Xing-Hua Zhang

Photosynthetic performance of maize hybrids to drought stress

Maintaining photosynthetic activities is a critical function that allows crops to adapt to drought stress. We evaluated drought-induced changes in photosynthetic performance via gas exchange as well as photosynthetic electron transport and carbon assimilation process in two maize (Zea mays L.) cvs. Shaandan 609 (SD609) and Zhengdan 958 (ZD958). Plants were subjected to different intensity of drought stress inside of rain shelter. In both cultivars, moderate and severe drought stress caused a decrease in photosynthetic rate and stomatal conductance, but an increase in the intercellular CO2 concentration. Moreover, chlorophyll a fluorescence transients showed that drought stress significantly increased the positive Land K-band, revealing decreased function of oxygen-evolving complex, and decreased the fluorescence parameters reflecting electron flow from the intersystem carriers to the final reduction of PSI end electron acceptors. Also, moderate and severe drought stresses reduced both total activity and Rubisco activity. These parameters were more affected in ZD958 by drought stress compared to SD609. Based on our results, damaged PSII, reduced electron transport, and inactivation of Rubisco were main non-stomatal limitation of photosynthesis inhibition in both cultivars under moderate and severe drought stress. Photosynthetic apparatus of SD609 was more resistant to drought stress than that of ZD958.

Transcriptome Dynamics during Maize Endosperm Development.

The endosperm is a major organ of the seed that plays vital roles in determining seed weight and quality. However, genome-wide transcriptome patterns throughout maize endosperm development have not been comprehensively investigated to date. Accordingly, we performed a high-throughput RNA sequencing (RNA-seq) analysis of the maize endosperm transcriptome at 5, 10, 15 and 20 days after pollination (DAP). We found that more than 11,000 protein-coding genes underwent alternative splicing (AS) events during the four developmental stages studied. These genes were mainly involved in intracellular protein transport, signal transmission, cellular carbohydrate metabolism, cellular lipid metabolism, lipid biosynthesis, protein modification, histone modification, cellular amino acid metabolism, and DNA repair. Additionally, 7,633 genes, including 473 transcription factors (TFs), were differentially expressed among the four developmental stages. The differentially expressed TFs were from 50 families, including the bZIP, WRKY, GeBP and ARF families. Further analysis of the stage-specific TFs showed that binding, nucleus and ligand-dependent nuclear receptor activities might be important at 5 DAP, that immune responses, signalling, binding and lumen development are involved at 10 DAP, that protein metabolic processes and the cytoplasm might be important at 15 DAP, and that the responses to various stimuli are different at 20 DAP compared with the other developmental stages. This RNA-seq analysis provides novel, comprehensive insights into the transcriptome dynamics during early endosperm development in maize.

QTL mapping for leaf area in maize (Zea mays L.) under multi-environments

Abstract Leaves are the main organs of photosynthesis in green plants. Leaf area plays a vital role in dry matter accumulation and grain yield in maize (Zea mays L.). Thus, investigating the genetic basis of leaf area will aid efforts to breed maize with high yield. In this study, a total of 150 F 7 recombinant inbred lines (RILs) derived from a cross between the maize lines Xu 178 and K12 were used to evaluate three ear-leaves area (TELA) under multi-environments. Inclusive composite interval mapping (ICIM) was used to identify quantitative trait loci (QTLs) for TELA under a single environment and estimated breeding value (EBV). A total of eight QTLs were detected under a single environmental condition, and four QTLs were identified for EBV which also can be detected in single environment. This indicated that the EBV-detected QTLs have high genetic stability. A major QTL ( qTELA_2-9 ) located in chromosome bin 2.04/2.05 could be detected in four environments and has a high phenotypic contribution rate (ranging from 10.79 to 16.51%) that making it a good target for molecular breeding. In addition, joint analysis was used to reveal the genetic basis of leaf area in six environments. In total, six QTL×environment interactions and nine epistatic interactions were identified. Our results reveal that the genetic basis of the leaf area is not only mainly determined by additive effects, but also affected by epistatic effects environmental interaction effects.

Effects of Abiotic Stress on Yield Traits of Maize Hybrids and Their Parental Inbred Lines

The field experiments were conducted to study the changes of grain yield and concerned physiological traits in stress-tolerant maize variety Zhengdan 958 and its parental inbred lines(Zheng 58 and Chang 7-2),as well as stress-sensitive maize variety Shaandan 902 and its parental inbred lines(K22 and K12) under different treatments of density(45 000 and 75 000 plants ha?1),nitrogen application(112.5 and 337.5 kg ha?1),and irrigation(normal irrigation and controlling water at prophase).The results showed that there were little differences in yield,mean leaf area index after anthesis,mean SPAD after anthesis,post-anthesis dry matter accumulation and harvest index between Zhengdan 958 and Shaandan 902 under resource-replete condi-tions(low density,high nitrogen and normal irrigation).But there were great differences in all traits(besides harvest index) be-tween Zhengdan 958 and Shaandan 902 under abiotic stress(high density,low nitrogen and drought stress),with much higher values in Zhengdan 958 than in Shaandan 902.Compared with Shaandan 902,mid-parent values of leaf area index,SPAD,post-anthesis dry matter accumulation and grain yield of Zhengdan 958 under abiotic stress(high density,low nitrogen and drought stress) increased by 45%,36%,51%,and 45%,respectively,and heterosis of Zhengdan 958 increased by 18%,9%,28%,and 22%,respectively.The mid-parent value of yield was much higher than heterosis of yield and both of them were higher in Zhengdan 958 than in Shaandan 902.So the maize variety Zhengdan 958 showed greater tolerance to abiotic stress which was mainly inherited from its parental inbred lines.Higher SPAD and LAI after anthesis contributed to post-anthesis dry matter accu-mulation,resulting in higher yield and higher stress tolerance.

Bivariate flow cytometric analysis and sorting of different types of maize starch grains

Particle‐size distribution, granular structure, and composition significantly affect the physicochemical properties, rheological properties, and nutritional function of starch. Flow cytometry and flow sorting are widely considered convenient and efficient ways of classifying and separating natural biological particles or other substances into subpopulations, respectively, based on the differential response of each component to stimulation by a light beam; the results allow for the correlation analysis of parameters. In this study, different types of starches isolated from waxy maize, sweet maize, high‐amylose maize, pop maize, and normal maize were initially classified into various subgroups by flow cytometer and then collected through flow sorting to observe their morphology and particle‐size distribution. The results showed that a 0.25% Gelzan solution served as an optimal reagent for keeping individual starch particles homogeneously dispersed in suspension for a relatively long time. The bivariate flow cytometric population distributions indicated that the starches of normal maize, sweet maize, and pop maize were divided into two subgroups, whereas high‐amylose maize starch had only one subgroup. Waxy maize starch, conversely, showed three subpopulations. The subgroups sorted by flow cytometer were determined and verified in terms of morphology and granule size by scanning electron microscopy and laser particle distribution analyzer. Results showed that flow cytometry can be regarded as a novel method for classifying and sorting starch granules.