Abstract
Hydrogen sulfide (H2S) is a novel type signaling molecule in plants. Seed germination is a key stage of life cycle of plants, which is vulnerable to environmental stress including high temperature. However, under high temperature stress, whether pre-soaking of maize seeds with NaHS (a H2S donor) could improve seed germination and seedling growth and the possible mechanisms are not completely clear. In this study, maize seeds pre-soaked with NaHS enhanced germination percentage, sprout length, root length, and fresh weight compared with the control without NaHS treatment, illustrating that H2S could improve maize seed germination and seedling growth under high temperature. In addition, in comparison to the control, NaHS pre-soaking stimulated antioxidant enzymes [ascorbate peroxidase (APX), glutathione reductase (GR), guaiacol peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT)] activities and the contents of water soluble non-enzymatic antioxidants [ascorbic acid (AsA) and glutathione (GSH)], as well as the ratio of reduced antioxidant to oxidized antioxidant. Moreover, pre-soaking with NaHS activated Δ1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase [OAT; both are rate-limiting enzymes in proline (Pro) synthesis], betaine aldehyde dehydrogenase [BADH; a key enzyme in glycine betaine (GB)], and trehalose (Tre)-6-phosphate phosphatase (a key step in Tre synthesis), which in turn accumulated Pro, GB, and Tre in germinating seeds compared with the control. Also, an improved germination by NaHS under high temperature was reinforced by the above osmotic adjustment substances (osmolytes) alone, while deteriorated by the inhibitors of osmolyte biosynthesis [gabaculine (GAB), disulfiram (DSF), and sodium citrate (SC)]. These results imply that H2S could improve maize seed germination and seedling growth under high temperature by inducing antioxidant system and osmolyte biosynthesis.
Highlights
For a long time, hydrogen sulfide (H2S) is viewed as a toxic gaseous molecule due to its strong affinity to heme-containing proteins, such as cytochrome oxidase, globin, and hemoglobin (Hancock and Whiteman, 2016; Li et al, 2016; Hancock, 2017)
In order to explore the effect of pre-soaking of maize seeds with NaHS on seed germination and seedling growth under high temperature stress at 39 ◦C, the germination percentage, sprout length, and root length were determined
Pre-soaking of maize seeds with NaHS stimulated the activities of pyrroline5-carboxylate synthetase (P5CS) and ornithine aminotransferase (OAT), which in turn elevated the content of endogenous Pro in germinating seeds, follow by increasing the germination percentage and ameliorated seedling growth under high temperature stress (Figure 5). These effects were enhanced by exogenous Pro under high temperature stress, while weakened by the addition of GAB (Figure 6), a specific inhibitor of OAT, which is a rate-limiting enzyme in Pro biosynthesis in plants (Yang et al, 2009; Kaur and Asthir, 2015). These results suggest that pre-soaking of maize seeds with NaHS could improve seed germination and seedling growth under high temperature stress by stimulating Pro biosynthesis enzymes and accumulating endogenous Pro
Summary
Hydrogen sulfide (H2S) is viewed as a toxic gaseous molecule due to its strong affinity to heme-containing proteins, such as cytochrome oxidase, globin, and hemoglobin (Hancock and Whiteman, 2016; Li et al, 2016; Hancock, 2017). In the last few years, H2S as signaling molecule has been much more attention in plant biology, from seed germination, plant growth and development to the response, and adaptation of plants to abiotic and biotic stress (Zhang et al, 2009; Li et al, 2012, 2014c, 2015; Lin et al, 2012; Christou et al, 2013, 2014; Fang et al, 2014; Li and He, 2015; Ma et al, 2015; Huo et al, 2018). It was found that pre-soaking of maize seed with H2S could alleviate a decrease in germination rate under high temperature stress (Li et al, 2013a).
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