Abstract
Norway maple (Acer platanoides L.) and sycamore (A. pseudoplatanus L.) are genetically closely related species that produce desiccation-tolerant (orthodox) and desiccation-sensitive (recalcitrant) seeds, respectively. Norway maple and sycamore seeds were analyzed during their development from the 14th to 24th weeks after flowering (WAF) and 11th to 21st WAF, respectively, to explore redox-related biochemical properties related to their contrasting physiology. Selected similar stages of seed development were characterized during the course of gradual decreasing water content in both seed types. The levels of protein and non-protein thiols peaked at the 18th WAF in Norway maple embryonic axes, whereas these levels constantly increased in maturing sycamore seeds. The glutathione half-cell reduction potential revealed that the cell environment adopted a more oxidized state in sycamore seeds. Peroxiredoxins (Prxs), including cytosolic/nuclear 1-Cys-Prx, cytosolic PrxIIC, mitochondrial PrxIIE, and plastidic PrxIIF, 2-Cys-Prx, and PrxQ, were detected in both species, but Norway maple embryonic axes contained higher levels of PrxIIC and PrxIIE, two Prxs with the highest peroxide detoxification potential in Arabidopsis. Redox proteomics revealed that 2-Cys-Prx was present in reduced form in both species, whereas 1-Cys-Prx was reduced uniquely in Norway maple seeds. Several enzymes, including glucose and ribitol dehydrogenase as well as fructose-bisphosphate aldolase, were oxidation-sensitive at all developmental stages in sycamore embryonic axes. Redox signaling as manifested by reactive oxygen species signals, and the oxidation of protein thiols to disulfides are discussed with respect to their significance in determining orthodox or recalcitrant seed characteristics.
Highlights
Seed development proceeds in two steps, morphogenesis and subsequent maturation
Norway maple and sycamore seeds were analyzed during their development from 14th to 24th weeks after flowering (WAF) and 11th to 21st WAF, respectively, to establish which biochemical properties might be related to their distinct physiology seeds contained constant H2O2 levels up to 15th WAF (Fig. 3)
Protein Thiol Levels and Glutathione Half‐Cell Reduction Potential given that Norway maple seeds are resistant to desiccation, whereas sycamore seeds are sensitive to desiccation
Summary
Regulation of the redox state of proteins can be modulated by ROS levels controlled by antioxidant enzymes; redox input elements, such as glutathione; redox transmitters, such as thioredoxins (Trxs) and glutaredoxins (Grxs); and redox sensors, such as Prxs (Dietz 2011; Foyer and Noctor 2011; Hanschmann et al 2013; Cejudo et al 2014; Gütle et al 2017). Redox processes are thought to participate in metabolic regulation in maturing seeds and may participate in the establishment of desiccation tolerance (De Gara et al 2003; Colville and Kranner 2010)
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