Chlorophyllase and Lamellar Structure in Phaeodactylum tricornutum: I. Chlorophyll → Chlorophyllide Conversion Within the Lamellae

Abstract

1. Chlorophyllase in the marine diatom Phaeodactylum tricornutum is inactive, or nearly so, in vivo, but becomes active upon desintegration of the cell structure by osmotic shock or French Press treatment. Cell desintegration is apparent from disappearance of long-wave chlorophyll forms (685 and 710 nm), present in the intact algae (Goedheer, 1973). 2. Chlorophyllase activity can be measured down to -10°C. 3. No correlation was found between the relative amount of the combined long-wave chlorophyll forms in the absorption spectrum of the intact cells and chlorophyllase activity measured in cells which had received an osmotic shock. 4. In the presence of Mg2+ (0.01 M) osmotic shock of the cells results in a lower chlorophyllase activity than that which is found upon the same treatment without Mg2+. The absorption difference spectrum of cells, treated in the presence and absence of Mg2+, shows a maximum at about 685 nm. 5. Treatment of the osmotically shocked cells with oleic acid (ratio oleic acid/ chlorophyll 8 : 1) increases chlorophyllase activity. Absorption at 685 nm has decreased as compared with that of cells not treated with oleic acid. 6. It is concluded that chlorophyll in the lamellae is in vivo protected from chlorophyllase, but becomes exposed to the enzyme upon cell desintegration. The disappearance of the 685 nm chlorophyll form is suggested to be quantitatively related to this effect.