Graduate Thesis Or Dissertation
 

Relationship of "near-lethal" stress on dormancy, cold hardiness and recovery of Red-Osier dogwood

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  • The effects of overcoming rest by application of "near-lethal" (NL) stress treatments on the subsequent development of cold hardiness of stem tissues of red-osier dogwood, Comus sericea L., at different rest stages under three post-environments (0°, 23°, and natural condition) were studied. NL-heat stress (47°C for one hour) treatment during early (October) and late rest (December), overcame rest at 23°C post-environment. The treated plants broke bud within 22-35 days and 8-12 days, respectively. In contrast, the control treatments at early rest took more than 150 days to broke buds. Under natural post-environment conditions NL-heat stress treatment applied at the early and late stage of rest resulted in the same and 50-55 days earlier budbreak than control plants, respectively. Other type of NL-stresses e.g., NL-freeze stress (-7°C, for one hour), and NL-hydrogen cyanamide (0.5-1M), treatments at early rest and late rest also resulted in early (8-16 days) budbreak in a warm greenhouse. To determine the effect of overcoming rest by NL-stresses on cold hardiness, NL-heat and NL-hydrogen cyanamide stress applications at early rest had a slight effect on cold acclimation at 23°C and no effect on cold hardiness under natural condition. In contrast NL-freeze stress applied at early rest caused the plants to rapidly increase in cold hardiness at 23°C post-environment. At late rest, all NL- stress treatments resulted in the rapid loss of hardiness at warm or natural post-environment conditions. Recovery of plants from NL-stresses was dependent on the stage of development and temperature. Plants exposed to NL-heat stress recovered to a greater extent from October to December at 0°C post environment. All NL- heat-stressed plants recovered at 23° and natural post-environment conditions. Conditions that favored recovery also favored glutathione production. At 23°C post-environment, reduced (GSH) and oxidized (GSSG) glutathione levels of NL-heat stressed plants increased, while at 0°C post-environment the levels of both decreased. Studies on the heat tolerance of red-osier dogwood at different growth stages and its relationship to ethylene production, showed that heat tolerance of stem tissues was highest during the post-rest and early quiescent phases and lowest during the spring growth phase. Heat stressed stem tissues did not produce ethylene during early rest, maximum rest, late-rest and quiescence. Highest levels of ethylene occurred during active growth. Application of 1- aminocyclopropane-1-carboxylic acid (ACC), methionine and indole acetic acid (IAA) during rest stages, enhanced ethylene production in non-heat and heat stressed stem tissues.
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