A chilling-insensitive stage in germination of a low-temperature-adapted radish, rat's tail radish (Raphanus sativus L.) cv. "Pakki-hood"

The rat's tail radish (Raphanus sativus cv. "Pakki-hood"), cultivated in th e northern part of Thailand, does not require low temperature for flower-bu d initiation and shows high germinability even at low temperature. To analy ze its characteristic temperature response, seedlings were subjected to a 3 day-chilling treatment at 0 degreesC after a series of incubations for ger mination at 26 degreesC which ranged from 3 h to 4 days. The chilling treat ment after an initial stage (3 h to less than 2 days) Of incubation at 26 d egreesC did not significantly affect the hypocotyl regrowth, but the same t reatment after a more than 2-day incubation at 26 degreesC reduced subseque nt hypocotyl. growth of plants. 1-aminocyclopropane-1-carboxylic acid (ACC) -dependent ethylene-forming activity was also reduced by the chilling treat ment after 2-4-day incubation at 26 degreesC. Electrolyte leakage from tiss ues of seedlings in the chilling treatment was increased in proportion to t he length of the incubation at 26 degreesC, indicating severe damage of chi lling to plasma membranes after a longer incubation. We found a transition of chilling-sensitivity at 2 days in the incubation period for germinating seeds of Pakki-hood. Seedlings of Pakki-hood chilled earlier than the trans ition are relatively unaffected in their subsequent growth, but the seedlin gs become sensitive to chilling after the transition. (C) 2001 Elsevier Sci ence B.V. All rights reserved.