Studies On The Cytology Of Pathogenic Mechanism Of LA-Toxin

Lecanosticta acicola was the main fungi that affected the growth of slash pine (Pinus elliottii var. Engelm) planted widely in South China, and it had stunted the development of slash pine. Previous research showed that the LA-toxin produced from the pathogen mainly caused the disease. In order to study its pathogenic mechanism and host resistant mechanism above cell level, the author built the interactive system between LA-toxin and slash pine suspension cell, studied the host cell shape, cell vigor during interactive procedure, and the metabolizability of active oxygen and propane benzene, and their relation during interactive process. The main research results are shown below:The host pines were inoculated with the toxin coarse extractions at different concentration levels by acupuncture-bioassay, including 2-month slash pine(P. elliottii) , torch pine(P. taeda), so-mao pine(P. kesiyd) and 1-year slash pine. Results showed that typical symptoms of disease were found on slash pine and torch pine leaves, so-mao pine and 1-year slash pine leaves were not sensitive to the toxin. The the ordinary susceptible and resistant families of slash pine treated by low concentration toxin showed different resistant and infection behavior.Cell-suspension of ordinary susceptible (C*) and resistant (32* and 34*) slash pine families were successfully built up by using good loose calli, which were induced by axenic-caudex explants raised from slash pine seeds. These suspension cells, including susceptible family and resistant families, were affected by different concentration LA-toxin. The statistical result of cell death indicated that the LA-toxin from 1/20 Co to 1/2 Co affected the cell vigor, cell death ratio increased according to concentration increase, which were higher than that of control specimens when toxin concentration increased and treatment period extended. In general cell death ratio of infection stirps were higher than that of resistant stirps. At the same condition, the cell death ratio of the resistant families was lower than that of the susceptible family. Optical microscopic observation showed that the cells of resistant and susceptible families were affected by LA-toxin in certain level when the toxin treatment time rose, for example, separation of cytoplasm and cellular, shrinkage of bioplasm, faintness of nucleus, reduction of inclusion, and rupture of cell with inclusion leak, while the shape of cell of control specimen were full and nucleus was clear.The physiological and biochemical change of host during initial interaction phase between LA-toxin and suspension cell were studied by using suspension cell within logarithmic growth phase. Results showed that no matter compatible interaction or not, LA-toxin excited increasmentof the membrane lipid peroxidation MDA production in host cells, the content of MDA in compatible interaction increased much, but accumulated slower than that in incompatible interaction, which meaned that LA-toxin destroyed the membrane of slash pine suspension cell, and caused the accumulation of peroxidation. After LA-toxin inoculation, the activities of SOD and CAT were repressed, and the activities of POD and PAL rose in compatible interaction. For compatible combination, the enzyme activity of SOD and CAT were restrained , but the enzyme activity of POD and PAL increased, and were larger than those of compatible. The enzyme activity changes of POD and PAL obviously showed they were comblined with host resistance.