Jie Xiong

Nitrogen plays a critical role in regulating rice growth and stress resistance, yet its influence on heat tolerance at the seedling stage remains poorly understood. To clarify the physiological mechanisms involved, this study subjected rice seedlings to a transient range of temperature treatments (30, 35, 40, and 45 °C) under varying nitrogen levels. We systematically evaluated plant growth and analyzed key metabolic responses related to carbohydrates, phytohormones, and reactive oxygen species (ROS). The results demonstrated that temperatures of 40 °C and 45 °C significantly suppressed seedling growth, while elevated nitrogen supply effectively mitigated heat-induced damage, as evidenced by reduced leaf wilting and higher chlorophyll retention. Under high-temperature stress, seedlings receiving high nitrogen maintained superior carbohydrate reserves, higher levels of hormones such as zeatin ribosides, indole-3-acetic acid, and gibberellins, as well as a greater activity of key nitrogen metabolism enzymes compared to those under low nitrogen. Furthermore, high nitrogen enhanced the activity of antioxidant enzymes (superoxide dismutase and catalase) and significantly lowered the accumulation of malondialdehyde and hydrogen peroxide. Collectively, these findings indicate that appropriate nitrogen application enhances heat tolerance in rice seedlings through an integrated regulation of carbohydrate and hormone metabolism coupled with strengthened antioxidant capacity and improved ROS homeostasis.

Rice is one of China’s primary staple crops, serving as the main food source for over 60% of the population. With the resolution of basic food security issues in China in recent years, the demand for high-quality rice has been steadily increasing. The taste quality of rice, a crucial indicator for evaluating rice quality, has attracted more attention from consumers. Although factors like variety, growing environment, and cultivation methods affect rice taste quality, the underlying mechanisms remain unknown, and no reliable control methods exist. This study selected 10 major rice cultivars, including 6 indica and 4 japonica varieties, and compared their differences in taste quality, focusing on yield and its components, taste quality, and dry matter accumulation. Among the tested varieties, Songxiangjing 1018 had the best taste quality, but not the highest yield. Zhongzheyou 8, Huazheyou 261, and Quanyousimiao showed both excellent taste quality and high yield. There was no significant correlation between taste quality and yield, suggesting the feasibility of breeding rice varieties with both superior taste and high productivity. Correlation analysis indicated that dry matter mass and net photosynthetic rate were significantly positively correlated with yield, but not with taste quality, highlighting the complexity of taste quality formation. Using a membership function comprehensive evaluation method (combines the outputs of multiple membership functions into a single composite value using specific rules (e.g., weighted average, extremum, logical operations) to produce a new membership degree.), a rice variety selection system balancing yield and quality was constructed, and three varieties (Zhongzheyou 8, Huazheyou 261, and Quanyousimiao) were identified as having both high yield and excellent quality. The results of this study can provide a theoretical basis for research on cultivation techniques and variety breeding aimed at synergistically improving rice yield and quality.

As the economy develops and urbanization progresses, the amount of arable land continues to decline. In this context, the cultivation of double-season rice is particularly important for enhancing yield per unit area. However, research on the physiological mechanisms that contribute to high yields in double-season early rice varieties with short growing seasons is still limited. To address this gap, we conducted a field study using two early rice varieties, Zhongzu18 and Yongxian15, to examine their production characteristics, photosynthesis, fluorescence, and energy metabolism. The results indicate that Zhongzu18 has a significantly higher seed-setting rate, grain weight, and total grain yield compared to Yongxian15. Additionally, Zhongzu18 exhibits a higher head rice rate and a lower degree of chalkiness, along with a reduced chalky grain rate. Furthermore, the total dry matter weight and the ratio of panicle weight to total weight for Zhongzu18 were significantly greater than those for Yongxian15. After anthesis, Zhongzu18 also demonstrated a higher leaf net photosynthetic rate and actual fluorescence quantum efficiency compared to Yongxian15. Moreover, the levels of ATP and ATPase, as well as the activities of antioxidant enzymes and the expression of sucrose transport-related genes, were significantly increased in Zhongzu18 plants relative to Yongxian15. We conclude that the enhanced photosynthetic efficiency and energy production in Zhongzu18 lead to more effective assimilation and carbohydrate transport to the grains, resulting in higher grain yields and improved rice quality.

With the progress of society and the improvement of agricultural scientific technology, the single focus on high yield for rice production has gradually shifted to high quality. Coordinated development of grain yield and rice quality has become a core issue for researchers, and the underlying mechanisms remain to be solved. Two varieties, Zhongzheyou1 (ZZY1) and Zhongzheyou8 (ZZY8), were used as study materials under field conditions. The yield of ZZY1 was higher than that of ZZY8, which was mainly characterized by a higher seed-setting rate and grain weight. The rice quality of ZZY8 was better than that of ZZY1, primarily due to lower chalkiness and a higher head rice rate. The total dry matter weight of ZZY1 was lower than that of ZZY8, but the proportion of panicle dry matter weight or nonstructural carbohydrate to the total in the former was higher than that of the latter. The maximum grain-filling rate, average grain-filling rate, and key enzyme activities of ZZY1 were significantly higher than those of ZZY8, while the active grain-filling period was shorter than that of ZZY8. Furthermore, the ATP/ATPase content and energy charge values in the grains of ZZY1 were higher than those of ZZY8 at the early grain-filling stage. Transcriptome analysis showed that carbohydrate and energy metabolism were the main ways affecting the yield and quality of the two varieties. The energy production of ZZY1 was insufficient to simultaneously supply the needs thus leading to the discordant formation in its grain yield and rice quality formation.

With the combustion of fossil fuels, unequal and unsustainable energy and land use, and irrational human activities, greenhouse gas emissions remain high, which leads to global warming

Aeration and water management increasing rhizosphere oxygen amount significantly promote rice (Oryza sativa) growth and yield, but the effect of root aeration on cadmium (Cd) toxicity and accumulation in rice seedlings under hydroponic culture remains unclear. Results showed that aeration promoted rice seedling growth and alleviated Cd toxicity. Transverse section discovered that Cd accelerated root mature and senescence while aeration delayed the mature and senescence of roots. Non-invasive Micro-test Technology (NMT) showed that aeration increased net O2 and Cd2+ influxes on the surface of roots while decreased net Cd2+ influx in xylem. Perls blue staining showed that aeration and Cd treatments increased iron plaque formation on the surface of roots. Results of metal concentration analysis showed that besides increasing Cd retention in iron plaque, aeration also increasing Cd retention in the cell wall of rice roots. Cell wall component analysis showed that aeration not only increased pectin content but also decreased pectin methylesterification degree (PMD) by increasing pectin methylesterase (PME) activity. All of these results indicate that aeration not only delays root mature and senescence but also increases Cd retention in roots by enhancing iron plaque formation and regulating pectin synthesis in the roots of rice seedlings.

Iron (Fe) and zinc (Zn) are important trace elements for people’s health around the globe. A lot of people, especially children and woman, are suffering from malnutrition caused by Fe and/or Zn deficiency. The deficiency is more pronounced in some parts of Africa and Asia due to low income, which makes it difficult to afford meat or sea foods that are rich in Fe and Zn. Biofortification of Fe and Zn in rice is the most economical and convenient way to supplement these important minerals in the diet of poor people. However, besides Fe and Zn, rice also can accumulate heavy metals, such as cadmium (Cd) and lead (Pb), which are harmful to people, especially for kids’ health. Previous researches have shown that there are connections and discrepancies for metal absorption, translocation, and accumulation in rice. So it is imperative to review these issues. This chapter compares the physiological and molecular mechanisms of Fe, Zn, Cd, and Pb uptake, mobilization, and accumulation in rice and discusses the progress and strategies for not only increasing Fe/Zn but also decreasing Cd/Zn accumulation in rice.

Iron (Fe) is essential for rice growth and humans consuming as their staple food but is often deficient because of insoluble Fe(III) in soil for rice growth and limited assimilation for human bodies, while cadmium (Cd) is non-essential and toxic for rice growth and humans if accumulating at high levels. Over-accumulated Cd can cause damage to human bodies. Selecting and breeding Fe-rich but Cd-free rice cultivars are ambitious, challenging and meaningful tasks for researchers. Although evidences show that the mechanisms of Fe/Cd uptake and accumulation in rice are common to some extent as a result of similar entry routes within rice, an increasing number of researchers have discovered distinct mechanisms between Fe/Cd uptake and accumulation in rice. This comprehensive review systematically elaborates and compares cellular mechanisms of Fe/Cd uptake and accumulation in rice, respectively. Mechanisms for maintaining Fe homeostasis and Cd detoxicification are also elucidated. Then, effects of different fertilizer management on Fe/Cd accumulation in rice are discussed. Finally, this review enumerates various approaches for reducing grain Cd accumulation and enhancing Fe content in rice. In summary, understanding of discrepant cellular mechanisms of Fe/Cd accumulation in rice provides guidance for cultivating Fe-fortified rice and has paved the way to develop rice that are tolerant to Cd stress, aiming at breeding Fe-rich but Cd-free rice.