Transcriptome profiling reveals the roles of pigment mechanisms in postharvest broccoli yellowing

Postharvest broccoli is prone to yellowing during storage,which is the key factor leading to a reduction in value.To explore appropriate control methods,it is important to understand the mechanisms of yellowing.We analyzed the genes related to the metabolism of chlorophyll,carotenoids,and flavonoids and the transcription factors(TFs)involved in broccoli yellowing using transcriptome sequencing profiling.Broccoli stored at 10℃showed slight yellowing on postharvest day 5 and serious symptoms on day 12.There were significant changes in chlorophyll fluorescence kinetics,mainly manifesting as a decrease in the Fv/Fm value and an increase in nonphotochemical quenching,during the yellowing process.Transcriptome sequencing profiles from samples of fresh broccoli and broccoli with slight and severe yellowing revealed 6,5,and 4 differentially expressed genes involved in chlorophyll metabolism,carotenoid biosynthesis,and flavonoid biosynthesis,respectively.The transcription factor gene ontology categories showed that the MYB,bHLH,and bZip gene families were involved in chlorophyll metabolism.In addition,the transcription factor families included NACs and ethylene response factors(ERFs)that regulated carotenoid biosynthesis.Reverse transcription polymerase chain reaction further confirmed that bHLH66,PIF4,LOB13,NAC92,and APL were vital transcription factors that potentially regulated the CAO and HYD genes and were involved in chlorophyll metabolism and the carotenoid biosynthetic process.The flavonoid biosynthetic pathway was mainly regulated by MYBs,NACs,WRKYs,MADSs,and bZips.The results of the differentially expressed gene(DEG)and pigment content analyses indicated that the transcriptome data were accurately and positively associated with broccoli yellowing.

Physical Properties of Si_(2)Ge and SiGe_(2) in Hexagonal Symmetry:First-Principles Calculations

We predict two novel group 14 element alloys Si_(2)Ge and SiGe_(2) in P6_(2)22 phase in this work through first-principles calculations.The structures,stability,elastic anisotropy,electronic and thermodynamic properties of these two proposed alloys are investigated systematically.The proposed P6_(2)22-Si_(2)Ge and P6_(2)22-SiGe_(2) have a hexagonal symmetry structure,and the phonon dispersion spectra and elastic constants indicate that these two alloys are dynamically and mechanically stable at ambient pressure.The elastic anisotropy properties of P6_(2)22-Si_(2)Ge and P6_(2)22-SiGe_(2) are examined elaborately by illustrating the surface constructions of Young’s modulus,the contour surfaces of shear modulus,and the directional dependence of Poisson’s ratio;the differences with their corresponding group 14 element allotropes P6_(2)22-Si_(3) and P6_(2)22-Ge_(3) are also discussed and compared.Moreover,the Debye temperature and sound velocities are analyzed to study the thermodynamic properties of the proposed P6_(2)22-Si_(2)Ge and P6_(2)22-SiGe_(2).

Physical Properties of Group 14 in P6222 Phase: First-Principles Calculations

Two new Group Ⅳ element allotropes Si3 and Ge3 in P6222 phase are predicted in this work and their physical properties are investigated using the density functional theory.Each of the newly predicted allotropes has a superdense structure, which is mechanically, dynamically, and thermodynamically stable, as verified by elastic constants,phonon dispersion spectra and relative enthalpies, respectively.The mechanical anisotropy properties are studied in detail by illustrating the directional dependence of Young’s modulus, discussing the universal anisotropic index, and calculating shear anisotropy factors together with bulk moduli.It shows that P6222–Si3 exhibits the greater anisotropy than P6222–Ge3, and interestingly both of the newly predicted crystals appear to be isotropic in the(001) plane.Additionally, the Debye temperature, sound velocities, and the minimum thermal conductivity are examined to evaluate the thermodynamic properties of C3, Si3, and Ge3 in P6222 phase, and the electronic band structures are achieved by HSE06 hybrid functional, which indicate that P6222–C3 and –Si3 are indirect band gap semiconductors and P6222–Ge3 exhibits the metallic feature.

A novel superhard boron nitride polymorph with monoclinic symmetry

In this work,a new superhard material named Pm BN is proposed.The structural properties,stability,mechanical properties,mechanical anisotropy properties,and electronic properties of Pm BN are studied in this work.Pm BN is dynamically and mechanically stable,the relative enthalpy of Pm BN is greater than that of c-BN,and in this respect,and it is more favorable than that of T-B_(3)N_(3),T-B_(7)N_(7),tP24 BN,Imm2 BN,Ni As BN,and rocksalt BN.The Young's modulus,bulk modulus,and shear modulus of Pm BN are 327 GPa,331 GPa,and 738 GPa,respectively,and according to Chen's model,Pm BN is a novel superhard material.Compared with its original structure,the mechanical anisotropy of Young's modulus of Pm BN is larger than that of C14 carbon.Finally,the calculations of the electronic energy band structure show that Pm BN is a semiconductor material with not only a wide band gap but also an indirect band gap.