本文利用玉米水培分根体系发现，局部供铵到缺氮根系可以显著诱导ZmAMT1;1a与ZmAMT1;3基因的表达水平。测定¹⁵N标记铵吸收速率与根组织氨基酸含量发现，铵诱导的ZmAMT1s基因表达与根系铵吸收能力及谷氨酰胺含量显著正相关。外界添加谷氨酰胺合成酶抑制剂MSX时，供铵则不能诱导缺氮根系中ZmAMT1;1a与ZmAMT1;3基因的表达，表明铵的同化产物谷氨酰胺，而不是铵本身，负责调控ZmAMT1s基因表达。此外，外界供应不同浓度谷氨酰胺到缺氮根系发现，较低浓度的谷氨酰胺就能够诱导ZmAMT1s基因表达，但高浓度谷氨酰胺却能够抑制其表达。以上研究结果表明，为了严格调节玉米根系铵吸收能力，铵转运蛋白ZmAMT1s基因在转录水平被严谨调控，与根内谷氨酰胺水平密切相关。

Rice, wheat and maize are the main staple food crops to ensure the food security in China with diversified climate condition, cropping system and environmental and socio-economic factors across provinces. Spatial variation of technical efficiency in farmers’ field is helpful to understand the potential to improve farmers’ yield given the inputs level and reduce the yield gap. The study is based on a large-scale farm household survey which covered 1 218 rice farmers, 3 566 wheat farmers and 2 111 maize farmers in the main producing areas. The results indicate that rice farmers are with very high technical efficiency level, nearly 0.9 on average, with little room to improve the efficiency of agricultural inputs. Similar results have been found in wheat and maize farmers’ fields, although the technical efficiency levels are lower than that of rice farmers while still at a high level with obvious variation across regions. Farmers with higher yield level also achieve better technical efficiency in most locations. Both local environmental and socio-economic factors significantly affect farmers’ technical efficiency. In the context of urbanization and economic development, improved and new agricultural technologies need to be prioritized and facilitated to improve cereal yield at farm level.

Yield gap analysis could provide management suggestions to increase crop yields, while the understandings of resource utilization efficiency could help judge the rationality of the management. Based on more than 110 published papers and data from Food and Agriculture Organization (FAO, www.fao.org/faostat) and the Global Yield Gap and Water Productivity Atlas (www.yieldgap.org), this study summarized the concept, quantitative method of yield gap, yield-limiting factors, and resource utilization efficiency of the three major food crops (wheat, maize and rice). Currently, global potential yields of wheat, maize and rice were 7.7, 10.4 and 8.5 t ha^–1, respectively. However, actual yields of wheat, maize and rice were just 4.1, 5.5 and 4.0 t ha^–1, respectively. Climate, nutrients, moisture, crop varieties, planting dates, and socioeconomic conditions are the most mentioned yield-limiting factors. In terms of resource utilization, nitrogen utilization, water utilization, and radiation utilization efficiencies are still not optimal, and this review has summarized the main improvement measures. The current research focuses on quantitative potential yield and yield gap, with a rough explanation of yield-limiting factors. Subsequent research should use remote sensing data to improve the accuracy of the regional scale and use machine learning to quantify the role of yield-limiting factors in yield gaps and the impact of change crop management on resource utilization efficiency, so as to propose reasonable and effective measures to close yield gaps.

Aldehyde dehydrogenases (ALDHs) represent a large protein family, which includes several members that catalyze the oxidation of an aldehyde to its corresponding carboxylic acid in plants. Genes encoding members of the ALDH7 subfamily have been suggested to play important roles in various stress adaptations in plants. In this study, quantitative RT-PCR analysis revealed that a maize ALDH7 subfamily member (ZmALDH7B6) was constitutively expressed in various organs, including roots, leaves, immature ears, tassels, and developing seeds. The abundance of ZmALDH7B6 mRNA transcripts in maize roots was increased by ammonium, NaCl, and mannitol treatments. To further analyze tissue-specific and stress-induced expression patterns, the 1.5-kb 5´-flanking ZmALDH7B6 promoter region was fused to the β-glucuronidase (GUS) reporter gene and introduced into maize plants. In roots of independent transgenic lines, there was significant induction of GUS activity in response to ammonium supply, confirming ammonium-dependent expression of ZmALDH7B6 at the transcript level. Histochemical staining showed that GUS activity driven by the ZmALDH7B6 promoter was mainly localized in the vascular tissues of maize roots. These results suggested that ZmALDH7B6 is induced by multiple environmental stresses in maize roots, and may play a role in detoxifying aldehydes, particularly in vascular tissue.