Auxin-induced, growth-related osmiophilic nano-particles along the expansion-limiting peripheral cell wall in maize coleoptiles. Transmission electron micrograph showing four osmiophilic particles (OP) in the periplasmic space between the plasma membrane and the outer epidermal wall (OEW) (a) and gazing section (b), showing numerous OPs and cortical microtubules (arrows) (a: 1 h + IAA, 10 μM; b: 0.5 h + IAA, 10 μM). The table (c) documents the relationship between the occurrence of OPs, which originate in the cytoplasm (Cy), and coleoptile elongation. CHX = cycloheximide, Fc = fusicoccin, IAA = auxin (treatment: 1 h ± IAA, 10 μM, or Fc 1 μM, respectively) (adapted from Bergfeld et al. 1988)