Hydrogen sulfide (H2S), is a crucial biological player in plants. Here, we primarily explored the interaction between sodium hydrosulfide (NaHS, a H2S donor) and the fluxes of Na+ and K+ from the salt glands of mangrove species Avicennia marina with non-invasive micro-test technology (NMT) and quantitative real-time PCR (qRT-PCR) approaches under salinity treatments. The results showed that under 400 mM NaCl treatment, the addition of 200 μM NaHS markedly increased the quantity of salt crystals in the adaxial epidermis of A. marina leaves, accompanied by an increase in the K+/Na+ ratio. Meanwhile, the endogenous content of H2S was dramatically elevated in this process. NMT result revealed that the Na+ efflux was increased from salt glands, while K+ efflux was decreased with NaHS application. On the contrary, the effects of NaHS were reversed by H2S scavenger hypotaurine (HT), and DL-propargylglycine (PAG), an inhibitor of cystathionine-γ-lyase (CES, a H2S synthase). Moreover, enzymic assay revealed that NaHS increased the activities of plasma membrane and tonoplast H+-ATPase. qRT-PCR analysis revealed that NaHS significantly increased the genes transcript levels of tonoplast Na+/H+ antiporter (NHX1), plasma membrane Na+/H+ antiporter (SOS1), plasma membrane H+-ATPase (AHA1), and tonoplast H+-ATPase subunit c (VHA-c1), while suppressed above-mentioned gene expressions by the application of HT and PAG. Overall, H2S promotes Na+ secretion from the salt glands of A. marina by up-regulating the plasma membrane and tonoplast Na+/H+ antiporter and H+-ATPase.

Background and aims Kandelia obovata, a dominant mangrove species in China, produces complex buttress roots and prop roots in intertidal wetlands where high quantities of nitric oxide (NO) are produced by reducing sediments. NO, a key signaling molecule, participates in an array of plant physiological and developmental processes. However, it is unclear whether NO functions in K. obovata root system establishment.Methods Here, we used a transcriptomic approach to investigate the potential role of NO in the regulation of K. obovata lateral root development and growth. Transcript pro les and bioinformatics analyses were used to characterize potential regulatory mechanisms.Results NO enhanced K. obovata lateral root development and growth in a dose-dependent manner. RNAseq analysis identified 1,593 differentially expressed genes (DEGs), of which 646 and 947 were up-and down-regulated in roots treated with NO donor. Functional annotation analysis demonstrated that the starch and sucrose pathway was signi cantly induced in response to NO. A suite of DEGs involved in hormone signal transduction and cell wall metabolism was also differentially regulated by NO. Taken together, our results suggest that a complex interaction between energy metabolism, multiple hormone signaling pathways, and cell wall biosynthesis is required for the NO regulation on lateral root development and growth in mangrove plant K. obovata.Conclusion NO appears to contribute to the formation of the unique root system of mangrove plants.

Avicennia marina, a mangrove plant growing in coastal wetland habitats, is frequently affected by tidal salinity. To understand its salinity tolerance, the seedlings of A. marina were treated with 0, 200, 400 and 600 mM NaCl. We found the whole plant dry weight, photosynthetic parameters increased at 200 mM NaCl but decreased over 400 mM NaCl. The maximum quantum yield of primary photochemistry (Fv/Fm) significantly decreased at 600 mM NaCl. Transmission electron microscopy observations showed high salinity caused the reduction in starch grain size, swelling of the thylakoids and separation of the granal stacks and even destruction of the envelope. In addition, the dense protoplasm and abundant mitochondria in the secretory and stalk cells, and abundant plasmodesmata between salt gland cells were observed in the salt glands of the adaxial epidermis. At all salinities, Na+ content was higher in leaves than in stems and roots, however, Na+ content increased in the roots while it remained constant level in the leaves over 400 mM NaCl treatment, due to salt secretion from the salt glands. As a result, salt crystals on the leaf adaxial surface increased with salinity. On the other hand, salt treatment increased Na+ and K+ efflux and decreased H+ efflux from the salt glands by the non-invasive micro-test technology, although Na+ efflux reached the maximum at 400 mM NaCl. Further RT-qPCR analysis indicated that the expression of Na+/H+ antiporter (SOS1 and NHX1), H+-ATPase (AHA1 and VHA-c1), K+ channel (AKT1, HAK5 and GORK) were up-regulated, only Na+ inward transporter (HKT1) was down-regulated in the salt glands enriched adaxial epidermis of the leaves under 400 mM NaCl treatment. In conclusion, salinity below 200 mM NaCl was beneficial to the growth of A. marina, and below 400 mM, the salt glands could excrete Na+ effectively, thus improving its salt tolerance.

Hydrogen sulfide (H 2 S) is considered to mediate plant growth and development.However, whether H 2 S regulates the adaptation of mangrove plant to intertidal flooding habitats is not well understood. In this study, sodium hydrosulfide (NaHS) was used as an H 2 S donor to investigate the effect of H 2 S on the responses of mangrove plant Avicennia marina to waterlogging. The results showed that 24-h waterlogging increased reactive oxygen species (ROS) and cell death in roots. Excessive mitochondrial ROS accumulation is highly oxidative and leads to mitochondrial structural and functional damage.However, the application of NaHS counteracted the oxidative damage caused by waterlogging. The mitochondrial ROS production was reduced by H 2 S through increasing the expressions of the alternative oxidase genes and increasing the proportion of alternative respiratory pathway in the total mitochondrial respiration. Secondly, H 2 S enhanced the capacity of the antioxidant system. Meanwhile, H 2 S induced Ca 2+ influx and activated the expression of intracellular Ca 2+ -sensing-related genes. In addition, the alleviating effect of H 2 S on waterlogging can be reversed by Ca 2+ chelator and Ca 2+ channel blockers. In conclusion, this study provides the first evidence to explain the role of H 2 S in waterlogging adaptation in mangrove plants from the mitochondrial aspect.

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