Abstract: A 10.6 kD heat resistant, proteinacious elicitor was purified from the culture filtrate of Phytophthora palmivora Butler but not from P. melonis Katsura. The 10.6 kD elicitor is a holoprotein devoid of glycoside. It can cause hypersensitive necrosis of the detached tobacco ( Nicotiatna tabacum L. ) leaves 48 h post-inoculation with dosages of above 40 μg. Four cell types were investigated by using Confocal microscopy, and 2' ,7'-dichlorodihydrofluorescein diacetate (DCFDA) as a probe of H2O2 production. It was showed that oxidative burst occurred in cultured suspension cells as well as in mesophyll cells, epidermal cells and guard cells within 10 min upon the elicitor treatment. The hypersensitive cell death appeared 6 h after the treatment when inoculated with fluorescein diacetate (FDA) as indicator of cell viability. These results suggest that H2O2 accumulation was the main cause of the hypersensitive cell death in tobacco induced by the 10.6 kD elicitor. This 10.6 kD elicitor may belong to the family of elicitins.

Key words: Phytophthora palmivora, Elicitin, Elicitor, Oxidative burst, Hypersensitive response, Tobacco