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Title: DIFFERENTIAL AND DEVELOPMENTAL STAGE SELECTIVE TOXICITY OF A PENTAPEPTIDE DERIVATIVE TO SUNFLOWER DOWNY MILDEW PATHOGEN

Author
item OROS, G. - HUNGARIAN ACAD SCIENCE
item Nachman, Ronald

Submitted to: Scientific Bulletin of North University of Baia Mare
Publication Type: Other
Publication Acceptance Date: 5/1/2003
Publication Date: 5/23/2003
Citation: Oros, G., Nachman, R.J. 2003. Differential and developmental stage selective toxicity of a pentapeptide derivative to sunflower downy mildew pathogen. Scientific Bulletin of North University of Baia Mare. p. 401-406.

Interpretive Summary: The work presented here represents a spin-off of research on the development of new, selective control measures based on insect neuropeptides (short chains of amino acids), which serve as potent messengers in insects to regulate vital functions. A metabolically stable insect neuropeptide mimic ('PPD') that had previously been found to disrupt critical life processes in a pest insect that targets agricultural crops was tested against a microbial disease that infects crops. The results demonstrate significant antifungal activity against the downy mildew that targets the sunflower, an important agricultural crop. This antimicrobial activity exceeds the effectiveness of the traditional antibiotic streptomycin, and this activity is greatly magnified in the presence of copper ions. The antimicrobial activity of the PPD/copper ion combination exceeds that of each one alone. Copper ions (the 'Bordeaux mixture') have been used for over 100 years to control fungal disease in crops, and peptide agents such as PPD, or related to PPD, could greatly enhance their effectiveness, leading to lower levels of copper in the environment. This work leads us one step closer to the development of peptide-like substances that will be effective in controlling certain microbial diseases of crops in an environmentally friendly fashion.

Technical Abstract: The activity of 2-amino-7-fluorenyl-succinamoyl-FTPRL-NH2 (PPD) against sunflower downy mildew pathogen was investigated with special regard to host independent ontogenetic stages. The size of the cells as well as the presence and structure of the cell wall apparently influenced the performance of PPD activity as the fungus showed a marked developmental stage dependent response to it: the cell-walled zoosporangia were more tolerant (MIC>1 micron), while the smallest cytospores MIC values were 0.03 micron. The early stages of zoosporogenesis were inhibited suggesting that PPD permeates the cell wall of zoosporangia. Functions regulating plasmalemma semipermeability were less sensitive (MIC~ 1 micron) of zoospores to PPD and Cu2+ ions. Those cells reacted rapidly, as the first observable changes occurred within 5-10 seconds after contact with the compound asserting a target site in the cell membrane. The inhibitory effect was manifested at the nanomolar level, indicating a highly specific binding affinity to the target site and highlighting the importance of the inhibited function for normal operation of the cell membrane. The overall lesson of our experiment is that the combination of microchemical methods with micro-techniques in screening lead to valuable toxicological data on the membrane-function disturbing activity of synthetic peptide analogues.