Integration of Acquired Thermotolerance within the Developmental Program of Seed Reserve Mobilization
Abiotic stresses alter seedling metabolism from imbibition to seedling emergence resulting in stand establishment delays, poor stand quality, and often regional catastrophic crop losses. Temperature stress is the most universal of all the stresses associated with germination and stand establishment. The present study evaluated changes in acquired thermotolerance during the developmentally programmed mobilization of seed reserves for early seedling growth in cucumber (Cucumis sativus L.). To accomplish this, the development of a new protocol for evaluating thermotolerance was required because of limitations inherent in existing viability assays. The procedure developed for this study took advantage of the temperature sensitivity of chlorophyll synthesis and enabled the detection of cellular injury at temperatures 8 to 10°C below those identified for high temperature-induced injury by the standard triphenyltetrazolium chloride reduction test. Cellular injury at temperatures similar to those reported previously for cellular regrowth studies could be seen with the Chi accumulation test. Developmental changes in inherent and acquired thermotolerance following germination were identified using this protocol. An inherent resistance observed during the first days following planting was lost with increasing seedling age, and the range of temperatures responsible for the induction of acquired thermotolerance narrowed with age. Seedlings grown at different temperatures exhibited differences in the time required for the induction of acquired thermotolerance when exposed to 40°C. In summary, this study has identified developmental changes in the inducibility and magnitude of acquired thermotolerance in cucumber cotyledons through the use of a novel viability assay.
KeywordsChlorophyll Polyethylene Glycol Germinate Mannitol
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