Development Of Walnut Endocarp Based On Anatomical Principle

Improving the shell character can improve the quality of walnut,so it is necessary to understand the formation process of hard shell more clearly.The hard shell is formed because the endocarp is lignified,which is a process of large amount of lignin deposition.In order to further study the growth and development process of walnut,five kinds of walnut germplasm resources with different core-shell thickness(’ Xinlu ’,’papery’,’Xinxin 2’ and ’Xinwen 185’ of walnut with thin shell,’Xincuifeng’ of walnut with thick shell)were selected as research objects to study the morphological and anatomical structure of female flower bud differentiation and endocarp development of walnut.These included paraffin sections at flower bud differentiation stage,lignin chemical staining at hard shell formation stage and endocarp site observation by electron microscope.The main research conclusions are as follows:The female flower bud differentiation of five walnut cultivars with different core and shell thickness(March to April next year)could be divided into two stages,namely,inflorescence development stage,pistil formation stage and development stage.Inflorescence development stage: petal primordium,sepal primordium,leaf and other tissue elongation growth;Pistil formation and development stage: pistil appeared on the ’Xinlu’ variety of walnut germplasm on April 6,and the female flower blossomed on April 18.The pistil appeared around March 21,and the full flowering was on April 10.The pistil of the thin shell walnut variety ’Xinwen 185’ appeared around March 25,and reached the full flowering stage around April 14.The pistil of the thin shell walnut variety ’Xinxin 2’ appeared around April 6 and reached full flowering stage on April 18.The thick-shelled variety ’Xinfuifeng’ appears pistil around April 6,and the full flowering time is around April 18.At this stage(late April to early May),the boundary between endocarp and mesocarp of five kinds of female walnut flowers with different core and shell thickness was not clear,and a large number of vascular bundles were distributed at the junction.In the hardcore stage,the endocarp of ’Xinlu’ walnut began to harden on the 47 th day after flowering(June 5),and the endocarp was not completely hardened,with dew kernel appearing.The "papery" walnut entered the endocarp hardening stage 50 days after flowering(May 31),the "Xinwen 185" walnut began to harden 46 days after flowering(May 31),and the "Xinxin 2" walnut endocarp hardening time 47 days after flowering(June 5).The pericarp of ’Xincuifeng’ walnut began to harden on June 5,47 days after flowering.Vascular bundles were distributed in the outer wall of the ovary when the endocarp hardened in five varieties.Vascular bundles were distributed in the outer wall of the ovary in walnut where the endocarp hardened first and the hard shell was thick(the suture line at the top of the fruit),and vascular bundles appeared later in the outer wall of the ovary in the middle of the fruit,and the cells close to the vascular bundles were squeezed and squeezed more severely with the hardening of the endocarp.The cells farther from the vascular bundle are more loosely arranged.Secondary walls appeared in endocarp region cells during hardening,and the walls gradually thickened.The distribution density of vascular bundles in the ovary wall of female walnut flowers was proportional to the amount of lignin accumulation in the durum stage.Vascular bundles were also distributed in the inner pericarp of walnut,and played a role in the durum stage together with the mesocarp vascular bundles.The exocarp and mesocarp of walnut are developed from receptacle and calyx,while the ovary wall is only developed into endopericarp.From the biological point of view,walnut can be divided into pseudofruit.