Abstract:More effective means are needed for early diagnosis and quantitative evaluation of plant injury caused by various stresses. Measuring of tissue electrical resistance has been used in the research of SO2 injury recently and satisfactory results has been obtained. The present paper describes the change of tissue electrical resistance in connection with the response of plants to high temperature. Wheat and tobacco leaves were tranted with different high temperatures (30–60℃). Electrical resistance was measured during and after the treatment by means of Zhu’s newly improved method of the determination of the mid-region voltake drop on passing a stable electric current through the leaf tissue. Experimental results showed that electrical resistance changed regularly with the increase of temperature. At the range of nninjurious temperature, tissue electrical resistance kept the same level as control. Around the subinjurious temperature, electrical resistance increased remarkably and could be gradually restored after the cease of treatment. At injurious temperatures, tissue electrical resistance rised at first, and then declined. The higher the temperature, the earlier and quicker the decline, and finally it reached the lowest level showing the death of the tissue. If leaves were taken back to ordinary temperature at the rising stage or just the beginning of decrease, they could recover, in general, in their electrical resistance. They conld not recover after a substantial drop of electrical resistance, showing the oeeurence of irreversible injnry. Therefore the changes of tissue electrical resistance reflected to a certain degree the extent of heat injury. Ion leakage and ethane production were also measured parallelly. As for reflection of the extent of heat injury, changes of tissue electrical resistance is more sensitive than both ion leakage and ethane produetlon. The rise of tissue electrical resistance at thc earlier stage of heat treatment is discussed in connection with the changes of the two constituents of tissue electrical resistance-membrane resistance and apoplast resistance.