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Purpose: The developmental status of the male and female spike determines grain number (GN) per ear and yield. A better understanding of the effect of N on male and female spike differentiation and GN formation could help to gain insight into the mechanism of N regulation on yield. Methods: A field experiment was conducted with four nitrogen rates: 0 (N0), 129 (N1), 185 (N2), and 300 kg N ha−1 (N3) with a single summer maize hybrid to determine tassel and ear development and the resulting GN. Results: The expression of key proteins and genes related to fatty acid metabolism of N0 were down-regulated and the tapetum was abnormally degraded. This inhibited the synthesis of long-chain fatty acids (LCFAs) in the tassel and ear. Both pollen and silk development at the mononucleate stage were abnormal and presented as misshapen pollen, uneven silk tube, reduced silk, and poor pollination. Finally, anthesis-silking interval (ASI) was increased and the length of male and female spikes, fertilized florets, floret fertility percentage, and grain set rate were reduced in N0 treatment resulting in reduced GN. N application promoted fatty acid metabolism but N application greater than 185 kg N ha−1 did not increase LCFA of either male or female spike traits. Conclusions: A nitrogen rate of 185 kg N ha−1 was sufficient to promote lipid metabolism, and increase the content of LCFAs. This resulted in normal pollen and silk development, shortened ASI and led to an increase in the number of fertile florets, fertilization percentage, and GN. [ABSTRACT FROM AUTHOR]

Aims: To realize the so-called "Second Green Revolution", it is imperative to study the roots of crop plants, and identify those traits that improve the efficiency of nitrogen (N) acquisition. We aimed to evaluate how the N acquisition efficiency of six hybrid maize lines commonly grown in northern China depends on their root anatomy. Methods: Maize hybrids classified as having high nitrogen uptake efficiency (HNUE) and low nitrogen uptake efficiency (LNUE) were grown under high-N and low-N conditions in the greenhouse and the field. Results: Under N stress in the field and the greenhouse, HNUE increased shoot dry weight, root length density, N content and nitrogen use efficiency compared to LNUE. Low N availability increased the percentage of root cortical aerenchyma and the size of cortical cells. Root anatomy, with greater formation of root cortical aerenchyma and larger cortical cell size, was associated with increased specific nitrogen absorption efficiency (SNAE) and shoot biomass under N stress. Under low N availability, the percentage of aerenchyma and their total area had significant positive correlations with the shoot dry weight, total N uptake, SNAE. Conclusions: The results suggest that plants in limited N availability form more root cortical aerenchyma and have larger cortical cells, which is of benefit to root growth, soil exploration, N acquisition, and shoot biomass. These observations support the hypothesis that root anatomical phenotypes that affect the metabolic and construction costs of producing root length merit consideration as selection criteria for breeding to improve N acquisition in hybrid maize. [ABSTRACT FROM AUTHOR]

3 Root anatomy parameter of different NUE maize varieties at 40 days in the greenhouse under high-N and low-N conditions. A, RXSA, root cross-section area; B, TCA, total cortex cross-section area; C, TSA, total stele cross-section area; D, AA, total aerenchyma area; E, CCA, cortical cell area; F, MXVA, total metaxylem vessel area; G, CCS, median cortical cell size; H, MXA, median single metaxylem vessel area; I, AAP, percentage of aerenchyma area in the cortex; J, CFN, number of cortical cell files; K, MXN, number of metaxylem vessels; L, MXP, percentage of total metaxylem vessel area in the stele The gray bar and pink bar represent the HNUE and LNUE group, respectively. [Extracted from the article]