AtNHX5 and AtNHX6, the endosomal Na+,K+/H+ antiporters in Arabidopsis, play an important role in plant growth and development. However, their function in K+ and pH homeostasis remains unclear. In this report, we characterized the function of AtNHX5 and AtNHX6 in K+ and H+ homeostasis in Arabidopsis. Using a yeast expression system, we found that AtNHX5 and AtNHX6 recovered tolerance to high K+ or salt. We further found that AtNHX5 and AtNHX6 functioned at high K+ at acidic pH while AtCHXs at low K+ under alkaline conditions. In addition, we showed that the nhx5 nhx6 double mutant contained less K+ and was sensitive to low K+ treatment. Overexpression of AtNHX5 or AtNHX6 gene in nhx5 nhx6 recovered root growth to the wild-type level. Three conserved acidic residues, D164, E188, and D193 in AtNHX5 and D165, E189, and D194 in AtNHX6, were essential for K+ homeostasis and plant growth. nhx5 nhx6 had a reduced vacuolar and cellular pH as measured with the fluorescent pH indicator BCECF or semimicroelectrode. We further show that AtNHX5 and AtNHX6 are localized to Golgi and TGN. Taken together, AtNHX5 and AtNHX6 play an important role in K+ and pH homeostasis in Arabidopsis. Three conserved acidic residues are essential for K+ transport.

Nitric oxide (NO) has emerged as a key molecule involved in many physiological events in plants. To characterize roles of NO in tolerance of tomato (Lycopersicom esculentum Mill.) to salt stress, the protective effects of NO against salt-induced oxidative stress in the leaves of tomato cultivar Hufan1480 (salt-tolerant) and Hufan2496 (salt-sensitive) were evaluated. Under salt stress, Hufan1480 showed higher biomass accumulation, and less oxidative damage when compared with the Hufan2496. Application of exogenous sodium nitroprusside, a NO donor, dramatically alleviated growth suppression induced by salt stress in two tomato ecotypes, reflected by decreased malondialdehyde and O 2 Á-production. Furthermore, the antioxidant enzymes superoxide dismutase, guaiacol peroxidase, catalase and ascorbate peroxidase, the antioxidant metabolites ascorbate and reduced glutathione, and the osmosis molecules proline and soluble sugar were increased in both ecotypes in the presence of NO under salt stress. Therefore, the protective effect of NO against salt-induced oxidative damages in tomato seedlings is most likely mediated through stimulation of antioxidant system.

Cytokinins were recently shown to control plant adaptation to environmental stresses. To characterize the roles of cytokinins in the tolerance of eggplant (Solanum melongena Mill.) to salt stress, the protective effects of 6-benzyladenine (6-BA) on the growth, photosynthesis, and antioxidant capacity in the leaves of two eggplant cultivars Huqie12 (salt-sensitive) and Huqie4 (salt-tolerant) were investigated. Under 90 mM NaCl stress, Huqie4 showed higher biomass accumulation and less oxidative damage compared to the Huqie12. Application of exogenous 10 μM 6-BA significantly alleviated the growth suppression caused by salt stress in two eggplant genotypes. In parallel with the growth, 6-BA application in salt-stressed plants resulted in enhanced chlorophyll contents, as well as photosynthetic parameters such as net CO2 assimilation rate (P n), stomatal conductance (g s), transpiration rate (E), and intercellular CO2 concentration (C i). Furthermore, exogenous 6-BA also significantly reduced the O2 (-) production rate and malondialdehyde content and markedly increased the antioxidant enzymes superoxide dismutase and peroxidase, the antioxidant metabolites ascorbate and reduced glutathione (GSH), and proline in both genotypes under salt stress. The results indicate that exogenous 6-BA is useful to improve the salt resistance of eggplant, which is most likely related to the increase in photosynthesis and antioxidant capacity.

No abstract

Background Anthocyanin synthesis is affected by many factors, among which temperature is an important environmental factor. Eggplant is usually exposed to high temperatures during the cultivation season in Shanghai, China. Therefore,RNA -seq analysis was used to determine the effects of high-temperature stress on gene expression in the anthocyanin biosynthetic pathway of eggplant ( Solanum melongena L.). Results We tested the heat-resistant cultivar ‘Tewangda’. The plants were incubated at 38 °C and 45 °C, and the suitable temperature for eggplant growth was used as a control. The treatment times were 3 h and 6 h. The skin of the eggplant was taken for transcriptome sequencing, qRT-PCR assays and bioinformatic analysis. The results showed that 770 genes were differentially expressed between different treatments. Gene Ontology (GO) database and Kyoto Encyclopedia of Genes and Genomes (KEGG) database analyses identified 16 genes related to anthocyanin biosynthesis, among which CHSB was upregulated. Other genes, including BHLH62, MYB380, CHI3, CHI, CCOAOMT, AN3, ACT-2, HST, 5MA-T1, CYP75A2, ANT17, RT, PAL2, and anthocyanin 5-aromatic acyltransferase were downregulated. In addition, the Myb family transcription factor PHL11 was upregulated in the CK 3 h vs 45 °C 3 h, CK 3 h vs 38 °C 3 h, and CK 6 h vs 38 °C 6 h comparisons, and the transcription factor bHLH35 was upregulated in the CK 3 h vs 38 °C 3 h and CK 6 h vs 38 °C 6 h comparisons. Conclusion These results indicated that high temperature will downregulate most of the genes in the anthocyanin biosynthetic pathway of eggplant. Our data have a reference value for the heat resistance mechanism of eggplant and can provide directions for molecular breeding of heat-resistant germplasm with anthocyanin content in eggplant. Electronic supplementary material The online version of this article (10.1186/s12870-019-1960-2) contains supplementary material, which is available to authorized users.