RESUMEN
To clarify the influences of shading stress and planting density on the lignin monomer composition of wheat stems and their relationship with lodging resistance, Lodging resistant variety Shannong 23 (SN23) and lodging sensitive variety Shannong 16 (SN16) were grown during 2018-2019 and 2019-2020 growing seasons. The planting densities were 150 × 104 plants ha-1 (D1), 225 × 104 plants ha-1 (D2) and 300 × 104 plants ha-1 (D3). At the jointing stage, an artificial shading shed was used to simulate shading stress. Then the effects of shading on stem morphological characteristics, lignin monomer composition and lodging resistance of wheat under different planting densities were studied. Results indicate that shading at the jointing stage increased the length of basal internodes and the plant height and moved the height of center of gravity (CG) upward. Moreover, the stem diameter and the wall thickness decreased by 0.10-0.53 mm and 0.18-0.40 mm, respectively. The stem filling degree was reduced accordingly. As indicated by the correlation analysis and the stepwise regression analysis, shading-induced lodging mainly resulted from changes in the stem morphological characteristics and lignin accumulation. The influential magnitude of these factors was ordered as follows: stem filling degree, wall thickness, lignin content, contents and proportions of monomers S and H, and length of the second internode. The expression abundance of TaPAL, TaCOMT, TaCCR, and TaCAD declined in response to shading stress and high planting density. As a result, the distribution ratios of photosynthetic carbon sources to lignin monomers S, G and H were changed. The lignin content of stems on the day 42 after the jointing stage decreased by 18.48%. The monomer S content decreased, while the content and proportion of monomer H increased, thus weakening the breaking strength of wheat stems.
RESUMEN
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.