| Popis: |
Unfixed and glutaraldehyde-fixed spinach chloroplasts were frozen on a copper block cooled by liquid helium and subsequently substituted in acetone at −87°C. Fixed chloroplasts were substituted in pure acetone, unfixed ones also in acetone containing 2% osmium tetroxide. Unfixed and aldehyde-fixed specimens were infiltrated with Low-icryl HM23 at −85°C. The resin was polymerized at −80°C. Osmium-fixed specimens were infiltrated with Epon 812 at room temperature, followed by polymerization at 65°C. The thylakoids of intact chloroplasts appeared similar in all embeddings, consisting of three, approximately equally wide layers: two peripheral, light ones and a central, darker one. A thin, very dark stratum, the partition gap, separated the grana thylakoids from one another. The grana were surrounded by an unevenly stained stroma. The chloroplast envelope could not be discerned. In lysed chloroplasts no stroma could be observed. In unfixed and aldehyde-fixed specimens the three-layered pattern seen in thylakoids of intact chloroplasts was replaced by a lightly stained band. In osmium-fixed specimens the thylakoids exhibited both structural types or resembled the thylakoids of conventionally fixed and embedded chloroplasts. |
