Sweet corn (Zea mays L.) and tomato (Lycopersicon esculentum Mill.) seeds were aged naturally for 18 months or artificially aged using saturated salt accelerated aging to provide seed lots that differed in seed vigor, but retained a high standard germination percentage. Seed vigor was confirmed using standard vigor tests, including time to radicle emergence, cold, and accelerated aging tests. Ethylene evolution from both sweet corn and tomato seeds during germination was positively correlated with seed quality. Differences in ethylene evolution between nonaged and aged seeds were greater in seeds germinated on exogenous 1-aminocyclopropane-1-carboxylic acid (ACC). After 36 hours, there was about a 15-fold increase in ethylene evolution from seeds treated with 5 mm ACC compared to untreated seeds. Naturally and artificially aged seeds responded similarly and showed reduced ethylene production compared to nonaged seeds. In contrast to ethylene production, endogenous ACC titers were less for nonaged compared to aged seeds. Exogenous application of ACC to artificially aged seeds reduced the time to radicle protrusion, but did not completely reverse age-related effects on vigor. The data indicate that the reduced ability to produce ethylene in aged seeds was related to ACC oxidase (ACCO) synthesis or activity. Using Northern blot analysis, ACCO mRNA was detected after 48 hours of imbibition in nonaged seeds, but was undetectable in aged seeds affirming the contention that ACCO synthesis was delayed or reduced by aging. The current study provides additional support for ethylene as a biochemical indicator of seed vigor in seed lots with reduced vigor but high germination capacity.
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