Effect of Delta pH indicators neutral red and 9-aminoacridine on chloroplast ultrastructure

The effect of Delta pH indicators (neutral red and 9-aminoacridine) on the ultrastructure of pea chloroplasts was studied. In the presence of 10-25 mu M neutral red or 9-aminoacridine, energization of chloroplasts causes specific ultrastructural changes differing from the effects of the local anesthetics dibucaine and tetracaine (Opanasenko et al. (1995) Biochemistry (Moscow), 60, 2053-2057). The structural change induced by neutral red and 9-aminoacridine is high amplitude local swelling of thylakoids. Local swelling is completely (in case of neutral red) or partially (in case of 9-aminoacridine) reversed in the dark; it is heterogeneous and involves only some thylakoids of the chloroplast. Intermediate phases of swelling of single thylakoids were observed, including loops and round protrusions of local membrane regions. At concentrations that cause local swelling, neutral red and 9-aminoacridine did not accelerate electron transfer, but they inhibited ATP synthesis by 20-60%.