Increasing plant density is one of the most efficient ways of increasing wheat (Triticum aestivum L.) grain production. However, overly dense plant populations have an increased risk of lodging. We examined lignin deposition during wheat stem development and the regulatory effects of plant density using the wheat cultivars shannong23 and weimai8. Plants were cultivated at densities of 75, 225 and 375 plants per m2 during two growing seasons. Our results showed that decreasing plant density enhanced culm quality, as revealed by increased culm diameter, wall thickness and dry weight per unit length, and improved the structure of sclerenchyma and vascular bundles by increasing lignification. In addition, more lignins were deposited in the secondary cell walls, resulting in strong lodging resistance. The guaiacyl unit was the major component of lignin and there was a higher content of the syringyl unit than that of the hydroxybenzyl unit. Furthermore, we hypothesised that the syringyl unit may correlate with stem stiffness. We describe here, to the best of our knowledge, the systematic study of the mechanism involved in the regulation of stem breaking strength by plant density, particularly the effect of plant density on lignin biosynthesis and its relationship with lodging resistance in wheat.

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Straw return is an important management tool for tackling and promoting soil nutrient conservation and improving crop yield in Huang-Huai-Hai Plain, China. Although the incorporation of maize straw with deep plowing and rotary tillage practices are widespread in the region, only few studies have focused on rotation tillage. To determine the effects of maize straw return on the nitrogen (N) efficiency and grain yield of winter wheat (Triticum aestivum L.), we conducted experiments in this region for 3 years. Five treatments were tested: (i) 3-year rotary tillage with straw removed (RT); (ii) 3-year deep plowing tillage with straw removed (DT); (iii) 3-year rotary tillage with straw return (RS); (iv) 3-year deep plowing tillage with straw return (DS); (v) rotary tillage and deep plowing interval of 2 years with straw return (TS). Treatments with straw return increased kernels no. ear -1 , thousand-kernel Weight (TKW), grain yields, ratio of dry matter accumulation post-anthesis, and nitrogen (N) efficiency whereas reduced the ears no. ha -1 in the 2011-2012 and 2012-2013 growing seasons. Compared with the rotary tillage, deep plowing tillage significantly increased the grain yield, yield components, total dry matter accumulation, and N efficiency in 2013-2014. RS had significantly higher straw N distribution, soil inorganic nitrogen content, and soil enzymes activities in the 0-10 cm soil layer compared with the DS and TS. However, significantly lower values were observed in the 10-20 and 20-30 cm soil layers. TS obtained approximately equal grain yield as DS, and it also reduced the resource costs. Therefore, we conclude that TS is the most economical method for increasing grain yield and N efficiency of winter wheat in Huang-Huai-Hai Plain.The Huang-Huai-Hai Plain is one of the most important agricultural regions in China. It produces more than 60% of China's winter wheat (Man et al. 2015). The average yield of winter wheat is approximately 5 540 kg ha -1 , and yields in excess of 9 000 kg ha -1 have also been reported in the region (NBSC 2013). However, the output of grain production in this region was based on the higher rate of fertilizer application (Jin et al. 2012;Chen et al. 2014). Although the use of fertilizer has temporarily increased the yield, its excessive application has brought a series of environmental problems, such as water pollution, field greenhouse gas emission, and

In order to clarify the transcriptional regulatory network and physiological mechanisms governing leaf senescence response to drought stress in wheat, experiments were performed using two wheat varieties with contrasting drought tolerance: Fu287 (F287, a drought‐sensitive genotype) and Shannong20 (SN20, a drought‐resistant genotype). The latter has higher SPAD values, salicylic acid (SA), jasmonic acid (JA), zeatin (Z), zeatin riboside (ZR), and gibberellin (GA3) content as well as higher expression levels of Cu/Zn‐SOD, Mn‐SOD, Fe‐SOD, POD, CAT, and APX under various water deficit conditions. Conjoint analysis of physiological and biochemical indicators and transcriptome data by weighted gene co‐expression network analysis (WGCNA) in the present study provides a useful genomic and molecular resource for studying drought adaptation in wheat. The flag leaf senescence process was changed by altering the concentration of phytohormones. SA, JA, abscisic acid (ABA), Z, ZR, and GA3 coordinate with each other to control leaf senescence and plant adaptation under drought stress. Further, the leaf senescence process was divided into two phases: the persistence phase and the rapid loss phase. Shorter Chltotal (duration of the flag leaf being photosynthetically active), shorter Chlper (persistence phase), reduced M (inflection point cumulative temperature when senescence rate is the maximum), decreased rmax (the maximum senescence rate), larger r0 (the initial senescence rate), and increased raver (the average senescence rate) were slightly associated with low grain mass. We speculated that extending the period of the persistence phase by cultivation or chemical control measures could further increase the drought survivability and productivity of wheat.

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Severe water deficit (SD) severely limited the photo-assimilate supply during the grain-filling stages. Although the ethylene and polyamines (PAs) have been identified as important signaling molecules involved in stress tolerance, it is yet unclear how 1-Aminocylopropane-1-carboxylic acid (ACC) and PA biosynthesis involving wheat abdominal phloem characters mitigate SD-induced filling inhibition. The results obtained indicated that the SD down-regulated the TaSUT1 expression and decreased the activities of sucrose synthase (SuSase, EC2.4.1.13), ADP glucose pyrophosphorylase (AGPase, EC2.7.7.27), soluble starch synthase (SSSase, EC2.4.1.21), then substantially limited grain filling. As a result, increased ACC and putrescine (Put) concentrations and their biosynthesis-related gene expression reduced spermidine (Spd) biosynthesis under SD condition. And, the ACC and PA biosynthesis in inferior grains was more sensitive to SD than that in superior grains. Intermediary cells (ICs) of caryopsis emerged prematurely under SD to compensate for the weakened photo-assimilate transport functions of sieve elements (SEs). Finally, plasmolysis and nuclear chromatin condensation of phloem parenchyma cells (PPC) and membrane degradation of SEs, as well as the decreased ATPase activity on plasma membranes of ICs and PPC at the later filling stage under SD were responsible for the considerably decreased weight of inferior grains.

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