This study was to explore the nitrogen metabolism and transcriptome mechanism of spermidine (Spd) under drought stress conditions. Firstly, maize variety Xianyu 335 (drought insensitive type) and Fenghe 1 (drought sensitive type) were chosen as experimental materials under hydroponic conditions. The effects of PEG-6000 combined with Spd application on nitrogen metabolism were studied. Secondly, we chose maize variety Xianyu 335 for the field experiment. At the flowering stage, normal water treatment and moderate drought stress were carried out, respectively. The results showed that: (1) Hydroponics experiment showed that the content of NH₄⁺ in the leaves of maize seedlings under drought stress increased significantly, while the content of NO₃⁻ and nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), glutamine dehydrogenase (GDH), glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) increased significantly. Spd can promote the assimilation of excess ammonia by enhancing the activities of ammonia assimilating enzymes GS/GOGAT and GDH, and transaminase (GOT and GPT), effectively alleviate the ammonia toxicity and nitrogen metabolism disorder induced by drought stress. (2) Pot experiment showed that Spd significantly promoted the root growth of maize under drought stress, so as to improve the absorption and utilization of water and nutrients. In addition, Spd can improve the chlorophyll content and photosynthetic rate of maize leaves under drought stress. After the application of exogenous Spd, the photosynthetic green leaf area increased, the leaf senescence rate slowed down, and the dry matter accumulation increased after anthesis, resulting in the increase of grain weight and grain number per ear, and finally improve the maize yield.

While increasing planting density is a viable strategy for enhancing maize yield, it concurrently elevates the risks of lodging and accelerated leaf senescence due to intensified inter-plant competition, which can ultimately compromise yield stability. A field experiment was conducted in Heilongjiang Province and the study investigated two maize cultivars, JNK728 (Jingnongke 728) and SD5 (Saide 5), under high-density planting conditions (90,000 plants ha⁻¹). The treatments were arranged in a factorial design, incorporating four nitrogen levels (0, 120, 240, and 360 kg N ha⁻¹) in combination with the presence or absence of a chemical regulator (30% diethyl aminoethyl hexanoate · ethephon), with water serving as the control. Results demonstrated that the integration of 240 kg N ha⁻¹ with chemical regulation significantly enhanced photosynthetic capacity—elevating chlorophyll content (SPAD), net photosynthetic rate (Pn), and activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCase) and phosphoenolpyruvate carboxylase (PEPCase)—while improving canopy structure through increased leaf area index (LAI) and optimized light distribution. This strategy also reinforced lodging resistance by optimizing plant morphology (reducing plant height and center of gravity), strengthening basal internodes (increasing stem diameter, dry weight per unit length, and mechanical strength), and promoting accumulation of stem structural components (cellulose, hemicellulose, lignin). Additionally, it facilitated post-anthesis nitrogen translocation to grains and up-regulated key nitrogen metabolism enzymes (glutamate synthetase-GS, glutamate dehydrogenase-GDH, and glutamate-pyruvate transaminase-GPT), thereby boosting nitrogen use efficiency. In contrast, excessive nitrogen (360 kg N ha⁻¹) suppressed these benefits and increased lodging. Consequently, the combined application of 240 kg N ha⁻¹ with chemical regulation achieved the highest yield, proving an effective approach for synergistically enhancing photosynthesis, lodging resistance, and nitrogen utilization in high-density maize systems.

Background: Maize is an important food crop in cold regions, especially in Northeast China. However, its short growth period and low-temperature stress pose challenges to the breeding of high-yield hybrids. With climate warming, the maize planting area continues to expand to high latitudes. Research on cold-region maize is of great significance to ensure food security and sustainable agricultural development. However, most of the current maize research is concentrated in temperate and tropical regions, and there are few studies on cold-region maize. Methods: Based on this, this study selected some representative cold-region maize materials and materials whose adaptability has not yet been verified, and used a semi-diallel hybrid design for hybridization to determine the general combining ability (GCA) and specific combining ability (SCA) to screen out excellent breeding materials suitable for cold regions. Field experiments were carried out under four different cold environments, and 55 hybrid progenies and their parents were evaluated. The double allele hybridization analysis based on the Griffing method 2 (model 1) showed that the specific combining ability (SCA) and general combining ability (GCA) effects of each trait were significant. Results: The GCA mean square of all traits except yield and number of grains per row was greater than the SCA mean square, indicating that additive gene effects were dominant and genetic improvement through selective breeding was feasible. Hayman plot analysis under four environments showed that yield, ear length, number of grains per row, water content, and plant height were mainly controlled by superdominant genes, while stem thickness, number of nodes, and ear position were controlled by some dominant genes. Conclusions: Parent P1 contained more recessive genes in yield traits, but more dominant genes in number of grains per row, number of nodes, and ear position; P3 contained more dominant genes in yield and water content, but more recessive genes in number of nodes and ear position; P7 contained more recessive genes in most traits; and P9 contained more dominant genes in most traits. P9 and P6 represent excellent parental germplasm, among which the hybrid combinations P1 × P9, P2 × P5, P3 × P10, P4 × P6, P5 × P8, P6 × P9, P7 × P10, and P8 × P10 all show hybrid vigor exceeding that of their parents and have high breeding value.

With the rapid development of industry and agriculture, soil heavy metal pollution has become increasingly severe. Copper (Cu) and cadmium (Cd) often co-occur in soils, exerting combined stress on crops. As a major food and feed crop, maize was studied under CuCd stress to assess the mitigating effects of exogenous Folcisteine (NATCA). Two varieties with contrasting tolerance (Jiuyuan 15 and Longfuyu 6) were subjected to composite stress (80 mg·L⁻¹ CuSO₄ + 100 mg·L⁻¹ CdCl₂), with or without 20 mg·L⁻¹ NATCA. The impacts on photosynthesis, reactive oxygen species (ROS) metabolism, the ascorbate–glutathione cycle, and endogenous hormones were investigated. The results showed that CuCd stress reduced the activities of RUBPCase and PEPCase, inhibiting CO₂ fixation, while NATCA application enhanced their activities and improved photosynthetic efficiency. Stress also induced ROS accumulation (elevated O₂·⁻ and H₂O₂) and elevated electrolyte leakage, whereas NATCA reduced oxidative damage and stabilized membrane integrity. Additionally, NATCA boosted both enzymatic and non-enzymatic antioxidant capacity in the ascorbate–glutathione cycle, improving ROS scavenging. Stress disrupted endogenous hormone balance, decreasing IAA, GA, and ZR, and increasing ABA. NATCA application restored hormone levels toward balance, promoting growth and enhancing tolerance to CuCd stress. These findings demonstrate NATCA’s role in improving maize resilience under heavy metal stress.

Low temperature is a major abiotic stress that affects maize across its entire growth cycle, with the germination stage being particularly sensitive. To investigate the genetic basis of early-stage cold tolerance, we used quantitative trait locus mapping and identified ZmbHLH30 as a candidate gene regulating maize responses to low temperature. The ZmbHLH30 protein is localized in the cytoplasm of maize protoplasts, and ZmbHLH30 promoter drives β-glucuronidase (GUS) expression in Arabidopsis thaliana leaves. The promoter region of ZmbHLH30 contains multiple environmental stress-responsive elements, including motifs associated with cold and auxin responses. Overexpression of ZmbHLH30 significantly enhanced cold tolerance at the germination, bud, and seedling stages, with the strongest effect observed during germination, where the cold-tolerance D-value increased by 0.366 relative to the control. In contrast, CRISPR/Cas9 knockout lines showed a 0.399 decrease in D-value. Under cold stress, ZmbHLH30 expression was markedly induced in overexpression lines but suppressed in knockout lines. Integrated transcriptomic and metabolomic analyses further identified ZmbHLH30 as a key regulator of cold tolerance in maize.

Copper (Cu) and cadmium (Cd) are common co-occurring environmental pollutants inducing combined stress, which severely harms maize growth. Previous studies have confirmed the involvement of the ascorbate–glutathione (AsA-GSH) cycle in heavy metal stress tolerance, but the regulatory effect of NATCA on this cycle under Cu-Cd combined stress—especially during maize seed germination and root development—remains unelucidated. Exogenous folcisteine (NATCA, 3-acetylthiazolidine-4-carboxylic acid) can enhance plant tolerance to abiotic stress. This study investigated the role of NATCA, a novel plant growth regulator with antioxidant potential, in alleviating Cu-Cd combined stress in maize. Two maize (Zea mays L.) varieties—Jiuyuan 15 (Cu/Cd-tolerant) and Longfuyu 6 (Cu/Cd-intolerant)—were exposed to combined stress (80 mg·L⁻¹ CuSO₄ + 100 mg·L⁻¹ CdCl₂) with/without 20 mg·L⁻¹ NATCA. Germination and hydroponic experiments were conducted to investigate NATCA’s effects on seed germination, growth, root traits, photosynthetic characteristics, reactive oxygen species (ROS) metabolism, AsA-GSH cycle (ascorbate–glutathione cycle), and endogenous hormones under stress. The results showed that combined Cu/Cd stress inhibited seed germination (reduced vigor, rate, index), while NATCA significantly reversed these declines, increased tolerance index, lowered relative damage rate, and improved seed activity—with more pronounced effects on Longfuyu 6. Stress stunted seedling growth (reduced dry/fresh weight, water content; increased water deficit), whereas NATCA promoted growth (taller plants, less leaf chlorosis, more fibrous roots), enhanced dry matter accumulation, and improved water metabolism. Stress impaired root morphology (shorter length, smaller surface area/volume, fewer tips) and absorption capacity; NATCA improved root traits, stress tolerance, and vitality. Stress weakened ROS scavenging, but NATCA elevated antioxidant enzyme activity and non-enzymatic antioxidant content, strengthened AsA-GSH cycle-mediated ROS clearance, mitigated stress damage, and maintained intracellular ROS balance in maize seedling root. These findings not only reveal a new regulatory role of NATCA in enhancing heavy metal stress tolerance via the AsA-GSH cycle but also provide a potential eco-friendly strategy for improving maize production in heavy metal-contaminated soils.