Abstract
Carbonylation of proteins associated with a stress response may contribute to the lowered viability of naturally aged beech seeds, especially the desiccation tolerance-associated proteins and USP-like protein. Proteins are modified by a large number of reactions that involve reactive oxygen species-mediated oxidation. The direct oxidation of amino acids produces 2,4-dinitrophenylhydrazine-detectable protein products. Carbonylation is irreversible, and carbonylated proteins are marked for proteolysis or can escape degradation and form high molecular weight aggregates, which accumulate with age. Beech (Fagus sylvatica L.) seeds stored under optimal conditions for different periods of time, ranging from 2 to 13 years, were analyzed. Protein carbonylation was examined as a potential cause for the loss of viability of beech seeds, and the characteristic spots of protein carbonyls were identified. Here, we present and discuss the role of carbonylation in the proteome of beech seeds that contribute to the loss of seed viability during natural aging. The long-term storage of beech seeds is intricate because their germination capacity decreases with age and is negatively correlated with the level of protein carbonyls that accumulate in the seeds. We establish that protein synthesis, folding and degradation are the most affected biochemical traits in long-term stored beech seeds. In addition, we suggest that proteins associated with the stress response may have contributed to the lowered viability of beech seeds, especially the desiccation tolerance-associated proteins that include T-complex protein 1 and the universal stress protein (USP)-like protein, which is identified as carbonylated for first time here.
Highlights
Carbonylation is a chemical reaction that produces organic carbonyl compounds containing the C=O functional group such as aldehydes and ketones
It can be hypothesized that beech seeds are unable to germinate after long-term storage due to loss of desiccation tolerance and effects on the processes of protein synthesis and native conformation preservation
The proteins associated with response to stress, such as dehydrin, universal stress protein (USP), TCP1, RAD23-3, and 14-3-3, might be possible candidates that after carbonylation may decrease the chances of seeds to cope with the stresses associated with natural aging and the environmental stresses that can occur during dormancy release and germination
Summary
Carbonylation is a chemical reaction that produces organic carbonyl compounds containing the C=O functional group such as aldehydes and ketones. The reaction involves several steps and is due to oxidative stress (Grune et al 2013). Carbonyl derivatives are produced directly in protein side chains as a result of amino acid oxidation (primarily Pro, Arg, Lys, and Thr) and by protein fragmentation, and protein aggregation and indirectly by lipid peroxidation (Dalle-Donne et al 2003; Møller et al 2011; Grune et al 2013). The main cause of protein carbonyl generation is reactive oxygen species (ROS) action. ROS react directly either with the protein or with sugars and lipids, which generate reactive carbonyl species (RCS) that react with proteins (Grune et al 2013). Carbonylated proteins are subjected to proteasome-dependent degradation or form aggregates
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