Low-nitrogen tolerance comprehensive evaluation and physiological response to nitrogen stress in broomcorn millet (Panicum miliaceum L.) seedling

Genome-wide association studies dissect low-phosphorus stress response genes underling field and seedling traits in maize

Phosphorus (P) is an essential element for plant growth, and its deficiency can cause decreased crop yield. This study systematically evaluated the low-phosphate (Pi) response traits in a large population at maturity and seedling stages, and explored candidate genes and their interrelationships with specific traits. The results revealed a greater sensitivity of seedling maize to low-Pi stress compared to that at maturity stage. The phenotypic response patterns to low-Pi stress at different stages were independent. Chlorophyll content was found to be a potential indicator for screening low-Pi-tolerant materials in the field. A total of 2900 and 1446 significantly associated genes at the maturity and seedling stages were identified, respectively. Among these genes, 972 were uniquely associated with maturity traits, while 330 were specifically detected at the seedling stage under low-Pi stress. Moreover, 768 and 733 genes were specifically associated with index values (low-Pi trait/normal-Pi trait) at maturity and seedling stage, respectively. Genetic network diagrams showed that the low-Pi response gene Zm00001d022226 was specifically associated with multiple primary P-related traits under low-Pi conditions. A total of 963 out of 2966 genes specifically associated with traits under low-Pi conditions or index values were found to be induced by low-Pi stress. Notably, ZmSPX4.1 and ZmSPX2 were sharply up-regulated in response to low-Pi stress across different lines or tissues. These findings advance our understanding of maize's response to low-Pi stress at different developmental stages, shedding light on the genes and pathways implicated in this response.

Enhancing maize resilience to drought stress: the synergistic impact of deashed biochar and carboxymethyl cellulose amendment

Drought stress poses a significant challenge to maize production, leading to substantial harm to crop growth and yield due to the induction of oxidative stress. Deashed biochar (DAB) in combination with carboxymethyl cellulose (CMC) presents an effective approach for addressing this problem. DAB improves soil structure by increasing porosity and water retention and enhancing plant nutrient utilization efficiency. The CMC provides advantages to plants by enhancing soil water retention, improving soil structure, and increasing moisture availability to the plant roots. The present study was conducted to investigate the effects of DAB and CMC amendments on maize under field capacity (70 FC) and drought stress. Six different treatments were implemented in this study, namely 0 DAB + 0CMC, 25 CMC, 0.5 DAB, 0.5 DAB + 25 CMC, 1 DAB, and 1 DAB + 25 CMC, each with six replications, and they were arranged according to a completely randomized design. Results showed that 1 DAB + 25 CMC caused significant enhancement in maize shoot fresh weight (24.53%), shoot dry weight (38.47%), shoot length (32.23%), root fresh weight (19.03%), root dry weight (87.50%) and root length (69.80%) over control under drought stress. A substantial increase in maize chlorophyll a (40.26%), chlorophyll b (26.92%), total chlorophyll (30.56%), photosynthetic rate (21.35%), transpiration rate (32.61%), and stomatal conductance (91.57%) under drought stress showed the efficiency of 1 DAB + 25 CMC treatment compared to the control. The enhancement in N, P, and K concentrations in both the root and shoot validated the effectiveness of the performance of the 1 DAB + 25 CMC treatment when compared to the control group under drought stress. In conclusion, it is recommended that the application of 1 DAB + 25 CMC serves as a beneficial amendment for alleviating drought stress in maize.

Strong Invasive Mechanism of Wedelia trilobata via Growth and Physiological Traits under Nitrogen Stress Condition

Nitrogen (N) is one of the most crucial elements for plant growth. However, a deficiency of N affects plant growth and development. Wedelia trilobata is a notorious invasive plant species that exhibits superior tolerance to adapt to environmental stresses. Yet, research on the growth and antioxidant defensive system of invasive Wedelia under low N stress, which could contribute to understanding invasion mechanisms, is still limited. Therefore, this study aims to investigate and compare the tolerance capability of invasive and native Wedelia under low and normal N conditions. Native and invasive Wedelia species were grown in normal and low-N conditions using a hydroponic nutrient solution for 8 weeks to assess the photosynthetic parameters, antioxidant activity, and localization of reactive oxygen species (ROS). The growth and biomass of W. trilobata were significantly (p < 0.05) higher than W. chinensis under low N. The leaves of W. trilobata resulted in a significant increase in chlorophyll a, chlorophyll b, and total chlorophyll content by 40.2, 56.2, and 46%, respectively, compared with W. chinensis. W. trilobata significantly enhanced antioxidant defense systems through catalase, peroxidase, and superoxide dismutase by 18.6%, 20%, and 36.3%, respectively, providing a positive response to oxidative stress caused by low N. The PCA analysis showed that W. trilobata was 95.3% correlated with physiological traits by Dim1 (79.1%) and Dim2 (16.3%). This study provides positive feedback on W. trilobata with respect to its comprehensive invasion mechanism to improve agricultural systems via eco-friendly approaches in N deficit conditions, thereby contributing to the reclamation of barren land.

Dynamic changes in microbial communities and flavor during different fermentation stages of proso millet Baijiu, a new product from Shanxi light-flavored Baijiu

Introduction

Proso millet, a high-quality fermentation material used for Chinese yellow wine production, can produce special flavored substances; however, its role in improving the flavor and altering microbial communities of light-flavored Baijiu during fermentation remain unknown. Thus, we aimed to investigate the effect of proso millet on improving the flavor of light-flavored Baijiu and altering microbial communities during different fermentation stages.

Methods

The dynamic changes in the microbial communities and flavor of proso millet (50%) + sorghum (50%) mixed fermentation samples were analyzed through intermittent sampling on days 7, 14, 21, and 28 of the fermentation process. Microbial high-throughput sequencing and the analysis of flavor characteristics were conducted through 16S DNA/ ITS amplicon sequencing and gas chromatography (multi-capillary column)-ion mobility spectrometry, respectively.

Results

Proso millet significantly changed the core flavor compound composition of traditional light-flavored Baijiu from ethyl acetate, ethyl hexanoate, ethyl hexanoate dimer, ethyl butanoate, ethyl lactate, and butyl acetate to oct-2-ene, 2-butanol, propyl propanoate, 2-pentenal, and 4-methylpentanal. The amplicon sequencing analysis revealed that the alpha diversity parameters of bacterial and fungal communities, including the Chao1, Pielou_e, Shannon, and Simpson indices, for proso millet-sorghum mixed fermentation samples were significantly higher than those for sorghum fermentation samples (p < 0.05). Of the 40 most significant microbial genera in two treatments, proso millet significantly increased the abundance of 12 bacterial and 18 fungal genera. Among the 40 most significant bacterial and fungal species, 23 bacterial species belonged to the Lactobacillus genus, whereas the 30 primary fungal species belonged to 28 different genera. The analysis of the relationship between microbial changes and the main flavor compounds of light-flavored Baijiu showed that bacteria from the Weissella, Acinetobacter, Bacteroides, Psychrobacter, Pseudarthrobacter, Lactococcus, Chloroplast, Saccharopolyspora, Psychrobacter, Saccharopolyspora, Pseudonocardiaceae, Bacteroides genera and fungi from the Thermoascus, Aspergillus, Pichia, Rhizomucor, Papiliotrema, Hyphopichia, and Mucor genera significantly inhibited the synthesis of ethyl hexanoate, ethyl butanoate, ethyl lactate ethyl lactate, and butyl acetate but increased the synthesis of ethyl acetate (p < 0.05). Moreover, these microbes exhibited a significantly greater abundance in proso millet-sorghum mixed fermentation samples than in sorghum samples. The synthesis of special flavored compounds in proso millet Baijiu was significantly positively correlated with the presence of fungi from the Rhizopus, Papiliotrema, Wickerhamomyces, Aspergillus, and Thermoascus genera but negative correlated with the presence of bacteria from the Weissella, Acinetobacter, Psychrobacter, Pseudarthrobacter, Bacteroides, and Saccharopolyspora genera. Regarding ethanol content, the low alcohol content of Fenjiu may be due to the significantly high abundance of fungi from the Psathyrella genus and bacteria from the Staphylococcus, Kroppenstedtia, Brevibacterium, and Acetobacter genera during fermentation. In summary, proso millet significantly altered the flavor of light-flavored Baijiu by inducing the formation of a special microbial community; however, it did not increase alcohol concentration.

Discussion

This study lays the foundation for future research on Baijiu fermentation. Additionally, the study findings may help improve the production efficiency and elevate the quality and flavor of the final product.

Integrated physiological, biochemical, and transcriptomics analyses reveal the underlying mechanisms of high nitrogen use efficiency of black sesame

Cultivating high nitrogen use efficient varieties is a sustainable solution to mitigating adverse effects on the environment caused by excessive nitrogen fertilizer application. However, in sesame, although immoderate nitrogen fertilizers are used to promote yield, the molecular basis of high nitrogen use efficiency (NUE) is largely unknown. Hence, this study aimed to identify high NUE black sesame variety and dissect the underlying physiological and molecular mechanisms. To achieve this, seventeen seedling traits of 30 black sesame varieties were evaluated under low nitrogen (LN) and high nitrogen (HN) conditions. Dry matter accumulation, root parameters, shoot nitrogen accumulation, and chlorophyll content are important factors for evaluating the NUE of sesame genotypes. The variety 17-156 was identified as the most efficient for N utilization. Comparative physiological and transcriptomics analyses revealed that 17-156 possesses a sophisticated nitrogen metabolizing machinery to uptake and assimilate higher quantities of inorganic nitrogen into amino acids and proteins, and simultaneously improving carbon metabolism and growth. Specifically, the total nitrogen and soluble protein contents significantly increased with the increase in nitrogen concentrations. Many important genes, including nitrate transporters (NPFs), amino acid metabolism-related (GS, GOGAT, GDH, etc.), phytohormone-related, and transcription factors, were significantly up-regulated in 17-156 under HN condition. In addition, 38 potential candidate genes were identified for future studies toward improving sesame's NUE. These findings offer valuable resources for deciphering the regulatory network of nitrogen metabolism and developing sesame cultivars with improved NUE.

Tolerance and adaptation characteristics of sugar beet (Beta vulgaris L.) to low nitrogen supply

Nitrogen (N) is an essential element required for sugar beet growth. Sugar beets with low N (LN) tolerance and high N use efficiency are excellent materials for breeding. Here, we comprehensively evaluated the morphological and physiological responses of nine sugar beet genotypes to LN supply. It was found that 0.5 mmol·L^-1 N (LN) significantly influenced the performance of leaves and the topology of roots by reducing the bioproduction of chlorophyll a (Chl a) and soluble protein (SP) and the accumulation of N in leaves and roots (LNA and RNA), thus differentially restricting the growth (hypocotyl diameter, HD; root length, RL) and biomass (leaf and root fresh weight; LFW and RFW; leaf dry weight, LDW) of these sugar beets. Principal component and cluster analyses showed that 780016B/12 superior (F) exhibited excellent tolerance to LN; it had higher SOD activity (62.70%) and APX activity (188.92%) and a higher proline content (131.82%) than 92011 (G, LN sensitive). These attributes helped 780016B/12 superior (F) to better endure LN stress, and the morphology and N distribution changed to adapt to N deficiency, such that the root length increased by 112.48%, leaf area increased by 101.23%, and leaf nitrogen accumulation reached a peak of 14.13 g/plant. It seems that LN-tolerant genotypes increased their root length and surface area by reducing the difference in biomass, thereby expanding the contact between roots and soil, which was conducive to the absorption of nutrients (N) by sugar beets and helped distribute more assimilation products to the roots.

Widely targeted metabolomic analysis revealed the effects of alkaline stress on nonvolatile and volatile metabolites in broomcorn millet grains

Broomcorn millet (BM) is a future smart food. However, no information is available on the metabolism of BM grains under alkaline stress. In this study, the effects of alkaline stress on nonvolatile and volatile metabolites in the BM grains of two varieties (S223 and T289) were investigated through metabolomics approaches. All 933 nonvolatile metabolites and 313 volatile metabolites were identified, with 114 and 89 nonvolatile metabolites and 16 and 20 volatile metabolites accumulating differentially under normal vs. alkaline stresses of S223 and T289, respectively. The results indicated that alkaline stress altered phenylpropanoids, flavonoids, flavone and flavonol, valine, leucine, and isoleucine biosynthesis, as well as arginine, proline, tryptophan, and ascorbate metabolism. The effects of alkaline stress were not identical between the two varieties, which could lead to variations in active substance content. These results provide valuable information for further studies on food chemistry and the functional food development of BM grains.

Effects of fertilization gradient on the production performance and nutritional quality of cultivated grasslands in karst areas

Optimal fertilization is an important measure for managing cultivated grasslands, and a necessary means for maintaining the nutrient balance, yield, and quality of grassland ecosystems. This study aimed to explore the effects of organic fertilizers on the production performance and nutritional quality of cultivated grasslands in karst areas. Two types of monocultured cultivated grasslands (i.e., Medicago sativa and Dactylis glomerata) were employed as the research objects, and a randomized block design was adopted to investigate the effects of five fertilization gradients on the forage height, coverage, yield, and nutritional quality of the cultivated grasslands. According to the results, the plant height, coverage, and yield of M. sativa first presented an increasing trend, then decreased with increasing fertilization gradient, with a peak at 20-30 t/hm2 fertilization gradient. The height, coverage, and yield of D. glomerata increased gradually with increase in fertilization gradient, and peaked at 40 t/hm2. Meanwhile, the crude protein (CP) and ether extract (EE) contents of both grassland types displayed first presented an increasing trend, then decreased with increasing fertilization gradient, and peaked at 10-30 t/hm2 fertilization gradient. The neutral detergent fiber (NDF) and acidic detergent fiber (ADF) contents of M. sativa presented "N-shaped" and "M-shaped" change trends with increasing fertilization gradient, while those of D. glomerata showed "V-shaped" and "M-shaped" change trends, reaching minimum values under fertilization gradients of 30 and 20 t/hm2, respectively. Year, fertilization, and year × fertilization (Y×F) significantly affected the plant heights, coverages, dry/fresh weight ratios, and yields of M. sativa and D. glomerata. The contribution of coverage to the subordinate function of M. sativa was greatest at a fertilization gradient of 20 t/hm2. Meanwhile, the subordinate function values of the height and coverage of D. glomerata increased gradually with increasing fertilization gradient, but the difference in the subordinate function value of height was only 0.09%-0.18% under the fertilization gradient of 20-40 t/hm2. Evaluation of forage nutrition revealed 10-30 t/hm2 and 20-30 t/hm2 as the optimal organic fertilizer application rates for M. sativa and D. glomerata, respectively.

Response of Canola productivity to integration between mineral nitrogen with yeast extract under poor fertility sandy soil condition

Canola is one of the important oil crops and is considered the most promising oil source and adapts to reclaimed soil conditions. The current study aimed to evaluate the influence of yeast extract (YE) integrated with nitrogen (N) rates and treatments were arranged as follows: Control (without F0), 95 kg N ha^-1 (F1), 120 kg N ha^-1 (F2), 142 kg N ha^-1 (F3), 95 kg N ha^-1 + YE (F4), 120 kg N ha^-1 + YE (F5) and 142 kg N ha^-1 + YE (F6) on physico-chemical properties, yield and its components for three Canola genotypes i.e. AD201 (G1), Topaz and SemuDNK 234/84 under the sandy soil. In this work, Results reveal that increasing rates of Nitrogen fertilization from 95 kg N ha^-1 to 142 kg N ha^-1 have a great effect on physicochemical properties yield and its components. The result proved that 142 kg N ha^-1 with yeast treatment was the best treatment for three Canola genotypes. Also, the result showed that seed yield was positively correlated with Chl. a/b ratio, plant height, number of branches/plant, number of pods/plant, and number of seeds/pod, and a strong negative correlation was detected between seed oil percentage when the amount of nitrogen fertilization applied without or with yeast extract is increased.

Cultivar sensitivity of broomcorn millet (Panicum miliaceum L.) to nitrogen availability is associated with differences in photosynthetic physiology and nitrogen uptake

In order to explore the influences of low nitrogen (N) fertilizer on the growth performances of two broomcorn millet (Panicum miliaceum L.) cultivars with different N tolerances, the field experiment was carried out with a low-N-tolerant cultivar (BM 184) and a low-N-sensitive cultivar (BM 230) under three N levels (0, 75 and 150 kg N ha^-1) in the Loess Plateau, China. 150 kg N ha^-1 was conventional N application rate and considered as the control. Compared to typical N supply, low N fertilizer significantly weakened the photosynthetic capacity by increasing the light transmission ratio and decreasing leaf area index, resulting in reduced biomass accumulation. BM 184 held the longer duration of the biomass increase phase and larger relative growth rate than BM 230 as well as higher photosynthetic parameters (i.e., relative chlorophyll content, net photosynthetic rate, and transpiration rate) did under low N treatments. Such optimized physiological characteristics contributed to more effective N uptake and transportation from the stems, leaves, and sheaths to grains in the BM 184. Furthermore, compared with BM 230, BM 184 had higher rhizosphere soil fertility and soil enzyme activity under low N conditions; consequently, combined with the physiological characteristics for aboveground and soil nutrient status for belowground, higher productivity was obtained in BM 184 than that in BM 230 over the two years study. Overall, our results demonstrated that low-N-tolerant cultivar achieved reduced N fertilizer input with increased efficiency by optimizing growth performances in semi-arid cultivation areas.

Comparative Proteomic Analysis of Two Contrasting Maize Hybrids’ Responses to Low Nitrogen Stress at the Twelve Leaf Stage and Function Verification of ZmTGA Gene

Nitrogen is one of the essential nutrients for plant growth and development. However, large amounts of nitrogen fertilizer not only increase the production costs, but also lead to serious environmental problems. Therefore, it is particularly important to reduce the application of nitrogen fertilizer and develop maize varieties with low nitrogen tolerance. The aim of this study was to determine the phenotypic and proteomic alterations of maize affected by nitrogen deficiency and to elucidate the molecular and physiological mechanisms underpinning maize tolerance to low nitrogen. Two maize hybrids with contrasting low nitrogen tolerance were used as the experimental materials. Maize plants were grown under different nitrogen application levels (N0 and N240) and proteomic analysis performed to analyze leaf differentially abundant proteins (DAPs) under different nitrogen conditions. The results showed that under the nitrogen deficiency condition, the nitrogen content, leaf dry weight, leaf area, and leaf area index of XY335 decreased by 15.58%, 8.83%, 3.44%, and 3.44%, respectively. However, in the variety HN138, the same parameters decreased by 56.94%, 11.97%, 8.79%, and 8.79%, respectively. Through proteomic analysis, we found that the low nitrogen tolerance variety responded to low nitrogen stress through lignin biosynthesis, ubiquitin-mediated proteolysis, and stress defense proteins. Transmembrane transporters were differentially expressed in both hybrids after low nitrogen treatment, suggesting that this was a common response to low nitrogen stress. Using bioinformatics analysis, we selected the key candidate gene (ZmTGA) that was assumed to respond to low nitrogen stress, and its function was characterized by maize mutants. The results showed that when compared with normal nitrogen treatment, the root length of the mutants under low nitrogen treatment increased by 10.1%, while that of the wild-type increased by 14.8%; the root surface area of the wild type under low nitrogen treatment increased by 9.6%, while that of the mutants decreased by 5.2%; the root surface area of the wild type was higher than that of the mutant at both nitrogen levels; and the activities of glutathione and guaiacol peroxidase enzymes in the mutant were lower than those in the wild-type under low nitrogen treatment. In summary, the mutant was less adaptable to a low nitrogen environment than the wild type. Our results provide maize genetic resources and a new direction for a further understanding of maize response to low nitrogen stress.

Waterlogging tolerance and recovery capability screening in peanut: a comparative analysis of waterlogging effects on physiological traits and yield

Fifteen peanut varieties at the pod filling stage were exposed to waterlogging stress for 7 days, the enzyme activities and fluorescence parameters were measured after 7 days of waterlogging and drainage. The waterlogging tolerance and recovery capability of varieties were identified. After waterlogging, waterlogging tolerance coefficient (WTC) of relative electrolyte linkage (REL), malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, and catalase (CAT) activity, non-photochemical quenching (NPQ) and photochemical quenching (qL) of leaves of most peanut varieties were increased, while the WTC of the soil and plant analysis development (SPAD) value, PS II actual quantum yield (Φ _PS II ), maximum photochemical efficiency (Fv/Fm) were decreased. After drainage, the WTC of REL, MDA content, SOD and CAT activity of leaves were decreased compared with that of after waterlogging, but these indicators of a few cultivars were increased. Φ _PS II , Fv/Fm and qL can be used as important indexes to identify waterlogging recovery capability. There was a significant negative correlation between recovery capability and the proportion of reduction in yield, while no significant correlation was found between waterlogging tolerance and the proportion of reduction in yield. Therefore, it is recommended to select varieties with high recovery capability and less pod number reduction under waterlogging in peanut breeding and cultivation.

Nitrogen fertilization stimulates nitrogen assimilation and modifies nitrogen partitioning in the spring shoot leaves of citrus (Citrus reticulata Blanco) trees

The spring shoot leaves are important sites of nitrogen (N) metabolism in citrus trees. Understanding the physiological and metabolic response of the spring shoot leaves under varying N fertilization is fundamental to the fertilization management in citrus orchards. Thus, the processes affecting N composition, the activities of N metabolism related enzymes, and the expression of relevant genes were explored in spring shoot leaves under four N levels (0, 207, 275, 413 g N tree^-1 y^-1, as N0, N207, N275, N413). The results showed that, compared with N0, N275 significantly increased total N by 24.81%, which was mainly attributed to enhancement of structural N by 30.92%, free amino acid N by 40.91% and nitrate N by 41.33%. The relative expression of nitrate reductase (NR) and glutamate dehydrogenase (GDH) under N275 increased by 19.32% and 73.48%, respectively, compared with that under N0 treatment. Compared with N0 treatment, the NR transcription level under N275 treatment increased by 381%. The relative transcription levels of NADP-GDH and GDH1 also increased with increasing N fertilization. However, compared with that under N275, the relative transcription of GDH2 under N413 treatment was inhibited. Therefore, the transcript abundance of NR, NADP-GDH,GDH1 and GDH2 affected the activities of NR and GDH and thereby contributed to the regulation of N composition in the leaves. In addition, the activities of glutamine synthetase and nitrite reductase were largely unaffected or even declined in the N207, N275 and N413 treatments compared with the N0. This study elucidated the mechanism of primary N metabolism and partitioning in citrus leaves and provided a theoretical basis for N management in citrus orchards.

The Alkali Tolerance of Broomcorn Millet (Panicum miliaceum L.) at the Germination and Seedling Stage: The Case of 296 Broomcorn Millet Genotypes

Broomcorn millet (BM), one of the earliest domesticated cereal crops originating in northern China, can tolerate extreme conditions, such as drought and high temperatures, which are prevalent in saline-alkali, arid, and barren landscapes. However, its adaptive mechanism to alkali stress is yet to be comprehensively understood. In this study, 80 and 40 mM standard alkali stress concentrations were used to, respectively, evaluate the alkali tolerance at the germination and seedling stages of 296 BM genotypes. Principal component analysis (PCA), Pearson's correlation analysis, and F-value comprehensive analysis were performed on the germination parameters (germination potential, germination index, germination rate, vigor index, root length/weight, sprout length/weight, and alkali damage rate). Based on their respective F-values, the BM genotypes were divided into five categories ranging from highly alkali resistant to alkali sensitive. To study the response of seedlings to alkaline stress, we investigated the phenotypic parameters (plant height, green leaf area, biomass, and root structure) of 111 genotypes from the above five categories. Combining the parameters of alkali tolerance at the germination and seedling stages, these 111 genotypes were further subdivided into three groups with different alkali tolerances. Variations in physiological responses of the different alkali-tolerant genotypes were further investigated for antioxidant enzyme activity, soluble substances, malondialdehyde (MDA) content, electrolyte leakage rate, and leaf structure. Compared with alkali-sensitive genotypes, alkali-tolerant genotypes had high antioxidant enzyme activity and soluble osmolyte content, low MDA content and electrolyte leakage rate, and a more complete stomata structure. Taken together, this study provides a comprehensive and reliable method for evaluating alkali tolerance and will contribute to the improvement and restoration of saline-alkaline soils by BM.

A promising crop for cadmium-contamination remediation: Broomcorn millet

Cadmium (Cd) pollution highly threatens food security and human health, and phytoremediation with Cd-tolerant plants is a cost-effective in situ method for remediation of Cd contamination. Broomcorn millet is known for its strong abiotic stress resistance and can be used as a pioneer crop in both marginal regions and newly reclaimed land. To evaluate their potential in remediation of Cd contamination, a total of 288 broomcorn millet core collections were investigated under hydroponic conditions to compare their capabilities in Cd tolerance, translocation, and accumulation. The core collections varied considerably in their growth parameters, Cd concentration, Cd translocation factor, Cd bioaccumulation factor, and Cd accumulation under Cd stress. According to the Cd tolerance index (TI) values, 160 varieties were Cd tolerant. The Cd TI was significantly positively correlated with Cd accumulation, and the shoot Cd concentrations of five Cd-tolerant varieties were more than 100 mgkg-1, the threshold for being Cd hyperaccumulators. Moreover, the concentrations of essential metal elements were significantly decreased in shoots, and Cd concentration had a significantly positive relationship with magnesium (Mg) and zinc (Zn) concentrations in roots under Cd stress. These results demonstrate that broomcorn millet shows considerable tolerance to Cd stress and great differences in Cd accumulation abilities among varieties. Accordingly, broomcorn millet is a promising plant species for Cd bioremediation, with valuable varieties that have been identified for further study on Cd tolerance mechanisms and the remediation of Cd contamination.

Comprehensive evaluation of physiological traits under nitrogen stress and participation of linolenic acid in nitrogen-deficiency response in wheat seedlings

BACKGROUND

Nitrogen (N) deficiency is a major constraint for plant production in many areas. Developing the new crop genotypes with high productivity under N deficiency is an important approach to maintain agricultural production. Therefore, understanding how plant response to N deficiency and the mechanism of N-deficiency tolerance are very important for sustainable development of modern crop production.

RESULTS

In this study, the physiological responses and fatty acid composition were investigated in 24 wheat cultivars under N-deficient stress. Through Pearson's correlation analysis and principal component analysis, the responses of 24 wheat cultivars were evaluated. The results showed that the plant growth and carbohydrate metabolism were all differently affected by N deficiency in all tested wheat cultivars. The seedlings that had high shoot biomass also maintained high level of chlorophyll content under N deficiency. Moreover, the changes in fatty acid composition, especially the linolenic acid (18:3) and the double bond index (DBI), showed close positive correlations with the shoot dry weight and chlorophyll content alterations in response to N-deficient condition. These results indicated that beside the chlorophyll content, the linolenic acid content and DBI may also contribute to N-deficiency adaptation, thus could be considered as efficient indicators for evaluation of different response in wheat seedlings under N-deficient condition.

CONCLUSIONS

The alteration in fatty acid composition can potentially contribute to N-deficiency tolerance in plants, and the regulation of fatty acid compositions maybe an effective strategy for plants to adapt to N-deficient stress.