Regulation of root-to-leaf Na and Cl transport and its association with photosynthetic activity in salt-tolerant soybean genotypes

ABSTRACT

Soil salinity is a major constraint to sustainable crop production. Genetic improvements are needed for growing soybean in salinity-prone environments. Salt-tolerant soybean genotypes alleviate a reduction in photosynthesis and growth under saline conditions; however, the detailed mechanisms involved remain unclear. Here, we aimed to clarify how Na and Cl root-to-leaf transport is quantitatively regulated, and to identify whether photosynthetic tolerance depends on traits associated with either stomata or with mesophyll tissues. Two pairs of pot-grown soybean near-isogenic lines (NILs) consisting of tolerant and susceptible counterparts, derived from a cross between salt-tolerant FT-Abyara and salt-sensitive C01, were subjected to salinity treatment in a rainout greenhouse. Comparison of photosynthetic responses between genotypes indicated that genotypic differences in salinity tolerance depended on the ability for sustained CO₂ assimilation in mesophyll tissues, rather than stomatal conductance. The ratio of photosynthetic rate to intercellular CO₂ concentration (A/Ci) declined exponentially with increasing Na and Cl concentration regardless of genotype, but tolerant genotypes effectively kept both elements at significantly low levels. Under saline conditions, tolerant genotypes reduced Na and Cl content at the two transport pathways: from root to stem, and from stem to leaf, but the reduction of Cl at each pathway was only minor. These results suggest that integrating genetic capacity for Cl transport regulation and osmotic adjustment should be an important target in salinity-tolerance soybean breeding.     

Purification and Biological Characterization of Host-Specific SV-Toxins from Stemphylium vesicarium Causing Brown Spot of European Pear

ABSTRACT Culture filtrates of a pathogenic isolate (IT37) of Stemphylium vesicarium, causing brown spot of European pear, induced veinal necrosis only on pear leaves susceptible to the pathogen. Two host-specific toxins, SV-toxins I and II, were purified from culture filtrates of IT37 by successively using Amberlite XAD-2 resin adsorption, cellulose thin-layer chromatography, and high-performance liquid chromatography under three different sets of conditions. Susceptible cultivars showed veinal necrosis at a SV-toxin I concentration of 0.01 to 0.1 mug/ml, whereas resistant cultivars were insensitive to the toxin at 1,000 mug/ml. SV-toxins I and II caused a dose-dependent increase in electrolyte loss from susceptible leaf tissues. No increase in electrolyte loss was detected in leaf tissues from resistant cultivars. The results of physiological studies indicated that SV-toxins appear to have an early effect on plasma membranes of susceptible leaves. Spores of a nonpathogenic isolate induced necrotic lesions on susceptible leaves in the presence of a small amount of toxin. SV-toxins were detected in intercellular fluids obtained from diseased leaves after inoculation with the pathogen. The results indicate that SV-toxins I and II produced by S. vesicarium can be characterized as host-specific toxins.     

PCR detection of Porcine circovirus type 2 DNA in whole blood,serum, oropharyngeal swab,nasal swab,and feces from experimentally infected pigs and field cases

Porcine circovirus type 2 (PCV2) shedding patterns were investigated by polymerase chain reaction (PCR) for the detection of PCV2 DNA, and the diagnostic suitability of a sample for the PCR was examined by using different types of samples. In the experimental infection, sixteen pigs were inoculated intranasally with PCV2. The samples, including oropharyngeal and nasal swabs, feces, whole blood and serum became positive for PCV2 DNA by PCR immediately after the inoculation, and almost all samples remained positive during the observation period, post-inoculation-day 70. Field samples were collected from 313 pigs in five different age groups. The overall percentages of positive samples in the whole blood, nasal swabs, and feces detected by PCR were 30.4%, 19.2%, and 20.4%, respectively. The frequency of positive samples increased after the nursery stages and reached a peak in the 3 to 4-month-old pigs. These results indicate that PCV2 infection may occur after weaning, that PCV2 DNA may be present in whole blood for a long period after infection, and that whole blood and serum are the most suitable sample types for the PCR analysis of PCV2.     

Kinetics of molecular encapsulation of 1-methylcyclopropene into alpha-cyclodextrin

1-methylcyclopropene (1-MCP), an ethylene inhibiting regulator, is commercially available in the form of an inclusion complex with alpha-cyclodextrin (alpha-CD). In this study, molecular encapsulation of gaseous 1-MCP into aqueous alpha-CD was investigated in a closed, agitated vessel with a flat gas-liquid interface. Molecular encapsulation of gaseous 1-MCP by alpha-CD is a simultaneous two-step reaction which involves the aqueous dissolution of gaseous 1-MCP and the encapsulation of the dissolved molecules by alpha-CD. The kinetics and mechanism of molecular encapsulation were analyzed based on the depletion rate of 1-MCP in the headspace of the vessel. The encapsulation rates could be explained quantitatively by the gas absorption theory with a pseudo-first-order reaction between 1-MCP and alpha-CD. The negative value of the calculated apparent activation energy of encapsulation (-24.4 kJ/mol) implied the significant effect of exothermic aqueous dissolution of 1-MCP. An encapsulation temperature of 15 degrees C was optimal; at this temperature, the highest 1-MCP yield and best inclusion ratio of inclusion complex were obtained. Changes in the X-ray diffraction pattern suggested that the crystal lattice structure of alpha-CD was altered upon inclusion of 1-MCP.     

Effect of infection timing on fusarium head blight and mycotoxin accumulation in open- and closed-flowering barley

ABSTRACT Barley has two flowering types, chasmogamous (open-flowering) and cleistogamous (closed-flowering). We examined the effect of the timing of Fusarium graminearum infection on Fusarium head blight (FHB) and mycotoxin accumulation in barley cultivars with different flowering types using greenhouse experiments. In the first experiment, 13 cultivars were spray inoculated at two different developmental stages, and the severity of FHB was evaluated. The effect of the timing of infection differed among cultivars. Cleistogamous cultivars were resistant at anthesis but susceptible at 10 days after anthesis, whereas chasmogamous cultivars were already susceptible at anthesis. In the second experiment, five cultivars were inoculated at three different developmental stages and the concentrations of deoxynivalenol (DON) and nivalenol (NIV) in mature grain were analyzed. Cleistogamous cultivars accumulated more mycotoxins (DON and NIV) when inoculated 10 or 20 days after anthesis than when inoculated at anthesis, whereas chasmogamous cultivars accumulated more mycotoxins when inoculated at anthesis. Thus, the most critical time for F. graminearum infection and mycotoxin accumulation in barley differs with cultivar, and likely is associated with the flowering type. Late infection, even without accompanied FHB symptoms, was also significant in terms of the risk of mycotoxin contamination.     

Annual net production of the five Sargassaceae species in Yoro,western Wakasa Bay,Sea of Japan

ABSTRACT:   Annual net production of the five Sargassaceae species was investigated in Yoro, western Wakasa Bay, Sea of Japan. The Sargassaceae species were collected at a depth of 2.0–2.5 m and subjected to stratified clipping for 13 months. Annual net production was estimated at 2407 g dry wt/m² for Sargassum patens , 2132 g dry wt/m² for Sargassum macrocarpum , 1458 g dry wt/m² for Sargassum siliquastrum , 1197 g dry wt/m² for Myagropsis myagroides , and 1471 g dry wt/m² for Sargassum piluliferum . The ratio of annual net production to maximum biomass (P/B_max) for these species ranged between 1.3 and 1.7, being higher than in previous studies which used the same method. Winter storms with strong wave exposure and relatively calm condition in Yoro were considered to augment P/B_max. The total losses estimated from the different units of stratified clipping were compared. If larger and less segregated units were applied, the total loss would decrease. It was suggested that a 50 cm stratum would be applicable to the larger species (3 m or longer) and a stratum of 20 cm or less would be applicable to mid-sized or smaller species (less than 3 m).