SUMMARY Exocytosis is a key event in plant cells, linking the internal and external environments. Cell‐wall precursors, membrane material, and soluble and membrane‐associated proteins are supplied by exocytosis and allow cells to grow and differentiate. In this review, we describe exocytotic systems in plants and summarize information on how exocytosis is controlled and itself controls cell development. Mechanisms regulating exocytosis in other organisms are outlined and some critical directions for future research on plant exocytosis are suggested.
We have examined the characteristics of Ca2"-dependent phospholipid-binding proteins (annexins) Iongiflorum. Immunolocalization at the light microscope level suggests that these proteins are predominantly confined to the nongranular zone at the tube tip, a region rich in secretory vesicles. Our hypothesis that plant annexins mediate exocytotic events is supported by the finding that p23, p33, and p35 bind to these secretory vesicles in a Ca2"-dependent manner.
There is evidence that Ca(2+) can regulate vesicle-mediated secretion in plant cells, but the mechanism for this is not known. One possibility is that Ca(2+) -dependent phospholipid-binding proteins (annexins) couple the Ca(2+) stimulus to the exocytotic response. Using a protocol developed for the isolation of animal annexins we have identified proteins in maize (Zea mays L.) coleoptiles that have similar characteristics to annexins. The predominant polypeptide species run as a doublet of relative molecular mass (Mr) 33000-35000 on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE); another less-abundant protein of Mr 23000 is also present. In the presence of Ca(2+) these proteins bind to liposomes composed of acidic phospholipids. Calcium-sensitivity of binding differs for each protein and is also influenced by the pH of the buffer used for the liposome-binding assay. Antiserum raised to the 33 to 35-kDa doublet purified on SDS-PAGE recognises the doublet in crude extracts from maize and proteins of similar Mr in Tradescantia virginiana and tobacco Nicotiana tabacum L. The antiserum also recognises p68 (Annexin VI) from chicken gizzard extracts, indicating homology between animal annexins and the maize proteins. For the maize proteins to be involved in the regulation of exocytosis, binding to phospholipids would be expected to occur at physiological levels of Ca(2+). The characteristics of the maize annexin-like proteins are described and attention drawn to the marked effect of pH in lowering the requirement for Ca(2+) for phospholipid binding.
The mechanism by which membranes fuse during vesicle‐mediated secretion is of considerable importance for plant cell growth, but remains unknown. We have identified Ca2+‐dependent phospholipid‐binding proteins (annexins) from maize (Zea mays), that may play a part in this process. An assay for Ca2+‐dependent binding of annexins to liposomes, revealed that the maize proteins (p23, p33 and p35) and annexins from bovine lung, bind over a similar range of Ca2+ concentrations. Turbidity assays further revealed that both maize and bovine annexins induced liposome aggregation and that the plant annexins were also effective at aggregating plant secretory vesicles. This aggregation occurred at levels of free Ca2+ similar to that required for the binding of annexins p33 and p35. We discuss the significance of these results for the plant secretory apparatus.
N.H. 1993. Annexin-mediated secretory vesicle aggregation in plants. -Physiol. Plant. 89: 27-32.The mechanism by which membranes fuse during vesicle-mediated secretion is of considerable importance for plant cell growth, but remains unknown. We have identified Ca-*-dependent phospholipid-binding proteins (annexins) from maize (Zea mays), that may play a part in this process. An assay for Ca'^*-dependent binding of annexins to liposomes, revealed that the maize proteins (p23, p33 and p35) and annexins from bovine lung, bind over a similar range of Ca-* concentrations. Turbidity assays further revealed that both maize and bovine annexins induced liposome aggregation and that the plant annexins were also effective at aggregating plant secretory vesicles. This aggregation occurred at levels of free Ca-* similar to that required for the binding of annexins p33 and p35. We discuss the significance of these results for the plant secretory apparatus.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.