Development of Embryo Suspensors for Five Genera of Crassulaceae with Special Emphasis on Plasmodesmata Distribution and Ultrastructure

Abstract

The suspensor in the majority of angiosperms is an evolutionally conserved embryonic structure functioning as a conduit that connects ovule tissues with the embryo proper for nutrients and growth factors flux. This is the first study serving the purpose of investigating the correlation between suspensor types and plasmodesmata (PD), by the ultrastructure of this organ in respect of its full development. The special attention is paid to PD in representatives of Crassulaceae genera: Sedum, Aeonium, Monanthes, Aichryson and Echeveria. The contribution of the suspensor in transporting nutrients to the embryo was confirmed by the basal cell structure of the suspensor which produced, on the micropylar side of all genera investigated, a branched haustorium protruding into the surrounding ovular tissue and with wall ingrowths typically associated with cell transfer. The cytoplasm of the basal cell was rich in endoplasmic reticulum, mitochondria, dictyosomes, specialized plastids, microtubules, microbodies and lipid droplets. The basal cell sustained a symplasmic connection with endosperm and neighboring suspensor cells. Our results indicated the dependence of PD ultrastructure on the type of suspensor development: (i) simple PD are assigned to an uniseriate filamentous suspensor and (ii) PD with an electron-dense material are formed in a multiseriate suspensor. The occurrence of only one or both types of PD seems to be specific for the species but not for the genus. Indeed, in the two tested species of Sedum (with the distinct uniseriate/multiseriate suspensors), a diversity in the structure of PD depends on the developmental pattern of the suspensor. In all other genera (with the multiseriate type of development of the suspensor), the one type of electron-dense PD was observed.

Developmental, ultrastructural and cytochemical investigations of the female gametophyte in Sedum rupestre L. (Crassulaceae)

“…A comparative analysis of the embryological features observed during ultrastructural and cytochemical studies of three Sedum species-S. hispanicum, S. sediforme, S. rupestre-revealed that S. rupestre has more similarity to S. sediforme than S. hispanicum. These embryological findings are consistent with morphological characteristics, molecular phylogenetic data and earlier observations made during embryogenesis (Thiede and Eggli 2007;Nikulin et al 2016;Czaplejewicz and Kozieradzka-Kiszkurno 2013;Kozieradzka-Kiszkurno et al 2020). Species from ser.…”

“…Some researchers have conducted ultrastructural and cytochemical analyses on the ovules of ser. Rupestria at the stages of embryogenesis (S. reflexum L. and S. sediforme) (Czaplejewicz and Kozieradzka-Kiszkurno 2013;Majcher 2017;Kozieradzka-Kiszkurno et al 2020), megasporogenesis and megagametogenesis (S. sediforme) (Brzezicka and Kozieradzka-Kiszkurno 2019). Mauritzon (1933) carried out embryological studies on two species of ser.…”

“…Rupestria, the suspensor is filamentous (composed of one basal cell and chalazal cells arranged in a row) and morphologically different from that described for most Sedum and Crassulaceae species. For instance, in S. reflexum and S. sediforme, the suspensors are made of ten cells (Mauritzon 1933;Czaplejewicz and Kozieradzka-Kiszkurno 2013;Majcher 2017;Kozieradzka-Kiszkurno et al 2020). The proposition to recognize ser.…”

“…Bramwell) and Echeveria ( E . lutea Rose) (Kozieradzka-Kiszkurno and Bohdanowicz 2006 , 2010 ; Kozieradzka-Kiszkurno et al 2011 , 2012 , 2020 ; Kozieradzka-Kiszkurno and Płachno 2012 ; Czaplejewicz and Kozieradzka-Kiszkurno 2013 ; Majcher 2017 ). To the best of our knowledge, cytochemical and ultrastructural analyses during the formation of megaspores and megagametophyte have been conducted on ovules collected from only two Sedum species— S. hispanicum L. and S. sediforme (Jacq.)…”

Embriogeneza u Crassulaceae: strukturalny aspekt rozwoju wieszadełka

“…Obecność wyrostków ściennych i brak plazmodesm w zewnętrznych ścianach haustorium wskazuje, że substancje odżywcze transportowane są apoplastycznie z wykorzystaniem tychże wyrostków. Transport taki wymaga nakładów energetycznych, które pokrywane są przez sąsiadujące z wyrostkami liczne mitochondria [16].…”