Improving the adaptability of rice leaves to high-light under heat stress is essential for maximizing photosynthetic efficiency. This study examined the responses of leaf gas exchange and hydraulic parameters to intense light under heat stress (40 °C) in wild type (Nipponbare) and four genetically modified rice varieties (NAL1-K, NAL1-O, Ghd7.1-K, and Ghd7.1-O) that exhibited significant differences in leaf area (LA). When measured irradiance increased from 1000 to 2000 μmol m-2 s-1 under heat stress, the changes of photosynthetic rate (A2000-A1000) ranged from -2.8 μmol m-2 s-1 in NAL1-O to 14.9 μmol m-2 s-1 in NAL1-K. A negative correlation between A2000-A1000 and LA was observed. The varying responses of A to high-light were primarily associated with stomatal conductance (gs). Enhanced leaf hydraulic conductance (Kleaf) facilitated the gs response to high-light under heat stress conditions. Furthermore, this study revealed that, under high-light and heat stress conditions, Kleaf is predominantly regulated by leaf hydraulic conductance inside the xylem (Kx), and reduced LA can significantly improve Kx. These findings demonstrate that reducing LA can enhance Kleaf, thereby improving the response of A to high-light under heat stress.

Irrigation, fertilization, and straw management are key determinants affecting the carbon footprint of rice production (CFP). To evaluate the synergistic effects among these practices, a three-factor experimental design was employed, involving straw return (R) vs no straw return (NR), continuous flooding (F) vs alternate dry-wet irrigation (D), and controlled-release nitrogen fertilizer (C) vs conventional fertilizer (U). Life cycle assessment was used to quantify the CFP per unit yield (CFPY) and area (CFPS) under different treatment combinations. Results indicated that straw return significantly increased both CFPY and CFPS compared to the NR treatment, whereas the irrigation D treatment reduced both more effectively than the F treatment. Furthermore, the fertilizer C treatment generally lowered both relative to the U treatment, with the reduction in CFPY being significant. Regarding synergistic effects, under NR conditions, both CFPY and CFPS in the D plots were significantly lower than in the F plots, regardless of fertilizer type. Under R conditions, however, only the combination of C and D yielded lower CFPY and CFPS values, which were significantly different from the other treatments. Among all treatments, NR-C-D, NR-U-D, and R-C-D exhibited comparable and significantly lower CFP. The CFP composition analysis revealed that embedded emissions from nitrogen fertilizer production and direct CH4 emissions were the primary contributors, with their trade-off regulated by irrigation and straw management. Overall, alternate dry-wet irrigation reduces CFP when straw is not returned, whereas the combined application of controlled-release fertilizer and alternate dry-wet irrigation is necessary to mitigate CFP under straw return conditions.

Accumulation of stem non-structural carbohydrates (NSC) at heading is crucial for mitigating grain-setting defects in large-panicle rice. While traditional panicle nitrogen fertilizer application at the emergence of the fourth leaf from the flag leaf stage (TL4) may weaken stem sink strength, delaying application to the emergence of the third leaf from the flag leaf stage (TL3) significantly enhances NSC accumulation. This study aimed to elucidate the molecular mechanisms through which TL3 remodels stem sink strength to promote NSC storage. Using two large-panicle rice varieties (Huiliangyou 280 and Yangliangyou 228), we compared stem NSC dynamics under TL4 and TL3 treatments and integrated sugar-related metabolite profiling with transcriptome analysis during the critical NSC accumulation phase. The results showed that TL3 treatment significantly increased stem NSC content and NSC per spikelet at heading, leading to a higher percentage of filled grains. The period from 5 days before heading (DBH) to heading showed the highest NSC accumulation rate. At the molecular level, TL3 treatment specifically up-regulated eight key genes in the sucrose-starch metabolism pathway, increasing the activities of sucrose phosphate synthase, sucrose synthase, and ADP-glucose pyrophosphorylase, and thereby promoting the accumulation of sucrose, trehalose, and D-fructose. In summary, delaying panicle nitrogen application to TL3 enhances stem NSC storage by remodeling sink strength via coordinated regulation of the sucrose-starch metabolic network.

Synergistically enhancing both photosynthetic rate (A) and intrinsic water use efficiency (iWUE) in rice remains a major challenge for achieving high productivity in the future. In this study, 37 cultivated rice (Oryza sativa) varieties with significant variation in stomatal morphological traits were selected for pot experiments. Among these, the two highest and two lowest stomatal density varieties were further subjected to drought treatments. Under well-watered conditions, stomatal density was identified as a key factor coordinating stomatal conductance (gs) and mesophyll conductance (gm) among rice varieties by influencing mesophyll cell arrangement through stomatal development. Although increased stomatal density enhanced A, it did not synergistically improve iWUE. Under water stress, however, stomatal aperture decreased rapidly as drought intensified, gradually diminishing the positive effect of high stomatal density on gs until it disappeared. Notably, varieties with high stomatal density maintained higher gm than those with low stomatal density across the entire range of leaf water potentials measured, enabling simultaneous enhancement of both A and iWUE under drought conditions. Our study demonstrates that high stomatal density can synergistically enhance both A and iWUE under drought conditions, underscoring its potential utility in breeding drought-tolerant rice varieties.

Context: The effects of root traits and aboveground agronomic traits on net CH4 emissions from paddy fields differ across rice growth stages. High-yielding rice varieties have double-peak CH4 reduction potential during tillering and heading, but the underlying mechanisms remain unclear. Methods: Four high-yield low-CH4-emission (HyLc) and four low-yield high-CH4-emission (LyHc) rice varieties, including indica and japonica subtypes, were tested over two field seasons (2022-2023). Aboveground agronomic traits, root traits, root exudates, and rhizosphere microbial communities were analyzed. Results: Compared to LyHc varieties, HyLc indica and japonica rice achieved yield increases of 27.5% and 32.6%, respectively, over 2 years. They reduced CH4 emissions by 51.8% and 43.6% during the tillering stage and by 47.8% and 71.1% during the heading stage, resulting in overall CH4 emission reductions of 49.0% and 52.4%, respectively. Path analysis of partial least square path modeling (PLS-PM) revealed that aboveground agronomic traits were the primary contributing factors influencing CH4 emissions during the tillering stage (path coefficient: 0.72). Reducing the LAI, number of tillers, and SPAD during the tillering stage decreased the number of transmission pathways, thereby lowering CH4 emissions. Root traits were the primary negative contributors to CH4 emissions during the heading stage (path coefficient: -0.63). Increasing the root diameter (RD) and root dry weight (RDW) during heading enhanced the root oxygen release potential, thereby reducing CH4. Additionally, HyLc varieties increased the relative abundance of CH4-oxidizing bacteria (Methylomicrobium, Methylomonas) and reduced the relative abundance of CH4-producing archaea (Methanosaeta, Methanobacterium, Methanoregula) in the rhizosphere soil during heading, which synergistically promoted CH4 oxidation and reduced CH4 production. This is associated with the increased stearic acid content in root exudates, regardless of indica and japonica subtypes. Conclusions: Overall, the reduction in CH4 emission from HyLc varieties during tillering was primarily associated with reduced aboveground agronomic traits, whereas the reduction during heading was associated with enhanced root traits, as well as stearic acid-mediated microbial regulation. Implications: Reducing early nitrogen and applying precise panicle nitrogen to match HyLc variety production may further increase rice yield and reduce CH4 emissions from paddy fields.

High-temperature stress during the flowering stage, exacerbated by climate change, has become a major abiotic constraint on global rice production. This study aimed to identify effective mitigation strategies by systematically evaluating the physiological effects of exogenous compound agents on rice under high-temperature stress at flowering. A heat-tolerant cultivar (N22) and a heat-sensitive cultivar (YR343) were subjected to high-temperature stress during flowering, and 17 different formulations comprising calcium chloride (CaCl2), salicylic acid (SA), abscisic acid (ABA) and potassium dihydrogen phosphate (KH2PO4) were applied. The results showed that high-temperature stress significantly reduced pollen viability, the net photosynthetic rate (P n), and the activities of peroxidase (POD) and catalase (CAT), while increasing malondialdehyde (MDA) content, ultimately leading to significant decreases in the seed-setting rate and yield. In contrast, exogenous compound treatments effectively alleviated this physiological damage. Among them, the ternary formulations ABC (CaCl2 + SA + ABA) and ABD (CaCl2 + SA + KH2PO4) were the most effective. The underlying physiological mechanisms involve the synergistic regulation of three key processes: first, improving anther carbohydrate metabolism and increasing pollen stainability, thereby stabilising the seed-setting rate; second, slowing chlorophyll degradation and maintaining a higher P n to ensure photosynthetic productivity; and finally, synergistically enhancing the activities of antioxidant enzymes (POD, CAT) and promoting the accumulation of osmotic regulators (e.g., soluble sugars and proteins), thereby reducing oxidative damage and maintaining cell membrane stability. This study demonstrates that foliar application of ABC or ABD can systematically enhance thermotolerance during flowering through multi-target synergistic effects. These findings not only elucidate the physiological mechanisms of crop responses to high temperature but also propose a feasible agronomic strategy to mitigate heat-induced yield losses.

Water-saving and drought-resistant rice (WDR) achieves drought resistance and stable yield by maintaining high photosynthetic potential in leaves under severe drought. We speculated that the sheath organ serving as a photosynthetic source can contribute to a positive response to drought in WDR. However, the synergetic photosynthetic adaptation mechanisms of leaf and sheath organs to drought remain unknown. In this study, a pot experiment was conducted to investigate the WDR of Hanyou73 (HY73) and its parents, Hanhui3 (HH3) and Huhan7A (HH7A). All varieties were subjected to drought at heading with -100 kPa soil water potential. The results demonstrated that chlorophyll content, relative water content, photosynthesis-related parameters, and sugar contents of leaf and sheath organs were significantly reduced during drought across three varieties. However, the activities of catalase and peroxidase and the contents of proline, hydrogen peroxide, and abscisic acid increased during drought treatment in leaf and sheath organs of all varieties. The stomatal conductance changed less in the sheath organ than in the leaf organ under drought stress. Further analyses revealed that stomatal conductance in leaf and sheath organs was mainly regulated by large stomatal apertures among anatomical structural characteristics of stomata across varieties and treatments. For HY73, high drought resistance was associated with a high sucrose-supplying capacity, resulting from high photosynthetic potential in leaf and sheath organs, which was achieved by improving stomatal aperture compared to its parents. This study provides a theoretical basis for the mechanism of photosynthetic adaptation of leaf and sheath organs, synergistically improving drought resistance in rice.

To increase the seed setting rate and yield of large-panicle rice varieties, one agronomic and breeding strategy is to increase the proportion of spikelets in the middle portion of the panicle as many of the lower spikelets fail to produce grains. Current nitrogen management during panicle development mainly focuses on fertilization at the emergence of the top fourth leaf, which increases the number of secondary branch spikelets on the lower part of the panicle. Two-year field experiments were conducted in 2021 and 2022 with two typical large-panicle hybrid indica rice cultivars, IIYM86 and JLY8612. Nitrogen was applied at the emergence of the top fifth (TL5), fourth (TL4), third (TL3), and second (TL2) leaves, with no nitrogen application as a control. This study aimed to investigate the effects of nitrogen application on the panicle structure, seed setting rate, and grain yield at different stages of panicle development. Nitrogen application at TL3 achieved the highest grain yield, followed by application at TL4, for both cultivars over the two years. TL3 did not significantly alter the number of spikelets per panicle but increased the proportion of spikelets located in the middle part of the panicle and reduced the proportions in the upper and lower parts compared to TL4. These effects were attributed to a significant increase in secondary branch spikelet differentiation in the middle part and a decrease in secondary branch spikelet differentiation in the upper and lower parts. Compared to TL4, TL3 significantly increased the seed setting rate by 9.46 and 9.48% and the grain yield by 6.86 and 8.92% in IIYM86 and JLY8612, respectively. In TL3, the significant increase in secondary branch spikelet differentiation in the middle part was primarily due to significantly reduced indole acetic acid (IAA) and an increased cytokinin/IAA ratio, which inhibited apical dominance. The significant decrease in secondary branch spikelet differentiation in the lower part of TL3 was mainly related to a significant increase in IAA and a reduction in the cytokinin/IAA ratio. Transcriptome analysis of young panicles confirmed these results, and differentially expressed genes between TL3 and TL4 were primarily enriched in plant hormone signal transduction related to IAA biosynthesis and degradation. These findings indicate that postponing nitrogen application until TL3 can improve the PTI and the seed setting rate by regulating hormonal balance, thereby optimizing nitrogen management during panicle development in large-panicle hybrid indica rice cultivars.

High temperatures during the rice panicle initiation stage can easily lead to yield loss. Although exogenous trehalose has been shown to significantly improve plant tolerance to abiotic stresses, its application in rice remains limited. Therefore, in this study, pot experiments were conducted using two rice varieties with differing heat tolerance to investigate whether exogenous trehalose could alleviate heat stress during the panicle initiation stage and to elucidate the underlying physiological mechanisms. The results demonstrated that exogenous trehalose significantly increased rice yield under high-temperature conditions. In the experiment in 2023, the maximum yield increases for N22 and YR343 were 89.5% and 110.3%, respectively, while in 2024, the increases were 89.2% and 111.6%, respectively. The optimal concentration for exogenous trehalose application was found to be 15 mmol L-1. The yield improvement was primarily attributed to the synergistic effects of exogenous trehalose, which not only enhanced leaf photosynthetic capacity but also improved the activity of key carbohydrate metabolism enzymes, up-regulated the expression of sucrose transporter genes, and enhanced sucrose utilisation in young panicles. Additionally, it elevated endogenous trehalose levels, increased the accumulation of osmoregulatory compounds, and enhanced antioxidant enzyme activity, while reducing membrane lipid peroxidation. Furthermore, the regulation of hormone metabolism contributed to improved high-temperature tolerance in rice. In conclusion, the application of trehalose may provide an effective strategy for mitigating high-temperature damage during the rice panicle initiation stage.

Enhancing rice photosynthesis is essential for increasing yield, yet the specific leaf morphological characteristics associated with high photosynthetic efficiency remain unclear. This study aims to investigate how reducing leaf width (LW) influences photosynthetic rate (A) and water-use efficiency (iWUE) in rice. Pot experiments were performed using 14 cultivated rice genotypes exhibiting considerable LW variations and genetically modified rice lines carrying the NARROW LEAF 1 (NAL1) gene. We observed a significant negative correlation between LW and A among the 14 cultivated rice varieties. Simultaneously, a 48.2% reduction in the LW of NAL1-K was accompanied by a 49.9% significant increase in A. Narrower leaves increased leaf hydraulic conductance and stomatal density, thereby synergistically augmenting stomatal conductance (gs). Furthermore, increased stomatal density enhances mesophyll conductance (gm) by facilitating airspace formation and less resistance to CO2 transfer. Reduced LW also increased leaf nitrogen content and enhanced the maximum carboxylation rate of RuBisCO (Vcmax). Although reduced LW synergistically increased gs, gm, Vcmax, and ultimately A, it did not concurrently achieve a coordinated improvement in iWUE. Our findings provide valuable insights into the physiological mechanisms underlying photosynthetic efficiency in rice, suggesting that optimizing LW may be a potential strategy for enhancing A without necessarily improving iWUE.

BACKGROUND:Appropriate nitrogen (N) fertilizer practices can be used to improve rice grain quality without compromising yield formation. The aim of this study is to investigate the performance of phenological N status in predicting rice grain yield and eating scores, and provide N fertilizer management recommendations. Two indica rice cultivars were selected for 3-year field experiments with multiple N application rates. The correlation between N diagnostic indicators [nitrogen nutrition index (NNI) and integrated NNI (NNIinte)] derived from two critical nitrogen dilution curves (CNDCs) based on shoot dry matter (DM) and leaf area index (LAI) with relative yield (RY) and relative eating score (RE) will be investigated. The optimal N fertilizer application rate obtaining high-yield and superior-quality (RY and RE ≥ 0.900) were recommended by the optimized phenological N status. RESULTS:NNI and NNIinte based on DM and LAI CNDC at each growth stage were significantly correlated with the RY and RE. The single-stage estimation performance of the NNIinte at the tillering stage were improved. The accumulated NNIinte (from transplanting to jointing) was better for estimating RY and RE than single-stage NNI and NNIinte. The LAI-CNDC can comprehensively and accurately estimate RY and RE. The optimal N fertilizer application rate was recommended as 126-209 kg ha-1, for rice to obtain high yield and good eating quality. CONCLUSIONS:This finding demonstrated the potential N diagnostic tool for estimating rice yield and eating quality in precision farming system, and NNIinte can be used to determine N requirement for rice high-yield and superior-quality. © 2025 Society of Chemical Industry.

Context: Enhancing nitrogen use efficiency (NUE) is a promising strategy to mitigate nitrogen losses, including those from NH3 volatilization. Research question: Both NH3 volatilization and NUE are influenced by variables such as soil properties, fertilization practices, and rice varieties. However, the interplay of these factors may complicate the trade-off between NUE and paddy NH3 volatilization. Methods: To bridge this knowledge gap, we quantified the correlation between NUE and NH3 volatilization in paddies, along with the key factors influencing both, by integrating the results from a meta-analysis and a 2-year field experiment. Results: The meta-analysis revealed that the fertilization effect on NH3 volatilization was remarkably correlated with NUE and N application rate. NH3 volatilization exhibited a significant negative linear relationship with NUE (y =- 0.0238x + 2.6804, P < 0.001) and a positive linear relationship with N application rate (y = 0.006x + 2.6028, P < 0.001). Interestingly, subset analysis showed that the fertilization effect was unaffected by all predictors at low N application rate (<= 150 kg/ha), but was influenced by both soil pH and the type of N fertilizer at high rate (>= 250 kg/ha). The field experiments confirmed a trade-off between NH3 volatilization and NUE. Importantly, NH3 volatilization was significantly negatively correlated with N absorption only during the tillering stage (y =-0.68x + 0.779, P < 0.001), with no such correlation at other stages. Moreover, NH3 volatilization during the tillering stage showed a significant negative correlation with amount of root bleeding sap (y =-0.71x + 0.814, P < 0.01) and leaf area index (y =-0.61x + 0.672, P < 0.05). The leaf angle of functional leaves was significantly positively correlated with N absorption, amount of root bleeding sap, and leaf area index, which are closely related to NH3 volatilization. Conclusions: NUE exhibited a clear trade-off with paddy NH3 volatilization, predominantly driven by N absorption capacity during the tillering stage. The leaf angle of functional leaves emerged as a key factor influencing indicators related to NH3 volatilization, including N absorption capacity, amount of root bleeding sap, and leaf area index. Implications or significance: These findings provide new insights into the relationship between NUE and NH3 volatilization, offering theoretical support for reducing NH3 volatilization in paddies by enhancing NUE in rice production.

Background Leaf water content (LWC) significantly affects rice growth and development. Real-time monitoring of rice leaf water status is essential to obtain high yield and water use efficiency of rice plants with precise irrigation regimes in rice fields. Hyperspectral remote sensing technology is widely used in monitoring crop water status because of its rapid, nondestructive, and real-time characteristics. Recently, multi-source data have been attempted to integrate into a monitored model of crop water status based on spectral indices. However, there are fewer studies using spectral index model coupled with multi-source data for monitoring LWC in rice plants. Therefore, 2-year field experiments were conducted with three irrigation regimes using four rice cultivars in this study. The multi-source data, including canopy ecological factors and physiological parameters, were incorporated into the vegetation index to accurately predict LWC in rice plants. Results The results presented that the model accuracy of rice LWC estimation after combining data from multiple sources improved by 6–44% compared to the accuracy of a single spectral index normalized difference index (ND). Additionally, the optimal prediction accuracy of rice LWC was produced using a machine algorithm of gradient boosted decision tree (GBDT) based on the combination of ND (1287,1673) and crop water stress index (CWSI) (R 2 = 0.86, RMSE = 0.01). Conclusions The machine learning estimation model constructed based on multi-source data fully utilizes the spectral information and considers the environmental changes in the crop canopy after introducing multi-source data parameters, thus improving the performance of spectral technology for monitoring rice LWC. The findings may be helpful to the water status diagnosis and accurate irrigation management of rice plants.

Water-saving and drought-resistant rice (WDR) coupled with alternate wetting and drying irrigation (AWDI) possesses a high photosynthetic potential due to higher mesophyll conductance (g(m)) under drought conditions. However, the physiological and structural contributions to the g(m) of leaves and their mechanisms in WDR under AWDI are still unclear. In this study, WDR (Hanyou 73) and drought-sensitive rice (Huiliangyou 898) were selected as materials. Three irrigation patterns were established from transplanting to the heading stage, including conventional flooding irrigation (W1), moderate AWDI (W2), and severe AWDI (W3). A severe drought with a soil water potential of -50 kPa was applied for a week at the heading stage across all treatments and cultivars. The results revealed that severe drought reduced gas exchange parameters and g(m) but enhanced antioxidant enzyme activities and malondialdehyde content in the three treatments and both cultivars. The maximal photosynthetic rate (A(max)) of HY73 in the W2 treatment was greater than that in the other combinations of cultivars and irrigation patterns. The contribution of leaf structure (54%) to g(m) (g(m)-S, structural g(m)) was higher than that of leaf physiology (46%) to g(m) (g(m)-P, physiological g(m)) in the W2 treatment of Hanyou 73. Additionally, g(m)-S was significantly and linearly positively correlated with g(m) under severe drought. Moreover, both the initial and apparent quantum efficiencies were significantly and positively with g(m) in rice plants (p < 0.05). These results suggest that the improvements in photosynthesis and yield in the WDR combined with moderate AWDI can mainly be attributed to the enhancement of g(m)-S under severe drought conditions. Quantum efficiency may be a potential factor in regulating photosynthesis by cooperating with the g(m) of rice plants under severe drought conditions.

The growth of rice (Oryza sativa L.) depends on various physiological and metabolic activities of the leaves. The decrease in photosynthesis and carbohydrate metabolism of rice flag leaves under high temperature stress at the flowering stage is an important cause of the loss of rice yields. The addition of exogenous trehalose has a significant effect on alleviating this loss of yields under high temperature stress at the flowering stage. It is highly important to elucidate the physiological reasons for the development of the management of heat-resistant rice. In this study, the heat-resistant rice variety Nagina22 (N22) and the heat-sensitive rice variety YR343 were used as the test varieties. The rice in a pot experiment were treated with high temperature (38 °C) and normal temperature (32 °C) during the flowering stage, and different concentrations of exogenous trehalose were added before the temperature treatment. The research results showed that under high temperature stress during the flowering stage, the seed setting rate of N22 and YR343 decreased by 42.1 and 82.2

[Objective]In order to explore the common agronomic and physiological characteristics of good taste and high yield type japonica rice in the lower reaches of the Yangtze River,the study could provide theoretical basis and technical support for realizing synergistic improvement of rice yield and quality in this region.[Method]The cultivar screening tests were conducted in 2018 and 2022 using 14 and 13 conventional japonica rice cultivars,respectively,to systematically compare the yield and composition,taste quality and textural characteristics,as well as agronomic and physiological indicators such as biomass,stem non-structural carbohydrates(NSC),and leaf area duration(LAD)among the different cultivars.[Result]The taste value and yield varied across the different cultivars,so through clustering by taste value and yield,they can be further divided into three types:medium taste and low yield(ML),medium taste and high yield(MH),good taste and high yield(GH).The average taste value and yield of GH in two years were 68.5 and 10.2 t·hm-2,respectively,which were 6.8%higher in taste value and 14.6%higher in yield than MH and ML.In terms of performance for yield and quality traits,GH showed the highest grain filling percentage and taste scores compared to MH and ML.In terms of the dry matter accumulation,GH increased the proportion of dry matter accumulation at the early stage of grain filling stage,and showed the highest dry matter accumulation from heading stage to 15 days after heading stage.Further analysis of the causes of dry matter accumulation at this stage revealed that GH significantly increased the NSC remobilization rate while steadily increasing LAD.Correlation analyses showed highly significant positive correlations between grain filling percentage and taste,dry matter accumulation and LAD from heading stage to 15 days after heading stage,and NSC remobilization rate.[Conclusion]While maintaining a high LAD from heading stage to 15 days after heading stage(100.4 m2·m-2·d),further increasing NSC remobilization rate during grain filling stage(79.9%)to promote the initiation of grain filling,increasing the dry matter accumulation from heading stage to 15 days after heading stage(3.6 t·hm-2),then improving the grain filling percentage(95.4%),and taste(9.6),which are the common characteristics of good taste and high yield type japonica rice in this region.In addition,the development of water and fertilizer management techniques targeting the enhancement of NSC remobilization at the grain filling stage and NSC accumulation at heading stage is expected to further exploit the yield and taste quality potential of the above good taste and high yield type japonica rice.

The reserve of stem nonstructural carbohydrates (NSC) at heading can enhance the sink strength and improve the grain-filling ability of large-panicle rice, which is beneficial to realizing its high-yield potential. Delaying panicle nitrogen (N) application is expected to increase stem NSC accumulation, but the relevant technical parameters and their impact on the yield of large-panicle rice remain unclear. Two-year field experiments were conducted in 2021 and 2022 with two large-panicle rice cultivars (HLY280 and YLY228) and five panicle N treatments: panicle N application at emergence of 4th leaf from flag leaf (TL4), 3rd leaf from flag leaf (TL3), 2nd leaf from flag leaf (TL2), flag leaf (TL1), and no panicle N application (CK) as the control, to study the effect of different panicle N treatments on the accumulation and translocation of stem NSC, as well as their impact on rice yield and its components. The results showed that the panicle N treatments significantly influenced rice yield. Among the panicle N application treatments, TL3 showed the highest yield for both cultivars over two years. Compared with TL4, TL3 significantly increased the percentage of filled grains and grain weight while maintaining a similar number of spikelets per panicle, which increased the yield of HLY280 and YLY228 by 10.1–13.6% and 12.4–12.7%, respectively. Among the panicle N application treatments, TL3 significantly increased the translocation of stem mass (net output of stem mass) and stem NSC (∆NSC) from heading to 15 days after heading (DAH), which led to the highest dry matter accumulation during the initiation of grain filling from heading to 15 DAH. The higher ∆NSC of TL3 was mainly due to the higher stem NSC at heading, which was contributed by the higher stem NSC accumulation from 5 days before heading (DBH) to heading. Additionally, the higher stem NSC accumulation under TL3 from 5 DBH to heading was significantly positively correlated with the higher leaf area duration (LAD) in this period. These results suggest that delaying panicle N application to TL3 can significantly increase the yield of large-panicle rice compared with TL4 by increasing the percentage of filled grains and grain weight, which is the result of increased stem NSC accumulation.

Due to its tropical origins, rice (Oryza sativa) is susceptible to cold stress, which poses severe threats to production. OsNAC5, a NAC-type transcription factor, participates in the cold stress response of rice, but the detailed mechanisms remain poorly understood. Here, we demonstrate that OsNAC5 positively regulates cold tolerance at germination and in seedlings by directly activating the expression of ABSCISIC ACID INSENSITIVE 5 (OsABI5). Haplotype analysis indicated that single nucleotide polymorphisms in a NAC-binding site in the OsABI5 promoter are strongly associated with cold tolerance. OsNAC5 also enhanced OsABI5 stability, thus regulating the expression of cold-responsive (COR) genes, enabling fine-tuned control of OsABI5 action for rapid, precise plant responses to cold stress. DNA affinity purification sequencing coupled with transcriptome deep sequencing identified several OsABI5 target genes involved in COR expression, including DEHYDRATION-RESPONSIVE ELEMENT BINDING FACTOR 1A (OsDREB1A), OsMYB20, and PEROXIDASE 70 (OsPRX70). In vivo and in vitro analyses suggested that OsABI5 positively regulates COR gene transcription, with marked COR upregulation in OsNAC5-overexpressing lines and downregulation in osnac5 and/or osabi5 knockout mutants. This study extends our understanding of cold tolerance regulation via OsNAC5 through the OsABI5-CORs transcription module, which may be used to ameliorate cold tolerance in rice via advanced breeding.

High yield, good eating quality, and high nitrogen (N) use efficiency present challenges in cultivating medium hybrid indica rice. We hypothesized that balanced source-sink relationships are key traits for achieving high yield, good eating quality, and high N use efficiency in medium hybrid indica rice under suitable N management regimes. Three field experiments were conducted with two medium hybrid indica rice cultivars. Five distinct N application levels, designated as N0, N75, N150, N225, and N300, were used to investigate varying source-sink characteristics and their impact on yield, eating quality, and N use efficiency. The results indicated that the ratio of dry matter at the heading stage to the number of spikelets per unit area (DM/Spik. R) exhibited a significant decrease with increasing N application rates in both cultivars over three years, except for the cultivar HLY898 in 2021. Conversely, an increase in N application rates generally increased the ratios of accumulated N rate and leaf area at the heading stage to the number of spikelets per unit area (AN/Spik. R and LA/Spik. R) across the cultivars and experimental years. Only AN/Spik. R showed significant relationships with yield, eating score, and N partial factor productivity (PFPN). In addition, significant differences were observed among the three study years for DM/Spik. R and LA/Spik. R, but no significant difference was found for AN/Spik. R across the three study years. Moreover, both N concentration and nitrogen nutrition index (NNI) at heading had significant and linear relationships with AN/Spik. R. Further analysis revealed that the highest yield and maximum eating scores, constituting 92 % of the total, were achieved when AN/Spik. R reached 3.65 mg per spikelet. Correspondingly, the NNI was recommended as 0.93 at heading when 90 % of the highest yield and maximum eating scores were harvested. Additionally, 79 % of the highest yield and maximum PFPN were obtained when AN/Spik. R and NNI were approximate to 2.58 mg per spikelet and 0.78 at heading, respectively. These results suggest that moderate AN/Spik. R corresponding to mild N deficiency at heading could be a key source-sink indicator for the integrated regulation of high yield, good eating quality, and high N use efficiency in medium hybrid indica rice.