| Concentrated rainfall,poor drainage and improper irrigation in orchard normaly resulted in waterlogging and followed by anoxia in soil.Then reducing substances such as hydrogen sulfide?H2S?would be accumulated.High H2S concentrations is toxic to plant,however,at low concentrations,H2S plays an important role in regulating the growth and development of plants and their adaptability to environmental stress as a signal molecule.As the base of fruit tree growth and development,the soil is also an important source of H2S production.However,the H2S production in different types of soils under non-waterlogging and waterlogging and H2S production in plant remains unknow.The role of H2S on physiology characteristics in plant is not completely understood.Explore those questions has a great significance in plant growth regulation and enhancing waterlogging resistance.In this research,the H2S production and the redox potential?Eh?were analyzed with different soil under non-waterlogging and waterlogging conditions.The endogenesis H2S production was also studied in Malus.hupehensis Rehd.var pingyiensis seedlings at the early growth stage.The effects of exogenous H2S on plant growth,root system architecture,photosynthesis,oxidation resistance,mitochondria function and root border cells were studied under waterlogging or Na Cl stress.Moreover,genes responding to waterlogging stress were screened in transcriptome level and the effects of exogenous H2S on regulation pattern of transcription factors were also conducted under waterlogging.Experimental results and conclusions were as follows:?1?Under non-flooding condition,H2S was detected in loam,sand and clay,and the highest level of H2S detected in loam,sand and clay was 2.85 ?mol?L-1?0.95 ?mol?L-1 and 4.14 ?mol?L-1,respectively.H2S mainly distributed in the upper and middle layers of soil and the distribution characteristic of H2S in soil within the depth showed a ‘zero-appear-increase-decrease' trend.Both the content of O2 and Eh in the three soils showed a continuous decreasing trend with in the depth,while clay decreased the most,followed by loam and sandy soil.The addition of organic fertilizer significantly increased the concentration of H2S in soil,while the addition of biochar reduced the concentration of H2S in soil.?2?The content of H2S in the 150-350 mm soil layer was significantly increased under waterlogging.Within 14 days of waterlogging,the content of H2S in soil was increased with the extension of the waterlogging time,however,increased slowly during the first 8 days of waterlogging.The Eh and O2 content both decreased with the extension of the waterlogging time and the depth of soil layer.The addition of organic fertilizer significantly increased the concentration of H2S in soil,while the addition of biochar reduced the concentration of H2S in soil under waterlogging.?3?In the cotyledon,the H2S content,D/L-cysteine desulfhydrase activity?Mh D/L-CDes?and gene expression of D/L-cysteine desulfhydrase?Mh D/L-CDes?were highest in the seedlings at the fourth day after emergence,and then gradually reduced to the lowest lever among the organs.The H2S content was highest at 16 d in the root,was highest at 20 d in the leaf,and was highest and maintained a relatively stable level in stem during the period from 16 to 20 d after seedling emergence.The period of high H2S content in root,stem and leaf was coinciding with the period of rapid growth of these organs.The Mh D/L-CDes activity and expression level of Mh D/L-CDes in each organ were basically consistent with the change trend of H2S content.External application of the H2S scavenger hypotaurine?HT?not only reduced the H2S content in various organs of seedlings but also significantly reduced the fresh weights of the root,stem,leaf and cotyledon as well as the length of the root and stem,thus exhibiting significant inhibition of seedling growth.The H2S content,Mh D/L-CDes activity and gene expression of Mh D/L-CDes in young leaves and aging leaves were both higher than in fully opened leaves,which indicated H2S is involved in the rapid growth and senescence of leaves.The H2S content,Mh D/L-CDes activity and gene expression of Mh D/L-CDes in different organs was significantly induced under waterlogging.?4?0.02-0.1 mmol?L-1 Na HS treatment improved root growth,fractal dimension and root vigor,alleviated root tip death caused by flooding stress.It was also found that Na HS increased the antioxidant enzyme activity,leaf photosynthetic rate?Pn?,water use efficiency?WUE?and apparent CO2 use efficiency?CUE?in leaves,and increaced seedling plant height and plant biomass.However,0.1 mmol?L-1 Na HS treatment showed a most significant effect.?5?The NO production in root and the soil of root zone were both promoted by waterlogging,and reached the highest lever at 6 d and 4 d after waterlooging,respectively,and then gradually decreased.The increased activity of nitric oxide synthase?NOS?and nitric acid reductase?NR?under waterlooging were both contributed to the production of NO in root and the soil of root zone.0.1 mmol?L-1 Na HS significantly increased NO production and NR activity both in root and the soil of root zone,compared to waterlogging treatment.However,0.1 mmol?L-1 Na HS had no effects on NOS activities,which indicated that Na HS promoted NO production in root and soil under waterlogging stress mainly through the NR pathway,and NR activity could be significantly induced by exogenous H2S under waterlogging.?6?The application of 0.02-0.1mmol·L-1Na HS rescued an Na Cl-induced inhibition on seeds germination and root elongation,induced the formation and survival rate of root border cells,and decreased H2O2 and MDA content under Na Cl stress.0.02-0.1mmol·L-1Na HS also enhanced superoxide dismutase?SOD?,guaiacol peroxidase?POD?,and catalase?CAT?activities in the mitochondria compared to Na Cl treatment alone.It was also found that 0.05 m M Na HS significantly decreased the mitochondrial permeability transition pore and increased mitochondrial membrane fluidity,mitochondrial membrane potential???m?,and cytochrome c/a?Cyt c/a?ratio under Na Cl stress.However,0.05 mmol?L-1 Na HS treatment showed a most significant,while 0.2 mmol?L-1 Na HS enhanced the damage on root growth and mitochondrial function under Na Cl stress.Moreover,15 ?mol?L-1 HT eliminated the beneficial effects of Na HS on root growth and mitochondrial function under Na Cl stress.?7?Transcriptome sequencing was performed on the the roots of Malus hupehensis Rehd.under waterlogging.A total of 14.68 Gb clean data was obtained,and 156,353 unigenes were de novo assembled.A total of 20,398 unigenes were annotated into 131 KEGG metabolic pathways.A total of 34,011 differentially expressed genes?DEGs?were obtained by sequencing,and 12,952 genes were up-regulated.The DEGs was classified by GO enrichment analysis into 20 biological processes,20 cell components and 5 molecular functions.DEGs involved in biological processes was enriched in oxidation-reduction process,involved in cell components was mainly enriched in the process of transcription factor complex,and involved in molecular function was mainly enriched in heme process.In oxidoreductase activity activity?GO:0016491?,370 genes were up-regulated and 432 genes were down-regulated.In oxidation-reduction process process?GO:0055114?,295 genes were up-regulated and 396 genes were down-regulated.The KEGG analysis showed that 10,840 DEGs were enriched in 124 metabolic pathways.The most significant enrichment pathway was plant hormone signal transduction and 272 DEGs were involved.18 DEGs were up-regulated and 11 DEGs were down-regulated in ethylene mediated waterlogging resistance metabolic pathway.?8?5203 transcription factors?TFs?belonging to 82 TF families were identified and in young roots by sequencing.Among these genes,807 TFs belonging to 62 TF families expressed differentially under waterlogging,308 were up-regulated and 499 were down-regulated.In all TF families,MYB had the largest numer of significantly differentially expressed transcription factors,followed by AP2-EREBP?GRAS?C2H2?b HLH?NAC?Orphans?b ZIPfamily.4 MYB transcription factors,4 NAC transcription factors and 5 b ZIP transcription factors which significantly up-regulated under waterlogging stress were selected by constructing the phylogenetic trees with MYB,NAC and b ZIP in Arabidopsis thaliana,respectively.q RT-PCR results showed that,when treated with 0.1 mmol?L-1 Na HS the expression of 3 MYB transcription factors,3 NAC transcription factors and 4 b ZIP transcription factors were increased under waterlogging. |
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