Maize and common bean seed exudates mediate part of nonhost resistance to Phytophthora sojae prior to infection

Phytophthora sojae does not infect nonhost maize (Zea mays) but infects nonhost common bean (Phaseolus vulgaris) under inoculation. Soybean seed exudates participate in mediating host resistance to P. sojae prior to infection. This study aims to elucidate the role of seed exudates in mediating the nonhost resistance to P. sojae prior to infection. The behaviors of P. sojae zoospores in response to the seed exudates were determined using an assay chamber and a concave slide. The proteomes of P. sojae zoospores in response to the seed exudates were analyzed with the tandem mass tag (TMT) method. The key proteins were quantitatively verified by parallel reaction monitoring (PRM). Maize seed exudates exerted a repellent effect on zoospores. This result explains why zoospores sense repelling signaling molecules that weaken and strongly inhibit chemotaxis signals in the phosphatidylinositol signaling pathway and arachidonic acid metabolism pathway. Common bean seed exudates did not exhibit any attraction to the zoospores because the G protein signaling pathway, had no significant change. The proteins protecting the cell membrane structure were significantly downregulated, and the early apoptosis signal glutathione was enhanced in zoospores responding to common bean seed exudates, which resulted in dissolution of the cysts. Maize and common bean seed exudates mediate part of the nonhost resistance to P. sojae via different mechanisms prior to infection. The immunity of maize to P. sojae is due to the repellent effect of maize seed exudates on zoospores. Common bean seed exudates participate in mediating nonhost resistance by dissolving cysts.

Maize and Common Bean Seed Exudates Mediate Part of Nonhost Resistance to Phytophthora Sojae before Infection

Purpose: Phytophthora sojae does not infect the nonhost maize (Zea mays L.) but could infect the nonhost common bean (Phaseolus vulgaris L.). Soybean seed exudates participate in mediating host resistance to P. sojae before infection. This study aimed to elucidate the role of nonhost seed exudates in mediating nonhost resistance to P. sojae before infection. Methods: The response behavior of P. sojae zoospores to the seed exudates was determined using an assay chamber and a concave slide, and the proteomes of P. sojae zoospores treated with the seed exudates were analysed with the tandem mass tag (TMT) method. The key proteins were quantified by parallel reaction monitoring (PRM).Results: Maize seed exudates exerted a repellent effect on zoospores, whereas common bean seed exudates did not exhibit any attraction to zoospores but could dissolve the cysts. The key proteins related to zoospores chemotaxis showed no significant changes in response to maize seed exudates, but the key proteins in arachidonic acid pathway were downregulated and controlled the repellent behavior of zoospores. Proteins protecting the cell membrane structure were significantly downregulated in zoospores responding to common bean seed exudates, which confirmed the bacteriolytic effect of common bean seed exudates on cysts. Conclusion: Maize and common bean seed exudates mediate part of the nonhost resistance via different mechanisms prior to P. sojae infection. The immune of maize to P. sojae is due to the repellent effect of maize seed exudates on zoospores. Common bean seed exudates participate in mediating nonhost resistance by dissolving cysts.

Persistence of Mating Suppression of the Indian Meal Moth Plodia Interpunctella in the Presence and Absence of Commercial Mating Disruption Dispensers

The Indian meal moth Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), is controlled by commercial mating disruption dispensers using passive release to emit high concentrations (relative to females or monitoring lures) of their principal sex pheromone component, (9Z,12E)-tetradecadienyl acetate. Since P. interpunctella is sexually active throughout the scotophase, an assay system was developed to determine the importance of direct interaction of the male with the dispenser, and whether exposure to mating disruption early in the night is sufficient to suppress mating throughout the night. Exposure to mating disruption dispensers in the mating assay chamber for the first two hours of a 10-h scotophase significantly reduced mating when females were introduced four hours later. Mating was also reduced to a lesser degree in a concentration-dependent manner based solely on re-emission of pheromone, and when males were exposed outside the mating assay chamber. These results indicate that the commercial mating disruption dispensers can suppress mating throughout the night based on interaction with the dispenser early in the night. Desensitization resulting from attraction to a high-concentration pheromone source is important to this suppression, but other factors such as re-emission from the environment may also have a role. These observations imply a non-competitive mechanism for P. interpunctella with the product studied, and suggest that effectiveness of the mating disruption dispenser might be augmented by using them in conjunction with another formulation such as an aerosol or micro-encapsulated product.

Quantification of Chemotaxis to Naphthalene by Pseudomonas putida G7

ABSTRACT The capillary assay was used to quantify the chemotactic response of Pseudomonas putida G7 to naphthalene. Experiments were conducted in which the cell concentration in the assay chamber, the naphthalene concentration in the capillary, or the incubation time was varied. Data from these experiments were evaluated with a model that accounted for the effect of diffusion on the distribution of substrate and the transport of cells from the chamber through the capillary orifice. By fitting a numerical solution of this model to the data, it was possible to determine the chemotactic sensitivity coefficient, χ0. The mean of the best-fit values for χ0from the three types of experiments was 7.2 × 10−5cm2/s. A less computationally intensive model based on earlier approaches that ignore cell transport in the chamber resulted in χ0 values that were approximately three times higher. The models evaluated in the present study could simulate the results of capillary assays only at low chamber cell concentrations, for which the effect of consumption on the distribution of substrate was negligible. Results from this work suggest that it is possible to use the capillary assay to quantify taxis towards environmentally relevant chemoeffectors that have low aqueous solubility.

Nitrogen Fixation by Nodulated Roots of Viminaria juncea (Schrad. & Wendl.) Hoffmans, (Fabaceae) When Submerged in Water

Nodulated seedlings of Viminaria juncea were raised in free-draining or flooded sand culture. Unflooded seedlings developed limited amounts of aerenchyma in lower stem, root and nodules, and responded to flooding by accelerated aerenchyma production and, after 10 days, by formation of pneumatophores from their near-surface lateral roots. Continuously flooded seedlings showed earlier and greater development of aerenchyma and pneumatophores, and had their nodules and roots restricted to the upper 10 cm of the rooting medium. Aerenchyma was developed from an inner cambium, distinct from the outer phellogen which subsequently developed on older parts of stem, root and nodules. Gas contents of plant parts varied from 4-8% for organs with little aerenchyma to over 30% for the aerenchyma-invested basal stem and root of continuously flooded seedlings. A role of the sheaths of aerenchyma in gaseous exchange between aerial environment and nodulated root was demonstrated by gas injection experiments, in situ C2H2 reduction assays and 15N2 feeding experiments on intact plants with flooded roots. Samples of gas removed from the aerenchyma of plants exposed to C2H2 contained up to 14 times the amount of C2H2 and 4 times the amount of CO2 than in the atmosphere of the assay chamber, indicating that gas exchange for both N2 fixation and respiration occurred via the aerenchyma. Previously unflooded, 12-week seedlings exposed to 14 days flooding gained as much dry matter and total N in the 2-week treatment as did control unflooded plants, but 21-week continuously flooded seedlings showed only half the dry matter and nitrogen gains of similarly aged unflooded seedlings. Observations on the seasonal growth, nodulation and pneumatophore development of natural populations of the species were discussed in relation to the above findings.