土壤中的氮素分布不均，在氮素富集的土壤区域内，植物根系大量的生长。然而，不同玉米基因型根系对局部施氮的响应与氮素吸收效率之间的关系尚不清楚。本研究以4个玉米品种为研究对象，探讨根系生长对局部施氮响应的基因型差异及对氮素吸收的影响。在水培采用分根培养体系局部供氮，在田间采用条施和穴施的局部施氮方法。结果表明，不同品种根系局部氮响应在水培和田间条件之间具有高度相关性（r>0.99）。在水培局部供氮条件下，强响应品种郑单958、先玉335和先锋32D22的侧根长增加了50-63%，根系生物量增加了36-53%，而弱响应品种蠡玉13的根系生长响应较小。田间条件下，3个强响应品种的根长在40-60 cm土层显著增加66-75%，而蠡玉13的根长变化幅度显著较低。此外，局部施氮肥促进强响应品种的花后氮吸收，增幅达16-88%，并且促进了郑单958的籽粒产量显著增加10-12%。相关分析发现，产量与40-60 cm土层根长呈显著正相关（r=0.39）。综上所述，可在苗期鉴定玉米品种对局部施氮的响应类型，生产中强响应型玉米品种与局部施用氮肥配套应用；同时可将“根系局部施氮响应能力”作为玉米氮高效遗传改良的目标性状。

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。

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.

Maize plants respond to low-nitrogen stress by enhancing root elongation. The underlying physiological mechanism remains unknown. Seedlings of maize (Zea mays L., cv. Zhengdan 958) were grown in hydroponics with the control (4 mmol L-1) or low-nitrogen (40 μmol L-1) for 12 d, supplied as nitrate. Low nitrogen enhanced root elongation rate by 4.1-fold, accompanied by increases in cell production rate by 2.2-fold, maximal elemental elongation rate (by 2.5-fold), the length of elongation zone (by 1.5-fold), and final cell length by 1.8-fold. On low nitrogen, the higher cell production rate resulted from a higher cell division rate and in fact the number of dividing cells was reduced. Consequently, the residence time of a cell in the division zone tended to be shorter under low nitrogen. In addition, low nitrogen increased root diameter, an increase that occurred specifically in the cortex and was accompanied by an increase in cell number. It is concluded that roots elongates in response to low-nitrogen stress by accelerating cell production and expansion.

Maize plants adapt to low phosphorus (P) stress by increasing root growth. It is of importance to know the extent to which genetic improvement of root growth can enhance P acquisiton. In the present study, the contribution of root growth improvement to efficient P acquisition was evaluated in two soils using T149 and T222, a pair of near isogenic maize testcrosses which were derived from a backcross BC4F3 population. T149 and T222 showed no difference in shoot biomass and leaf area under normal growth conditions, but differed greatly in root growth. T149 had longer lateral roots and a larger root surface area compared to T222. In calcareous soil, when P was insufficient, i.e., when P was either supplied as KH2PO4 at a concentration of 50 mg P kg-1 soil, or in the form of Phy-P, Ca3-P or Ca10-P, a 43% increase in root length in T149 compared to T222 resulted in an increase in P uptake by 53%, and shoot biomass by 48%. In acid soil, however, when P supply was insufficient, i.e., when P was supplied as KH2PO4 at a concentration of 100 mg P kg-1 soil, or in the form of Phy-P, Fe-P or Al-P, a 32% increase in root length in T149 compared to T222 resulted in an increase in P uptake by only 12%, and shoot biomass by 7%. No significant differences in the exudation of organic acids and APase activity were found between the two genotypes. It is concluded that genetic improvement of root growth can efficiently increase P acquisition in calcareous soils. In acid soils, however, improvements in the physiological traits of roots, in addition to their size, seem to be required for efficient P acquisition.