Protease Inhibitors and Reproduction of Reniform Nematode in Pineapple

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2002

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University of Hawaii at Manoa

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Protease inhibitors (PI) are thought to serve as defense compounds against pathogen attack in many plant systems. PIs have been found in pineapple roots, and populations of Rotylenchulus reniformis remain untypically low for 6-9 months after pineapple planting. A potted plant experiment was conducted to determine if PIs present in pineapple roots affected nematode reproduction and could account for the observed field population dynamics. Pineapple plants with and without R. reniformis were harvested monthly. Roots were removed from the plant, weighed, shaken in NaOCI to determine number of nematode eggs, then cut into 1 cm pieces. Roots were homogenized in EDTA/phosphate buffer at pH 6.0 to extract PIs. An aliquot of the root extract was added to purified papain and colorimetric protein substrate, and inhibition activity determined. Pineapple PI activity increased for the first 6 months after planting (in both inoculated and not inoculated treatments), and was higher in nematode inoculated plants. Nematode reproduction (egg numbers) was not correlated to PI activity. A second potted plant experiment was conducted to determine if PI levels in pineapple roots varied along root length in the presence and absence of nematodes. PI activity increased in the presence of nematodes and this increase was concentrated in the basal portion of the roots where nematode densities were highest. These results support a defensive role for PI in pineapple roots. More work is necessary to elucidate the role of pineapple PIs in nematode population regulation.

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