Disintegration of F-actin in EGTA and restoration of actin network prompted by calcium or magnesium ions. (A) Formation of actin foci in response to 0,5–1 h incubation with 1 mM EGTA in dark-adapted cells. Fluorescent spots and loops of various sizes (arrowheads) are visible throughout the cytoplasm. Chloroplasts are arranged into tight clusters (asterisk). Thin filaments are present on chloroplast surfaces (a). (B) Actin foci persist after wBL irradiation. Distinct baskets around chloroplasts (arrowheads) became more visible after exposure to weak light. Effect of 5 mM Ca2+ (C, D) or 5 mM Mg2+ (E, F), each applied for 2 h on actin organization in EGTA pre-treated cells. In both cases, F-actin network recovered in dark-adapted cells (C, E) and after additional exposure to continuous wBL for 1 h (D, F). Scale bars, 10 μm.