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

Abstract

The rat’s tail radish ( Raphanus sativus cv. “Pakki-hood”), cultivated in the northern part of Thailand, does not require low temperature for flower-bud initiation and shows high germinability even at low temperature. To analyze its characteristic temperature response, seedlings were subjected to a 3 day-chilling treatment at 0°C after a series of incubations for germination at 26°C which ranged from 3 h to 4 days. The chilling treatment after an initial stage (3 h to less than 2 days) of incubation at 26°C did not significantly affect the hypocotyl regrowth, but the same treatment after a more than 2-day incubation at 26°C reduced subsequent hypocotyl growth of plants. 1-aminocyclopropane-1-carboxylic acid (ACC)-dependent ethylene-forming activity was also reduced by the chilling treatment after 2–4-day incubation at 26°C. Electrolyte leakage from tissues of seedlings in the chilling treatment was increased in proportion to the length of the incubation at 26°C, indicating severe damage of chilling 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 transition are relatively unaffected in their subsequent growth, but the seedlings become sensitive to chilling after the transition.