Remobilization Efficiency Research Articles

Multi-scale phenotyping of senescence-related changes in roots of Rapeseed in response to nitrate limitation.

Root senescence remains largely unexplored. In this study, the temporality of the morphological, metabolic, and proteomic changes occurring with root aging were investigated, providing a comprehensive picture of the root senescence program. We found novel senescence-related markers for the characterization of the developmental stage of root tissues. The rapeseed root system is unique in that it consists of the taproot and lateral roots. Our study confirms that the taproot, which transiently accumulates large quantities of starch and proteins, is specifically dedicated to nutrient storage and remobilization, while the lateral roots are mainly dedicated to nutrient uptake. Proteomic data from the taproot and lateral roots highlight the different senescence-related events that control nutrient remobilization and nutrient uptake capacities. Both the proteome and enzyme activities revealed senescence-induced proteases and nucleotide catabolic enzymes that deserve attention as they may play important roles in nutrient remobilization efficiency in rapeseed roots. Taking advantage of publicly available transcriptomic and proteomic data on senescent Arabidopsis leaves, we have highlighted new lists of senescence-related proteins specific or common to root organs and/or leaves.

Biochar application affected biochemical properties, yield and nutrient content of safflower under water stress

A two-year field trial was set up to investigate the effects of applying 3 tons ha-1 of wheat (3WB) and cotton biochar (3CB) alone or in combination with chemical nitrogen (N) and phosphorus (P) fertilizers on biochemical properties, yield and nutrient content of safflower under normal irrigation and water stress (irrigation cut-off at flowering stage) conditions. The total water applied in the chemical treatments [150 kg ha−1 N + 50 kg ha−1 P (100% of the recommended dose) and 112.5N + 37.5P (75% of the recommended dose)] under water stress, was significantly higher than other treatments. Application of 112.5N + 37.5P + 3CB increased RWC from 57.5 to 59.4% and the total chlorophyll content from 80.7 to 128.1%, compared to the control. The carotenoid content, catalase and peroxidase in 112.5N + 37.5P + 3CB were lower than chemical fertilizers. Under water stress, the seed yield of 112.5N + 37.5P + 3CB was 10.2–12.6% higher than 112.5N + 37.5P + 3WB. The higher chlorophyll content, RWC, remobilization efficiency and nutrient content in 112.5N + 37.5P + 3CB compared to other treatments was associated with seed yield enhancement. The findings indicate that the combination of CB with 75% recommended dosage of N and P, may be the optimal approach for enhancing safflower production under water stress conditions.

Synergistic effect of salicylic acid and biochar on biochemical properties, yield and nutrient uptake of triticale under water stress

In arid regions, one of the practical solutions to overcome the water shortage and increasing soil fertility is application of salicylic acid (SA) with biochar. A pot experiment was conducted to consider the combination of SA with biochar on biochemical and physiological parameters of triticale as a factorial experiment using a completely randomized design (RCD) with four replicates. Treatments consisted of irrigation regime (normal irrigation and irrigation according to 50 % field capacity), salicylic acid application [without SA (SA0) and 3 mM SA (SA3)] and fertilizer type including without fertilizer (control), application of 50 kg ha−1 phosphorus (P), and application of wheat biochar (WB), cotton biochar (CB) and sesame biochar (SB) (2 % w/w). Under water stress, CB at SA0 and SA3 could improve the total chlorophyll by 119.4 and 70.6 %, compared to control, respectively. Also, carotenoid content in SA3 treatments increased in the range of 75.8 to 34.6 % compared to SA0. CB at SA3, increased catalase activity by 11.4 % compared to SB. At SA3, the highest RWC was observed in WB and CB by 26.7 and 18.1 % increases compared to SA0, respectively. At SA3, CB could enhance grain yield by 24.8 % under water stress. Under water stress, at SA3, remobilization efficiency from 63.2 % in control was enhanced to 69.2, 74.3 and 68.1 % in WB, CB and SB, respectively. CB and WB had better chemical properties in terms of EC, N, P, K and micronutrients compared to SB. These properties of BC and WB enhanced their ability to increase the nutrient availability, biochemical properties and consequently the grain yield enhancement, especially when applied with SA3.

Impact of nitrogen on photosynthesis, remobilization, yield, and efficiency in winter wheat under heat and drought stress

Droughts and high temperatures often occur during the late reproductive periods of winter wheat, greatly threatening winter crop production. However, the potential of nitrogen (N) management to mitigate the adverse effects of heat and drought stress on winter wheat remains unclear. Therefore, a two-season wheat experiment was performed to examine the impacts of temperature, soil moisture, and N supply on the photosynthetic rate, N accumulation and remobilization efficiency, and water and N use efficiency. Drought and heat stress resulted in a significant reduction in gas exchange, which was exacerbated by combined stress. In the combined stress treatment (HD), the stomatal conductance and transpiration rate under low N (N1) application increased by approximately 20 % and 15 %, respectively, compared to those under high N (N3) application. The highest net photosynthetic rate and instantaneous water use efficiency were observed under medium N (N2) application. An appropriate reduction in N supply alleviated the impacts of combined stress on growth traits, with the aboveground dry mass and green leaf area under N1 application increasing by 8.49 % and 24.10 %, respectively, compared with those under N3. Drought and heat stress significantly reduced the mean grain-filling rate, grain N accumulation (GNA), and contribution to grain N by post-anthesis N uptake (CANU), especially under combined stress. Compared with that under N1, the GNA in the DH treatment under N2 increased by 7.16 %, whereas the CANU gradually decreased with increasing N supply. Compared with the control, combined stress slightly increased WUE-biomass but decreased WUE-yield, and 19.91 % and 10.77 % lower NUE-yield and NUE-biomass, respectively, were observed under combined stress. The yield, WUE-biomass, and NUE-biomass of the DH treatment with N1 application increased by 16.19 %, 9.27 %, and 6.97 %, respectively, compared with those of the N3 treatment, whereas the WUE-biomass and NUE-yield were greatest under the N2 treatment. Entropy-topsis analysis revealed that the DH treatment under the N1 supply had a greater composite evaluation index than did the N2 and N3 supplies. Reducing nitrogen application effectively mitigated yield suppression and improved water and nitrogen use efficiency in winter wheat under post-anthesis combined stress.

Adaptive Responses of Hormones to Nitrogen Deficiency in Citrus sinensis Leaves and Roots.

Some citrus orchards in China often experience nitrogen (N) deficiency. For the first time, targeted metabolomics was used to examine N-deficient effects on hormones in sweet orange (Citrus sinensis (L.) Osbeck cv. Xuegan) leaves and roots. The purpose was to validate the hypothesis that hormones play a role in N deficiency tolerance by regulating root/shoot dry weight ratio (R/S), root system architecture (RSA), and leaf and root senescence. N deficiency-induced decreases in gibberellins and indole-3-acetic acid (IAA) levels and increases in cis(+)-12-oxophytodienoic acid (OPDA) levels, ethylene production, and salicylic acid (SA) biosynthesis might contribute to reduced growth and accelerated senescence in leaves. The increased ethylene formation in N-deficient leaves might be caused by increased 1-aminocyclopropanecarboxylic acid and OPDA and decreased abscisic acid (ABA). N deficiency increased R/S, altered RSA, and delayed root senescence by lowering cytokinins, jasmonic acid, OPDA, and ABA levels and ethylene and SA biosynthesis, increasing 5-deoxystrigol levels, and maintaining IAA and gibberellin homeostasis. The unchanged IAA concentration in N-deficient roots involved increased leaf-to-root IAA transport. The different responses of leaf and root hormones to N deficiency might be involved in the regulation of R/S, RSA, and leaf and root senescence, thus improving N use efficiency, N remobilization efficiency, and the ability to acquire N, and hence conferring N deficiency tolerance.

Nutrient remobilization and C:N:P stoichiometry in response to elevated CO2 and low phosphorus availability in rice cultivars introgressed with and without Pup1

The continuously rising atmospheric CO2 concentration potentially increase plant growth through stimulating C metabolism; however, plant C:N:P stoichiometry in response to elevated CO2 (eCO2) under low P stress remains largely unknown. We investigated the combined effect of eCO2 and low phosphorus on growth, yield, C:N:P stoichiometry, and remobilization in rice cv. Kasalath (aus type), IR64 (a mega rice variety), and IR64-Pup1 (Pup1 QTL introgressed IR64). In response to eCO2 and low P, the C accumulation increased significantly (particularly at anthesis stage) while N and P concentration decreased leading to higher C:N and C:P ratios in all plant components (leaf, sheath, stem, and grain) than ambient CO2. The remobilization efficiencies of N and P were also reduced under low P with eCO2 as compared to control conditions. Among cultivars, the combined effect of eCO2 and low P was greater in IR64-Pup1 and produced higher biomass and grain yield as compared to IR64. However, IR64-Pup1 exhibited a lower N but higher P concentration than IR64, indicating that the Pup1 QTL improved P uptake but did not influence N uptake. Our study suggests that the P availability along with eCO2 would alter the C:N:P ratios due to their differential partitioning, thereby affecting growth and yield.

Response of nutrient accumulation, remobilization and yield to combined application of nitrogen and potassium in waxy maize

Unbalanced fertilizers supply with highly intensity and excessive nitrogen (N) and less potassium (K), lead to the decrease of soil fertility year by year. Balanced fertilization is one of the most effective measures to reduce fertilizer use while improving maize yield and efficiency. Two N levels (180 and 225 kg N ha−1, abbreviated N12 and N15) and four K treatments (0, 75, 150, and 75+75 kg K2O ha−1, abbreviated K0, K5, K10, and K5+5) were set to study the effects of combined application of N and K on the biomass and nutrient accumulation and remobilization characteristics in waxy maize. The results demonstrated that grain yield increased when higher amounts of K were applied at constant N levels, showing an average increase of 1,254.8 kg ha−1 (2020) and 727.3 kg ha−1 (2021) compared with K0. Under same N and K application, K5+5 increased grain yield by increasing kernel weight. Under K5+5 treatment, the biomass and nutrient accumulation had no significant difference between N12 and N15. Compared with K10, K5+5 not only enhanced the average remobilization amount (RBA) of biomass, but also increased RBA of N, phosphorus (P) and K. In addition, the average remobilization efficiency (RBE) of biomass, N, P and K in K5+5 were increased 3.3, 4.6, 10.6 and 4.2%, respectively. Furthermore, topdressing K improved the apparent contribution to grain (AC) of biomass, N, P and K, which promoted more nutrient to grains, and significantly increased nutrient harvest index. Considering yield and fertilizer use efficiency, we recommend optimized K application (basal and topdressing 75 kg ha−1) and moderately reduced N application (from 225 to 180 kg ha−1) in the production of spring-sown waxy maize in southern China.

Shading and waterlogging interactions exacerbate summer maize yield losses by reducing assimilate accumulation and remobilization processes

Persistent overcast rain was an essential limiting factor for summer maize production, of which immediate impact was the dual pressure of waterlogging and shading. However, the mechanism of independent and combined effects of waterlogging and shading induced maize yield losses are rarely studied, especially at different growth stages. Denghai 605 (DH605) was selected to be subjected shading, waterlogging, and their combined stress at the 3rd leaf stage (V3), the 6th leaf stage (V6), and tasseling stage (VT). Results showed that shading, waterlogging and their combination significantly limited the expansion of leaf area, and decreased leaf net photosynthetic rate (Pn) and net assimilation rate (NAR), thus reducing the crop growth rate (CGR) and biomass accumulation. At the same time, compared to control, the process of lignin synthesis was inhibited under stressed treatment, resulting in reduced stem mechanical strength and a poor development of the vascular system, of which change significantly reduced efficiency of assimilate remobilization to the ear and ultimately grain yield. The most significant effects of waterlogging and combined stresses on yield were occurred at V3 stage, followed by the V6 and VT stages. The most significant effects of shading were occurred at VT stage, followed by the V6 and V3 stages. Moreover, the compound stress exacerbated the damage brought about by a single stress. It is predicted that climate change will increase the frequency of abiotic stress assemblages, and the results of these findings provide some direction for further research on maize breeding in summer maize under continuous rainy conditions in the future.

Chronic ozone exposure affects nitrogen remobilization in wheat at key growth stages

The interaction between nitrogen storage and translocation, senescence, and late phase photosynthesis is critical to the post-anthesis grain fill period in wheat, but ozone's effect on nitrogen dynamics within the wheat plant is not well understood. This study used solardomes to expose a widely grown elite spring wheat cultivar, cv. Skyfall, to four levels of ozone (30 ppb, 45 ppb, 70 ppb, 85 ppb) for 11 weeks, with two levels of nitrogen fertilization, 140 kg ha−1 and 160 kg ha−1, the higher rate including an additional 20 kg N ha−1 at anthesis. Chronic ozone exposure triggered earlier senescence in the 4th, 3rd and 2nd leaves but not the flag leaf, with a similar pattern of reduced chlorophyll content in the lower, older leaf cohorts, which started before senescence became visible. At anthesis there was no evidence of any effect of ozone on nitrogen storage in upper plant parts. However, high ozone increased levels of residual nitrogen found within plant parts at harvest, with concomitant reductions in C:N ratios and Nitrogen Remobilization Efficiency. Extra nitrogen fertilization applied at anthesis appeared to ameliorate the effect of ozone on nitrogen content and nitrogen translocation. The application of 15N ammonium nitrate at anthesis confirmed that the majority of post-anthesis nitrogen uptake had been translocated to the ear/grain by harvest, with no effect of ozone on the translocation of nitrogen around the plant. These data can inform future modelling of ozone's effect on nitrogen dynamics and global wheat yields.

Genetic portrait of polyamine transporters in barley: insights in the regulation of leaf senescence.

Nitrogen (N) is one of the most expensive nutrients to supply, therefore, improving the efficiency of N use is essential to reduce the cost of commercial fertilization in plant production. Since cells cannot store reduced N as NH3 or NH4 +, polyamines (PAs), the low molecular weight aliphatic nitrogenous bases, are important N storage compounds in plants. Manipulating polyamines may provide a method to increase nitrogen remobilization efficiency. Homeostasis of PAs is maintained by intricate multiple feedback mechanisms at the level of biosynthesis, catabolism, efflux, and uptake. The molecular characterization of the PA uptake transporter (PUT) in most crop plants remains largely unknown, and knowledge of polyamine exporters in plants is lacking. Bi-directional amino acid transporters (BATs) have been recently suggested as possible PAs exporters for Arabidopsis and rice, however, detailed characterization of these genes in crops is missing. This report describes the first systematic study to comprehensively analyze PA transporters in barley (Hordeum vulgare, Hv), specifically the PUT and BAT gene families. Here, seven PUTs (HvPUT1-7) and six BATs (HvBAT1-6) genes were identified as PA transporters in the barley genome and the detailed characterization of these HvPUT and HvBAT genes and proteins is provided. Homology modeling of all studied PA transporters provided 3D structures prediction of the proteins of interest with high accuracy. Moreover, molecular docking studies provided insights into the PA-binding pockets of HvPUTs and HvBATs facilitating improved understanding of the mechanisms and interactions involved in HvPUT/HvBAT-mediated transport of PAs. We also examined the physiochemical characteristics of PA transporters and discuss the function of PA transporters in barley development, and how they help barley respond to stress, with a particular emphasis on leaf senescence. Insights gained here could lead to improved barley production via modulation of polyamine homeostasis.

Variation in nitrogen partitioning and reproductive stage nitrogen remobilization determines nitrogen grain production efficiency (NUEg) in diverse rice genotypes under varying nitrogen supply.

Nitrogen (N) is an important macronutrient needed for grain yield, grain N and grain protein content in rice. Grain yield and quality are significantly determined by N availability. In this study, to understand the mechanisms associated with reproductive stage N remobilization and N partitioning to grain 2 years of field experiments were conducted with 30 diverse rice genotypes during 2019-Kharif and 2020-Kharif seasons. The experiments were conducted with two different N treatments; N deficient (N0-no external N application, available soil N; 2019-234.15 kgha-1, 2020-225.79 kgha-1) and N sufficient (N120-120 kgha-1 external N application, available soil N; 2019-363.77 kgha-1, 2020-367.95 kgha-1). N application increased the NDVI value, biomass accumulation, grain yield, harvest index and grain N accumulation. Post-anthesis N uptake and N remobilization from vegetative tissues to grain are critical for grain yield and N harvest index. Rice genotypes, Kalinga-1, BAM-4234, IR-8384-B-B102-3, Sahbhagi Dhan, BVD-109 and Nerica-L-42 showed a higher rate of N remobilization under N sufficient conditions. But, under N deficiency, rice genotypes-83929-B-B-291-3-1-1, BVD-109, IR-8384-B-B102-3 and BAM-4234 performed well showing higher N remobilization efficiency. The total amount of N remobilization was recorded to be high in the N120 treatment. The harvest index was higher in N120 during both the cropping seasons. RANBIR BASMATI, BAM-832, APO, BAM-247, IR-64, Vandana, and Nerica-L-44 were more efficient in N grain production efficiency under N deficient conditions. From this study, it is evident that higher grain N accumulation is not always associated with higher yield. IR-83929-B-B-291-3-1-1, Kalinga-1, APO, Pusa Basmati-1, and Nerica-L-44 performed well for different N use efficiency component traits under both N deficient (N0) and N sufficient (N120) conditions. Identifying genotypes/donors for N use efficiency-component traits is crucial in improving the fertilizer N recovery rate and site specific N management.

Natural variations and dynamics of macronutrients for 87 tea plant (Camellia sinensis) varieties throughout the growing seasons in Wuhan

The tea plant (Camellia sinensis (L.) O. Kuntze) is the most extensively consumed beverage crop in the world, with steadily increasing consumption over the last decade. Tea plantations are frequently over-fertilized to achieve enhanced growth and yield, which ultimately influences the soil acidification and compaction, resulting in low quality and yield. However, the effect of optimum nutrient concentrations in the leaves on tea yield and quality is poorly understood. In this study, the dynamics of macronutrients nitrogen (N), phosphorus (P) and potassium (K) levels, nutrient use and remobilization efficiencies, and nutrient requirements (NR) were quantified among the diverse tea plant varieties over the entire growing seasons. Leaf samples of two categories, young leaves and mature canopy leaves, were collected from 87 elite tea varieties during the growing seasons to illustrate their biological significance. The results revealed that the highest average N levels were observed in the 2nd spring tea, P levels in summer tea, and K levels in autumn tea in both young and mature leaves. The results further revealed that a higher average nutrient utilization efficiency for nitrogen (NUtE-N) was identified in the summer followed by autumn. The NUtE-P in autumn and the NUtE-K in the 1st spring tea were relatively higher. Nutrient remobilization efficiencies (NRE) (NRE < 0 and NRE > 0) for N, P and K within canopy leaves were calculated, indicating the alternative roles of sources and sinks during the growth period. Moreover, NRE < 0 was almost exclusively found in the spring and summer, whereas NRE > 0 was mainly observed in the autumn. In terms of requirements, N was the most required for optimal tea yield, followed by K, and then P. Seasonally, maximum N, P and K requirements were coincidentally observed in the 2nd spring tea, whereas the minimum were in summer tea, autumn tea and the 1st spring tea, respectively. Based on nutrient utilization, the nutrient requirements of tea plants and the understanding of natural variability in N, P and K dynamics were elucidated to address agronomic, economic and environmental issues.

Grain protein concentration at elevated [CO2] is determined by genotype dependent variations in nitrogen remobilisation and nitrogen utilisation efficiency in wheat

Predictions for wheat grown under future climate conditions indicate a decline in grain protein concentration accompanied with an increase in yield due to increasing carbon dioxide concentrations. Currently, there is a lack of understanding as to the complete mechanism that governs the response of grain protein concentration (GPC) to elevated carbon dioxide (e[CO2]). We investigated the GPC of 18 wheat genotypes from a doubled haploid wheat population and the two parental genotypes, Kukri and RAC0875. In addition, other nitrogen and biomass related traits were analysed to further elucidate which traits are connected with the decline in GPC. Wheat was grown under ambient and elevated [CO2] in an environmentally controlled glasshouse. Plant nitrogen and biomass accumulation were measured at anthesis and maturity. We found that GPC declined under e[CO2] and that the response of GPC to e[CO2] was negatively correlated with nitrogen utilisation efficiency and harvest index. The extent that total biomass (anthesis), harvest index, photosynthesis, nitrogen utilisation and remobilisation efficiency, total nitrogen remobilisation and post-anthesis nitrogen uptake impacted GPC in response to e[CO2] varied across genotype, suggesting that multiple mechanisms are responsible for GPC decline at e[CO2] and that these mechanisms are effected differentially across genotypes.

Temporal complementarity between roots and mycorrhizal fungi drives wheat nitrogen use efficiency.

Improving nitrogen (N) use efficiency (NUE) to reduce the application of N fertilisers in a way that benefits the environment and reduces farmers' costs is an ongoing objective for sustainable wheat production. However, whether and how arbuscular mycorrhizal fungi (AMF) affect NUE in wheat is still not well explored. Three independent but complementary experiments were conducted to decipher the contribution of roots and AMF to the N uptake and utilisation efficiency in wheat. We show a temporal complementarity pattern between roots and AMF in shaping NUE of wheat. Pre-anthesis N uptake efficiency mainly depends on root functional traits, but the efficiency to utilise the N taken up during pre-anthesis for producing grains (EN,g ) is strongly affected by AMF, which might increase the uptake of phosphorus and thereby improve photosynthetic carbon assimilation. Root association with AMF reduced the N remobilisation efficiency in varieties with high EN,g ; whilst the overall grain N concentration increased, due to a large improvement in post-anthesis N uptake supported by AMF and/or other microbes. The findings provide evidence for the importance of managing AMF in agroecosystems, and an opportunity to tackle the contradiction between maximising grain yield and protein concentration in wheat breeding.

Band Phosphorus and Sulfur Fertilization as Drivers of Efficient Management of Nitrogen of Maize (Zea mays L.).

Increasing the efficiency of nitrogen use (NUE) from mineral fertilizers is one of the most important priorities of modern agriculture. The objectives of the present study were to assess the role of different nitrogen (N), phosphorus (P) and sulfur (S) rates on maize grain yield (GY), crop residue biomass, NUE indices, N concentration in plants during the growing season, N management indices and to select the most suitable set of NUE indicators. The following factors were tested: band application of di-ammonium phosphate and ammonium sulphate mixture (NPS fertilizer at rates 0, 8.7, 17.4, 26.2 kg ha−1 of P) and different total N rates (0, 60, 120, 180 kg ha−1 of N). In each year of the study, a clear trend of increased GY after NP(S) band application was observed. A particularly positive influence of that factor was confirmed at the lowest level of N fertilization. On average, the highest GY values were obtained for N2P3 and N3P1 treatments. The total N uptake and NUE indices also increased after the band application. In addition, a trend of improved N remobilization efficiency and the N contribution of remobilized N to grain as a result of band application of NP(S) was observed. Among various NUE indices, internal N utilization efficiency (IE) exhibited the strongest, yet negative, correlation with GY, whereas IE was a function of the N harvest index.

Terminal heat stress in Indian mustard (Brassica juncea L.): Variation in dry matter accumulation, stem reserve mobilization, carbohydrates translocation and their correlation with seed yield

The rapeseed mustard is one of the most important sources of edible oil in India and contributes 28.6% in total oilseed production. The mustard growing areas in India are experiencing the vast diversity in the agro climatic conditions. Here, we studied forty-nine advanced breeding lines of Brassica juncea L. for two consecutive years (2016-18) to examine the variations in the remobilization of assimilates from flowering to maturity stage and their contribution to seed filling under stressed environment. Further, we investigated the impact of high temperature on dry matter accumulation and partitioning from source to sink in Brassica germplasm. The synchronization between the seed filling stage and the onset of heat spell is critical event that determines the overall yield. Imbalances caused due to miss-matching of above events created hindrance in source-sink translocation, thus resulted in yield losses. Amount of remobilized dry matter, remobilization efficiency and remobilization percentage increased significantly, while the dry matter accumulation, total carbohydrates content and seed yield per plant declined in the late sown genotypes during both crop seasons. Reduced accumulation of photo assimilates under stress and higher sink demand resulted in more number of shriveled seeds leading to yield depression. The higher remobilization efficiency in late sown genotypes was strongly associated with dry matter at flowering that consequently tended to affect the final seed weight. This study will provide insights for better understanding of source-sink relationships in Indian mustard under heat stress and the differential remobilization efficiencies in the advanced breeding lines.

Induction of somatic embryogenesis in Tecomella undulata (Sm.) Seem using a pistillate explant

Desert teak (Tecomella undulata (Sm.) Seem) a multipurpose ornamental tree native to the arid and semi-arid tropics has entered the endangered plant category mainly as a result of the species' ineffective seed reproduction system. The tree usually reproduces through a few root suckers in old stands. Conventional methods of plants multiplication could not offer a viable practice for its mass multiplication. Low adventitious rooting of the cuttings has been the principal cause of failure in its vegetative propagation. Hence, the present research was planned and conducted to evaluate the feasibility of somatic embryogenesis in this species, the pathway that bypasses the need for rooting stage by developing bipolar embryos. Ovary explant was cultured in modified Murashigue &amp; Skoog (MS) medium supplemented with different auxins and cytokinins. The results showed α-naphthalene acetic acid (NAA) was superior in inducing embryogenic callus. NAA ranging 5.4-21.5 μM could induce the highest embryogenic calli which exhibited developing pro-embryogenic masses (PEM) and globular somatic embryos. The calli which were induced by the use of 2,4-dichlorophenoxyacetic acid (2,4-D) were poor in quality and showed no morphogenesis potency. Individual application of Thidiazuron (TDZ) and N6-benzyladenine (BA) induced good callogenesis at low concentrations but the calli were non-embryogenic with both. The proliferation of embryogenic calli was the best in a hormone-free medium. However, the media containing 40.5 and 54 μM NAA alone could induce somatic embryos along with callus proliferation. Low BA-contained medium (0.9-4.44 μM) led to recurrent somatic embryogenesis. Neither BA and GA3, nor the elevating sucrose concentration could cause further development and maturation of the somatic embryos induced during previous stages (callogenesis and callus proliferation). More research is required to optimize the maturation stage. The findings of the present study can be useful for future studies in the micropropagation of this recalcitrant specieslationships in Indian mustard under heat stress and the differential remobilization efficiencies in the advanced breeding lines.

The Genetic Architecture of Nitrogen Use Efficiency in Switchgrass (Panicum virgatum L.).

Switchgrass (Panicum virgatum L.) has immense potential as a bioenergy crop with the aim of producing biofuel as an end goal. Nitrogen (N)-related sustainability traits, such as nitrogen use efficiency (NUE) and nitrogen remobilization efficiency (NRE), are important factors affecting switchgrass quality and productivity. Hence, it is imperative to develop nitrogen use-efficient switchgrass accessions by exploring the genetic basis of NUE in switchgrass. For that, we used 331 diverse field-grown switchgrass accessions planted under low and moderate N fertility treatments. We performed a genome wide association study (GWAS) in a holistic manner where we not only considered NUE as a single trait but also used its related phenotypic traits, such as total dry biomass at low N and moderate N, and nitrogen use index, such as NRE. We have evaluated the phenotypic characterization of the NUE and the related traits, highlighted their relationship using correlation analysis, and identified the top ten nitrogen use-efficient switchgrass accessions. Our GWAS analysis identified 19 unique single nucleotide polymorphisms (SNPs) and 32 candidate genes. Two promising GWAS candidate genes, caffeoyl-CoA O-methyltransferase (CCoAOMT) and alfin-like 6 (AL6), were further supported by linkage disequilibrium (LD) analysis. Finally, we discussed the potential role of nitrogen in modulating the expression of these two genes. Our findings have opened avenues for the development of improved nitrogen use-efficient switchgrass lines.

Sink Strength Promoting Remobilization of Non-Structural Carbohydrates by Activating Sugar Signaling in Rice Stem during Grain Filling.

The remobilization of non-structural carbohydrates (NSCs) in the stem is essential for rice grain filling so as to improve grain yield. We conducted a two-year field experiment to deeply investigate their relationship. Two large-panicle rice varieties with similar spikelet size, CJ03 and W1844, were used to conduct two treatments (removing-spikelet group and control group). Compared to CJ03, W1844 had higher 1000-grain weight, especially for the grain growth of inferior spikelets (IS) after removing the spikelet. These results were mainly ascribed to the stronger sink strength of W1844 than that of CJ03 contrasting in the same group. The remobilization efficiency of NSC in the stem decreased significantly after removing the spikelet for both CJ03 and W1844, and the level of sugar signaling in the T6P-SnRK1 pathway was also significantly changed. However, W1844 outperformed CJ03 in terms of the efficiency of carbon reserve remobilization under the same treatments. More precisely, there was a significant difference during the early grain-filling stage in terms of the conversion of sucrose and starch. Interestingly, the sugar signaling of the T6P and SnRK1 pathways also represented an obvious change. Hence, sugar signaling may be promoted by sink strength to remobilize the NSCs of the rice stem during grain filling to further advance crop yield.

Effects of supplemental irrigation on the accumulation, partitioning, and remobilization of nitrogen, yield and water use efficiency of wheat cultivars

In the Mediterranean, unbalanced precipitation distribution causes drought stress in rainfed wheat cultivation. Under such conditions, supplemental irrigation (SI) is a highly efficient practice to reduce the adverse effects of drought stress and improve yield. The present study aimed to assess the effects of SI on traits related to N accumulation and remobilization, chlorophyll concentration, yield and yield components, and water use efficiency (WUE) in different cultivars. Two field experiments with four irrigation levels (I0= rainfed, I1= SI at booting stage, I2= SI at booting and anthesis stages, I3= SI at booting, anthesis, and grain filling stages) and five cultivars (Rejaw, Sardari, Homa, Azar2, and Sirwan) was conducted during the 2015–2016 and 2016–2017 wheat growing seasons. Overall, results showed that SI notably had a positive effect on chlorophyll concentration, N content of plant parts, N remobilization (NR), grain number per spike, 1000-grain weight, biological yield, and grain yield in cultivars. Although the grain yield in the three SI treatments was 237.1 kg ha−1 and 630.4 kg ha−1 more than the other two (I2) and one (I1) SI, respectively, but the WUE was slightly lower in this treatment. The cultivars exhibited apparent differences in their responses to SI. The Sirwan cultivar showed a higher reaction to SI amongst cultivars. The highest N remobilization efficiency (NRE) was observed in I1 (73.69%) and I0 (73.34%) irrigation treatments. Sardari (74.03%) and Azar2 (73.60%) cultivars had higher NRE than other cultivars. The minimum contribution of NR to grain appeared in the I3 treatment (74.54%).