The Molecular Mechanism of Seed Deterioration in Relation to the Accumulation of Protein—Acetaldehyde Adducts

Abstract

Many dry seeds evolve various volatile compounds during storage, of which carbonyl compounds, especially acetaldehyde (Aid), are the most active in causing their deterioration. Although the longevity of seeds is generally prolonged with decreasing RH during storage, the contents of Aid were higher at 44% RH than at 75% RH in short-lived seeds, such as lettuce and cocklebur, compared with long-lived pea seeds. The production and accumulation of Aid in seeds occurred even at -3.5 degrees C, in which the operation of mitochondrial respiration was undetectable but seed vigour was gradually lost. In cocklebur, Aid was contained in both axial and cotyledonary tissues, which content increased as the storage period was prolonged, and the loss of seed vigour occurred in both tissues. Moreover, the contents of proteins soluble in phosphate-buffered saline (PBS, pH 7.4) declined as their viabilities were lost. Thus, we presumed that the endogenously accumulated Aid in the seeds may cause seed ageing by deteriorating seed proteins. Hence, a sensitive competitive ELISA method, which was improved by us, was used for the quantification of endogenous Aid-protein adducts (APA) in dry seeds. As a result, the seeds treated with exogenous Aid rapidly lost their viabilities with increasing RH, accompanied by the accumulation of APAs. However, this adduct was detected even in the PBS-insoluble but urea-soluble proteins from lettuce seeds exposed to Aid, and in naturally aged seeds of lettuce and cocklebur that had been stored at low RHs. Thus, the modification of functional proteins in seeds by Aid seems to be the most important primary trigger of seed deterioration under dry storage conditions.