Systemic Acquired Resistance And Hypersensitive Response Induced By 90 KD Elicitor Protein From Phytophthora

Bioactivity and stability of purified 90 kD extracellular elicitor protein from Phytophthora boehmeriae and induction of hypersensitive response (HR) and systemic acquired resistance (SAR) by the elicitor were studied. And the role of two molecular signals, salicylic acid (SA) and hydrogen peroxide (H2O2) in HR and SAR and relationship between SA and hydrogen peroxid during plant-elicitor interactions were studied.Bioactivity and stability of 90 kD extracellular elicitor protein were studied. The elicitor could induced HR on tobacco leaves at different doses ranging from 0.5 nmol/L to 100 nmol/L but not at 100 pmol/L, which indicated that the minimal efficient dosage of inducing HR on tobacco was between 100 pmol/L and 0.5 nmol/L. The elicitor could also induce HR on other cultivars of Nicotiana tobaccum but not on other Solanaceae (eggplant and pepper) or on cotton (Gossypium arborewri), which suggested that this 90 kD elicitor was host-specific. When the 90 kD elicitor was infiltrated into the tobacco leaves, it could induce the systemic acquired resistance (10%-68%) to Phytophthora nicotianae that was inoculated on the tobacco stem. The highest level of induced resistance was acquired when tobacco stems were inoculated immediately. After its leaves being treated with elicitor at different pH (pH2-pH14) for 30 minutes or at different temperature (4癈, 25癈, 60癈, 100 癈) for 5 minutes, the elicitor could maintain its activity of inducing HR. However, the treatment with proteinase K could cause the loss of its ability of inducing HR in tobacco. Results showed that the elicitor was not sensitive to acid, alkali or temperature, but wassensitive to proteinase K.SAR to TMV, Pseudomonas syringe pv. tabacci and Alternaria alternata in tobacco elicited by 90 kD extracellular elicitor protein, a HR elicitor on tobacco leaves was studied. Inoculation of TMV at 24 h after infiltration of tobacco leaves (cv. Samsun harboring N gene) with the elicitor at dosage of 10 nmol/L, resulted in fewer and smaller visible necrotic lesions on treated leaves than that on buffer-infiltrated ones. Fewer lesions were also observed on the 1 st and 2nd upper or lower leaves of the elicitor-treated leaf on the sameplant when TMV was inoculated, but the average diameter of necrotic lesion did not significantly differ from that of the control leaves. The reduction rates in lesion number were about 40.9%~53.1% and the induced resistance lasted for about seven days. All the dosages ranging from 0.5 to 100 nmol/L tested could trigger the resistance significantly and the resistance level (34.9%~58.2%) was positively correlated with the dosages used. Whereas, the elicitor only provided low level of induced resistance to TMV (4%) when the treated leaves were inoculated immediately or at seven day after elicitor applied. Similar induced resistance by elicitor protein against P. syringae pv. (abaci and A. alternata was also found in this study. When inoculation with P. syringae pv. (abaci or A. alternata performed on tobacco plants (cv. W38) at 48 h after elicitor treatment, smaller or fewer lesions which significantly differed from the control were observed on treated leaves and their upper and lower non-elicitor-treated leaves. Results showed that the induced resistance of tobacco by 90 kD extracellular elicitor protein from P. boehmeriae was typically a SAR characterized by systemicity, durability and a broad-spectrum, which indicated the 90 kD protein elicitor is a kind of natural specific trigger for SAR. Results also indicated an endogenous mobile signaling mechanism be elicited and functioned between treated leaves and their upper or lower non-elicitor-treated ones, where it induced strong responses without HR.Induction of hypersensitive cell death, changes of phenylalanine ammonia-lyase (PAL) activity and activation of PR5 (osmotin) in tobacco by 90 kD extracellular elicitor protein was studied. At 24 hours after infiltration into tobacco (cv. W38) leaves at dosage of 10 nmol/L, a bright blue autofluorescence became visible und...