Identification of plant hormones and candidate hub genes regulating flag leaf senescence in wheat response to water deficit stress at the grain-filling stage.

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 (GA 3) 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 GA 3 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 r max (the maximum senescence rate), larger r 0 (the initial senescence rate), and increased r aver (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.

Involvement of ethylene and polyamines biosynthesis and abdominal phloem tissues characters of wheat caryopsis during grain filling under stress conditions.

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.

Manipulation of lignin metabolism by plant densities and its relationship with lodging resistance in wheat.

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.