The Relationship among the Structural, Cellular, and Physical Properties of Walnut Shells

in HortScience

The role of the walnut (Juglans regia L.) shell in nut development, transportation, cleaning, and storage is often ignored. The shell suture seal and thickness are directly associated with kernel characteristics. In the present study, shell differentiation and microstructure were observed with an optical microscope using paraffin-sectioning and cryosectioning. The results showed that the parenchymal cells of the endocarp began to differentiate into sclerenchymal cells from 49 d after flowering (DAF), and the entire process continued until fruit maturation. The mature shell consists of three parts, including the sclereid layer (L1), sclerenchymal cell layer (L2), and shrunken cell layer (L3), from the outside to the inside. The shell thickness, suture seal grade, and mechanical strength were evaluated, as well as the lignin, cellulose, and phenolic compounds of the shell. Suture seal grade was positively correlated with lignin content, shell thickness, and L1 thickness and negatively correlated with shell cell diameter. Similarly, the mechanical strength of the shell was positively correlated with lignin content and L1 thickness. ‘Qingxing’ fruits were subjected to two treatments, namely, 30% shading and 70% shading, from 10 d after anthesis to maturity, with no shading used as control. After harvesting in September, nutshell sections showed thinner shells, with decreased contents of lignin and polyphenols, obtained under shaded conditions, and two of the three parts of the shell changed dramatically. The thinning of L1 and thickening of L3 eventually led to a thinner shell. The aim of this study was to evaluate the relationship among the shell structure, cellular components, and physical properties and provide a theoretical basis for cultivar breeding, rational planting density, and regulation of shell development.

Contributor Notes

This work was supported by the National Science Foundation Special Project (2013FY111700-5). We thank LetPub (www.letpub.com) for providing linguistic assistance during the preparation of this article.

These authors contributed equally to this work.

Corresponding authors. E-mail: whx@hebau.edu.cn or zzh@hebau.edu.cn.

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Article Figures

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    Development process of the walnut pericarp. The boundary of the pericarp, mesocarp, and endocarp could not be distinguished clearly at 7 d after flowering (DAF) (A and 1). The mesocarp and endocarp could be distinguished clearly at 21 DAF (B). The endocarp cells continued to divide and increase from 35 to 42 DAF (C and D). The endocarp cells underwent lignification and moderately increased in size (E–I). The endocarp consisted of three parts from the outside in L1, L2, and L3 (J). The development of parenchymal cells between the husk and endocarp (1–6). h = husk; e = endocarp; v = vascular bundle; s = sclereids; p = parenchymal cell; L1 = sclereids layer; L2 = sclerenchymal cells layer; L3 = shrunken cell layer.

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    Lignin deposition process in the walnut pericarp. The lignin is present mainly in endocarp sclereids as a red color based on the Wiesner reaction. No lignin was deposited at 35 d after flowering (DAF) (A). After 49 DAF, the endocarp showed gradual lignification from the apical tip to the base (B–D). After 70 DAF, the endocarp lignified from the outside to the inside (E–H). A significant increase in lignin deposition in the endocarp was observed before maturity.

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    Lignin content in the shells of nine walnut cultivars.

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    Polyphenol content in the shells of nine walnut cultivars.

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    Cellulose content in the shells of nine walnut cultivars.

Article References

  • AbelesF.B.BilesC.L.1991Characterization of peroxidases in lignifying peach fruit endocarpPlant Physiol.95269273

  • AbidiN.CabralesL.HaiglerC.H.2014Changes in the cell wall and cellulose content of developing cotton fibers investigated by FTIR spectroscopyCarbohydr. Polym.100916

    • Search Google Scholar
    • Export Citation
  • AlwisR.D.FujitaK.AshitaniT.KurodaK.I.2009Induced monoterpene and lignin production in mechanically stressed and fungal elicited cultured Cupressus lusitanica cellsPlant Biotechnol. Rpt.35765

    • Search Google Scholar
    • Export Citation
  • AmiriR.VahdatiK.MohsenipoorS.MohammadR.M.LeslieC.2010Correlations between some horticultural traits in walnutHortScience4516901694

  • ArzaniK.Mansouri-ArdakanH.VezvaeiA.RoozbanM.R.2008Morphological variation among persian walnut (Juglans regia) genotypes from central IranN. Z. J. Crop Hort. Sci.36159168

    • Search Google Scholar
    • Export Citation
  • AvanzatoD.McGranahanG.H.VahdatiK.BotuM.IannamicoL.AsscheJ. Van2014Following walnut footprints (Juglans regia L.). cultivation and culture folklore and history traditions and uses. International Society for Horticultural Science Leuven Belgium

  • CuiH.Y.GuoS.P.2008Research on impact of some factors on poor development of thin-skinned nutsHebei Fruits378

  • DingD.ZhaoY.YangS.ShiW.ZhangZ.LeiZ.YangY.2013Adsorption of cesium from aqueous solution using agricultural residue—walnut shell: Equilibrium, kinetic and thermodynamic modeling studiesWater Res.4725632571

    • Search Google Scholar
    • Export Citation
  • FahnA.1967Plant anatomy. Pergamon Press Ltd. Oxford UK

  • GhafariA.CheginiG.R.KhazaeiJ.VahdatiK.2011Design, construction and performance evaluation of the walnut cracking machineIntl. J. Nuts Related Sci.21116

    • Search Google Scholar
    • Export Citation
  • HahlbrockK.ScheelD.2003Physiology and molecular biology of phenylpropanoid metabolismAnnu. Rev. Plant Biol.40347369

  • KhantwalR.GuptaG.NegiR.S.2016Walnut shell reinforced composite: A ReviewIntl. J. Sci. Eng. Res.7179189

  • LeeS.H.ChoiJ.H.KimW.S.HanT.H.ParkY.S.GemmaH.2006Effect of soil water stress on the development of stone cells in pear (Pyrus pyrifolia cv.‘Niitaka’) fleshScientia Hort.110247253

    • Search Google Scholar
    • Export Citation
  • LinJ.HeX.HuY.KuangT.CeulemansR.2002Lignification and lignin heterogeneity for various age classes of bamboo (Phyllostachys pubescens) stemsPhysiol. Plant.114296302

    • Search Google Scholar
    • Export Citation
  • LuM.ZhangQ.YangJ.2010Research on preservation and year-round supply technique of fresh-eating walnutShandong Agr. Sciences38183

  • MaY.MaH.LiuX.LiS.2011Comparison of physiology and nutrition in dry and fresh walnut during the storageFood and Fermentation Ind.37235238

    • Search Google Scholar
    • Export Citation
  • PeiD.LuX.Z.2011Walnut germplasm resources in China. China Forestry Press Beijing China

  • PinneyK.PolitoV.S.1983English walnut fruit growth and developmentScientia Hort.211928

  • TaoS.KhanizadehS.ZhangH.ZhangS.2009Anatomy, ultrastructure and lignin distribution of stone cells in two Pyrus speciesPlant Sci.176413419

    • Search Google Scholar
    • Export Citation
  • TaylorteeplesM.LinL.De LucasM.TurcoG.ToalT.GaudinierA.YoungN.F.TrabuccoG.M.VelingM.T.LamotheR.2014An Arabidopsis gene regulatory network for secondary cell wall synthesisNature517571575

    • Search Google Scholar
    • Export Citation
  • UpdegraffD.M.1969Semimicro determination of cellulose in biological materialsAnal. Biochem.32420424

  • XavierJ.A.1992Study of macadamia nut breakage. Unpublished M.Sc. Thesis Botucatu SP UNESP

  • XiS.K.1990Walnut improvement in ChinaActa Hort.284195197

  • XiaoL.XuY.ZhaoX.LuoJ.1998The developmental anatomy on the pericarp of Juglans regiaActa Botanica Boreali-Occidentalia Sinica18577580

    • Search Google Scholar
    • Export Citation
  • YangA.Z.ZhangZ.Y.CaoA.J.MengH.L.WangY.N.2009Studies of changes in sugar accumulation and lignin deposition during peach fruit endocarp developmentActa Hort. Sinica3611131119

    • Search Google Scholar
    • Export Citation
  • YuanH.R.LiuR.H.2007Study on pyrolysis kinetics of walnut shellJ. Therm. Anal. Calorim.89983986

  • ZhangH.LanH.TangY.LiY.2014aStudy on fracture mechanism of walnut shell according to brittle fracture area p. 954–957. In: J.E. Guerrero (ed.). Fifth International Conference on Intelligent Systems Design and Engineering Applications Conference Publishing Services Danvers MA

  • ZhangH.MaY.GuoW.ZhangR.LiY.2014bAnalysis on the embrittlement mechanism of Wen-185 walnut shell based on the cellular tissueJ. Huazhong Agr. Univ.33128132

    • Search Google Scholar
    • Export Citation
  • ZhaoQ.DixonR.A.2011Transcriptional networks for lignin biosynthesis: More complex than we thought?Trends Plant Sci.16227233

  • ZhaoQ.NakashimaJ.ChenF.YinY.FuC.YunJ.ShaoH.WangX.WangZ.Y.DixonR.A.2013Laccase is necessary and nonredundant with peroxidase for lignin polymerization during vascular development in ArabidopsisPlant Cell2539763987

    • Search Google Scholar
    • Export Citation
  • ZhaoS.ZhaoY.WangH.GaoY.ZhangZ.FengD.2011Factors affecting nutshell structure of walnutScientia Silvae Sinicae477075

  • ZhaoS.WenJ.WangH.ZhangZ.LiX.2016Changes in lignin content and activity of related enzymes in the endocarp during the walnut shell development periodHort. Plant J.2141146

    • Search Google Scholar
    • Export Citation
  • ZhaoY.ZhaoS.WangH.ZhangZ.GaoY.2007The relations between shell structures and kernel qualities of Juglans regiaScientia Silvae Sinicae438185

    • Search Google Scholar
    • Export Citation

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