Globally recurrent extreme high temperature (HT) events severely limit rice production. This study investigated whether a controlled moderate soil drying (MD) could replace the conventional well-watered (WW) regime to more effectively mitigate HT stress on pistil fertilization in photo-thermosensitive genetic male-sterile (PTGMS) rice, and examined the role of brassinosteroids (BRs). Two PTGMS rice varieties were cultivated under normal temperature (NT) and HT conditions, paired with WW and MD strategies during anthesis. In the conventional WW regime, waterlogging reduced BR levels in roots and pistils due to excessive decomposition, weakening active water uptake driven by root activity and failing to alleviate transpiration-pulled passive water extraction hampered by restricted stomatal openings. Thereby, it caused water imbalance in plants and weakened pistil function due to a suppressed ascorbate-glutathione (AsA-GSH) cycle and hyperactive nicotinamide adenine dinucleotide phosphate oxidase (NOX) activity. This exacerbated pistil fertilization impairment and hybrid seed yield loss under HT stress. Conversely, by promoting BR synthesis and inhibiting its decomposition in roots and pistils, the MD strategy enhanced root activity and transpiration-driven water uptake. It maintained plant water balance and supported pistil function by suppressing NOX activity and enhancing AsA-GSH cycle-driven redox homeostasis. Thus, it mitigated HT-induced pistil fertilization impairment and hybrid seed yield loss. The precise function of BRs in moderating the protective effects of MD against the detrimental impacts of HT stress on pistil fertilization in PTGMS rice was confirmed through genetic and chemical approaches. Consequently, a controlled MD method proved more effective than the conventional WW regime in alleviating HT stress on pistil fertilization in PTGMS rice by promoting BR enhancement.

This study examined the involvement of cytokinins in the process by which moderate water limitation (MWL) mediates nitrogen (N) remobilization from source to sink during the grain-filling phase in wheat. Field experiments were performed using N application rates of low (LN), medium (MN), and high (HN). Two soil moisture regimes were implemented for each N rate: conventional well-watered (CWW) and MWL post anthesis. The MWL application optimized N, total free amino acids (FAA), and trans-zeatin (Z)+trans-zeatin riboside (ZR) reallocation from the source organs (stems and leaves) to the sink organ (spikes) in wheat. Compared to those in the CWW regime, the activities of proteolytic enzymes, including endopeptidase, carboxypeptidase, and aminopeptidase within stems and leaves, and the expression levels of total FAA transporter genes in spikes were significantly elevated in the MWL regime, showing a close correlation with the Z+ZR levels in the spikes. Application of kinetin to stems and leaves significantly inhibited proteolytic enzyme activities, promoting N retention in stems and leaves, decreasing N accumulation in the sink organ, and reducing the N harvest index. In contrast, applying kinetin to spikes significantly upregulated expression levels of FAA transporter genes, reducing N retention in stems and leaves, increasing N accumulation in the sink organ, and raising the N harvest index. Such facilitation induced by the MWL in the remobilization of N from source to sink was greater at HN than at LN or MN. Results demonstrate that post-anthesis MWL can significantly intensify the remobilization of N from source to sink, while also synergistically enhancing grain yield and N use efficiency through strategically redistributing cytokinins (Z+ZR) between source and sink in wheat.

Alternate wetting and drying irrigation (AWD) significantly influences the cooking and eating quality of rice (Oryza sativa L.). However, the mechanisms by which AWD affects rice cooking and eating quality remain unclear. Lipid and free fatty acid contents in grains correlate positively with cooking and eating quality of rice. This study examined Yangdao 6 (YD6, a conventional taste indica inbred) and Nanjing 9108 (NJ9108, a superior taste japonica inbred) cultivated under conventional irrigation (CI), alternate wetting and moderate drying irrigation (AWMD), and alternate wetting and severe drying irrigation (AWSD) from 10 days after transplanting to maturity. The research investigated the relationship between lipid and free fatty acid biosynthesis in grains and the cooking and eating quality of rice. Compared to CI treatment, AWMD significantly enhanced the contents of lipid, total free fatty acids (TFFAs), free unsaturated fatty acids (FUFAs), linoleic acid, and oleic acid in milled rice by increasing activities of enzymes associated with lipid synthesis, while AWSD produced opposite effects. Correlation analysis revealed that elevated levels of lipid, TFFAs, FUFAs, linoleic acid, and oleic acid contribute to improved rice cooking and eating quality. The findings demonstrate that AWMD enhances cooking and eating quality of milled rice through optimization of lipid and fatty acid synthesis in rice grains.

Alternate wetting and soil drying irrigation (AWD) technique is crucial in influencing grain quality in rice (Oryza sativa L.). Lipids are the third most abundant constituents in rice grains, after starch and proteins, and are closely related to grain quality. However, it remains unclear about the changes in lipids profiling under different AWD regimes. This study set up three irrigation regimes including conventional irrigation (CI), alternate wetting and moderate soil drying irrigation (AWMD), and alternate wetting and severe soil drying irrigation (AWSD). It explored lipidome changes in milled rice of Yangdao 6 (YD6) using the untargeted lipidomics approach and analyzed rice cooking and eating quality. The results identified seven lipid classes, 55 lipid subclasses, and 1,086 lipid molecular species. Compared with the CI regime, the AWMD regime mainly altered lipid subclasses consisting of triglyceride (TG), ceramide (Cer), diglyceride (DG), bis-methyl lysophosphatidic acid (BisMePA), phosphocholine (PC), phosphoethanolamine (PE), monogalactosyldiacylglycerol (MGDG), and digalactosyl diglyceride (DGDG) in milled rice and improved cooking and eating quality of rice; in contrast, the AWSD regime distinctly changed lipid subclasses like TG, Cer, DG, PC, PE, hexosylceramide (Hex1Cer), DGDG, and BisMePA and degraded cooking and eating quality of rice. Specifically, AWMD most significantly altered the expressions of lipid molecules, including DGDG(18:0_18:2), DGDG(16:0_14:0), PC(33:1), Cer(t17:0_26:0), and Cer(t17:0_16:0); AWSD most obviously influenced the expressions of TG(6:0_14:0_18:3), PC(41:1), TG(19:1_18:4_18:4), Hex1Cer(d18:2_24:0+O), and Hex1Cer(d18:2_24:1). These 10 altered lipid molecules in milled rice can be preferentially used for investigating their relationships with grain quality in rice.

Lysine content is a criterion of the nutritional quality of rice. Understanding the process of lysine biosynthesis in early-flowering superior grain (SG) and late-flowering inferior grain (IG) of rice would advance breeding and cultivation to improve nutritional quality. However, little information is available on differences in lysine anabolism between SG and IG and the underlying mechanism, and whether and how irrigation regimes affect lysine anabolism in these grains. A japonica rice cultivar was grown in the field and two irrigation regimes, continuous flooding (CF) and wetting alternating with partial drying (WAPD), were imposed from heading to the mature stage. Lysine content and activities of key enzymes of lysine biosynthesis, and levels of brassinosteroids (BRs) were lower in the IG than in the SG at the early grain-filling stage but higher at middle and late grain-filling stages. WAPD increased activities of these key enzymes, BR levels, and contents of lysine and total amino acids in IG, but not SG relative to CF. Application of 2,4-epibrassinolide to rice panicles in CF during early grain filling reproduced the effects of WAPD, but neither treatment altered the activities of enzymes responsible for lysine catabolism in either SG or IG. WAPD and elevated BR levels during grain filling increased lysine biosynthesis in IG. Improvement in lysine biosynthesis in rice should focus on IG.

High temperature (HT) stress has become one of the most detrimental stresses in crop production among constantly changing environmental factors. Exploiting approaches to enhance crop thermotolerance would have great significance in assuaging adverse effects of HT stress on crop growth and development. As jasmonates (JAs) and brassinosteroids (BRs) are novel phytohormones and play important roles in responses to biotic and abiotic stresses and in a wide range of plant developmental processes, this paper reviewed the roles and mechanisms of JAs and BRs in mitigating HT stress, with focus on rice (Oryza sativa L.) subjected to HT stress during anthesis. It is demonstrated that JAs alleviate spikelet-opening impairment and BRs ameliorate pistil fertilization ability under HT stress during anthesis of rice, although there are controversial observations. Activating the defense system, enhancing osmotic regulation, protecting photosynthesis, and interacting with other phytohormones, especially with ethylene and abscisic acid, are main physiological mechanisms by which JAs or BRs attenuate HT stress to plants. Elevating levels of JAs or BRs in plants could be considered as an important approach to enhance crop thermotolerance through breeding new varieties. Using JAs or BRs as chemical regulators and adopting proper water and nitrogen management practices could reduce the harm of HT stress to rice. Further research is needed to elucidate the roles of JAs and BRs in different plant tissues in responses to HT stress under different genetic backgrounds and environments, reveal the molecular mechanism underlying JAs and BRs mediating HT stress, understand the cross-talk between phytohormones in modulating HT stress, and establish integrated crop management to minimize the hazard of HT stress in rice production.

Brassinosteroids (BRs) play critical roles in a wide range of plant developmental processes. However, it is unknown whether and how BRs mediate the effect of high temperature (HT) stress during anthesis on the pistil activity of photo-thermosensitive genetic male-sterile (PTSGMS) rice (Oryza sativa L.) lines. This study investigated the question. Three pot-grown PTSGMS rice lines were subjected to HT stress during anthesis. The contents of 24-epibrassinolide (24-EBL) and 28-homobrassinolide (28-HBL), the major forms of BR in rice plants, and levels of reactive oxygen species (ROS) or antioxidants (AOS), hydrogen peroxide (H₂O₂), 1-aminocylopropane-1-carboxylic acid (ACC), ascorbic acid (AsA), and catalase activity in pistils, were determined. HT stress significantly reduced the contents of both 24-EBL and 28-EBL relative to those under normal temperatures, but the reduction varied by PTSGMS line. A line with higher BR contents under HT stress showed lower contents of ACC and H₂O₂, higher catalase activity and AsA content in pistils, and higher fertilization rate, seed-setting rate, and seed yield when the line was crossed with a restorer line, indicating that higher levels of BRs increase HT stress resistance. Applying 24-EBL, 28-HBL or an inhibitor of BR biosynthesis confirmed the roles of BRs in response to HT stress. The results suggest that BRs mediate the effect of HT stress on pistil activity during anthesis and alleviate the harm of HT stress by increasing AOS and suppressing ROS generation.

Phosphorus use efficiency (PUE) can be improved through cultivation techniques and breeding. However, little is known about rice (Oryza sativa L.) agronomic and physiological traits associated with high PUE. We characterized the agronomic and physiological traits of rice varieties with different tolerances to low phosphorus in nutrient solution. Two varieties with strong tolerance to low phosphorus (STVs) and two with weak tolerance (WTVs) were grown at normal (NP, control) and low phosphorus (LP, 1/20 of NP) concentrations. Plants grown at LP produced significantly lower grain yield than those grown at NP. WTVs yields were lower than STVs yields. Compared to NP, LP significantly increased phosphorus translocation efficiency (PTE), internal phosphorus efficiency (IPE) and phosphorus harvest index (PHI). Under the LP condition, PTE and IPE were higher for STVs than for WTVs. LP also reduced tiller number, shoot biomass, leaf area index (LAI), leaf photosynthetic rate, and mean root diameter of both kinds of varieties at the main growth stages, but to a lower extent in STVs. LP significantly increased the number of productive tillers, root biomass, root-shoot ratio, root bleeding rate, and root acid phosphatase (RAP) activity. Total root length, root oxidation activity (ROA), and root total and active absorbing surface areas for STVs were significantly increased under LP, whereas the opposite responses were observed for WTVs. Total root length, ROA, root bleeding rate, root active absorbing surface area, and RAP activity were positively and significantly correlated with grain yield, PTE, and IPE. These results suggest that the tolerance of rice varieties to a low-phosphorus growth condition is closely associated with root growth with higher biomass and activity.

In previous studies, integrative crop management (ICM) improved shoot growth and grain yield of rice (Oryza sativa L.). However, little is known about the effect of ICM on root growth and methane (CH₄) emission of paddy rice. In this study, two rice varieties, Wuyunjing 24 and Yongyou 2640, were grown. A field experiment was conducted with three crop management treatments including zero nitrogen fertilization (0N), local farmer practice (LFP), and ICM. Root morphophysiological traits and CH₄ emission from the paddy field were investigated. ICM significantly increased mean grain yield by 29.9%, with the effect attributed mainly to an increase in mean total number of spikelets by 26.4% compared to LFP. ICM increased root and shoot biomass, root length, number of roots, root oxidation activity (ROA), root bleeding rate, and root total and active absorbing surface area by respectively 24.4%, 25.7%, 17.1%, 9.3%, 18.7%, 29.5%, 12.1%, and 24.7%. The concentrations of malic, succinic, and acetic acids in root exudates were respectively 5.8%, 6.0%, and 10.5% higher in ICM than in LFP. Compared to LFP, ICM significantly decreased the rate of CH₄ emission during emission peak stages and reduced total CH₄ emission by 17.1%. The root morphophysiological traits were positively and significantly correlated with grain yield, whereas root length, specific root length, ROA, and root total and active absorbing surface area were negatively and significantly correlated with total CH₄ emission. These results suggest that ICM could achieve the dual goals of increasing grain yield and reducing the greenhouse gas effect by improving the root morphology and physiological traits of paddy rice.