Morphological and Ultrastructural Features of Formation of the Skin of Wheat (Triticum aestivum L.) Kernel

Inna A Chaban; Alexander A Gulevich; Elena A Smirnova; Ekaterina N Baranova

doi:10.3390/plants10112538

Morphological and Ultrastructural Features of Formation of the Skin of Wheat (Triticum aestivum L.) Kernel

Plants (Basel). 2021 Nov 21;10(11):2538. doi: 10.3390/plants10112538.

Authors

Inna A Chaban¹, Alexander A Gulevich², Elena A Smirnova^{1

3}, Ekaterina N Baranova^{1

4}

Affiliations

¹ Plant Cell Biology Laboratory, All-Russia Research Institute of Agricultural Biotechnology, Timiryzevskaya 42, 127550 Moscow, Russia.
² Plant Cell Engineering Laboratory, All-Russia Research Institute of Agricultural Biotechnology, Timiryazevskaya 42, 127550 Moscow, Russia.
³ Biology Faculty, Lomonosov Moscow State University, Leninskie Gory 1, Building 12, 119991 Moscow, Russia.
⁴ Plant Protection Laboratory, N.V. Tsitsin Main Botanical Garden of Russian Academy of Sciences, 127276 Moscow, Russia.

Abstract

The integumentary tissues of plant seeds protect the embryo (new sporophyte) forming in them from unfavorable external conditions; therefore, comprehensive knowledge about the structural and functional specificity of seed covers in various plants may be of both theoretical and practical interest. As a result of our study, additional data were obtained on the morphological and ultrastructural features of the formation of a multilayer skin of wheat (Triticum aestivum L.) kernel (caryopsis). The ultrastructure research analysis showed that differentiation of the pericarp and inner integument of the ovule leads to the formation of functionally different layers of the skin of mature wheat grain. Thus, the differentiation of exocarp and endocarp cells is accompanied by a significant thickening of the cell walls, which reliably protect the ovule from adverse external conditions. The cells of the two-layer inner integument of the ovule differentiate into cuticular and phenolic layers, which are critical for protecting daughter tissues from various pathogens. The epidermis of the nucellus turns into a layer of mucilage, which apparently helps to maintain the water balance of the seed. Morphological and ultrastructural data showed that the formation of the kernel's skin occurs in coordination with the development of the embryo and endosperm up to the full maturity of the kernel. This is evidenced by the structure of the cytoplasm and nucleus, characteristic of metabolically active protoplasts of cells, which is observed in most integumentary layers at the late stages of maturation. This activity can also be confirmed by a significant increase in the thickness of the cell walls in the cells of two layers of the exocarp and in cross cells in comparison with the earlier stages. Based on these results, we came to the conclusion that the cells of a majority in the covering tissues of the wheat kernel during its ontogenesis are transformed into specialized layers of the skin by terminal differentiation.

Keywords: caryopsis; cell layers; cuticular layer; integument; kernel; maternal tissue; nucellus; pericarp; phenolic layer; terminal differentiation; wheat.