Intracellular haemolytic agents of Heterocapsa circularisquama exhibit toxic effects on H. circularisquama cells themselves and suppress both cell-mediated haemolytic activity and toxicity to rotifers (Brachionus plicatilis).

A harmful dinoflagellate, Heterocapsa circularisquama, is highly toxic to shellfish and the zooplankton rotifer Brachionus plicatilis. A previous study found that H. circularisquama has both light-dependent and -independent haemolytic agents, which might be responsible for its toxicity. Detailed analysis of the haemolytic activity of H. circularisquama suggested that light-independent haemolytic activity was mediated mainly through intact cells, whereas light-dependent haemolytic activity was mediated by intracellular agents which can be discharged from ruptured cells. Because H. circularisquama showed similar toxicity to rotifers regardless of the light conditions, and because ultrasonic ruptured H. circularisquama cells showed no significant toxicity to rotifers, it was suggested that live cell-mediated light-independent haemolytic activity is a major factor responsible for the observed toxicity to rotifers. Interestingly, the ultrasonic-ruptured cells of H. circularisquama suppressed their own lethal effect on the rotifers. Analysis of samples of the cell contents (supernatant) and cell fragments (precipitate) prepared from the ruptured H. circularisquama cells indicated that the cell contents contain inhibitors for the light-independent cell-mediated haemolytic activity, toxins affecting H. circularisquama cells themselves, as well as light-dependent haemolytic agents. Ethanol extract prepared from H. circularisquama, which is supposed to contain a porphyrin derivative that displays photosensitising haemolytic activity, showed potent toxicity to Chattonella marina, Chattonella antiqua, and Karenia mikimotoi, as well as to H. circularisquama at the concentration range at which no significant toxicity to rotifers was observed. Analysis on a column of Sephadex LH-20 revealed that light-dependent haemolytic activity and inhibitory activity on cell-mediated light-independent haemolytic activity existed in two separate fractions (f-2 and f-3), suggesting that both activities might be derived from common compounds. Our results suggest that the photosensitising haemolytic toxin discharged from ruptured H. circularisquama cells has a relatively broad spectrum of phytoplankton toxicity, and that physical collapse of H. circularisquama cells can lead not only to the disappearance of its own toxicity, but also to mitigation of the effects of other HABs.

ELECTRON MICROSCOPIC DEMONSTRATION OF TYROSINASE IN PTERINOSOMES OF THE FROG XANTHOPHORE, AND THE ORIGIN OF PTERINOSOMES.

In the frog, Rana japonica, the successive appearance of types I, II and III pterinosomes, which were defined according to the degree of lamellar structure, is in keeping with the xanthophore differentiation at the larval stage, but these three types coexist in a single xanthophore in the adult. An intense tyrosinase reaction was found in type I-II intermediate form in the larval and adult xanthophores, but it was rarely observed in types I and III. A tyrosinase reaction was always found in the GERL (Golgi-associated Endoplasmic Reticulum) of larval and adult xanthophores, and it was similarly evident in small Golgi vesicles which were separated from the GERL and dispersed in the cytoplasm. The above findings suggest that tyrosinase and pterinosome originate from different parts of the cytoplasm. The hypothesis that small Golgi vesicles are transported to the tyrosinase-negative premelanosomes involved in the origin of the melanosome is also applicable to the origin of pterinosomes.