Calcium ion promotes successful penetration of powdery mildew fungi into barley cells

To determine whether Ca²⁺ promotes powdery mildew penetration, Ca²⁺-treated barley coleoptiles were inoculated with conidia of pathogenic and nonpathogenic fungi. Penetration efficiency of the pathogenic powdery mildew Blumeria graminis was enhanced by Ca²⁺ treatment, but that of the necrotrophic pathogen Helminthosporium sp. remained unaffected. Similarly, when actin-dependent penetration resistance is suppressed with cytochalasin A, Ca²⁺ treatment specifically enhanced penetration of the nonpathogenic powdery mildew Erysiphe pisi but not that of other nonpathogens. Calmodulin inhibitors suppressed the promotive effect of Ca²⁺ on B. graminis penetration. These results suggest that barley powdery mildew specifically requires Ca²⁺ and calmodulin for penetration.     

Defense Mechanism of Rice Plant to Respiratory Inhibition by a Promising Candidate Blasticide, SSF126

A new candidate systemic rice blasticide, SSF126, dose-dependently inhibited NADH oxidation by submitochondrial particles from rice roots. However, oxidation by the root submitochondrial particles was much less susceptible to SSF126 compared to that by submitochondrial particles from mycelial cells ofPyricularia grisea, a pathogen causing rice blast. Interestingly, SSF126 did not completely suppress the respiration by intact rice roots, and the respiratory activity of the roots recovered from inhibition time-dependently even in the presence of SSF126 at concentrations sufficient to fully block oxidation by the submitochondrial particles. This recovery was not due to selective extrusion of SSF126 from the roots, but to switching from the cytochrome pathway to the alternative cyanide-resistant respiratory pathway. In immunoblots of the alternative oxidase, high molecular mass species were detected in the mitochondria from rice roots in addition to low molecular mass species. Quantification of high and low molecular mass species revealed an increase in the amount of a protein corresponding to a 36-kDa species equivalent to a decrease in the amount of a protein corresponding to a 72-kDa species following a 5-h incubation with SSF126. This conversion of the alternative oxidase to the low molecular mass species in the mitochondria was correlated with the respiratory recovery found in intact rice roots, suggesting that the low molecular mass species is the active form of the alternative oxidase and the high molecular mass species is the inactive form. These results suggest that rice plants can block the severe injury caused by limiting the cytochrome pathway by SSF126 through utilization of the alternative pathway promoted by the interconversion of the alternative oxidase protein.     

Production and characterisation of monoclonal antibodies to cell wall components of the flax rust fungus

Monoclonal antibodies have been raised against an haustorium-enriched sample prepared from flax leaves infected with the biotrophic flax rust pathogen Melampsora lini. The monoclonal antibodies were produced following conventional and co-immunisation procedures and the range of antibody specificities was compared. The preparation used as immunogen for the conventional protocol was a crude isolate of haustoria consisting of approx. 65% fungal haustoria, the other components being mainly mesophyll cells or cell wall and chloroplast fragments. Following hybridoma production, 40% of positive cell lines produced antibodies that reacted with haustoria and other fungal cells, but 60% bound to plant cells in the infected leaves. For the co-immunisation protocol, the preparation used for immunisation consisted of the crude isolate of haustoria mixed with serum raised against an haustorium-depleted leaf homogenate. In two fusions, 92-94% of the antibodies reacted with fungal cells, including 3 cell lines that localised specifically to the cell wall of haustoria. Only 6-8% of the antibodies produced via co-immunisation reacted with plant cells. The antigens targeted by the three haustorium-specific monoclonal antibodies are incorporated into the wall at early stages of haustorium development, remain in the wall throughout haustorium maturation, and are present in both compatible and incompatible interactions. The epitopes recognised by the monoclonal antibodies are oligosaccharide in nature and the antigens are highly resistant to extraction from the wall. These results highlight the value of the co-immunisation protocol for the production of monoclonal antibodies to specific components in an impure preparation and provide direct evidence for molecular differentiation within the wall of the haustorium of M. lini.     

Transnationalism through the life course: Hong Kong immigrants in Canada

Abstract: Transnationalism needs to be understood as a set of practices fashioned through the life course as well as in relation to contextual factors that include state policy and experiences of discrimination that affect entry to the labour force. The paradox of transnationalism is that families make strategic decisions to separate in order to maintain family unity and to advance the welfare of children. Emigrants from Hong Kong to Canada in the latter decades of the twentieth century were motivated by concern for family welfare and the quality of education in Canada. Yet economic livelihood prospects remained greater in Hong Kong than in Canada, prompting many families to become transnational ‘astronaut’ families with one or more members working in Hong Kong. Migration decisions tend to occur around key points of life‐course transition involving entry to and graduation from education, and entry to and exit from the labour force. Transnational practices are complex and multigenerational, involving different patterns for young adults, those in their middle years and the elderly.     

Simultaneous measurements of quantum yield and CO2 uptake for the assessment of non-assimilative electron flow in tree leaves

Using attached and detached leaves ofAcer palmatum Thunb. andRhaphiolepsis umbellata Makino, pulse-modulated chlorophyll fluorescence and CO₂ exchange were measured. Quantum yield of photosynthesis was determined from the fluorescence parameter(Fm′−Fs)/Fm′, where (Fm′−Fs) was defined as the difference between steady state chlorophyll fluorescence (Fs) and maximum fluorescence (Fm′) elicited by a saturating light pulse. The rate of electron transport through photosystem II (total electron flow) was calculated from the product of quantum yield andA (PFD), whereA is the rate of absorbed photons as given by leaf absorptance, and PFD is the photon flux density at the leaf surface. The rate of electron transport dependant on CO₂ uptake (assimilative electron flow) was calculated from the gross photosynthetic rate in a leaf. The difference between the rates of total and assimilative electron transport was denoted as the rate of non-assimilative electron transport which depends on photorespiration and oxygen reduction. Available data provided quantitative information on the rate of non-assimilative electron flow in intact leaves. When leaf photosynthesis ofA. palmatum was measured under sunlight, the rates of total and assimilative electron transport were determined to be approximately 900 and 150 μmol equiv. e/mg Chl·h, respectively. The difference (750 μmol equiv. e/mg Chl·h) was attributed to the activity of non-assimilative electron flow. The ratio of total to assimilative electron flow was found to increase gradually with rising in irradiance. The results suggest that non-assimilative electron flow occurred at much higher rate than assimilative electron flow at high irradiance. Implications of the results are briefly discussed in relation to photosynthesis limitation in tree leaves.     

Plantation future of bamboo in China

In the past, utilization of bamboo resources in China has been traditionally dominated by direct consumption of local farmers as minor forest products with weak linkage with market. In recent years, the over-supply of grains and rapid degradation of agricultural environment call for alternative crops that can be developed through integrating the environmental plantation with the market demands. Closely associated with forestry and agriculture, bamboo is able to deal with the new challenges which China‘s agriculture is facing. Of 534 documented bamboo species in China, 153 species produce edibleshoots and of which 56 species are recommended for agricultural plantation; 139 species provide timbers and of which 58 species recommended; 116 species can be splited as good strips for weaving and of which 22 species recommended; 88 species are considered as garden bamboos and of which 34 species recommended; 45 species are able to produce paper pulp and of which 18 species recommended.     

Effect of intermittent heat treatment on crystallinity in wood cellulose

The effect of intermittent heat treatment on cellulose crystallites in wood was studied to evaluate quantitatively the changes of crystallinity induced by intermittent and continuous heating. The changes in crystallinity were found to be strongly affected by the intermittent heat treatment. The increased crystallinity, the width of the crystals, and the piezoelectric properties were the same for the first intermittent heating as for continuous heating. Further intermittent heating for the same time duration and temperature had no effect on the above properties, probably due to the stopping of the thermal reaction during the interval. Our results suggested that intermittent heat treatment has certain critical cooling temperatures that stop the thermal reaction and are closely related to the duration of the interval. Samples once exposed to a certain duration of heat treatment and then cooled need more time, about twice that of the first duration of intermittent heating compared with continuous heating, to reach maximum crystallinity in wood cellulose.