Incorporating oilseed-rape straw in soil is one of the effective methods for enhancing the use efficiency of agricultural resources in the rape-rice rotation system. However, the impacts of oilseed-rape straw incorporation on root growth and dynamic changes in soil are still unclear. In order to provide a deeper understanding of the oilseed rape straw return on rice growth and productivity, the experiment was conducted in the field and in a specially-designed pots system from 2016 to 2017 by means of two straw returning methods and four straw returning amounts. In the early stage of rice growth (0–36 days after rice transplanting) the straw returning treatments decreased 1.0–8.6 mg/plant in bleeding density and 0.10–6.11, 0.06–0.31, and 0.52–0.84 μmol/(g h) in the activity of glutamine synthetase (GS), glutamic-oxalacetic transaminase (GOT), and glutamic-pyruvic transaminase (GPT), respectively. Oilseed rape straw returned by mulching induced negative impacts on new germinating roots in 0–10 cm of soil, while the negative impacts were observed on roots in 10–30 cm of soil for straw returned by plowing. In the later stage of rice growth (56–75 days after rice transplanting), oilseed rape straw returning produced some positive impacts on rice roots, which enhanced the yield of rice. Conclusively, our findings suggested that dynamic root growth and the activity of root enzymes are two major factors behind the slow reviving of rice after transplanting in the straw returning field. Plowing is a more appropriate method of straw returning than mulching in the rape-rice rotation system in the Sichuan basin area, with a straw incorporation rate of 3.0 t/hm².

Drought is one of the major factors limiting rice yield worldwide. A total of 46 hybrid rice varieties were chosen to investigate their root distribution and their response to drought. A field experiment was carried out in a dry shed building to evaluate the drought tolerance capacity of hybrid rice varieties on the basis of CTIRDE (complex tolerance index of rice under drought environment) values. Next, the experiment was conducted in a specially designed pot system and seed bags to analyze the root distribution and activity of antioxidant enzymes in different rice varieties. Moreover, the DEEPER ROOTING 1 (DRO1) gene was sequenced to elucidate its role in the root distribution of typical rice varieties. On the basis of CTIRDE values, the 46 hybrid rice varieties were classified as tolerant (CTIRDE ≥ 0.75), semi-tolerant (0.75 > CTIRDE > 0.65), or sensitive (CTIRDE ≤ 0.65) to drought stress. The tolerant varieties (Chuanguyou208 and Deyou4727) displayed a significantly larger length, had higher number and weight of roots in the 30–50 cm soil layer, and exhibited a significantly higher activity of Superoxide dismutase (SOD) and Peroxidase (POD) enzymes in roots during the drought stress period. The DRO1 gene sequencing results revealed that the tolerant and sensitive varieties exhibited a single-nucleotide polymorphism (SNP) in the 3-exon region, and the tolerant varieties (Chuanguyou208 and Deyou4727) exhibited a larger root growth angle with the horizontal axis, hence developing a deeper root system as compared with the other two group varieties. A significant correlation was found not only between the DRO1 gene and root distribution but also between DRO1 and the activity of SOD and POD enzymes. Conclusively, as a key feature, a deep root system enabled tolerant rice varieties (Chuanguyou208 and Deyou4727) to avoid drought stress by absorbing more water stored in deep soil layers. The root distribution, activity of POD and SOD enzymes in roots, and DRO1 gene can be used to screen tolerant rice varieties that can survive better under drought stress during the seedling stage of rice growth.

Light is one of the most important environmental factors that affect many aspects of plant growth, including chlorophyll (Chl) synthesis and flowering time. Here, we identified a rice mutant, yellow leaf and early flowering (ye1), and characterized the gene YE1 by using a map-based cloning method. YE1 encodes a heme oxygenase, which is localized to the chloroplasts. YE1 is expressed in various green tissues, especially in leaves, with a diurnal-rhythmic expression pattern, and its transcripts is also induced by light during leaf-greening. The mutant displays decreased Chl contents with less and disorderly thylakoid lamellar layers in chloroplasts, which reduced the photosynthesis rate. The early flowering phenotype of ye1 was not photoperiod-sensitive. Furthermore, the expression levels of Chl biosynthetic genes were downregulated in ye1 seedlings during de-etiolation responses to light. We also found that rhythmic expression patterns of genes involved in photoperiodic flowering were altered in the mutant. Based on these results, we infer that YE1 plays an important role in light-dependent Chl biogenesis as well as photoperiodic flowering pathway in rice.

Panicle-type structure is an important factor affecting rice yield, and an excellent panicle type has become a key indicator in rice breeding. In this study, the indica rice variety R766, which has an open panicle type, was obtained through natural mutation and hybrid selection. Through analyzing differences in panicle structure, panicle yield, and chemical composition between open panicle rice R766 and conventional panicle rice R2928, we found that the angles of the middle and lower branches in R766 were 186.99% and 135.93% greater than those in R2928, respectively. By comparing the grain-filling characteristics of different panicle positions in the two rice varieties, we found that the grain filling at the middle and lower panicle positions of R2928 was significantly lower, accompanied by an increase in the percentage of empty spikelets. However, in R766, the grain-filling rates in the middle and lower panicle positions were consistent with those in the upper panicle position, with significantly higher rates of grain filling and grain plumpness in the middle and lower panicle positions than in R2928. The empty grain rate at the lower panicle position of R766 was 15.25% lower than that of R2928, and the grain filling was 24.75% higher than that of R2928. Additionally, the variation in the 1000-grain weight of grains at different panicle positions in R766 was relatively small, with decreases of 1.55% and 0.38% in the middle and lower panicle positions, respectively, compared with the upper position, whereas R2928 showed decreases of 5.99% and 7.12% in the 1000-grain weight of grains at the middle and lower panicle positions, respectively, compared with the upper position. The cellulose content in the stems of R766 was 7.51% higher than that of R2928, with no significant difference in the cellulose content in the panicle axis and primary branches compared to R2928. The lignin content of the panicle axis in R766 was 8.03% higher than that in R2928, whereas there was no significant difference between the lignin content of the stems and primary branches. This preliminary study revealed the open panicle characteristics of R766 and the reasons for its high basal grain setting rate. This study provides a reference for promoting this open panicle-type indica rice variety to improve yield and disease resistance in environments with high humidity and low sunlight levels.

Rice is an important food crop, acting as the staple food for more than 50% of the global population. We selected seedlings (two sterile male lines: WA803A and JW803A) that had different cytoplasmic but the same nuclear composition and were heterogeneous. The maintainer line 803B was also used. We aimed to study their nitrogen uptake rate in different concentrations of NH₄⁺ and NO₃⁻ and explore the differences in nitrogen uptake efficiency between different cytoplasmic genes. The results showed a significant difference in the nitrogen uptake rate for different seedlings. With ammonium nutrition, the nitrogen uptake efficiency of the JW cytoplasm was significantly higher than that of the WA cytoplasm. In low concentrations of ammonium nitrogen, the JW cytoplasm had an additive effect to the nuclear gene regulation of ammonium uptake. The JW cytoplasm’s ammonium nitrogen absorption effect on nuclear gene regulation was higher than that of the WA cytoplasm. The effect of the WA and JW cytoplasms on the nitrate uptake rate was not significant, and the nuclear gene regulation of both cytoplasms was reduced by absorbing nitrate. Under nitrogen deficiency conditions, the material output and conversion rate of the JW-type cytoplasmic hybrid rice combination was relatively high, significantly higher than those of other cytoplasmic combinations. Under medium nitrogen conditions, the material output and conversion rate of the (N2) W-type hybrid rice combination were significantly higher than those of the other cytoplasmic combinations. The yield of JW-type rice first increased and then decreased with the increase in the nitrogen application rate and was highest, 8195.55 kg/hm², under the N2 treatment.

The aim of this study was to determine the different mechanisms of nitrogen absorption and nitrogen regulation response of different rice varieties with diverse nitrogen efficiencies.On the premise of the same root distribution angle and the same type of DRO1 gene, the DRO1 gene of the low-nitrogen-efficient rice variety was highly expressed under low-nitrogen conditions, which made the root length and the depth of rooting significantly increased compared to that of the high-nitrogen-efficient rice variety. The high expression of key enzyme genes of nitrogen absorption and assimilation (OsAMT2;1, OsGS2, OsGS1;1, OsGS1;2) under low-nitrogen conditions in the low-nitrogen-efficient rice variety had higher nitrogen and phosphorus absorption capacity, and thus improved the accumulation of dry matter in plants. The expression of nitrogen metabolism genes at the seedling stage of different nitrogen-efficient rice varieties showed significant differences in the corresponding laws of nitrogen regulation. The high expression of nitrogen metabolism genes in the high-nitrogen-efficient rice varieties under the condition of sufficient nitrogen fertilizer ensured the full absorption and assimilation of nitrogen.The limiting factors of nitrogen absorption in the seedling stage of the two nitrogen-efficient rice varieties differed under the control of nitrogen fertilizer. The main reason for low nitrogen and high efficiency was that low-nitrogen-efficient rice varieties had a strong rooting ability under low-nitrogen conditions.