Characterization of Growth-related Osmiophilic Particles in Corn Coleoptiles and Deepwater Rice Internodes

Osmiophilic particles are secreted from the epidermal cellsinto the outer epidermal cell wall of deepwater rice internodesand corn coleoptiles that have been induced to elongate rapidlyby treatment with gibberellin or auxin, respectively. The diameterof the osmiophilic particles is 80 to 100 nm in deepwater riceand up to 300 nm in corn coleoptiles. Because these particlesare secreted to the outer epidermal wall only, they may containeither cell wall components that are specific for the outerepidermal wall or components of the cuticle that coats the outerepidermal wall. Monensin inhibited the appearance of these particles,indicating that they are derived from the Golgi apparatus. Anattempt was made to identify the contents of the osmiophilicparticles by enzyme-gold or antibody-gold labelling. Cutinase-goldaccumulated mostly in the region of the cell wall just belowthe cuticle. The osmiophilic particles became densely labelledafter incubation with proteinase K-gold, indicating that theyare, at least in part, proteinaceous. In excised tissue andultrathin sections treated with proteinase K, the number ofosmiophilic particles was reduced, while glucanase and cutinasetreatments were without effect. Antibodies against lipid transferprotein, an extensin-like protein, an arabinogalactan protein,a peroxidase, and expansin bound to the cell wall or plasmamembrane but not to the osmiophilic particles.Copyright 1994,1999 Academic Press Epidermal cell wall, gibberellin, indoleacetic acid, osmiophilic particles, Oryza sativa, Zea mays