Integument cell gelatinisation—the fate of the integumentary cells in Hieracium and Pilosella (Asteraceae)

Abstract

Members of the genera Hieracium and Pilosella are model plants that are used to study the mechanisms of apomixis. In order to have a proper understanding of apomixis, knowledge about the relationship between the maternal tissue and the gametophyte is needed. In the genus Pilosella, previous authors have described the specific process of the “liquefaction” of the integument cells that surround the embryo sac. However, these observations were based on data only at the light microscopy level. The main aim of our paper was to investigate the changes in the integument cells at the ultrastructural level in Pilosella officinarum and Hieracium alpinum. We found that the integument peri-endothelial zone in both species consisted of mucilage cells. The mucilage was deposited as a thick layer between the plasma membrane and the cell wall. The mucilage pushed the protoplast to the centre of the cell, and cytoplasmic bridges connected the protoplast to the plasmodesmata through the mucilage layers. Moreover, an elongation of the plasmodesmata was observed in the mucilage cells. The protoplasts had an irregular shape and were finally degenerated. After the cell wall breakdown of the mucilage cells, lysigenous cavities that were filled with mucilage were formed.Electronic supplementary materialThe online version of this article (doi:10.1007/s00709-017-1120-1) contains supplementary material, which is available to authorized users.

Distinct Differentiation Characteristics of Endothelium Determine Its Ability to Form Pseudo-Embryos in Tomato Ovules

“…This results in the separation of the protoplast from the cell wall, and excessive accumulation of mucilage in periplasmic space induces the shrinkage of the protoplast. Eventually, the mucilage fills in the space between the cell wall and shrinking and degenerating protoplast, and integumental cells are replaced with mucilage, which contributes to the unobstructed growth of the embryo [13,[15][16][17][18]. On the contrary, our study showed that in tomato, the mucilage zone was localized distantly from the dying integumental cells, and was formed by the endothelium and the endosperm.…”

“…The plasma membranes at the inner cell walls of both tissues bordering each other had a sinuate contour, most evident in the endosperm cells. According to many authors, such ultrastructural composition is common for cells producing polysaccharide mucilage [13][14][15][16][17][18].…”

“…By the time of the late globular-shaped embryo, the endosperm is finally differentiated into the central (storage) and peripheral (secretory) zones, which, apparently, is a unique feature of the endosperm in tomato ovule. It has been suggested that endothelium cells synthesize lytic enzymes, which are active during lysis of dying cells of integumental parenchyma [24][25][26], and lyzed products are utilized later for the nutrition of the growing embryo sac [15,17,18].…”

Secondary‐cell‐wall release: a particular pattern of secretion in the mucilaginous seed coat of Magonia pubescens

“…The acidic polysaccharides composing the mucilage of M. pubescens are compartmentalized in vacuoles formed by the fusion of dictyosome vesicles. Dictyosomes, associated with the synthesis of strongly hydrophilic acidic polysaccharides having a fibrillar appearance (when viewed with transmission electron microscopy) are well documented in seeds (McFarlane et al., ; Young et al., ; Haughn and Western, ; Voiniciuc, ; Płachno et al., ; Phan and Burton, ) and other mucilage‐secreting structures (Mercadante‐Simões and Paiva, ; Ballego‐Campos and Paiva, ; Gonçalves et al., ; Rodrigues et al., ).…”

“…Seed development and the chemical constituents of the mucilaginous layer in M. pubescens have been previously studied (Oliveira et al., , ), but neither the mucilaginous secretions nor their ecological roles have yet been investigated. Considering the economic potential of seed mucilages (Plachno et al., ; Phan and Burton, ) and the structural peculiarities of secretory cells (Haughn and Western, ; Kreitschitz and Gorb, ), numerous lines of investigation still need to be pursued. The present work was designed to study the development and function of the mucilage of M. pubescens seeds to (1) relate structural and ultrastructural aspects of the mucilage to secretion and hydration mechanisms and (2) to evaluate the role of the mucilage capsule in seed germination.…”