Mode of action of 2,6-dichloro-4-nitroaniline in plant tissue cultures and A characterization of the ribosomes of the phycomycete Pythium debaryanum



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The effectiveness of 2,6 dichloro-4-nitroaniline as a general fungicide has been well established, and the use of this product to control both pre- and post-harvest rots of fruits and vegetables has become commonplace. Much research has been done to demonstrate the effectiveness of DCNA to control the activity of various pathogens, and a limited amount of work has been done to explore the mode of interaction between the fungicide and the metabolic systems of the pathogen being treated. Only limited reports have appeared concerning the effect of DCNA on the host organism. Part I of this thesis deals with the question of the effect of DCNA on higher plant systems. The results dramatically demonstrate the inhibitory effect DCNA has on development of both seedlings and callus tissues of Nicotiana tabacum grown in sterile cultures. The work reported here has been completed and the results published in the Journal Phytopathology (57, 1969). Several findings have indicated DCNA is interfering in some way with protein metabolism in the tissues. A natural continuation of this study is to isolate and establish a cell free protein synthesis system from N. tabacum and use this in vitro system as a tool in further exploring the effect of DCNA. Such an attempt was made, but considerable difficulty was experienced while trying to isolate a quantity of ribosomal material sufficient for use in the cell free system. The decision was made to obtain the ribosomes to be used in the study from another source only after much time and effort had gone into attempts to work with N. tabacum. The phycomycete, Pythium debaryanum was selected as the source of ribosomal material. Cultures were obtained from Dr. Stewart Lydia, Department of Plant Sciences, Texas A & M University. The choice of this organism was felt to be wise since the amount of work done on protein synthesis studies of phycomycetes is limited. Part II of the thesis reports the isolation, purification, chemical analysis, and physical description of the ribosomal particles obtained from P. debaryanum. The methods described outline a procedure of obtaining pure homogeneous preparations of the ribosomes to be later used in other studies.