Search

Leymus chinensis is the most promising grass species for salt-alkaline grassland restoration in northern China. However, little information exists concerning the role of arbuscular mycorrhizal (AM) symbiosis in the adaptation of seedlings to salt-alkali stress, particularly under increased nitrogen deposition, which has become a major environmental problem throughout the world. In this study, Leymus chinensis seedlings were cultivated in soil with 0, 100 and 200 mM NaCl/NaHCO 3 under two forms of nitrogen (10 mM NH 4 NO 3 or NH 4 Cl: NH 4 NO 3 = 3:1), and the root colonization, growth and photosynthetic characteristics of the seedlings were measured. The results showed that the colonization rate and intensity decreased with increasing salt-alkali stress and were much lower under alkali stress. The nitrogen treatments also decreased the colonization, particularly under the NH 4 + -N treatment. Compared with the non-mycorrhizal controls, mycorrhizal seedlings generally presented higher plant biomass, photosynthetic parameters and contents of photosynthetic pigments under stresses, and the inhibitive effects of alkali stress were substantially stronger. In addition, both nitrogen forms decreased the physiological indexes compared with those of the AM seedlings. Our results suggest that salt stress and alkali stress are significantly different and that the salt-alkali tolerance of Leymus chinensis seedlings could be enhanced by associations with arbuscular mycorrhizal fungi, in which would yield better plant growth and photosynthesis. Excessive nitrogen in the soil affects mycorrhizal colonization and thereby inhibits the growth and photosynthetic ability of the seedlings. [ABSTRACT FROM AUTHOR]

The effects of the seed maturation time on salt-alkali tolerance during the germination stage and seedling establishment at different burial depths were determined for the seeds of Leymus chinensis , a species that is considered to be the most promising grass species for grassland rehabilitation in northeastern China. Seeds were collected at different maturation times (24 d, 29 d, 34 d and 39 d after peak anthesis) and germinated under salt stress (NaCl: 50, 100, 200 and 400 mM), alkali stress (Na 2 CO 3 : 25, 50, 100 and 200 mM), and also at different burial depths (1-cm, 2 cm and 3 cm). The results showed that the highest germination and recovery percentages in Leymus chinensis were observed for seeds that matured at 39 d after peak anthesis under both salt and alkali stresses, but the lowest percentage was recorded in seeds that matured at 24 d. In addition, the deeper the seeds in the soil, the lower and slower the germination and seedling emergence. A 1-cm depth is optimum for planting the seeds of this species. Moreover, the seeds that matured at 39 d after peak anthesis also showed the strongest vigor at all burial depths. The above results suggest that although these seeds have the ability to germinate at different maturation times, the seeds that matured at 39 d after peak anthesis have the strongest capacity to establish seedlings and resist salt-alkali stress. Our results will help to develop a better understanding of the relations between seed development and quality, and they will also provide an important theoretical basis on how to use the best seeds for restoring deteriorated grassland. [ABSTRACT FROM AUTHOR]

Early seedling development is one of the most crucial period of the plant's life cycle, which is highly susceptible to adverse environmental conditions, especially those impose by salt stress. Castor plant (Ricinus communis) is a famous non-edible oilseed and salt-resistant crop worldwide. However, the specific metabolic responses in the cotyledons and roots of this species during seedling establishment under salt stress are still not clearly understood. In the present study, 16 d castor seedlings were treated with 150 mM NaCl for 6 d, and the metabolite profiling of cotyledons and roots was conducted using liquid chromatography (LC) combined with electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). The Principal Component Analysis (PCA) results showed that the metabolites were great differed in cotyledons and roots under salt stress. There were 38 differential metabolites, mainly including fatty acid, nucleic acid and organic acids in the cotyledons, but only 19 differential metabolites, mainly including fatty acid and organic acids in the roots under such condition. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that flavone and flavonol biosynthesis, pantothenate and CoA biosynthesis, citrate cycle and carotenoid biosynthesis were the common metabolic pathways in response to salt stress in the two organs. Salt stress caused metabolite process alteration mainly on carbon and nitrogen metabolisms, and the carbon allocation from root to cotyledon was increased. Additionally, changes of amino acids and nucleic acids profiles were only found in the cotyledons, and the roots could enhance the activity of antioxidant enzyme systems to scavenge ROS under salinity. In conclusion, the present research provides an improved understanding on specific physiological changes in the cotyledons in castor early seedlings, and explores their interaction under salt stress. • Castor seedling can adjust strategy of carbon partitioning, reprogram of multiple metabolic pathways and shift to accumulate unsaturated fatty acids in the cotyledons and roots to improve its salt tolerance. • Changes of amino acids and nucleic acids profiles are found in the cotyledons, but the roots can mainly enhance the activity of antioxidant enzyme systems to scavenge ROS under salinity. • The cotyledons and roots have different physiological changes, which interact in response to salt stress. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi as an important soil microbe have been demonstrated to mitigate the harmful effects of stress on plants. However, little is known about the molecular mechanisms underlying the AM symbiotic response to low temperature. Here, differentially expressed genes (DEGs) in the maize seedlings were identified after inoculating AMF under low temperature conditions. A total of 10,400 DEGs were obtained among four treatments, including non-inoculated AMF under ambient temperature (NMA), inoculated AMF under ambient temperature (MA), non-inoculated with low temperature stress (NML), and inoculated with low temperature stress (ML). The relative expression of 858 genes increased and that of 497 genes decreased in AM plants under low temperature stress. 24 DEGs were identified related to photosynthesis and respiratory metabolism. Among these DEGs, 10 genes were upregulated, and 14 genes were downregulated. The results show that inoculating AMF might decrease the production and transmission of electrons under low temperature, and the cyclic electron flow process in chloroplasts was stimulated to protect plants against low temperature. The fungi also influenced transmission of electrons and production of phosphoric acid in mitochondria in response to low temperature. CO 2 assimilation capacity was affected and the tricarboxylic acid cycle was promoted by the adjustments in the glycolysis, pentose phosphate pathway, gamma-aminobutyric acid shunt pathway, and glyoxylic acid cycle to produce more adenosine triphosphate and raw materials for other metabolic pathways under low temperature. These findings provide new insight into low temperature tolerance induced by AMF, and help identify genes for further investigation and functional analyses. • AMF can enhance low temperature tolerance in maize seedlings. • Genes related to photosynthesis and respiratory metabolism were affected by AM symbiosis. • Photosynthesis and respiratory metabolism were changed by AMF under low temperature. [ABSTRACT FROM AUTHOR]

Castor (Ricinus communis L.) is an important oilseed crop worldwide, and is also considered as one of the most promising plants for alkali-affected soil amelioration in the northeast of China. Seed germination plays a vital role in seedling establishment, and is always sensitive to alkali stress. However, little is known about the dynamic changes and regulatory mechanisms of gene expression and metabolic processes of this species during germination stage under alkali stress. In the present study, physiological, metabolome and transcriptome responses in germinating seeds of castor were investigated when exposed to 0, 50, 100 and 150 mM alkalinity (NaHCO 3). The results showed that alkali stress sharply decreased germination percentage. The Na+ content increased but K+ content decreased under alkalinity. In addition, the malondialdehyde and proline contents increased with the increasing alkalinities. Meanwhile, 50, 100 and 150 mM alkalinity induced 31, 48 and 113 differential metabolites, respectively. Furthermore, transcriptome profiling result showed that there were 138, 845 and 694 differentially expressed genes in the seeds under different concentrations alkali stresses, respectively. The integrating analysis of metabolite and gene expression changes indicating that germination response of castor seeds under alkali stress was closely related to amino acid metabolism, carbohydrate metabolism, lipid metabolism and nucleotide metabolism. The adaptive strategies of castor seeds under alkaline stress were promoting amino acid metabolism and tricarboxylic acid cycle to regulate osmotic balance and ROS level; as well as providing materials and energy for secondary metabolism, although alkali stress affected the membrane fluidity due to the reduction of unsaturated fatty acid content. Moreover, castor seeds increased metabolites on nucleotide biosynthesis to ensure their germination process under alkaline salt stress. The present research provides a deeper insight into overall understanding alkali-tolerant mechanisms of oil crops during germination in a holistic level. • l Using metabolomics and transcriptomics explored physiological adaptation mechanisms of castor seeds under alkali stress. • l 31, 48 and 113 differential metabolites and 138, 845 and 694 differentially expressed genes were found under alkali stress. • l Germination of castor at alkalinity was closely related to amino acid, carbohydrate, lipid and nucleotide metabolisms. • l Seeds of castor promoted amino acid metabolism and tricarboxylic acid cycle under stress. l Seeds of castor provided materials and energy for secondary metabolism under stress. [ABSTRACT FROM AUTHOR]

• Cotyledons and roots of castor have different adaptive mechanisms under alkali stress. • Roots could sequester a large amount of Na+, so that cotyledons can maintain physiological functions such as photosynthesis. • Cotyledons retain efficiency of photosynthetic electron transport and accumulation of osmolytes. • Roots enhance the transfer efficiency of the mitochondrial electron transport chain and promote PA biosynthesis Soil alkalinity is a major environmental problem influencing plant growth and productivity in northeastern China. Castor plant (Ricinus communis) is one of the most important oilseed crops worldwide, and has good salt tolerance. The early seedling stage is extremely vulnerable to abiotic stresses, but little is known about the physiological and molecular mechanisms involved in the cotyledons and roots of castor seedlings under alkali stress. In this study, biomass, photosynthesis, root vitality, inorganic ions, organic solutes and antioxidant enzyme activities were measured. Two-dimensional gel electrophoresis-based proteomic approaches were also applied to identify differentially abundant proteins in alkali-treated seedlings. The results showed that alkali stress strongly inhibited seedling growth, especially of the roots. Na+ content increased with increasing alkalinity, and the roots had much higher Na+ and lower K+ than cotyledons. The proline and soluble sugars were both increased in cotyledons, but kept unchanged in the roots under alkali stress. Moreover, proteomic analysis revealed a total of 15 and 25 alkali-responsive proteins in the cotyledons and roots, respectively. For cotyledons, most of the identified proteins were involved in photosynthesis, stress and defense (＞10 %), while those for roots were mainly involved in carbohydrate and energy metabolism, genetic information, stress and defense (＞10 %). These results suggest that cotyledons and roots respond differently to alkali stress. Cotyledons retain efficiency of photosynthetic electron transport and accumulation of osmolytes, while the roots enhance transfer efficiency of the mitochondrial electron transport chain, adjust fatty acid biosynthesis, and promote phosphatidic acid biosynthesis under alkali stress. Additionally, the co-increased abundance of chaperonins indicated that both cotyledons and roots maintained folding of proteins into their proper 3D structures in response to alkali stress. These findings provide new insights into different physiological mechanisms in cotyledon and root responses to alkali stress during the early seedling stage in castor. [ABSTRACT FROM AUTHOR]

• Cotyledon removal significantly altered photosynthesis in the leaf of castor bean under salt stress. • Cotyledons could maintain the structural integrity of leaf chloroplast in salt stress. • Cotyledon removal increased malondialdehyde, proline and soluble sugar contents in the leaf of castor bean under salt stress. • Cotyledons could intercept the toxic Na+ and alleviate osmotic stress caused by salinity in the leaf of castor bean. Early seedling growth is the most sensitive and critical periods for most plant establishment in saline environments. Castor bean (Ricinus communis) is an important oilseed crop species worldwide and has good salt tolerance. However, the specific functions of cotyledons during early seedling establishment of this species under salt stress are still not clearly understood. Here, the biomass, gas exchange, chlorophyll fluorescence, leaf ultrastructure, inorganic ion and organic solute contents of Ricinus communis seedlings whose cotyledons were partially or completely removed were measured in both salt and non-salt treatments. The results indicated that cotyledon removal decreased both the growth and photosynthesis of the seedlings under salt stress. The ultrastructure of the chloroplasts was greatly altered and distorted in the leaves of plants whose cotyledons were removed. With increasing salinity, cotyledon removal dramatically increased the Na+ content and simultaneously reduced the K+ content in the castor bean leaves. In addition, cotyledon removal also increased the contents of malondialdehyde (MDA), proline and soluble sugars in the leaves of plants under salt stress. These results suggest that cotyledons can alleviate the reduction in photosynthetic capability caused by stomatal closure in the leaves of castor bean plants and can maintain the structural integrity of chloroplasts under salt stress. Moreover, cotyledons can also counteract Na+ toxicity and alleviate osmotic stress caused by salt stress. Together, these findings provide an improved understanding of cotyledon function in young castor bean seedlings under salt stress. [ABSTRACT FROM AUTHOR]