Physiological and biochemical changes in lettuce seeds during storage at different temperatures

Dormancy in lettuce seeds is a process not yet fully understood. High storage temperatures can cause seed dormancy promoting physiological and enzymatic changes. The goal of this study was to investigate the influence of storage period and environments on the quality and dormancy of different lettuce cultivars. We also investigated the biochemical changes. A completely randomized experimental design was used in a 4x8x3 factorial arrangement to evaluate physiological quality on different storage periods (30, 60, 90 and 120 days) and environments (15, 25 and 35 degrees C) of seeds from eight lettuce cultivars (Everglades, Baba de Verao, Elisa, Luiza, Grand Rapids, Hortencia, Salinas 88 and Rubete). The biochemical activity was accessed by tetrazolium test and the activity of the endo-beta-mannanase. There occurred physiological and biochemical changes on lettuce seeds under periods and high temperature storage environments. A reduction of seed quality occurred at high storage temperatures mainly when stored during 120 days. The storage period up to six months maintains the viability and vigor of lettuce seeds, when stored at 15 degrees C. Germination is compromised when seeds are stored over 60 days on temperatures over 25 degrees C. Everglades is a tolerant cultivar to germination conditions of 35 degrees C and maintains its quality during storage at 15 degrees C. Temperatures over 25 degrees C induce thermodormancy on lettuce seeds during storage. The tetrazolium test indicates that the seeds were viable; nevertheless, there was no germination at high temperatures. Enzymatic changes occurred in seeds stored at 35 degrees C due to dormancy. There was a decrease in the expression of endo-beta-mannanase enzyme being influenced by the environment and storage period. The Everglades cultivar is thermotolerant.