortical pyramidal neurons

We found that, in the mouse visual cortex, action potentials generated in a single layer-2/3 pyramidal (excitatory) neuron can reliably evoke large, constant-latency inhibitory postsynaptic currents in other nearby pyramidal cells. This effect is mediated by axo-axonic ionotropic glutamate receptor-mediated excitation of the nerve terminals of inhibitory interneurons, which connect to the target pyramidal cells. Therefore, individual cortical excitatory neurons can generate inhibition independently from the somatic firing of inhibitory interneurons.     

Effect of a Bowman-Birk proteinase inhibitor from Phaseolus coccineus on Hypothenemus hampei gut proteinases in vitro

The coffee berry borer, Hypothenemus hampei (Ferrari), is an important devastating coffee pest worldwide. Both trypsin and chymotrypsin enzyme activities from H. hampei larval midgut can be inactivated by proteinaceous enzyme-inhibitors. A serine proteinase inhibitor belonging to the Bowman-Birk class was purified from a wild accession of Phaseolus coccineus L. seeds. The inhibitor (PcBBI1) is a cysteine-rich protein that is heat-stable at alkaline pH. MALDI-TOF/MS analysis showed that PcBBI1 occurs in seeds as a monomer (8689 Da) or dimer (17,378 Da). Using in vitro inhibition assays, it was found that PcBBI1 has a high inhibitory activity against H. hampei trypsin-like enzymes, bovine pancreatic chymotrypsin, and trypsin. According to this, PcBBI1 could be a promising tool to make genetically modified coffee with resistance to coffee berry borer.     

Seasonality of serum levels of vitellogenin in male Japanese whiting, Sillago japonica, reared under natural temperature and photoperiod

ABSTRACT:   Because blood vitellogenin (Vg) has been considered a biomarker for environmental estrogens, the basal levels of Vg and 17β-estradiol (E₂) were determined in male Japanese whiting reared under natural conditions. Serum levels of Vg and E₂ were measured and gonadal development was assessed by gonadosomatic index (GSI) and histological observation in 8–10 male fish at monthly intervals throughout the annual reproductive cycle. Serum E₂ was <60 pg/mL throughout the study period. In contrast, serum Vg exhibited seasonal changes: serum levels of Vg gradually increased from April to May (mean 63 ± 13 ng/mL and 124 ± 48 ng/mL in April and May, respectively), and then reached a peak value (mean 352 ± 68 ng/mL) in June. Thereafter, serum Vg gradually decreased, reaching undetectable levels (<50 ng/mL) in October. Serum levels of Vg tended to increase in the male fish in which the GSI was >1%. Histological observation revealed that testes in such male fish were in active spermatogenesis and then all of the testes of male fish in which serum Vg decreased to ND levels were regressed. These results suggest that Vg productive potency (sensitivity to estrogens) may increase in the spermatogenic stage, resulting in production of Vg in response to very low levels of natural or xenobiotic estrogens.     

Inhibitory effect of isoprothiolane on metabolism of a phosphoramidate by isolates of Pyricularia oryzae cav. in relation to fungicide sensitivity

The inhibitory effect of isoprothiolane(diisopropyl 1,3-dithiolan-2-ylidenemalonate), a fungicide for rice blast control, on the metabolism of dibutyl N-methyl-N-phenylphosphoramidate (BPA) by 20 isolates of Pyricularia oryzae was examined in relation to sensitivity of the isolates to the reference fungicide IBP(S-benzyl diisopropylphosphorothiolate). The isolates were divided into five groups based on the modes of BPA metabolism and the inhibition of BPA metabolism by isoprothiolane. Every isolate in groups I and II, which was either a field isolate or a stock culture, decomposed BPA rapidly and produced both hydroxylated and N-demethylated BPA as metabolites. BPA decomposition by these isolates was strongly inhibited by isoprothiolane, resulting in the decreased production of both metabolites in group I and of the hydroxylated metabolite in group II. These isolates were almost equally sensitive to isoprothiolane. Isolates in groups III, IV, and V were all obtained from selection of the fungus mutants found growing on media containing isoprothiolane. Isolates in group III, derived by plating large numbers of conidia, did not decompose BPA to any extent. Mutants of groups IV and V were obtained from fast-growing sectors on agar containing isoprothiolane. Both these groups decomposed BPA, but isolates belonging to group IV produced copious amount of N-demethylated BPA whereas isolates in group V did not. BPA metabolism by these in vitro mutants in groups III, IV, and V was not inhibited by isoprothiolane. Thus, the inhibitory effect of isoprothiolane on BPA metabolism was correlated with sensitivity of an isolate to isoprothiolane. The inhibitory effect of IBP on BPA metabolism was not always correlated with the sensitivity of an isolate to IBP.     

Analysis of 46-kDa protein in the perivitelline membrane of Japanese quail (Coturnix japonica)

The extracellular matrix surrounding the oocyte before ovulation is called the perivitelline membrane (PL) in avian species. The PL is constructed with two major glycoproteins, ZPC and ZP1, which are synthesized in the ovarian granulosa cells and the liver, respectively. Although the properties of the major components in the PL have been examined, knowledge about the nature of its minor constituents is lacking. In this study we focused on PL protein, which migrates at 46‐kDa in the gel of SDS‐PAGE. N‐terminal sequence analysis demonstrated that the 46‐kDa protein is the C‐terminal fragment of ZP1. Analysis of lysylendopeptidase digests or cyanogens bromide‐degraded fragments of ZP1 confirmed this postulate. Western blot analysis using antiserum against 46‐kDa protein indicated the absence of 46‐kDa protein in the serum. Moreover, small immunoreactive bands, thought to be cleaved fragments of ZP1, were detected in the PL lysate by western blot analysis using antiserum against the N‐terminal peptide of ZP1. These results indicated that the N‐terminal proteolytic processing of ZP1 might take place after the arrival of ZP1 at the ovary, and the resulting product, 46‐kDa protein, is incorporated into the PL.     

Fibrinonecrotic rhinitis caused by a concurrent infection of Fusobacterium necrophorum and Arcanobacterium pyogenes in a cow

An 8 year-old cow showing severe dyspnea and nasal mucosal necrosis immediately after parturition was subjected to pathological examination. The principal lesions were fibrinonecrotic rhinitis, necrotic bronchopneumonia and renal infarction. Fusobacterium necrophorum biotype A and Arcanobacterium pyogenes antigens were detected in the nasal and pulmonary lesions. These results suggest that the lesions were caused by a concurrent infection of the detected bacteria and that the pulmonary lesions were caused by the aspiration of infectious materials from the nasal ones. Mucosal coagulative necroses observed as the initial lesions in rhinitis were frequently associated with multiple thrombosis. The findings might suggest that thrombosis played an important role in the development of the nasal lesions.