Exogenous 2-(3,4-Dichlorophenoxy) triethylamine alleviates salinity stress in maize by enhancing photosynthetic capacity, improving water status and maintaining K+/Na+ homeostasis

Morphological, physiological, element absorption, and transcriptomic analysis reveals the mechanism of 2-(3,4-Dichlorophenoxy) trimethylamine alleviating copper stress in cucumber seedlings

Copper (Cu) pollution resulting from human activities has emerged as a prominent issue stemming from industrial development. The entry of copper into the soil, either directly or through industrial wastewater, exerts adverse effects on plant growth, leading to its accumulation in significant quantities within the plant and subsequent endangerment of human health through the food chain. DCPTA [2-(3, 4-dichlorophenoxy) triethylamine] mitigates certain abiotic stresses, yet the precise mechanism by which it alleviates Cu-induced phytotoxicity remains unknown. This study has demonstrated that DCPTA reduces the impact of copper stress on plants by enhancing leaf pigment and photosynthesis, regulating root growth, and balancing the antioxidant system. Furthermore, the accumulation of Cu in leaves and roots of cucumber treated with DCPTA was significantly lower than that in seedlings treated with Cu alone. Transcriptome analysis showed that copper absorption, transport, detoxification genes, cell wall component related genes and nitrogen metabolism related genes played a crucial role. In conclusion, exogenous application of DCPTA can partially alleviate copper stress in cucumber.

Exogenous Melatonin Reinforces Photosynthesis, Antioxidant Defense and Gene Expression to Ameliorate Na2CO3 Stress in Maize

Salt stress can seriously affect the growth and development of maize (Zea mays L.), resulting in a great yield loss. Melatonin (MT), an indole hormone, is a potential enhancer of plant tolerance against salt stress. However, the complex mechanisms of MT application in enhancing maize salt tolerance are still unclear. Herein, three-leaf seedlings of salt-susceptible P138 and its salt-resistant ethyl methane sulfonate (EMS)-104 mutant were cultured with or without 150 μM MT application under 0 and 100 mM Na2CO3 treatments for seven days, to systematically explore the response mechanisms of exogenous MT in improving the salt tolerance of maize. The results showed that salt stress triggered an escalation in reactive oxygen species production, enhanced multiple antioxidant enzymes' activities, impaired cellular membrane permeability, inhibited photosynthetic pigment accumulation, and ultimately undermined the vigor and photosynthetic prowess of the seedlings. While suitable MT application counteracted the detrimental impacts of Na2CO3 on seedlings' growth and photosynthetic capacity, the seedling length and net photosynthetic rate of P138 and EMS-104 were increased by 5.5% and 18.7%, and 12.7% and 54.5%, respectively. Quantitative real-time PCR (qRT-PCR) analysis further showed that MT application activated the expression levels of antioxidant enzyme-related genes (Zm00001d025106, Zm00001d031908, Zm00001d027511, and Zm00001d040364) and pigment biosynthesis-related genes (Zm00001d011819 and Zm00001d017766) in both maize seedlings under Na2CO3 stress; they then formed a complex interaction network of gene expression, multiple physiological metabolisms, and phenotype changes to influence the salt tolerance of maize seedlings under MT or Na2CO3 stress. To sum up, these observations underscore that 150 μM MT can alleviate salt injury of maize seedlings, which may provide new insights for further investigating MT regulation mechanisms to enhance maize seedlings' salt resistance.

Luffa rootstock enhances salt tolerance and improves yield and quality of grafted cucumber plants by reducing sodium transport to the shoot

Soil salinity severely limits crop yield and quality. Grafting onto tolerant rootstocks is known as an effective means to alleviate salt stress. The present study was planned to find out the potential roles, mechanisms and applications of luffa rootstock to improve salt tolerance of grafted cucumber plants. Here, we screened a highly salt-tolerant luffa rootstock by evaluating the growth, photosynthetic performance, antioxidant defense and the accumulation of Na⁺ and K⁺ under salt stress. Reciprocal grafting between cucumber and luffa showed that luffa rootstock significantly improved the salt tolerance of cucumber plants, as evidenced by higher fresh weight, photochemical efficiency (Fv/Fm), and lower relative electrical conductivity (REC), which was closely associated with the decreased accumulation of Na⁺ and increased the accumulation of K⁺ in shoots of luffa grafted cucumber seedlings, leading to a lower Na⁺:K⁺ ratio in shoot when compared with self-grafted cucumber. Furthermore, grafting with intermediate stock of luffa also sufficiently alleviated cucumber salt stress by reducing Na⁺ accumulation in shoot and the whole plant but increasing Na⁺ accumulation in interstock and root under salt stress, fully proving the salt tolerance depending on the capacity of luffa interstock to limit the transport of Na⁺ from the root to the shoot. More importantly, luffa rootstock improved the growth, yield and quality of grafted cucumber plants grown in pots in solar greenhouse as revealed by increased net photosynthetic rate, plant height, leaf number, yield, Vitamin C and soluble sugar but decreased titratable acid under both salinity and normal conditions. Together, these results, for the first time, clearly demonstrated that luffa,a new highly salt-tolerant rootstock, enhances salt tolerance and improves yield and quality of grafted cucumber plants by reducing sodium transport to the shoot.

Mild water and salt stress improve water use efficiency by decreasing stomatal conductance via osmotic adjustment in field maize

Water and salt stress often occur simultaneously in heavily irrigated arid agricultural areas, yet they are usually studied in isolation. To understand the physiological bases of water use efficiency (WUE) of field-grown maize (Zea mays) at multi-scales under combined water and salt stress, we investigated the joint effects of water and salt stress on physiology, growth, yield, and WUE of two genotypes (XY335 and ZD958). We measured leaf stomatal conductance (g_s), net photosynthesis rate (A) and hydraulic traits, whole-plant growth and water use (ET), and final biomass and grain yield. Leaf osmotic adjustment was a key trait of the physiological differences between XY335 and ZD958 under water and salt stress. Although the responses of the two genotypes were different, mild water and salt stress improved intrinsic water use efficiency (iWUE = A/g_s) by (i) decreasing g_svia increasing osmotic adjustment and hydraulic resistance, and (ii) declining A via increasing stomatal limitations rather than reducing photosynthetic capacity. Joint water and salt stress had a synergistic effect on reproductive growth and grain formation of maize. Mild water and salt stress reduced ET, stabilized grain yield, and improved grain WUE via declining g_s, maintaining photosynthetic capacity, and improving harvest index. Collectively, our study provides a novel insight into the physiological mechanisms of WUE and demonstrates an approach for the efficient management of water and salt by using a growth stage-based deficit irrigation strategy or/and selecting genotypes with strong osmotic adjustment capacity and high harvest index.

Glycine betaine increases salt tolerance in maize (Zea mays L.) by regulating Na+ homeostasis

Improving crop salt tolerance is an adaptive measure to climate change for meeting future food demands. Previous studies have reported that glycine betaine (GB) plays critical roles as an osmolyte in enhancing plant salt resistance. However, the mechanism underlying the GB regulating plant Na⁺ homeostasis during response to salinity is poorly understood. In this study, hydroponically cultured maize with 125 mM NaCl for inducing salinity stress was treated with 100 μM GB. We found that treatment with GB improved the growth of maize plants under non-stressed (NS) and salinity-stressed (SS) conditions. Treatment with GB significantly maintained the properties of chlorophyll fluorescence, including Fv/Fm, ΦPSII, and ΦNPQ, and increased the activity of the antioxidant enzymes for mitigating salt-induced growth inhibition. Moreover, GB decreased the Na⁺/K⁺ ratio primarily by reducing the accumulation of Na⁺ in plants. The results of NMT tests further confirmed that GB increased Na⁺ efflux from roots under SS condition, and fluorescence imaging of cellular Na⁺ suggested that GB reduced the cellular allocation of Na⁺. GB additionally increased Na⁺ efflux in leaf protoplasts under SS condition, and treatment with sodium orthovanadate, a plasma membrane (PM) H⁺-ATPase inhibitor, significantly alleviated the positive effects of GB on Na⁺ efflux under salt stress. GB significantly improved the vacuolar activity of NHX but had no significant effects on the activity of V type H⁺-ATPases. In addition, GB significantly upregulated the expression of the PM H⁺-ATPase genes, ZmMHA2 and ZmMHA4, and the Na⁺/H⁺ antiporter gene, ZmNHX1. While, the V type H⁺-ATPases gene, ZmVP1, was not significantly regulated by GB. Altogether these results indicate that GB regulates cellular Na⁺ homeostasis by enhancing PM H+-ATPases gene transcription and protein activities to improve maize salt tolerance. This study provided an extended understanding of the functions of GB in plant responses to salinity, which can help the development of supportive measures using GB for obtaining high maize yield in saline conditions.

Salicylic acid modulates ACS, NHX1, sos1 and HKT1;2 expression to regulate ethylene overproduction and Na+ ions toxicity that leads to improved physiological status and enhanced salinity stress tolerance in tomato plants cv. Pusa Ruby

Tomato is an important crop for its high nutritional and medicinal properties. The role of salicylic acid (SA) in 1-aminocyclopropane-1-carboxylate synthase (ACS), sodium-hydrogen exchanger (NHX1), salt overly sensitive 1 (sos1) and high-affinity K⁺ transporter (HKT1;2) transcripts, and ACS enzyme activity and ethylene (ET) production, and growth and physiological attributes was evaluated in tomato cv. Pusa Ruby under salinity stress. Thirty days-old seedlings treated with 0 mM NaCl, 250 mM NaCl, 250 mM NaCl plus 100 µM SA were assessed for different growth and physiological parameters at 45 DAS. Results showed ACS, NHX1, sos1 and HKT1;2 transcripts were significantly changed in SA treated plants. The ACS enzyme activity and ET content were considerably decreased in SA treated plants. Shoot length (SL), root length (RL), number of leaves (NL), leaf area per plant (LA), shoot fresh weight (SFW) and root fresh weight (RFW) were also improved under SA treatment. Conversely, the electrolyte leakage and sodium ion (Na⁺) content were significantly reduced in SA treated plants. In addition, the endogenous proline and potassium ion (K⁺) content, and K⁺/Na⁺ ratio were considerably increased under SA treatment. Likewise, antioxidant enzymes (SOD, CAT, APX and GR) profile were better in SA treated plant. The present findings suggest that SA reverse the negative effects of salinity stress and stress induced ET production by modulating ACS, NHX, sos1 and HKT1;2 transcript level, and improving various growth and physiological parameters, and antioxidants enzymes profile. This will contribute to a better understanding of salinity stress tolerance mechanisms of tomato plants involving SA and ET cross talk and ions homeostasis to develop more tolerant plant.