Abstract
Willow (Salix spp.) seeds are able to tolerate desiccation, but differ from typical orthodox seeds in that they lose viability in a few days at room temperature, and in that the chloroplasts in embryo tissues do not dedifferentiate during maturation drying, thus retaining chlorophyll and maintaining intact their thylakoid membranes. In the present study, we investigated the damage generated in willow seeds during storage under appropriate conditions to exclude the eventual generation of reactive oxygen species by photooxidation. To this end, we measured different indicators of molecular damage, such as changes in the fatty acid profile, protein degradation, nuclease activities, and DNA damage, and evaluated normal germination and total germination in seeds stored for one, ten and sixteen years. We found: (i) a decrease in the fraction of unsaturated fatty acids; (ii) changes in the protein profile due to a decrease in protein solubility; (iii) activation of nucleases; and (iv) DNA fragmentation. Taken together, our findings identified programmed cell death as a key mechanism in seed deterioration during storage. We also found that, although the seeds maintained high percentages of total germination, the death program had already started in the seeds stored for ten years and was more advanced in those stored for sixteen years.
Highlights
Typical orthodox seeds, when stored, age and gradually lose their viability[1,2,3,4]
According to Shaban[12], autoxidation occurs in two steps: a first step related to the process of aging during the first time of storage, which includes spontaneous oxidation of unsaturated fatty acids and a second step in seeds that have lost their ability to germinate, which affects both saturated and unsaturated fatty acids
At an intermediate range of moisture (6–14%), lipid peroxidation reaches a minimum because water is enough to serve as a buffer against the free radical attack generated by autoxidation, but not to activate the oxygenases involved in free radical production
Summary
Typical orthodox seeds, when stored, age and gradually lose their viability[1,2,3,4]. ROS levels initially increase in several diffusion and production centers, generating a cascade through specific transduction sensors and inducing the expression of genes related to programmed cell death (PCD). In this respect, Hu et al.[7] detected ROS in elm seeds under controlled deterioration treatment and suggested that PCD plays an important role in seed deterioration. Modifications in molecules, including fatty acid peroxidation, protein oxidation, nuclease activation, and DNA damage, affect both membranes and organelles[3,5,6,8,9,10,11,12] Among these modifications, fatty acid peroxidation and glycation of proteins have been reported to be the main biochemical processes involved in the deterioration most frequently associated with seed aging[12,13,14]. Subcellular studies have shown that embryonic cells contain chloroplasts with well-developed grana www.nature.com/scientificreports/
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