Enhanced Na+ and Cl- sequestration and secretion selectivity contribute to high salt tolerance in the tetraploid recretohalophyte Plumbago auriculata Lam

Priming effect of ascorbic acid on the growth and biomass of quinoa under saline conditions

Ascorbic acid (ASA) is often recommended to mitigate the effects of saline stress on crop growth. However, no such research exists on its priming effect on the growth of quinoa (Chenopodium quinoa Willd.). Thus, the main goal of this study was to evaluate the potential benefits of ASA (0.1 and 0.5 μM) against salt-induced stress in quinoa seedlings. The results showed that ASA significantly improved germination, and biomass, especially fresh weight (≥47.14%) and dry weight (≥83.33%) even higher than CK, indicating enhanced plant vigor under such salt stress of 200 mM. Additionally, ASA-treated plants enhanced chlorophyll and carotenoid biosynthesis, with low ASA increased carotenoids by 95.45%, improving photosynthesis. Furthermore, ASA enhanced gas exchange, non-photochemical quenching (NPQ), and antioxidants enzymes activities, suggesting improve energy dissipation and potential support for oxidative stress tolerance. Notably, metabolic indicators, especially proline (≥29.89%) showed higher levels, indicating enhanced osmotic adjustment. Moreover, ASA effectively mitigated sodium (Na+) and chloride (Cl-) in roots through potassium (K+) uptake by at least 93.41% and elevated K+ levels by 99.76% in shoots, underscoring its role in mediating ion homeostasis under salinity. This study provides the first evidence that ASA could enhance biological, physiological and biochemical responses in quinoa. Applying ASA at 0.1 μM/L is feasible and effective as a priming concentration under suitable salt stress conditions.

Ceratostigma willmottianum mineralizes atmospheric carbon dioxide into calcium carbonate in a high-calcium environment

Calcium carbonate biomineralization is an ancient evolutionary feature of life that plays a key role in environmental adaptation. In plants, calcium carbonate deposition is found in several taxa; however, current knowledge of its formation and ecological adaptive implication is limited. Here, we used the chalk gland plant Ceratostigma willmottianum to gain insight into calcium carbonate biomineralization. We found that secretion crystals are mainly composed of calcium carbonate (>90%), and the chalk gland consists of 16 cells with 4 secretory pores on the surface. Calcium carbonate accumulation was highly dependent on atmospheric carbon dioxide and independent of soil dissolved inorganic carbon. Calcium carbonate accumulation occurred mainly during the day, with diurnal variations in the carbon source, mainly atmospheric carbon dioxide during the day and metabolic carbon dioxide at night. Hydration of carbon dioxide to bicarbonate (HCO3-) occurred within the leaves, and the reaction rate was controlled by the activity of extracellular carbonic anhydrases. C. willmottianum showed a high tolerance to calcium stress, potentially related to enhanced calcium compartmentalization and calcium carbonate excretion in the chalk gland under high-calcium environments. The conversion of atmospheric carbon dioxide into calcium carbonate by C. willmottianum may represent an ecological adaptation of plants to high-calcium environments. These results provide cases and theoretical references for studying calcium carbonate biomineralization mechanisms and plant calcium adaptation.

Ethyl methanesulfonate (EMS) mediated dwarfing mutation provides a basis for CaCO3 accumulation by enhancing photosynthetic performance in Ceratostigma willmottianum Stapf

Ceratostigma willmottianum Stapf is a unique chalk gland (salt-excreting) plant from China, with a salt gland structure that excretes white crystals of calcium carbonate (CaCO3), which has potential biomineralization and carbon sequestration functions. Due to the narrow distribution of wild germplasm resources, there is a lack of diversity of new varieties to satisfy commercial development and scientific exploration. Therefore, we used ethyl methanesulfonate (EMS) mutagenesis to obtain new dwarf mutant germplasm, and analysed it in terms of morphology, growth, photosynthesis, salt glands, and excretion traits. All four dwarfing mutant strains (DM1, DM2, DM3, and DM4) exhibited extreme dwarfing (62.28%, 62.28%, 74.55% and 61.68% reduction in plant height, respectively), faster growth, increased belowground root biomass, and earlier bud differentiation and flowering. Photosynthetic capacity was enhanced: chlorophyll content, maximum quantum yield of PSII (Fv/Fm), effective quantum yield of PSII (ΦPSII), photochemical quenching coefficient (qP), electron transfer rate (ETR), net photosynthesis (Pn), intercellular CO2 concentration (Ci), stomatal conductance (Gs), and transpiration (Tr), were significantly higher in leaves of DM mutants. The density of salt glands per unit leaf area and average Ca2+ excretion rate of individual salt glands increased significantly (especially in DM2), and CaCO3 accumulation per unit leaf area was 28.57% higher than that of the wild type. Pearson correlation analysis showed that photosynthetic capacity was significantly and positively correlated with CaCO3 excretion. The above study not only provided enriched new germplasm of C. willmottianum, but also important research material for studying the mechanism of CaCO3 excretion by salt glands and carbon sequestration capacity of biomineralization.

Salinity stress mitigation in wheat through synergistic application of ascorbic acid, nanoparticles and Salvadora oleoides extract

Salinity stress adversely affects wheat growth and productivity, necessitating effective mitigation strategies. This study investigates the combined impact of ascorbic acid (AsA), silver nanoparticles (NPs), and Salvadora oleoides aqueous leaf extract (LE) on wheat tolerance to salinity stress. A randomized complete design (RCD) was employed with fourteen treatments: T1 (5 mM AsA), T2 (10 mM AsA), T3 (20 ppm AgNPs), T4 (40 ppm AgNPs), T5 (5% S. oleoides LE), T6 (10% S. oleoides LE), T7 (20 ppm AgNPs + 5 mM AsA), T8 (20 ppm AgNPs + 10 mM AsA), T9 (40 ppm AgNPs + 5 mM AsA), T10 (40 ppm AgNPs + 10 mM AsA), T11 (20 ppm AgNPs + 5% S. oleoides LE), T12 (20 ppm AgNPs + 10% S. oleoides LE), T13 (40 ppm AgNPs + 5% S. oleoides LE), and T14 (40 ppm AgNPs + 10% S. oleoides LE). Wheat plants were subjected to salinity stress (SS) and no-stress conditions (NoSS) for 50 days. Chlorophyll content, DPPH activity, total soluble proteins and sugars, antioxidant enzyme activities, lipid peroxidation, leaf ion concentrations, and nutrient uptake were analyzed. Under SS, T6 (10% LE) showed the lowest chlorophyll-a (90.04%) and b (57.84%). DPPH activity was highest in NoSS with T9 (40 ppm NPs + 5 mM AsA) at 14.40%, and lowest in SS with T6 (10% LE) at 6.67%. Total soluble proteins and sugars were highest in NoSS with T9 (40 ppm NPs + 5 mM AsA) and T6 (10% LE). In SS, SOD activity peaked with T6 (10% LE) at 8.39 U/mg protein, while CAT activity was highest with T9 (40 ppm NPs + 5 mM AsA) at 6.25 U/mg protein. Lipid peroxidation was highest in SS with T6 (10% LE) at 14.67 µM MDA/g fresh weight. Leaf Na and Cl concentrations were highest in SS with T9 (40 ppm NPs + 5 mM AsA), at 14.26% and 44.15%, respectively. The combined application of 40 NPs and 5 AsA (T9) proved most effective in enhancing chlorophyll content and DPPH activity under NoSS, while 10% LE (T6) showed significant improvements in SOD activity and lipid peroxidation mitigation under SS. Future research should explore optimizing treatment concentrations and combinations to further enhance wheat stress tolerance and evaluate long-term effects on crop yield and quality.

Increasing Ca2+ accumulation in salt glands under salt stress increases stronger selective secretion of Na+ in Plumbago auriculata tetraploids

Under salt stress, recretohalophyte Plumbago auriculata tetraploids enhance salt tolerance by increasing selective secretion of Na+ compared with that in diploids, although the mechanism is unclear. Using non-invasive micro-test technology, the effect of salt gland Ca2+ content on Na+ and K+ secretion were investigated in diploid and tetraploid P. auriculata under salt stress. Salt gland Ca2+ content and secretion rates of Na+ and K+ were higher in tetraploids than in diploids under salt stress. Addition of exogenous Ca2+ increased the Ca2+ content of the salt gland in diploids and is accompanied by an increase in the rate of Na+ and K+ secretion. With addition of a Ca2+ channel inhibitor, diploid salt glands retained large amounts of Ca2+, leading to higher Ca2+ content and Na+ secretion rate than those of tetraploids. Inhibiting H2O2 generation and H+-ATPase activity altered Na+ and K+ secretion rates in diploids and tetraploids under salt stress, indicating involvement in regulating Na+ and K+ secretion. Our results indicate that the increased Na+ secretion rate of salt gland in tetraploids under salt stress was associated with elevated Ca2+ content in salt gland.

Polyploidization: A Biological Force That Enhances Stress Resistance

Organisms with three or more complete sets of chromosomes are designated as polyploids. Polyploidy serves as a crucial pathway in biological evolution and enriches species diversity, which is demonstrated to have significant advantages in coping with both biotic stressors (such as diseases and pests) and abiotic stressors (like extreme temperatures, drought, and salinity), particularly in the context of ongoing global climate deterioration, increased agrochemical use, and industrialization. Polyploid cultivars have been developed to achieve higher yields and improved product quality. Numerous studies have shown that polyploids exhibit substantial enhancements in cell size and structure, physiological and biochemical traits, gene expression, and epigenetic modifications compared to their diploid counterparts. However, some research also suggested that increased stress tolerance might not always be associated with polyploidy. Therefore, a more comprehensive and detailed investigation is essential to complete the underlying stress tolerance mechanisms of polyploids. Thus, this review summarizes the mechanism of polyploid formation, the polyploid biochemical tolerance mechanism of abiotic and biotic stressors, and molecular regulatory networks that confer polyploidy stress tolerance, which can shed light on the theoretical foundation for future research.

ISSR molecular markers and anatomical structures can assist in rapid and directional screening of cold-tolerant seedling mutants of medicinal and ornamental plant in Plumbago indica L

Plumbago indica L. is a perennial herb with ornamental and anticancer medicinal functions widely distributed in the tropics. It is affected by temperature and cannot bloom normally in colder subtropical regions, which seriously affects its ornamental value. To create low-temperature resistance mutants and enrich new germplasm resources, this study used tissue culture and chemical reagent (0.5 mmol/L NaN₃) and low-temperature stress (0°C, full darkness for 48h) induction to target and screen for cold-resistance mutants. The results showed that the ISSR band polymorphism ratio of the 24 suspected mutant materials was 87.5%. The DNA profiles of the 9 mutants initially identified were altered. The content of plumbagin in the stems and leaves of the mutants was examined, and it was found that the accumulation in the leaves of the mutant SA24 could be as high as 3.84 times that of the control, which was 0.5991%. There were significant differences in the anatomical structures of roots, stems and leaves. The mutants mostly exhibited reduced root diameter (only 0.17-0.69 times that of CK), increased stem diameter (up to 2.19 times that of CK), enlarged mesophyll cells, increased thickness (up to 1.83 times that of CK) and high specificity, which are thought to be important for the different cold resistance obtained by the mutants. In the cold resistance experiment, four cold-tolerant mutants were successfully screened according to their morphological characteristics and physiological indexes, and the mutagenesis efficiency could be as high as 2.22% and did not affect the accumulation of plumbagin in their stems and leaves, even higher than CK. The responses of the screened mutants SA15, SA19, SA23 and SA24 to low temperature showed slower leaf wilting, higher light energy conversion efficiency, less accumulation of MDA content, increased enzymatic activities of antioxidant enzymes (SOD, CAT, POD) and more accumulation of soluble sugars and proline content. These characteristics are consistent with the response of cold-resistance plants to low temperatures. The cold- resistance mutants cultivated in soil were observed of agronomic and ornamental traits for one year, mainly manifested as delayed flowering and delayed entry into the senescence stage. This study provides a more rapid and accurate technique for identifying and screening cold-tolerant mutants, and lays the foundation for future experiments on the creation of new cold-resistant varieties.