Physiological Adaptive Strategies of Oil Seed Crop Ricinus communis Early Seedlings (Cotyledon vs. True Leaf) Under Salt and Alkali Stresses: From the Growth, Photosynthesis and Chlorophyll Fluorescence

Application of prohexadione-calcium priming affects Brassica napus L. seedlings by regulating morph-physiological characteristics under salt stress

Salinity stress imposes severe constraints on plant growth and development. Here, we explored the impacts of prohexadione-calcium (Pro-Ca) on rapeseed growth under salt stress. We designed a randomized block design pot experiment using two rapeseed varieties, 'Huayouza 158R' and 'Huayouza 62'. We conducted six treatments, S0: non-primed + 0 mM NaCl, Pro-Ca+S0: Pro-Ca primed + 0 mM NaCl, S100: non-primed + 100 mM NaCl, Pro-Ca+S100: Pro-Ca primed + 100 mM NaCl, S150: non-primed + 150 mM NaCl, Pro-Ca+S150: Pro-Ca primed + 150 mM NaCl. The morphophysiological characteristics, and osmoregulatory and antioxidant activities were compared for primed and non-primed varieties. Our data analysis showed that salt stress induced morph-physiological traits and significantly reduced the antioxidant enzyme activities in both rapeseed varieties. The Pro-Ca primed treatment significantly improved seedlings, root, and shoot morphological traits and accumulated more dry matter biomass under salt stress. Compared to Huayouza 158R, Huayouza 62 performed better with the Pro-Ca primed treatment. The Pro-Ca primed treatment significantly enhanced chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and actual photochemical quantum efficiency (ФPSII). Furthermore, the Pro-Ca primed treatment also improved ascorbic acid (ASA) content, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) activity, and stimulated the accumulation of soluble proteins. These findings strongly suggested that the Pro-Ca primed treatment may effectively counteract the negative impacts of salinity stress by regulating the morph-physiological and antioxidant traits.

Arbuscular Mycorrhizal Fungi-Mediated Modulation of Physiological, Biochemical, and Secondary Metabolite Responses in Hemp (Cannabis sativa L.) under Salt and Drought Stress

The increasing impact of global climate change has resulted in adversity stresses, like salt and drought, gradually becoming the main factors that limit crop growth. Hemp, which contains numerous medicinal active components and multiple bioactive functions, is widely used in the agricultural, industrial, and medical fields, hence promoting the rapid development of related industries. Arbuscular mycorrhizal fungi (AMF) can establish a symbiotic relationship with 80% of vascular plants. This symbiosis promotes host plant growth, regulates plant physiology and biochemistry, facilitates secondary metabolite synthesis, and enhances resistance to abiotic stresses. However, the effects of salt stress, drought stress, and AMF interaction in hemp are not well understood. In this study, to investigate this, we performed a study where we cultured hemp that was either inoculated or uninoculated with Funneliformis mosseae and determined changes in effective colonization rate, growth, soluble substances, photosynthesis, fluorescence, ions, and secondary metabolites by cultivating hemp under different concentrations of NaCl (0 mM, 100 mM, and 200 mM) and different soil moisture content (45%, 25%, and 15%). The results showed that salt, drought stress, or salt-drought interaction stress all inhibited colonization rate after stress, plant growth, mainly due to ion toxicity and oxidative damage. Inoculation with F. mosseae effectively alleviated plant growth inhibition under 100 mM NaCl salt stress, drought stress, and salt-drought interaction stress conditions. It also improved osmoregulation, photosynthetic properties, fluorescence properties, and ion homeostasis, and promoted the accumulation of secondary metabolites. However, under 200 mM NaCl salt stress conditions, inoculation with F. mosseae negatively affected plant physiology, biochemistry, and secondary metabolite synthesis, although it did alleviate growth inhibition. The results demonstrate that there are different effects of salt-drought interaction stress versus single stress (salt or drought stress) on plant growth physiology. In addition, we provide new insights about the positive effects of AMF on host plants under such stress conditions and the effects of AMF on plants under high salt stress.

Impact of cellulose and lignin on restoration of vegetation and soil chemical properties for saline-alkali soil of songnen plain

To explore the effects of cellulose and lignin on stimulating vegetation restoration and improving soil chemical properties in saline-alkali soil, a large area test was carried out, and 2 treatments were set up: T (cellulose and lignin+ Planted seeds) and CK (Planted seeds). In this study, the species, quantity, plant height, above-ground biomass, biodiversity of vegetation in the treated plots, the determination of soil chemical nutrient content, and the effect of cellulose and lignin on vegetation restoration in saline-alkali land were investigated. The results showed that: 1) Cellulose and lignin contributed to vegetation growth. Compared with CK treatment, plant height and aboveground biomass of T increased by 158.73% and 240.13%, respectively; 2) Cellulose and lignin improved soil structure, and soil porosity, and decreased soil compaction (21.95%); 3) Compared with CK treatment, T treatment decreased soil pH by 0.5 units, total salt content decreased by 30.95%, exchangeable Na+ decreased by 63.00%, and exchangeable sodium percentage (ESP) decreased by 61.51%. Furthermore, cellulose and lignin effectively improved the physical and chemical properties of saline-alkali soil, promoted the recovery of ecological environment in saline-alkali soil, and improved regional biodiversity, which will provide new methods for soil remediation and improvement in saline-alkali areas.

Comprehensive analysis revealed that titanium dioxide nanoparticles could strengthen the resistance of apple rootstock B9 to saline-alkali stress

Apple growth and development can be adversely affected by saline-alkali stress, which has become a significant factor restricting the high yield of the apple industry. In recent years, nanomaterials have become a potential source for plant growth and development. Titanium dioxide nanoparticles (TiO2 NPs) play an important role in multiple plant development processes, including mitigating environmental stress. In this study, one-year-old apple rootstock B9 stem cuttings were used as research objects. Different concentrations of TiO2 NPs were applied to the roots before saline-alkali treatment. Principal component analysis showed that 1gkg-1 TiO2 NPs treatment had the best effect in alleviating the stress for B9. It significantly reduced the damage to B9 under salt-alkali stress, increased the content of photosynthetic pigment, enhanced the performance of Photosystem II, and promoted photosynthesis. At the same time, the content of K+ was increased, and the ion toxicity was alleviated. In addition, TiO2 NPs have also been shown to reduce B9 cell damage and lipid peroxidation, increase antioxidant enzyme activity, and regulate the accumulation of solutes. Overall, this study provides a theoretical basis for TiO2 NPs to mitigate the adverse effects of plants under saline-alkali stress and provides useful insights for managing other plants affected by global salinity and alkalinity.

Advances and future research in ecological stoichiometry under saline-alkali stress

Saline-alkali stress is a serious abiotic factor which negatively impacts agricultural production and the ecological environment. Thus, improving the development of saline-alkali soil and reducing the effects of saline-alkali stress is a key issue for sustainable agricultural development and environmental protection. As such, it is unsurprising that researchers have lately focused on how to improve saline-alkali soil, increase the agricultural yield of saline-alkali land, and promote the adaptive growth of plants in saline-alkali soil. This paper reviews the latest research concerning nutrient content changes in saline-alkali soil, along with the associated changes in key nutrients in plants, to summarize which methods are most effective for improving the plant growth under saline-alkali stress. Finally, the prospects for alleviating saline-alkali stress and improving saline-alkali soil are put forward as a theoretical foundation for the stabilization of plant growth in saline-alkali soil, expansion of arable land area, crop yield improvement, and effective environmental protection.

Arbuscular mycorrhizal fungi improve the growth and performance in the seedlings of Leymus chinensis under alkali and drought stresses

Alkali and drought stresses are increasing severe environmental problems throughout the world, especially in the Songnen grassland of northern China. Leymus chinensis is the dominant grass species in the Songnen grassland of northern China and the most promising species for grassland restoration. Arbuscular mycorrhizal fungi (AMF) can colonize 80% of vascular plants, which can enhance the growth of host plants and provide extrinsic protection against abiotic stresses. However, little is known about the interaction effect of alkali and drought stresses on plant-AM symbionts. Here, seedlings of Leymus chinensis inoculated with or without mycorrhizae were cultivated in soil with 0, 100 or 200 mM NaHCO₃ under 0, 5 or 10% (w/v) PEG treatment, and the changes in growth, osmotic adjustment substances and ions were measured. The results showed that the interaction of alkali and drought stresses caused greater seedling growth inhibition than either single alkali or drought stress due to ion toxicity and oxidative damage. Mycorrhizae could alleviate the growth inhibition of seedlings under alkali or drought stress. The interaction of alkali and drought stresses did not affect the alleviating effect of mycorrhizae on seedling growth but improved the osmotic regulation ability and ionic balance of the seedlings. Our results clearly show different effects of the interaction of alkali and drought stresses versus a single stress (alkali or drought) on plant development and provide new insights into the positive effect of arbuscular mycorrhizal fungi on host plants under such stress conditions.

Role of arbuscular mycorrhizal fungi as an underground saviuor for protecting plants from abiotic stresses

To increase food production, prevalent agricultural malpractices such as intensive use of fertilizers and pesticides have led to degradation of the ecosystem. In this situation, there is a need to encourage eco-friendly and sustainable methods for improving crop production under ever increasing abiotic stress conditions. One such method can be through use of arbuscular mycorrhizal fungi (AMF or AM fungi). Soil microorganisms such as AMF serve as a link between plants and the soil resources. AMF represent a key functional group of soil microbiota that is fundamental for soil fertility, crop productivity, yield, quality and ecosystem resilience. AMF potentially increases bioavailability of water as well as various micro- and macro- nutrients which enhances production of plant photosynthates. In plants, inoculation with AMF led to increased photochemical efficiency ultimately resulting in enhanced plant growth. In this review we have summarized amelioration of drought or water scarcity, salt stress, increasing temperature or high temperature and heavy metal stresses etc. in crop plants by AMF through its effects on various physiological and biochemical processes including photosynthesis. The review also highlights AMF induced tolerance and adaptive mechanisms which protect crops from stresses. We conclude the review with a discussion of unseen issues and suggestions for future researches.

Physiological and comparative transcriptome analysis of leaf response and physiological adaption to saline alkali stress across pH values in alfalfa (Medicago sativa)

Soil salinization is a critical factor limiting growth and causing physiological dysfunction in plants. The damage from alkaline salt in most plants is significantly greater than that from neutral salt. However, there is still a lack of research on the action mechanism by which saline alkali stress on plants under the same salt concentration across different pH values. The present study examined the effects of different pH values (7.0, 8.0, 9.0, and 10.0) under the same salt concentration (200 mmolL^-1) on photosynthetic function, photoprotective mechanism, nitrogen metabolism, and osmotic regulation in alfalfa (Medicago sativa) leaves, including a transcriptomic analysis of changes in gene expression related to the above metabolic processes. The results showed that low pH saline alkali stress (pH 7.0 and 8.0) promoted chlorophyll synthesis in alfalfa leaves, and non-photochemical quenching (NPQ) and cyclic electron transfer (CEF) were promoted. There was no significant effect on plant growth or photochemical activity. The soluble sugar, proline, and soluble protein contents did not change significantly, and there was no obvious oxidative damage in alfalfa leaves. However, when pH increased to 9.0 and 10.0, KEGG enrichment analysis showed that photosynthesis (map00195) and nitrogen metabolism (map00910) were significantly enriched (P < 0.05), and PSII antenna protein coding genes were down-regulated under pH 9.0 and 10.0 treatments. The activities of PSII and PSI were decreased under high pH saline alkali stress, and the expression levels of the photosynthetic electron transporter-related genes PetA, PetB, petE, and petF were also significantly down-regulated. PSII was more sensitive to high pH saline alkali stress than PSI, and the PSII receptor side was more sensitive to high pH saline alkali stress than the PSII donor side. The activities of the oxygen-evolving complex (OEC) and PSI were significantly damaged only at pH 10.0. The activities of nitrate reductase (NR) and nitrite reductase (NiR), the expression levels of their genes, and the content of soluble protein were also decreased under pH 9.0 and 10.0 treatments. The inhibition of plant growth and oxidative damage to alfalfa leaves caused by high pH saline alkali stress were mainly related to the inhibition of photosynthesis (light energy absorption, electron transfer) and nitrogen metabolism (NO₃^- reduction). Under high pH saline alkali stress (pH 10.0), the photoprotection mechanisms such as CEF and NPQ were inhibited, which was also one of the important reasons for photoinhibition in alfalfa leaves. The accumulation of osmotic adjustment substances, such as soluble sugar and proline, was an important mechanism by which alfalfa physiologically adapted to high pH alkaline salt stress.

Uniform Water Potential Induced by Salt, Alkali, and Drought Stresses Has Different Impacts on the Seedling of Hordeum jubatum: From Growth, Photosynthesis, and Chlorophyll Fluorescence

Hordeum jubatum is a halophyte ornamental plant wildly distributed in the Northeast of China, where the low water potential induced by various abiotic stresses is a major factor limiting plant growth and development. However, little is known about the comparative effects of salt, alkali, and drought stresses at uniform water potential on the plants. In the present study, the growth, gas exchange parameters, photosynthetic pigments, and chlorophyll fluorescence in the seedlings of H. jubatum under three low water potentials were measured. The results showed that the growth and photosynthetic parameters under these stresses were all decreased except for carotenoid (Car) with the increasing of stress concentration, and alkali stress caused the most damaging effects on the seedlings. The decreased net photosynthetic rate (Pn), stomatal conductance (Gs), and intercellular CO₂ concentrations (Ci) values under salt stress were mainly attributed to stomatal factors, while non-stomatal factors were dominate under drought and alkali stresses. The reduced chlorophyll and slightly increased Car contents occurred under these stresses, and most significant changed under alkali stress. In addition, the maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), and photochemical quenching coefficient (q_P) under the stresses were all decreased, indicating that salt, alkali, and drought stresses all increased susceptibility of PSII to photoinhibition, reduced the photosynthetic activity by the declined absorption of light for photochemistry, and increased PSII active reaction centers. Moreover, the non-photochemical quenching coefficient (NPQ) of alkali stress was different from salt and drought stresses, showing that the high pH of alkali stress caused more damaging effects on the photoprotection mechanism depending on the xanthophyll cycle. The above results suggest that the H. jubatum has stronger tolerance of salt than drought and alkali stresses, and the negative effects of alkali stress on the growth and photosynthetic performance of this species was most serious.

Untargeted LC-MS-based metabolomics revealed specific metabolic changes in cotyledons and roots of Ricinus communis during early seedling establishment under salt stress

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.

Influence of Cathodic Water Invigoration on the Emergence and Subsequent Growth of Controlled Deteriorated Pea and Pumpkin Seeds

The quality of seeds in gene banks gradually deteriorates during long-term storage, which is probably, at least in part, a result of the progressive development of oxidative stress. Here, we report a greenhouse study that was carried out to test whether a novel approach of seed invigoration using priming with cathodic water (cathodic portion of an electrolysed calcium magnesium solution) could improve seedling emergence and growth in two deteriorated crop seeds. Fresh seeds of Pisum sativum and Cucurbita pepo were subjected to controlled deterioration to 50% viability at 14% seed moisture content (fresh weight basis), 40 °C and 100% relative humidity. The deteriorated seeds were thereafter primed with cathodic water, calcium magnesium solution and deionized water. In addition, to study the mechanism of the impacts of invigoration, the effects of such priming on the lipid peroxidation products malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) and on the reactive oxygen species (ROS) scavenging enzymes superoxide dismutase and catalase were also determined in the fresh and deteriorated seeds. All priming treatments improved seed emergence parameters, subsequent seedling photosynthesis and growth relative to the unprimed seeds. In general, cathodic water was most effective at invigorating deteriorated seeds. Analysis of the lipid peroxidation products and antioxidant enzyme activities in invigorated seeds provided support for the hypothesis that the effectiveness of cathodic water in invigoration of debilitated orthodox seeds in general and of pea and pumpkin seeds in particular derive from its ability to act as an antioxidant.

Metabolomics Analysis Reveals the Alkali Tolerance Mechanism in Puccinellia tenuiflora Plants Inoculated with Arbuscular Mycorrhizal Fungi

Soil alkalization is a major environmental threat that affects plant distribution and yield in northeastern China. Puccinellia tenuiflora is an alkali-tolerant grass species that is used for salt-alkali grassland restoration. However, little is known about the molecular mechanisms by which arbuscular mycorrhizal fungi (AMF) enhance P. tenuiflora responses to alkali stress. Here, metabolite profiling in P. tenuiflora seedlings with or without arbuscular mycorrhizal fungi (AMF) under alkali stress was conducted using liquid chromatography combined with time-of-flight mass spectrometry (LC/TOF-MS). The results showed that AMF colonization increased seedling biomass under alkali stress. In addition, principal component analysis (PCA) and orthogonal projections to latent structures discriminant analysis (OPLS-DA) demonstrated that non-AM and AM seedlings showed different responses under alkali stress. A heat map analysis showed that the levels of 88 metabolites were significantly changed in non-AM seedlings, but those of only 31 metabolites were significantly changed in AM seedlings. Moreover, the levels of a total of 62 metabolites were significantly changed in P. tenuiflora seedlings after AMF inoculation. The results suggested that AMF inoculation significantly increased amino acid, organic acid, flavonoid and sterol contents to improve osmotic adjustment and maintain cell membrane stability under alkali stress. P. tenuiflora seedlings after AMF inoculation produced more plant hormones (salicylic acid and abscisic acid) than the non-AM seedlings, probably to enhance the antioxidant system and facilitate ion balance under stress conditions. In conclusion, these findings provide new insights into the metabolic mechanisms of P. tenuiflora seedlings with arbuscular mycorrhizal fungi under alkali conditions and clarify the role of AM in the molecular regulation of this species under alkali stress.