Temperature-drop stress overlooked up to now in horticultural crop production - Importance of the leaf injury and the clarification of its mechanism

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(1) Three species of the Acanthaceae of 15 species of the Gesneriaceae were found as a sensitive plant to the temperature drop shock in this study.(2) The leaf injury occurred when the temperature dropped at the speed of 3℃/second or more. The shrinkage of epidermis caused by the rapid temperature drop was thought to be perceived as the external stimulus.(3) Wounding treatment to the plant body including the excision of a leaf or a shoot caused the injury similar to the leaf temperature drop shock at sites distant from the wound. It was guessed that wounding treatment and the leaf temperature drop shock caused the same reaction as a trigger of the injury.(4) Environmental factors such as temperature, light intensity and relative humidity affected the cell death caused by wounding treatment. Hypersensitive state was thought to be induced by the wound and the temperature drop to improve be sensitivity of the whole body to the external stimuli afterwards.(5) Hypersensitive state tended to be induced much more by water stress under the dry condition and the high temperature.(6) There was a diurnal change in the inducement of the hypersensitive state. The level of the inducement was low in the morning, rose in the afternoon, and was not induced at night. Then, it was suggested that overhead irrigation was recommended to conduct in the morning when needed.