Hormetic doses of UV-C light decrease the susceptibility of tomato plants to Botrytis cinerea infection

Preharvest hormetic doses of UV-C radiation can decrease the susceptibility of tomato leaves to Botrytis cinerea L. infection. UV-C light treatments have been shown to be very effective for reducing disease development in several species, including tomato (Solanum lycopersicum L.). Treating cultivated tomato plants with UV-C light is of interest not only because of the disinfecting effects of UV-C light but also because of its ability to stimulate plant defences (SDP) against diseases, provided that the applied doses are high enough to be effective while low enough to prevent deleterious effects. In the present study, the effects of UV-C light on plants were evaluated by biochemical analyses, including analyses of the activities of antioxidant enzymes and phenylalanine lyase (PAL); the concentration of malondialdehyde (MDA), an indicator of membrane integrity; and chlorophyll fluorescence parameters, such as the maximum quantum efficiency of photosystem II (F_V/F_M) and the Strasser performance index (PI). In this work, treatments with single doses of 0.85 kJ/m² of UV-C light were found to significantly increase plant defences against B. cinerea, reducing the affected leaf area by 51% compared to the affected area of control plants. This decrease in susceptibility was associated with increased PAL activity and the amount of bound phenolics compared to levels in control plants (not treated with UV-C).     

The effect of wavelength of light on stomatal opening

The effect of broad band green, blue and red light on stomatal opening of Vicia faba L. (broad bean) leaves was examined. In air, blue light caused greater stomatal opening than red light. In air with green light stomata were only slightly opened. In a nitrogen atmosphere red light caused greater opening than blue light, and green light caused only slight opening. Opening in air or nitrogen atmosphere in red or blue light was inhibited by the uncoupler CCCP, while the photosynthetic inhibitor DCMU inhibited opening in air but not in nitrogen atmosphere. We concluded that more than one light activated metabolic pathway can supply the energy needed to effect stomatal opening and that different pathways are operative under different conditions.     

The effect of protein-deprivation on the susceptibility to influenza virus infection: a murine model system.

The effect of a 4% albumin diet initiated at weaning on the susceptibility to influenza virus infection was studied in C57Bl mice. Protein-deprivation was found to enhance markedly the susceptibility to a lethal infection with both mouse-virulent and avirulent strains of virus. Viraemia was observed more frequently in protein-deprived mice, and virus persisted longer in the lungs. The humoral immune response following intranasal infection was depressed, with normal levels of IgG antibody but reduced levels of IgM antibody. No difference was found in the seroconversion frequencies between well-nourished and protein-deprived mice. Pre-immunization did not affect the virus titres in the lungs of protein-deprived mice after challenge with the homologous virus, nor did it prevent the spread of virus to the thymus and brain. The results were discussed in terms of the immunocompetence of the malnourished host and of the potential risk of epidemic influenza in children suffering from severe forms of protein-energy malnutrition.     

Aerosol susceptibility of influenza virus to UV-C light

The person-to-person transmission of influenza virus, especially in the event of a pandemic caused by a highly virulent strain of influenza, such as H5N1 avian influenza, is of great concern due to widespread mortality and morbidity. The consequences of seasonal influenza are also substantial. Because airborne transmission appears to play a role in the spread of influenza, public health interventions should focus on preventing or interrupting this process. Air disinfection via upper-room 254-nm germicidal UV (UV-C) light in public buildings may be able to reduce influenza transmission via the airborne route. We characterized the susceptibility of influenza A virus (H1N1, PR-8) aerosols to UV-C light using a benchtop chamber equipped with a UVC exposure window. We evaluated virus susceptibility to UV-C doses ranging from 4 to 12 J/m(2) at three relative humidity levels (25, 50, and 75%). Our data show that the Z values (susceptibility factors) were higher (more susceptible) to UV-C than what has been reported previously. Furthermore, dose-response plots showed that influenza virus susceptibility increases with decreasing relative humidity. This work provides an essential scientific basis for designing and utilizing effective upper-room UV-C light installations for the prevention of the airborne transmission of influenza by characterizing its susceptibility to UV-C.     

Genetics of susceptibility to Theiler's virus infection

Theiler's virus is a picornavirus of mouse which causes an acute encephalomyelitis followed by a persistent infection of the white matter resulting in chronic inflammation and demyelination. This disease has been studied as a model for multiple sclerosis. Inbred strains of mice are either resistant--they clear the infection after the acute encephalomyelitis--or susceptible to persistent infection and demyelination. Susceptibility is a polygenic trait which has been analyzed using methods of association with “candidate” genes, and linkage analysis after a complete genome scan. The H-2D^b gene is responsible for an efficient CTL response which makes some strains resistant. Non H-2 genes responsible for the susceptibility of other strains have been mapped by linkage analysis to the Ifng and, possibly, the Mbp loci. The analysis of a set of congenic mice ruled out the possiblity that the relevant gene codes for interferon gamma, and showed that the region around Ifngprobably contains two susceptibility genes. The analysis of mutant mice showed further that the Mbp gene, which codes for the myelin basic protein, has a major effect on viral persistence. BioEssays 20 :627–633, 1998. © 1998 John Wiley & Sons Inc.     

Human susceptibility and resistance to Norwalk virus infection

Infectious diseases have influenced population genetics and the evolution of the structure of the human genome in part by selecting for host susceptibility alleles that modify pathogenesis. Norovirus infection is associated with approximately 90% of epidemic non-bacterial acute gastroenteritis worldwide. Here, we show that resistance to Norwalk virus infection is multifactorial. Using a human challenge model, we showed that 29% of our study population was homozygous recessive for the alpha(1,2)fucosyltransferase gene (FUT2) in the ABH histo-blood group family and did not express the H type-1 oligosaccharide ligand required for Norwalk virus binding. The FUT2 susceptibility allele was fully penetrant against Norwalk virus infection as none of these individuals developed an infection after challenge, regardless of dose. Of the susceptible population that encoded a functional FUT2 gene, a portion was resistant to infection, suggesting that a memory immune response or some other unidentified factor also affords protection from Norwalk virus infection.     

The effect of light wavelength on the production and quality of eggs of the domestic hen

The effect of light color on egg-laying and on egg quality during the first 50 wk of egg production and during a second cycle of 19 wk following molting was examined. Hens were exposed to one of the following six sources of light: blue (B), green (G), red (R), tungsten (T), cool-white (C) fluorescent or simulated-sunlight (V) fluorescent tubes. Light intensity was equalized at photon output. Total egg production per hen was significantly influenced by the color of light with the most eggs being procuced in R light and the fewest in B light. Hens were more sensitive to light color in response to egg production during the second cycle than during the first cycle. Hens in C light produced significantly fewer eggs than those under V light in both laying cycles. Eggs laid under B or G light were consistently larger than those under R light. Egg weights of hens in V light were heavier than those for the C or T light groups. In the first cycle, shell quality was significantly better in G light than in B or R light. Percent of yolk increased and percent of albumen decreased with age during the first cycle in all treatments and the rate of change was directly related to light color (wavelength). In the second cycle, shell quality, percent of shell, yolk and albumen did not change significantly with age in any of the light treatments. It can be concluded that the wavelength of light may influence egg production, egg components and shell quality of the domestic laying hen.     

The effect of short wavelength light on retinula cell structure in white-eye Drosophila.

Recent electron microscopic examination of the retinula cells of white-eyed fruitflies has shown gross disruption of the ordered membrane system of the rhabdomeres, and extensive vesiculation of retinula cells 1 to 6 within each ommatidium following blue irradiation. Central retinula cells 7 and 8 are unaffected. The selective disruption is not observed in white-eyed fruitflies similarly irradiated with equal-energy yellow light.     

The effect of starvation on the susceptibility of teneral and non-teneral tsetse flies to trypanosome infection

Transmission of vector-borne diseases depends largely on the ability of the insect vector to become infected with the parasite. In tsetse flies, newly emerged or teneral flies are considered the most likely to develop a mature, infective trypanosome infection. This was confirmed during experimental infections where laboratory-reared Glossina morsitans morsitans Westwood (Diptera: Glossinidae) were infected with Trypanosoma congolense or T. brucei brucei. The ability of mature adult tsetse flies to become infected with trypanosomes was significantly lower than that of newly emerged flies for both parasites. However, the nutritional status of the tsetse at the time of the infective bloodmeal affected its ability to acquire either a T. congolense or T. b. brucei infection. Indeed, an extreme period of starvation (3-4 days for teneral flies, 7 days for adult flies) lowers the developmental barrier for a trypanosome infection, especially at the midgut level of the tsetse fly. Adult G. m. morsitans became at least as susceptible as newly emerged flies to infection with T. congolense. Moreover, the susceptibility of adult flies, starved for 7 days, to an infection with T. b. brucei was also significantly increased, but only at the level of maturation of an established midgut infection to a salivary gland infection. The outcome of these experimental infections clearly suggests that, under natural conditions, nutritional stress in adult tsetse flies could contribute substantially to the epidemiology of tsetse-transmitted trypanosomiasis.     

Maneuvering for advantage: the genetics of mouse susceptibility to virus infection

Genetic studies of host susceptibility to infection contribute to our understanding of an organism's response to pathogens at the immunological, cellular, and molecular levels. In this review we describe how the study of host genetics in mouse models has helped our understanding of host defense mechanisms against viral infection, and how this knowledge can be extended to human infections. We focus especially on the innate mechanisms that function as the host's first line of defense against infection. We also discuss the main issues that confront this field, as well as its future.     

The effect of ultraviolet light on the production of bacterial virus protein

The amount of phage-specific protein in T2-infected bacteria growing in a medium containing radiosulfur, S³⁵, has been studied by measuring the radioactivity in specific antiphage serum precipitates of lysates. In the course of normal infection, non-infective phage antigen has been found to make its first intracellular appearance shortly before the end of the eclipse period, in agreement with the findings of Maaløe and Symonds with phage T4. No such phage antigen is produced either in bacteria infected with UV-inactivated T2 or in T2-infected bacteria whose survival as an infective center has been destroyed by UV irradiation during the early stages of the eclipse period. If the infected bacteria are UV-irradiated only at later stages of the eclipse period however, then phage antigenic protein continues to be synthesized in those infected cells in which DNA synthesis and, a fortiori, production of infective progeny have been almost completely suppressed. It is concluded from these results that once the mechanism for formation of phage-specific protein has been established within the infected cell under the influence of the parental DNA, synthesis of phage-specific protein can continue independently of the synthesis of phage DNA. The possibility that the phage DNA controls the specificity of the phage protein indirectly through substances other than DNA is discussed.     

The biology of Peronospora viciae on pea: factors affecting the susceptibility of plants to local infection and systemic colonization

Peronospora viciae (Berk.) Casp. penetrated leaf disks of Pisum sativum L. through the cuticle. Resistance of pea plants and of individual leaves to infection by P. viciae increased with age, but decreased again at senescence. Resistance was shown by a restriction in fungal growth and sporulation and by a chlorotic reaction in the leaves. Systemic invasion followed infection of meristematic tissue, and was induced by inoculation into the apical bud of young plants, or on to the epicotyl or hypocotyl, but not roots of germinating seedlings. Most plants whose growth was retarded showed an increased resistance to systemic infection. Pods were infected externally by sporangia, rather than by mycelial growth through the peduncle and pedicel. Oospores and mycelium were found in the testas of some seeds, but seeds from infected pods did not give rise to infected seedlings.     

Effect of virus infection on the rhizosphere mycoflora of papaya plants

Summary Rhizosphere mycoflora of PLRV (Papaya Leaf Reduction Virus)- infected and healthy papaya plants have been investigated at the pre-flowring, flowering and post-flowering stages of plants. The fungal population per g of soil was higher in rhizosphere of diseased plants at all the three stages than that of healthy ones. The increased C/N ratio in the leaves of PLRV-infected papaya plants is responsible for the increased rhizosphere mycoflora concentration of infected plants.