Osmotic Regulatory Substances Research Articles

Transcriptomics and Metabolomics Analysis Revealed the Ability of Microbacterium ginsengiterrae S4 to Enhance the Saline-Alkali Tolerance of Rice (Oryza sativa L.) Seedlings

Soil salinization is a major factor that reduces crop yields. There are some plant growth-promoting rhizobacteria (PGPR) that can stimulate and enhance the salt tolerance of plants near their roots in saline–alkali environments. Currently, there is relatively little research on PGPR in rice saline–alkali tolerance. In the early stages of this study, a strain of Microbacterium ginsengiterrae S4 was screened that could enhance the growth of rice in a laboratory-simulated saline–alkali environment (100 mM NaCl, pH 8.5). The experiment investigated the effects of S4 bacteria on the growth, antioxidant capacity, and osmotic regulation of rice seedlings under saline–alkali stress. RNA-Seq technology was used for transcriptome sequencing and UPLC-MS/MS for metabolite detection. Research has shown that S4 bacteria affect the growth of rice seedlings under saline–alkali stress through the following aspects. First, S4 bacteria increase the antioxidant enzyme activity (SOD, POD, and CAT) of rice seedlings under saline–alkali stress, reduce the content of MDA, and balance the content of osmotic regulatory substances (soluble sugar, soluble protein, and proline). Second, under saline–alkali stress, treatment with S4 bacteria caused changes in differentially expressed genes (DEGs) (7 upregulated, 15 downregulated) and differentially metabolized metabolites (101 upregulated; 26 downregulated) in rice seedlings. The DEGs are mainly involved in UDP-glucose transmembrane transporter activity, while the differentially metabolized metabolites are mainly involved in the ABC transporters pathway. Finally, key genes and metabolites were identified through correlation analysis of transcriptomes and metabolomes, among which OsSTAR2 negatively regulates L-histidine, leading to an increase in L-histidine content. Furthermore, through gene correlation and metabolite correlation analysis, it was found that OsWRKY76 regulates the expression of OsSTAR2 and that L-histidine also causes an increase in 2-methyl-4-pentenoic acid content. Based on the above analysis, the addition of S4 bacteria can significantly improve the tolerance of rice in saline–alkali environments, which has a great application value for planting rice in these environments.

Seedlings of Poncirus trifoliata exhibit tissue-specific detoxification in response to NH4 + toxicity.

Ammonium nitrogen (NH4 +-N) is essential for fruit tree growth, but the impact of excess NH4 +-N from fertilizer on evergreen citrus trees is unclear. In a climate chamber, 8-month-old citrus plants were exposed to five different hydroponic NH4 +-N concentrations (0, 5, 10, 15 and 20 mm) for 1 month to study effects of NH4 +-N on growth characteristics, N uptake, metabolism, antioxidant enzymes and osmotic regulatory substances. Application of 10 mm NH4 +-N adversely affected root plasma membrane integrity, root physiological functions, and plant biomass. MDA, CAT, POD, APX and SOD content were significantly correlated with leaf N metabolic enzyme activity (GOGAT, GDH, GS and NR). GDH was the primary enzyme involved in NH4 +-N assimilation in leaves, while the primary pathway involved in roots was GS-GOGAT. Under comparatively high NH4 + addition, roots were the main organs involved in NH4 + utilization in citrus seedlings. Our results demonstrated that variations in NH4 + concentration and enzyme activity in various organs are associated with more effective N metabolism in roots than in leaves to prevent NH4 + toxicity in evergreen woody citrus plants. These results provide insight into the N forms used by citrus plants that are important for N fertilizer management.

CsAFS2 Gene from the Tea Plant Intercropped with Chinese Chestnut Plays an Important Role in Insect Resistance and Cold Resistance

α-Farnesene, a crucial secondary metabolite in sesquiterpenes, is crucial for plant biotic and abiotic stress resistance. In this study, we screened an AFS gene from transcriptome data of tea plants (Camellia sinensis) intercropped with Chinese chestnut (Castanea mollissima), resulting in the cloning of CsAFS2. CsAFS2 expression increased following treatment with MJ (Methyl jasmonate), SA (Salicylic acid), GA3 (Gibberellin A3), and various plant growth regulators, as well as under high-salt, drought, and low-temperature conditions. The heterologous genetic transformation of tobacco with CsAFS2 led to an enhanced resistance to low-temperature stress and aphid feeding, evident from elevated levels of osmotic regulatory substances, increased protective enzyme activity, and the upregulation of cold and insect resistance-related genes. Trichomes, crucial in cold and insect resistance, exhibited significantly greater length and density in transgenic tobacco as compared to control plants. These results confirm the vital role of CsAFS2 in enhancing cold and insect resistance, providing comprehensive insights into stress regulation mechanisms in tea plants and advancing stress-resistant tea plant breeding.

Morphological and physiological responses of 14 macadamia rootstocks to drought stress and a comprehensive evaluation of drought resistance

Planting macadamia in karst rocky desertification areas has significant ecological and economic benefits. However, the production of macadamia in karst area are facing serious drought challenges due to the poor water holding capacity of soil, and less and uneven precipitation resulting with the rising of temperature in the world. Selecting and breeding drought-resistant rootstocks is one of the main measures to solve this problem in macadamia nut production in karst area. In this study, the morphological and physiological performance of half-sib family offspring of 14 macadamia cultivars were investigated under severe drought conditions and their drought resistance was evaluated comprehensively in order to select the most suitable macadamia rootstocks. Results revealed that the leaves of all rootstocks were damaged after drought stress. Among the tested rootstocks, the leaves of QA5 were damaged the most severely, and the leaves of the whole plants were chlorotic, followed by C11, A4, and NY2, while the symptoms in leaves of O.C and H2 was less obvious after drought stress for 30 d. At the same time, the O.C and H2 had the lowest drought injury index (DII), which was 0.40, while the QA5 had the highest DII value (0.82). The physiological indices, including malonaldehyde (MDA), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), soluble protein (SP), soluble sugar (SS), proline (Pro) and relative electrolyte leakage (REL) increased (Drought tolerance coefficient, DTC > 1) after drought stress, while relative water content of leaves (LRWC), chlorophyll (Chl), relative water content of roots (RRWC) and root activity (RA) decreased (DTC < 1) in all cultivars. Except SP, SS and Pro, there were significant differences in other indexes among different rootstocks. The 13 physiological indices were transformed into seven independent, comprehensive indices through principal component analysis (PCA), whose cumulative contribution ratio reached 82.905%. The 14 rootstocks were divided into 3 categories based on the comprehensive evaluation value (D). The O.C and H2 were clustered into the drought-tolerant group, whose D values were 0.743 and 0.669, respectively. The NY3, 333, 788, NY116, NY1, NY2 were belonged to the intermediate drought tolerance group, the D values were 0.530, 0.508, 0.497, 0.465, 0.457 and 0.441 respectively. Lastly, A16, A4, C11. GR1, 695 and QA5 were clustered into low drought tolerance group with the lowest D values of 0.396, 0.391, 0.360, 0.360, 0.355, 0.324, respectively. The result of stepwise regression analysis showed that MDA, POD, APX, SS, REL, RRWC and RA were the most significant physiological and biochemical indices that played a significant role in drought tolerance, and could be used as the primary evaluation and identification indicators of drought tolerance of macadamia. These results indicated that the drought-resistant rootstocks of macadamia could improve their drought resistance by stimulating the cluster root development, increasing antioxidant enzyme activity and raising the content of osmotic regulatory substances under drought stress. Our study not only provided alternative rootstocks for macadamia drought-resistant cultivation, but also provided the theoretical basis for the drought-resistant rootstock breeding of macadamia by expounding the physiological mechanism of drought-resistance.

The Effects of Shading on the Photosynthetic Performance of Endangered Plant Horsfieldia hainanensis Seedlings

Shading is one of the management practices for preventing the damage or injury of plant seedlings during extreme weather and climate events, such as very high temperatures and heat stress. In this study, we investigated the effects of different shading conditions on the photosynthetic characteristics of the endangered plant Horsfieldia hainanensis in Guangxi, China. The H. hainanensis seedlings in this study underwent five shading treatments, including 20% (L1), 40% (L2), 60% (L3), 80% (L4), and 100% (control) of full sunlight. The net growth of their diameter and height, and photosynthetic gas exchange parameters including their photosynthesis rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci), and water use efficiency (WUE) were measured for the examined seedlings. The OJIP curve and 820 nm light absorption curve, and the osmotic substances and products of membrane lipid peroxidation were employed to assess photosynthetic capacity, identify the factors constraining photosynthetic carbon assimilation, and investigate the mechanisms influencing photosystem II (PSII) and photosystem I (PSI) in the seedlings under shade stress. The results showed that the seedlings in the L2 treatments had the highest net growth and Pn, the best photosynthetic performance, and the best coordination between PSII and PSI. The net photosynthesis (Pn) levels exhibited a declining trend in the following order: L2 &gt; L3 &gt; L4 &gt; L1. In the L1 treatment, non-stomatal factors emerged as the primary determinant affecting the Pn of the seedlings. The performance index (potential) of PSII, representing the conservation of absorbed photon energy to intersystem electron acceptor reduction (PIABS and ΔI/I0) of the seedlings, decreased in the order of L2 &gt; L3 &gt; L4 &gt; L1. The photosystem performance and the coordination between PSII and PSI (Φ(PSI/PSII)) of the seedlings decreased in the order of L2 &gt; L1 &gt; L3 &gt; L4. Under the low and moderate shading stresses (L1–L3), more serious damages occurred in PSII than in PSI, including on the donor side of PSII and in the electron transfer from QB to the acceptor side of PSI. In contrast, more considerable injury occurred in PSI than in PSII under the stress of the heavy shading treatment (L4). Considering the alterations in their leaf osmotic regulatory substances and membrane lipid peroxidation products, our findings indicate that the L2 treatment was the most conducive to the growth of the H. hainanensis seedlings. In contrast, the L1 treatment subjected H. hainanensis seedlings to the most significant stress, resulting in substantial damage to their growth and photosynthetic mechanisms. Our research provides a scientific insight into and a practical guide for the selection of an appropriate light intensity for the conservation and cultivation of endangered plant species, such as H. hainanensis.

Responses of the desert green algae, Chlorella sp. to drought stress.

Desert algae are important components of the desert soil crust and play an essential role in desert soil ecosystem development. Owing to their special habitat, desert algae are often exposed to harsh environments, among which drought represents the most common stress. Green algae are considered to have drought tolerance potential; however, only a few studies have investigated this. In this study, we selected the green alga Chlorella sp., which was isolated from desert soil, and studied its physiological response to polyethylene glycol (PEG) 6000-induced drought stress. The results showed that drought stress can affect the photosynthetic efficiency of Chlorella sp., reduce its water retention ability, and destroy its ultrastructure. However, Chlorella sp. can cope with drought stress through a series of physiological regulatory strategies. Protective strategies include quick recovery of photosynthetic efficiency and increased chlorophyll content. In addition, induced synthesis of soluble proteins, lipids, and extracellular polysaccharide (EPS), and accumulation of osmotic regulatory substances, such as sucrose and trehalose, also contribute to improving drought tolerance in Chlorella sp. This study provides insights into the physiological responses of Chlorella sp. to drought stress, which may be valuable for understanding the underlying drought adaptation mechanisms of desert green algae.

Regulation of cold resistance by the polyamine biosynthetic gene SlSPDS2 via modulating the antioxidant enzyme system and osmotic regulatory substances in Solanum lycopersicum

The essential role of polyamine in cold stress resistance in tomato has been widely studied. However, the involvement of Spermidine synthase (SPDS) in the regulation of cold stress and their relationship with the antioxidant enzyme system and osmotic regulatory substances in tomato are not well characterized. In the current study, we found that cold stress induced the expression of polyamine biosynthetic genes and the accumulation of polyamine. The overexpression of SlSPDS2 (SlSPDS2-OE), a key Spermidine biosynthetic gene, significantly improved seedlings growth and increased seedlings index as well as alleviated the cold stress injury with decreased O2∙−, H2O2 and malondialdehyde contents. In SlSPDS2 overexpression lines, the contents of free polyamine, free salicylic acid, chlorophyll, proline and soluble sugar were increased compared with wild type (WT) under cold stress. The antioxidant enzyme activities and their coding genes expression were increased compared with WT under cold stress. SlSPDS2 silencing seedlings with weakened cold resistance showed oxidative damage and inhibition of growth. These results indicated that SlSPDS2 plays a positive role in tomato cold tolerance by regulating polyamine metabolism, antioxidants, and osmolytes.

ROS-mediated waterlogging memory, induced by priming, mitigates photosynthesis inhibition in tomato under waterlogging stress.

With global climate change, the frequency and intensity of waterlogging events are increasing due to frequent and heavy precipitation. Little is known however about the response of plants to repeated waterlogging stress events. The aim is to clarify physiological regulation mechanisms of tomato plants under repeated waterlogging stress, and whether Trichoderma harzianum can alleviate waterlogging injury. We identified two genotypes of tomato, 'MIX-002' and 'LA4440', as waterlogging tolerant and sensitive genotypes, respectively, based on plant biomass accumulation. The two tomato genotypes were subjected to a waterlogging priming treatment for 2 days (excess water for 1cm above substrate surface) followed by a recovery stage for 2 days, and then a second waterlogging stress for 5 days (excess water for 1cm above substrate surface) followed by a second recovery stage for 3 days. Leaf physiological, plant growth parameters, and the expression of five key genes were investigated. We found that the two genotypes responded differently to waterlogging priming and stress in terms of photosynthesis, reactive oxygen species (ROS), and osmotic regulatory mechanisms. Waterlogging stress significantly increased H2O2 content of 'MIX-002', while that of 'LA4440' had no significant change. Under waterlogging stress, photosynthesis of the two genotypes treated with waterlogging priming returned to the control level. However, Trichoderma harzianum treatment during the second recovery stage did not show positive mitigative effects. The plants of 'LA4440' with priming showed lower peroxidase (POD) activity and proline content but higher H2O2 content than that without priming under waterlogging stress. Under waterlogging stress with priming as compared to without priming, SODCC2 was downregulated in two tomatoes, and AGR2 and X92888 were upregulated in 'MIX-002' but downregulated in 'LA4440'. Overall, the two tomato genotypes exhibited distinct photosynthetic, ROS and osmotic regulatory mechanisms responding to the waterlogging stress. Waterlogging priming can induce stress memory by adjusting stomatal conductance, sustaining ROS homeostasis, regulating osmotic regulatory substances and key gene expressions mediated by H2O2, and thus alleviate the damage on tomato photosynthesis when waterlogging reoccurred.

Brassinosteroids Regulate the Water Deficit and Latex Yield of Rubber Trees.

Brassinolide (BR) is an important plant hormone that regulates the growth and development of plants and the formation of yield. The yield and quality of latex from Hevea brasiliensis are regulated by phytohormones. The understanding of gene network regulation mechanism of latex formation in rubber trees is still very limited. In this research, the rubber tree variety CATAS73397 was selected to analyze the relationship between BR, water deficit resistance, and latex yield. The results showed that BR improves the vitality of rubber trees under water deficit by increasing the rate of photosynthesis, reducing the seepage of osmotic regulatory substances, increasing the synthesis of energy substances, and improving the antioxidant system. Furthermore, BR increased the yield and quality of latex by reducing the plugging index and elevating the lutoid bursting index without decreasing mercaptan, sucrose, and inorganic phosphorus. This was confirmed by an increased expression of genes related to latex flow. RNA-seq analysis further indicated that DEG encoded proteins were enriched in the MAPK signaling pathway, plant hormone signal transduction and sucrose metabolism. Phytohormone content displayed significant differences, in that trans-Zeatin, ethylene, salicylic acid, kinetin, and cytokinin were induced by BR, whereas auxin, abscisic acid, and gibberellin were not. In summary, the current research lays a foundation for comprehending the molecular mechanism of latex formation in rubber trees and explores the potential candidate genes involved in natural rubber biosynthesis to provide useful information for further research in relevant areas.

Plant growth-promoting rhizobacteria Bacillus velezensis JB0319 promotes lettuce growth under salt stress by modulating plant physiology and changing the rhizosphere bacterial community

Salt stress inhibits plant growth, which is an important factor that restricts crop yield. Plant growth-promoting rhizobacteria (PGPR) promote plant growth, but their effect on lettuce under salt stress has not been reported. In this study, the salt-tolerant growth-promoting bacteria Bacillus velezensis JB0319 in the plant rhizosphere was screened and used as microbial inoculum in a pot experiment to explore the effects of B. Velezensis JB0319 on growth, reactive oxygen scavenging, osmotic adjustment, and the rhizosphere bacterial community of lettuce planted in soils with different NaCl concentrations (0, 50, 100, 150 mM). B. Velezensis JB0319 inoculation significantly promoted the shoot height, root length and shoot biomass of lettuce, increased the activity of SOD, POD, decreased the accumulation of MDA in lettuce, and increased the accumulation of osmotic regulation substance SS, Pro. Most importantly, Inoculation B. Velezensis changed bacterial community structure in the rhizosphere of lettuce. The LDA analysis showed that B. Velezensis inoculation helped lettuce enrich more nitrogen-fixing bacteria. These results showed that B. Velezensis inoculation could alleviate the inhibitory effect of salt stress on lettuce and promote lettuce growth. This study provides a theoretical basis for plant growth-promoting rhizobacteria to alleviate salt stress in the future.

Foliar water uptake and its influencing factors differ between female and male Populus euphratica

In arid ecosystems, foliar water uptake (FWU) plays an important role in improving plant physiological performance. However, the structural and physiological response mechanism of FWU between male and female woody desert plants has not been reported. Using the dioecious desert woody plant Populus euphratica, the current study explored the structural and physiological response mechanism of male and female P. euphratica leaves to water absorption via an FWU capacity experiment based on leaf epidermal cell wall components and cell structure, osmotic adjustment, and oxidative metabolism indicators. The results showed that both male and female P. euphratica plants could absorb water through leaves. The per unit area of leaf water absorption (AFWU) and the leaf absorption speed (k) of female P. euphratica were higher than those of male P. euphratica, and the TFWU was approximately twice that of male P. euphratica. The leaf thickness (LT), palisade tissue thickness (TP) and the contents of cellulose and pectin of female were significantly larger than those of male P. euphratica. The contents of sucrose, glucose, soluble sugar, proline and peroxidase in female leaves were significantly higher than those in male leaves. Multivariate factor analysis showed that the AFWU of the leaves was strongly correlated with glucose, cellulose, TP, and catalase, and the k was strongly correlated with starch, pectin, LT, and malondialdehyde. The FWU capacity of female P. euphratica was stronger than that of male P. euphratica, which was caused by the difference in cell structure and osmotic regulatory substances. These results provide a new perspective for understanding the water utilization mechanism reproduction strategy of dioecious plants.

Alleviation effect of GR24, a strigolactone analogue, on low-nitrogen stress in Malus baccata seedlings.

To investigate the efficacy of foliar application of GR24, a strigolactone analogue, in alleviating low-nitrogen stress in Malus baccata, we applied GR24 with different concentrations (0, 1, 5, 10, and 20 μmol·L-1) to leaves of plants under low nitrogen stress. We evaluated the changes in photosynthetic characteristics of leaves, reactive oxygen metabolism, and nitrogen assimilation in roots. The results showed that shoot biomass of seedling significantly decreased and root-shoot ratio increased under low-nitrogen stress. The chlorophyll contents decreased, the carotenoid content increased, and the photosynthetic activity decreased. The activities of superoxide dismutase and catalase enzymes in roots changed little, while the activities of peroxidase and ascorbic acid peroxidase enzymes, along with the levels of soluble sugar, free proline, and reactive oxygen species showed a significant increase, and the soluble protein content decreased. The NO3- content in roots decreased, the NH4+ content increased, while activities of nitrate reductase and glutamine synthase decreased. Compared to the control group without GR24 application, foliar sprays of 10 and 20 μmol·L-1 GR24 under both normal and low-nitrogen increased biomass and root-shoot ratio to varying degrees. Additionally, GR24 application increased chlorophyll content, photosynthesis indices (net photosynthetic rate, transpiration rate and stomatal conductance), and fluorescence (maximum photochemical efficiency of PSⅡ and quantum yield of electron transfer per unit area) performance parameters, as well as the contents of osmotic regulation substances (soluble protein, soluble sugar, and free proline) and glutamine synthase activity. Application of 10 and 20 μmol·L-1 GR24 under low-nitrogen stress decreased carotenoid, reactive oxygen species, and NH4+ contents, while increased the activities of antioxidases and key enzymes in nitrogen metabolism (nitrate reductase and glutamine synthase) and NO3- content. The 10 μmol·L-1 GR24 treatment was the most effective in alleviating low nitrogen stress, which has potential for application in apple orchards with low nitrogen soil.

Effects of elevated CO2 concentration on cell structure and stress resistance physiology of Setaria italica under drought stress.

The frequency of drought will increase under further warming. The increase in atmospheric CO2 concentration, along with more frequent drought, will affect crop growth. We examined the changes of cell structure, photosynthetic physiology, antioxidant enzymes, osmotic regulatory substances, and yield of foxtail millet (Setaria ita-lica) leaves under different CO2 concentrations (ambient air CO2 concentration and ambient atmospheric CO2 concentration + 200 μmol·mol-1) and water treatment (soil moisture content maintained at 45%-55%, and 70%-80% of field capacity, representing mild drought and normal water condition, respectively). The results showed that elevated CO2 concentration increased the number of starch grains, the area of single starch grains, and the total area of starch grains in the chloroplast of millet mesophyll cells. Under mild drought condition, elevated CO2 concentration increased net photosynthetic rate of millet leaves at the booting stage by 37.9%, but did not affect water use efficiency at this stage. Elevated CO2 concentration increased net photosynthetic rate and water use efficiency of millet leaves under mild drought condition at the filling stage by 15.0% and 44.2%, respectively. Under mild drought condition, elevated CO2 concentration increased the content of peroxidase (POD) and soluble sugar in millet leaves at the booting stage by 39.3% and 8.0%, respectively, but decreased proline content by 31.5%. It increased the content of POD in millet leaves at the filling stage by 26.5% but decreased the content of MDA and proline by 37.2% and 39.3%, respectively. Under mild drought condition, elevated CO2 concentration significantly increased the number of grain spikes by 44.7% and yield by 52.3% in both years compared with normal water condition. The effect of elevated CO2 concentration on grain yield under mild drought conditions was higher than that under normal water condition. Under mild drought conditions, elevated CO2 concentration increased leaf thickness, vascular bundle sheath cross-sectional area, net photosynthetic rate, and water use efficiency of millet, improved the antioxidant oxidase activity, and changed the concentration of osmotic regulatory substances, alleviated the nega-tive effect of drought on foxtail millet, and finally increased the number of grains per ear and yield of foxtail millet. This study would provide a theoretical basis for millet production and sustainable agricultural development in arid areas under future climate change.

Differential physiological responses and tolerance to potentially toxic elements in Primula forbesii Franch.

Environmental pollution caused by potentially toxic elements (PTEs) has become a global problem that endangers environmental sustainability due to industrial, agricultural, and urban pollution. Primula forbesii Franch. (a synonym of Primula filipes G. Watt.) is a biennial flower native to China with excellent stress resistance and ornamental value. In this study, we examined the phenotypic traits, growth indexes, and physiological properties of P. forbesii in response to five representative PTEs (Cd, Ni, Cr(III), Cu, and Zn) under hydroponic culture conditions. High concentrations of Zn and Cr had little effect on the growth and physiological properties of P. forbesii, indicating that the species has strong tolerance to Zn and Cr stress. Alternatively, high concentrations of Cd, Ni, and Cu seriously affected plant growth and development, resulting in leaf chlorosis and even death, and therefore may have a serious negative impact on the growth of P. forbesii. However, activity levels of some antioxidant enzymes and osmotic regulatory substances remained high, indicating that P. forbesii resisted PTE stress by regulating physiological and biochemical metabolism to a certain extent. Furthermore, principal component analysis and membership function were used to comprehensively evaluate P. forbesii resistance to PTEs. These analyses revealed that P. forbesii exhibits distinct sensitivities and physiological responses to different PTEs and suggested that the resistance to five PTEs in decreasing order is Zn > Cr > Cd > Cu > Ni. These results provide a theoretical basis for the future application of P. forbesii in environments with PTE pollution and may expand its practical utilization.

Prohexadione-calcium alleviates the leaf and root damage caused by salt stress in rice (Oryza sativa L.) at the tillering stage.

Salt stress, as a principal abiotic stress, harms the growth and metabolism of rice, thus affecting its yield and quality. The tillering stage is the key growth period that controls rice yield. Prohexadione-calcium (Pro-Ca) can increase the lodging resistance of plants by reducing plant height, but its effects on rice leaves and roots at the tillering stage under salt stress are still unclear. This study aimed to evaluate the ability of foliar spraying of Pro-Ca to regulate growth quality at the rice tillering stage under salt stress. The results showed that salt stress reduced the tillering ability of the rice and the antioxidant enzyme activity in the roots. Salt stress also reduced the net photosynthetic rate (Pn), stomatal conductance (Gs) and intercellular CO2 concentration (Ci) of the rice leaves and increased the contents of osmotic regulatory substances in the leaves and roots. The application of exogenous Pro-Ca onto the leaves increased the tiller number of the rice under salt stress and significantly increased the photosynthetic capacity of the leaves. Additionally, it increased the activities of antioxidant enzymes and the AsA content. The contents of an osmotic regulation substance, malondialdehyde (MDA), and H2O2 in the leaves and roots also decreased. These results suggested that Pro-Ca can increase the tillering ability, photosynthetic capacity, osmotic adjustment substance content levels and antioxidant enzyme activity levels in rice and reduce membrane lipid peroxidation, thus improving the salt tolerance of rice at the tillering stage.

Growth changes of tomato seedlings responding to sodium salt of α-naphthalene acetic acid and potassium salt of fulvic acid

In present study, sodium salt of α-naphthalene acetic acid (NA), potassium salt of fulvic acid (KF) and their combinations were applied to the growth substrates of tomato seedlings (Solanum lycopersicum L.) under chilling stress. The changes in aboveground biomass, root attributes, pigment contents, chlorophyll fluorescence, photosynthesis, osmotic regulation substances, and antioxidant enzymes activity of the tomato seedlings in response to NA and KF were investigated. The application of NA, KF and their combination could promote the growth of plant height and stem diameter of tomato seedlings under chilling stress to varying degrees, and improve root characteristics by increasing root volume, root length and root activity, and increase dry matter accumulation. In addition, the combined use of NA and KF improved the seedling leaf chlorophyll content, qP, Fv/Fm, ΦPSII , Pn and increased the activity of antioxidant enzymes in the tomato plants. The above results suggested a synergistic effect between NA and KF to stimulate the seedlings growth and to enhance the ROS scavenging ability of tomato, which has never been reported in previous research before. However, further researches are needed to explore the physiological and molecular mechanism underlying the synergistic effect between NA and KF.

Seed priming with selenite enhances germination and seedling growth of Sorghum [Sorghum bicolor (L.) Moench] under salt stress

ABSTRACT Justify that the use of selenium has been shown to promote seed germination and seedling growth of some crops under salt stress but the physiological mechanisms in sorghum remain poorly understood. Herein, grain sorghum [Sorghum bicolor (L.) Moench] variety Jinza 2002 was used to explore the effects and mechanisms of seed priming with 25 μmol/L sodium selenite [Se(IV)] on seed germination, seedling growth, antioxidant enzyme activity and osmotic regulatory substances under 120 mmol/L NaCl. The results showed that soaking sorghum seeds in Se(IV) effectively alleviated the harm of salt stress. Compared with the Na group, Se(IV) application increased germination percentage (by 23.8%), while facilitating the elongation of radicles (by 4.2%) and plumules (by 18.4%) under salt stress. Salt-stressed seedlings showed increased levels of leaf chlorophyll, soluble sugar, soluble protein and proline contents, and antioxidant enzyme activities, as well as root activity, and total biomass following Se(IV) application, along with decreased relative electrical conductivity and malondialdehyde content in the leaves. Findings of this study indicate that seed priming with Se(IV) facilitates sorghum seed germination and seedling growth under salt stress by improving root activity, enhancing leaf photosynthesis and antioxidant responses, and reducing cell membrane damage.

Response of Alhagi sparsifolia Seedlings to AMF Inoculation and Nitrogen Addition under Drought Stress

Riparian forest veg etation in the lower Tarim River desert often faces a water and nitrogen deficiency. To investigate the ecological effects of drought stress and nitrogen limitation of arbuscular mycorrhizal fungi (AMF) on Alhagi sparsifolia seedlings at the vulnerable stage of growth, a control experiment was conducted on Alhagi sparsifolia seedlings with indoor potted plants. The main findings are as follows: drought stress inhibited the normal growth and development of Alhagi sparsifolia seedlings. When Alhagi sparsifolia seedlings were inoculated with AMF and at the N1 (50 mmol·L−1) nitrogen addition level, the mycorrhizal infection rate of Alhagi sparsifolia seedlings was the best: 84.44% under sufficient moisture content and 77.78% under drought stress. Under the same nitrogen treatment, the relative growth rate of Alhagi sparsifolia seedling height and base diameter, plant biomass, root system indicators (total root length, root surface area, root volume, average root diameter, the number of tips, and root shoot ratio), chlorophyll content (except for the chlorophyll a/b content at the N0 (0 mmol·L−1) nitrogen addition level), Fv/Fm, total nitrogen content, idole acetic acid (IAA) and gibberellic acid (GA) content were initially decreased, then increased and finally decreased again. Each of these indicators was increased significantly after being inoculated with AMF, and they reached their maximum value under the normal moisture and AMF treatment; however specific root length (except for at the N0 (0 mmol·L−1) nitrogen addition level), minimal fluorescence (Fo), antioxidant enzyme activity, the contents of osmotic regulation substances, abscisic acid (ABA) and strigolactones (SLs) contents were initially increased, then decreased and finally increased again, and they reached their maximum value under drought stress and AMF treatment. Under the same CK (black control), D (drought stress), CK + A (inoculated with AMF under black control), and D + A (inoculated with AMF under drought stress) treatments, all of the above indicators, except for specific root length, chlorophyll a/b content, minimal fluorescence (Fo), maximum fluorescence (Fm) and malondialdehyde (MDA) content initially increased and then decreased with the increasing nitrogen addition rate, and they reached the maximum value at the N1 (50 mmol·L−1) nitrogen addition level. Therefore, in the arid and N-deficient lower Tarim River region, Alhagi sparsifolia seedlings established an efficient symbiotic structure with AMF, which improved the drought resistance of seedlings and promoted the rapid passage of seedlings through the growth vulnerability period. This indicates that AMF inoculation is a key link in the survival strategy of Alhagi sparsifolia.

Genes related to osmoregulation and antioxidation play important roles in the response of Trollius chinensis seedlings to saline-alkali stress.

Saline-alkali stress is one of the main abiotic stress factors affecting plant growth and development. Trollius chinensis is a perennial herbal medicinal plant with high values for garden application. However, its response and tolerance to saline-alkali stress is unclear. In this study, we mixed four salts (NaCl: Na2SO4: NaHCO3: Na2CO3) with a concentration ratio of 1:9:9:1, and applied low (40 and 80 mM) and high (120 and 160 mM) saline-alkali stress to analyze osmotic regulation substances, antioxidant systems and the gene expression of T. chinensis. Along with higher saline-alkali stress, the leaf relative water content (RWC) started to decrease only from high stress, while the malondialdehyde (MDA) content in leaves decreased continuously, and the contents of proline (Pro), soluble sugar (SS) and soluble protein (SP) increased compared with control. The activities of antioxidant enzymes and the contents of non-enzymatic antioxidants were increased positively with the accumulation of superoxide anion (O2 •-) and hydrogen peroxide (H2O2). For instance, the ascorbic acid-glutathione (AsA-GSH) cycle was enhanced in T. chinensis seedling leaves subject to saline-alkali stress. Principal Component Analysis (PCA) indicates that MDA, Pro, SS, SP, H2O2, O2 •-, and GSH are important indexes to evaluate the response and tolerance of T. chinensis to saline-alkali stress. Through RNA-Seq, a total of 474 differentially expressed genes (DEGs) were found in plant under low saline-alkaline stress (40 mM, MSA1) vs. control. Among them, 364 genes were up-regulated and 110 genes were down-regulated. DEGs were extensively enriched in carbohydrate transport, transferase activity, zeatin biosynthesis, ABC transporters, and spliceosome. The transcription factor family MYB, BZIP, WRKY, and NAC were related to its saline-alkali tolerance. In addition, some DEGs encode key enzymes in the processes of osmoregulation and antioxidation, including betaine aldehyde dehydrogenase (BADH), inositol monophosphatase (IMP), chloroperoxidase (CPO), thioredoxin (Trx), and germin-like protein (GLPs) were found. Overall, these findings provide new insights into the physiological changes and molecular mechanism of T. chinensis to saline-alkali stress and lay a foundation for application of T. chinensis in saline-alkali environment.

Metabolomics analysis reveal the molecular responses of high CO2 concentration improve resistance to Pb stress of Oryza sativa L. seedlings

Rice seedlings were exposed to two CO2 concentrations (400 ± 20 and 800 ± 20 μmol mol−1) and three PbNO3 concentrations (0, 50 and 100 µmol L−1) for 10 days to explore the regulatory mechanisms of elevated CO2 for Pb stress resistance. Electrical conductivity, MDA content, SOD, POD, CAT activities and metabolomics changes were studied. Results showed that: Pb stress damaged cell membrane system, electrical conductivity and MDA content increased 49.34 % and 73.27 %, respectively, and some antioxidant enzymes activities increased. Sugar, polyol, amino acid metabolism and fatty acid β-oxidation were all enhanced to improve osmotic adjustments, maintain cell membrane stability, supply energy, nitrogen assimilates and antioxidant capacity; Under composite treatments, cell membrane damage was reduced, activities of protective enzymes increased compared with only Pb stress, POD activity increased the most (49.14 %) under severe Pb composite treatment. High CO2 caused the enhance of cells antioxidant capacity, TCA cycle intermediate products contents and fatty acid desaturation under mild Pb stress. Many sugars, polyols and amino acids contents were increased as osmotic regulatory substances by high CO2 under severe Pb stress; Secondary metabolites played an important role under Pb stress and composite treatments. The object of this study is to provide a possible molecular mechanism of rice response to Pb stress under high CO2 in the future.