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High temperature (HT) at flowering hinders pollen shedding, but the mechanisms underlying stress-induced spikelet closure are poorly understood in maize. In this study, yield components, spikelet opening, and lodicule morphology/protein profiling upon HT stress during flowering were examined in two contrasting maize inbred lines, Chang 7-2 and Qi 319. HT induced spikelet closure and reduced pollen shed weight (PSW) and seed set in both lines, but Qi 319 had a 7-fold lower PSW than Chang 7-2, and was thus more susceptible to HT. In Qi 319, a smaller lodicule size reduced the spikelet opening rate and angle, and relatively more vascular bundles hastened lodicule shrinking compared with Chang 7-2. Lodicules were collected for proteomics analysis. In lodicules of HT-stressed plants, proteins involved in stress signals, cell wall, cell constructure, carbohydrate metabolism, and phytohormone signaling were associated with stress tolerance. HT down-regulated the expression of ADP-ribosylation factor GTPase-activating protein domain2 , SNAP receptor complex member11 , and sterol methyltransferase2 in Qi 319 but not in Chang 7-2, which was in good agreement with the observed changes in protein abundance. Exogenous epibrassinolide increased the spikelet opening angle and extended the duration of spikelet opening. These results suggest that dysfunction of the actin cytoskeleton and membrane remodeling induced by HT probably limits lodicule expansion. In addition, a reduction in the vascular bundles in the lodicules and application of epibrassinolide might confer spikelet tolerance to HT stress. [ABSTRACT FROM AUTHOR]

High temperature reduces crop production; however, little is known about the effects of high night temperature (HNT) on the development of male and female reproductive organs, pollination, kernel formation and grain yield in maize (Zea mays L.). Therefore, a temperature‐controlled experiment was carried out using heat‐sensitive maize hybrid and including three temperature treatments of 32/22°C (day/night; control), 32/26°C and 32/30°C during 14 consecutive days encompassing the flowering stage. When exposed to 30°C night temperature, grain yield and kernel number reduced by 23.8 and 25.1%, respectively, compared with the control. The decrease in grain yield was mainly because of the lower kernel number rather than change in kernel weight under HNT exposure around flowering. No significant differences in grain yield and kernel number were found between 22 and 26°C night temperatures. HNT had no significant effects on the onset of flowering time and anthesis‐silking interval but significantly reduced time period of pollen shedding duration and pollen viability, and increased leaf night respiration. Different from high daytime temperature, HNT had no lasting effects on daytime leaf photosynthesis, biomass production and assimilate transportation. From the perspective of source–flow–sink relationship, the unchanged source and flow capacities during daytime are supposed to alleviate the adverse effects on sink strength caused by HNT compared with daytime heat stress. These new findings commendably filled the knowledge gaps concerning heat stress in maize. [ABSTRACT FROM AUTHOR]

Ideotype root system architecture is crucial for achieving high yields in maize by enhancing lodging resistance and nitrogen absorption, particularly under high planting densities. However, there is limited research on this topic in maize. The objectives of this study were to reveal the relative importance of different root system traits in root anchorage strength and nitrogen absorption, and to investigate their variations in response to increased plant density. To clarify this, a two-year field experiment was conducted in 2018 and 2019, involving four different lodging resistant maize genotypes and two plant densities. Root system traits including root crown architecture, root morphology per whorl, and root distribution in upper and lower soil layers were fully characterized. Root lodging resistance and nitrogen absorption capacity were quantified through artificial root lodging tests and 15N labeling, respectively, based on measuring root lodging rate and plant nitrogen content. In comparison to lodging susceptible genotypes XY335 and XD20, lodging resistant genotypes LS1 and FM985 exhibited stronger root anchorage strength and lower root lodging risk. These characteristics were primarily attributed to their wider root crown width, larger projected root area, larger root angle, thicker brace roots, and wider distribution of the root system in the upper soil layer. However, LS1 was unfavorable for nitrogen absorption due to the larger root skeleton increased metabolic costs of soil exploration, which led to reduced root elongation, shallower rooting depth, and thus limited nitrogen acquisition from the soil. FM985 demonstrated a comparable nitrogen absorption capacity to XY335 (slightly higher than LS1) mainly because of the larger growth angle of the outermost crown root and greater specific root length of embryonic roots. With increased plant density, LS1and FM985 had larger reductions in root system traits, but maintained a larger root crown architecture than that of XY335 and XD20, leading to a lower lodging risk. XY335 and XD20 exhibited a stronger capacity for nitrogen acquisition at high plant densities, attributed to the increased root surface area, root volume and root dry matter of embryonic roots and root dry matter in the subsoil. Taken together, maintaining an optimized root crown architecture, coupled with an increase in surface area, volume and dry matter of embryonic roots and root dry matter in the subsoil, appears to be a more feasible approach for reducing lodging incidents and enhancing nitrogen absorption at a dense population. [Display omitted] • Larger growth angle of outermost crown root is favorable for both root lodging resistance and nitrogen absorption. • Larger specific root length of embryonic roots is conductive to root lodging resistance and N absorption capacity. • Deep rooting is advantageous for accessing deeper nitrogen resources. • Increasing the surface area, volume and dry matter of embryonic roots able to reduce lodging and reinforce N absorption. [ABSTRACT FROM AUTHOR]