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Peptide transport is important for plant tissues where rapid proteolysis occurs, especially during germination and senescence, to enhance redistribution of organic nitrogen (N). However, the biological role of peptide transporters is poorly investigated in rice. We characterized the function of the peptide transporter OsNPF8.1 of rice nitrate transporter 1/peptide transporter family (NPF). Ectopic expression of OsNPF8.1 in yeast revealed that OsNPF8.1 encoded a high-affinity di-/tri-peptide transporter, and the osnpf8.1 mutants had a lower uptake rate of the fluorescent-labelled dipeptide c in leaves of rice seedlings. Histochemical assays showed that OsNPF8.1 was highly expressed in mesophyll cells and vascular parenchyma cells, but not detected in root hairs and epidermises. Expression of OsNPF8.1 was induced by N deficiency, drought, NaCl and abscisic acid, and kept at a high level in senescing leaves. Under N deficiency conditions, compared with the wild type Zhonghua 11, the osnpf8.1 mutants grew slower at the seedling stage, and had lower grain yield and lower N content in the grains. In contrast, OsNPF8.1-over-expressing rice (OsNPF8.1-OE) grew faster at the seedling stage and had a higher grain yield. The osnpf8.1 seedlings were less tolerant to salt and drought stresses. These results suggested that stress-induced organic N transportation mediated by OsNPF8.1 might contribute to balance plant growth and tolerate to salt/drought stress and N-deficiency.

BACKGROUND: Adjusting nitrogen (N) input based on actual seedling density (ASD) and plant N status is a practical approach for improving the yield stability of direct‐seeded rice. However, the adjustment of topdressing N rates has been empirical in the past. This study aimed to establish a quantitative approach for determining N topdressing rates during tillering (Ntil) and panicle development (NPI) based on ASD and crop N status in direct‐seeded rice. Field experiments were conducted involving 12 treatments, consisting of four Ntil and three seeding rates in 2017, and eight treatments combining seeding rate, Ntil, and NPI in 2020. RESULTS: Linear regression analysis revealed that the tiller number at panicle initiation (TILPI) was predominantly influenced by ASD and Ntil. The determination coefficients (R2) of the regression models ranged from 0.887 to 0.936 across the four‐season experiments. The results indicated that Ntil could be determined accurately using ASD and the target maximum tiller number. Similarly, grain yield was influenced significantly by the N uptake at panicle initiation (NUPPI) and NPI, with R2 of 0.814 and 0.783 in the early and late seasons of 2020, respectively. This suggested that NPI could be calculated based on NUPPI and the target grain yield. CONCLUSION: The findings offer a quantitative method for establishing N topdressing rates for tillering and panicle development, relying on the monitoring of actual seedling density and plant N status in direct‐seeded rice production. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Author(s): Zhenling Cui [1]; Hongyan Zhang [1]; Xinping Chen [1]; Chaochun Zhang [1]; Wenqi Ma [2]; Chengdong Huang [1]; Weifeng Zhang [1]; Guohua Mi [1]; Yuxin Miao [1]; Xiaolin Li [...]

Reducing water input and CH 4 emission while maintaining grain yield is important for the sustainable rice production in south China. However, water-saving technology has not been widely adopted by farmers because of constrains in handling, effectiveness and reliableness. Recently a simplified and easy-to-use alternate wetting and drying technology, namely “safe” AWD, has been developed and recommended to farmers in Asian countries. However, the performance of the safe AWD technology has not yet been evaluated in south China. The objective of this study was to determine whether the safe AWD technology could maintain grain yield with reduced water input and CH 4 emission as compared to the conventional farmer’s practice (FP) in south China. Two on-station field experiments were conducted in Guangzhou, Guangdong province during 2014 early and late seasons. In the early season, a hybrid rice variety, Tianyou 3618 (TY3618), was arranged in a randomized complete block design with three water treatments, i.e., AWD15, AWD30 and continuous flooding (CF). In the late season, a split-plot design was employed with four water management (AWD15, AWD30, CF and FP) as main plots and two varieties as subplots. The two varieties were TY3618 and Hefengzhan (HFZ, inbred). Field water level and soil water potential were recorded daily and the CH 4 emission was monitored at 7-day intervals. Crop growth, grain yield and water productivities were measured. Results showed that grain yields under AWD15 and AWD30 were comparable with CF, while water input and total CH 4 emissions were significantly reduced under the two AWD treatments for both seasons. In the late season, there were no significant differences in grain yield among the four irrigation treatments for HFZ. While for TY3618, grain yield in AWD30 was significantly lower than AWD15. Irrigation water input in AWD15 and AWD30 was 19.4% and 29.7% lower, and irrigation water productivity was 31.7–37.6% and 48.4–53.2% higher than FP, respectively. Over all, no significant differences were found in maximum tiller number, leaf area index, total aboveground dry weight, among the four irrigation treatments for HFZ. While for TY3618, the crop growth rate during grain-filling stage in AWD30 was significantly lower than CF and FP. The CH 4 emission under AWD15 and AWD30 were 37.4–45.7% and 61.1–77.1% lower than FP, respectively. Multi-location on-farm comparisons were conducted in north, central, and southwest region of Guangdong province and the results confirmed that AWD15 could obtain comparable grain yield as FP with fewer irrigations. These findings suggested that the AWD15 could be used for water-saving and CH 4 emission mitigation while maintaining grain yield in rice production in south China. This is the first report on the performance of safe AWD in south China. [ABSTRACT FROM AUTHOR]

In an earlier greenhouse screening, we identified a local indica cultivar HT54 tolerant to high temperature at both seedling and grain-filling stages. In this study, we develop an optimized procedure for fine assessment of this heat tolerance. The results indicated that HT54 seedlings could tolerate high temperature up to 48 °C for 79h. The genetic analysis of F(1) and F(2) offspring derived from the cross between HT54 and HT13, a heat-sensitive breeding line, reveals that the heat tolerance of HT54 was controlled by a dominant major locus, which has been designated as OsHTAS (Oryza sativa heat tolerance at seedling stage). This locus was mapped on rice chromosome 9 within an interval of 420kb between markers of InDel5 and RM7364. The determined candidate ZFP gene has been confirmed to be cosegregated with a single nucleotide polymorphism (SNP) developed PCR-restriction fragment length polymorphism (RFLP) marker RBsp1407 in its promoter region. Another heat tolerance-associated SNP was identified in the first intron of its 5'-untranslated region. The existence of these SNPs thereby indicated that the OsHTAS locus contains at least two alleles. We named the one from HT54 as OsHTAS ( a ) and the one from HT13 as OsHTAS ( b ). Further dynamic expression analysis demonstrated that OsHTAS ( a ) was actively responsive to 45 °C high temperature stress compared with the OsHTAS ( b ) allele.