Anatomy and Histochemistry of Seed Coat Development of Wild (Pisum sativum subsp. elatius (M. Bieb.) Asch. et Graebn. and Domesticated Pea (Pisum sativum subsp. sativum L.)

Abstract

In angiosperms, the mature seed consists of embryo, endosperm, and a maternal plant-derived seed coat (SC). The SC plays a role in seed filling, protects the embryo, mediates dormancy and germination, and facilitates the dispersal of seeds. SC properties have been modified during the domestication process, resulting in the removal of dormancy, mediated by SC impermeability. This study compares the SC anatomy and histochemistry of two wild (JI64 and JI1794) and two domesticated (cv. Cameor and JI92) pea genotypes. Histochemical staining of five developmental stages: 13, 21, 27, 30 days after anthesis (DAA), and mature dry seeds revealed clear differences between both pea types. SC thickness is established early in the development (13 DAA) and is primarily governed by macrosclereid cells. Polyanionic staining by Ruthenium Red indicated non homogeneity of the SC, with a strong signal in the hilum, the micropyle, and the upper parts of the macrosclereids. High peroxidase activity was detected in both wild and cultivated genotypes and increased over the development peaking prior to desiccation. The detailed knowledge of SC anatomy is important for any molecular or biochemical studies, including gene expression and proteomic analysis, especially when comparing different genotypes and treatments. Analysis is useful for other crop-to-wild-progenitor comparisons of economically important legume crops.

Evaluation of Seed Dormancy, One of the Key Domestication Traits in Chickpea

“…In our study of chickpea seeds we observed the light line, the presence of which was confirmed also in cultivated and wild pea genotypes. However, the light line of wild pea genotypes was more pronounced [61], which cannot be unambiguously stated for wild chickpea. A light line that lays within the macrosclereids was interpreted variously, but its main purpose is not yet clarified [61][62][63][64][65][66].…”

“…Lipidic compounds stained with Sudan Red mostly occur in the cuticle on the surface of the seed coat of chickpea, which is similar to pea [25,61], with a strong signal observed in middle and basal parts of the macrosclereid cells. In addition, nearly mature pea seeds had signal above the light line [61] that can be observed in some chickpea lines.…”

“…Lipidic compounds stained with Sudan Red mostly occur in the cuticle on the surface of the seed coat of chickpea, which is similar to pea [25,61], with a strong signal observed in middle and basal parts of the macrosclereid cells. In addition, nearly mature pea seeds had signal above the light line [61] that can be observed in some chickpea lines. The presence of non-cuticular waxy extracellular compounds was observed in the tips of the macrosclereids above the light line in another pea study [25] and was confirmed by autofluorescence.…”

“…Pectin is one of the chemical compounds that may significantly influence the physicochemical properties of different cell types during its development and the further processing of seeds [68]. This class of polysaccharides was confirmed also in the cell walls of pea seed coats where its concentration varied by location and developmental stage [34,70] and was differently localized between wild and cultivated pea seed coats [25,61]. Nevertheless, we did not conduct analysis of developmental stages, which would probably show us certain changes in pectin seed coat distribution.…”

“…A light line that lays within the macrosclereids was interpreted variously, but its main purpose is not yet clarified [61][62][63][64][65][66]. It is believed that the light line is the result of an altered orientation of cellulose microfibrils or structural discontinuity between the lignified and non-lignified parts of the cell wall [61,67,68].…”