Cytochemical localization of cellulase activity in pollen mother cells of david lily during meiotic prophase I and its relation to secondary formation of plasmodesmata

Abstract

Summary. Cellulase activity was localized at the ultrastructural level in pollen mother cells (PMCs) of David lily [Lilium davidii var. willmottiae (Wilson) Roffill] at different stages of meiotic prophase I. The enzyme was observed to appear at the early leptotene stage and reached its highest level at the subsequent zygotene stage, and its subcellular distribution revealed by the presence of electron-dense deposits of reaction product was found to be restricted exclusively to the endoplasmic reticulum (ER), the vesicles derived from that, and the cell wall, especially at the sites of secondary plasmodesmata and cytoplasmic channels where the wall was being digested. Other cytoplasmic organelles, such as dictyosomes and Golgi vesicles, lacked such deposits of reaction product. After zygotene the enzyme activity decreased abruptly, and at the pachytene stage only very few deposits could be observed in the cell wall. Our results indicate that cellulase is synthesized on rough ER and secreted directly via the smooth ER and ER-derived vesicles into the cell wall by exocytosis, where it brings about local wall breakdown, leading to the secondary formation of plasmodesmata and cytoplasmic channels.

Ultrastructural characterization of the cytoplasmic channel formation between pollen mother cells of David lily

“…Recently, ultrastructurally cytochemical investigations revealed that the CC was formed via local wall digestion by cellulase released by endoplasmic reticulum (ER)-derived vesicles (WANG et al 1998). However, we still lack the detailed ultrastructural features characterizing this process, especially those at the early stage.…”

“…However, these early views were not supported by experimental evidence. Most recently, in exploring the mechanism responsible for secondary PD formation in lily PMCs, we found that the reaction product of cellulase was restricted to the ER, ER-derived vesicles and the wall (especially at the sites of secondary PD and CC under formation) (WANG et al 1998). This finding suggested that the wall digesting enzymes were synthesized in rough ER and then secreted directly, via smooth ER and ER-derived vesicles, into the CW by exocytosis, where they brought about a local wall breakdown, leading to the formation of both secondary PD and CC.…”

New insights into cytomixis: specific cellular features and prevalence in higher plants

“…3b, channel 3) and, on the other, de novo (Fig. 3b, channel 2) on the cell wall regions lacking any plasmodesmata (Wang et al 1998;Yu et al 2004;Mursalimov et al 2010).…”

“…Their emergence in the cell wall allows the nuclei and other organelles to migrate from one cell to another. Unlike plasmodesmata, CCs have no internal structure, such as desmotubules and, as a rule, CCs are considerably larger than plasmodesmata; the CC diameter ranges from 50 to 3,500 nm (Heslop-Harrison 1966;Wang et al 1998;Wang et al 2002;Mursalimov et al 2010). In addition, CCs may occupy over 25 % of the cell surface (HeslopHarrison 1966).…”

“…3a). Note that the hydrolytic enzymes released by the endoplasmic reticulum and Golgi apparatus are involved in the CC formation (Wang et al 1998;Yu et al 2004). At this stage, CCs can be formed, on the one hand, based on plasmodesmata via enlargement of a single plasmodesma (Fig.…”