In the previous paper
8, 9), it was shown that the excitement of metabolism in blight-resistant potato tuber tissue, when infected by
P. infestans, is inhibited by the pre-infectional ethanol narcosis, resulting in a reduction of the plant's resistance to
P. infestans. Further studies on this point are reported in the present paper.
The cut surface of halves, or slices of tuber 0.45mm thick were treated with 10% ethanol for 10min., and then washed in running water for some time.
From one to four hours after treatment, the rate of O
2-uptake was found to be lowered slightly (about 8%). About 20hrs. after treatment, the rate of O
2-uptake in the non-anaesthetized tissue was accelerated remarkably, but in the ethanol treated tissue, such a remarkable increase in O
2-uptake was not observed. So it seems to indicate that the ethanol narcosis strongly inhibits the mechanism of the acceleration of respiration induced by injury in handling. Polyphenol oxidase activity of expressed sap from ethanol-anaesthetized tissue is lower than that from non-anaesthetized tissue. The inhibitory activity of polyphenol oxidase is proportional to the O
2-uptake. This coincidence seems to show that polyphenol oxidase plays a part in the respiratory enzyme system of potato tuber slice. Twenty-four hours after treatment, the extracted juice from ethanol-treated tissue showed lower pH and a greater amount of succinic and oxalic acids than that from non-treated one. It is possible that the increase in oxalic acid content is due to the conversion of ethanol to oxalic acid via acetic, succinic, fumaric, malic acids, etc., but the fact that the respiratory rate is lowered in spite of the increase in organic acid content, may be explained by the inhibition of dehydrogenase activity.
The above described facts lead the writers to the conclusion that the ethanol inhibits the respiratory enzyme system and lowers the metabolic activity, with the simultaneous conversion of itself to organic acids through oxidation. The period for which the ethanol could be detected by means of Davy and Agulhon reaction in the extracted juice after treatment was about 2 days under the condition pertaining to the present experiments.
The period for which the ethanol reaction was recognized in ethanol-treated tissue, was in coincidence with the period for which the resistance of tuber tissue to the infection of
P. infestans was kept lowered. When the ethanol treatment was repeated 2 days after initial treatment, the appearance of necrotic brown spots was more delayed.
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