Monoclonal antibodies were compared with conventional antisera from the view point of theoretical serology. Their advantages and disadvantages for practical use were discussed.

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Antibodies have a highly specific and sensitive reactivity for antigens. Immunohistochemical technique is based on the antigen-antibody reaction. It is therefore possible to localize the antigen within tissues or cells with a high specificity and sensitivity. Recently, considerable progress has been made in the development of immunohistochemistry, and its application to various aspects of research has increased significantly. Two main immunohistochemistry techniques have been applied to the study of the multiplication and distribution of plant viruses within tissues and cells of plants and insect vectors, by light microscopy. The fluorescent antibody method has been used more extensively, but the radioisotope-labelled antibody method has not been much used in studies of plant viruses. In this paper, the results of a study on the multiplication and distribution of viruses in various organs and tissues of plants infected with tobacco mosaic virus, cucumber mosaic virus and potato virus X are described. Formerly pre-embedding methods using ferritin conjugate antibody and radioisotope conjugate antibody had been employed to localize viral antigens in host plant cells by electron microscopy. However, the pre-embedding methods are laborious because the permeability of the cell wall or cell membranes to the labeled antibodies is low. Recently, resins consisting of polar acrylates and methacrylates have been introduced as a low temperature embedding medium particularly well suited for applications in immunoelectron microscopy, and protein A-gold methods have been applied for immunolabelling. These methods enable to detect antigens directly on ultrathin sections(post-embedding method) and alleviate the penetration problems. By using these techniques, it was possible to detect viral antigens in tobacco cells infected with potato virus X and cucumber mosaic virus. The protein A-gold method offers a wide potential for the study of plant viruses.

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Sero-diagnosis is a convenient and rapid method for the detection of plant viruses. The technique is actually employed for routine field inspection of virus diseases. Antiserum, prepared in animals such as rabbit, consists of polyclonal antibodies. A new technique for cloning a single mouse spleen cell, sensitized with individual antigenic determinant, has been established. Highly specific monoclonal antibodyies can be obtained. On the basis of recent immunological advances, it is suggested that the precise detection and quantitative analysis of soil micro-organisms in a complex environment can be achieved.

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Ecological studies on Rhizobium in soil were carried out by applying the buried slide method in using the fluorescent antibody technique. A Kasugamycin-resistant mutant strain of Rhizobium japonicum which displayed effective nodulation and nitrogen fixation was used as a marker strain. Antiserum against the mutant strain was obtained from rabbits given hypodermic injections of the heat treated cells of the strain as an antigen. Gamma-globulin from the antiserum was purified and was conjugated with a fluorescent pigment, FITC. The fluorescent antibody obtained was so specific that it reacted only with the homologous strain. Non-specific adsorption of the fluorescent antibody by soil particles seldom occurred and if it did, the fluorescent bacterial cells were easily distinguished, because the color of the soil particles rouged from yellow to dark-brown, whereas the fluorescence of the cells was green. Survival of the bacterial cells on the buried glass slides was highest in soil amended with nitrogen and became gradually lower in the following order: sterilized soil ≫ soil amended with phosphorus ≧ non-treated soil ≧ soil with low pH. The fluorescent antibody technique was very effective in the observation of Rhizobium japonicum added to soil.

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This report deals with a thorough review of the microorganisms capable of solubilizing insoluble mineral phosphates in soil by the production of organic acids. The importance of the presence or addition of a sufficient amount of available organic matter was emphasized for the activation of inoculated or native microorganisms to promote the solubilization of insoluble phosphates in soil. The importance of the following process was also underlined: most of the solubilized phosphates are incorporated into the soil microbial biomass in the presence of organic matter and plants utilize the available phosphates later released from the microbial biomass after its turnover. The practical use of phosphate-solubilizing organisms in agriculture is discussed.

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