Figure 3

Reduction of the chloroplast system. The approximate dimensions of the photosynthetic machinery were assessed using confocal laser scanning microscopy and subsequent three-dimensional reconstruction of the chlorophyll autofluorescence signal. A plot of total cellular chloroplast volume versus total cellular chloroplast surface area shows a reduction of the chloroplast system in iron-limited T. oceanica cells. Iron-limited cells have a reduced number of two chloroplasts instead of four. Total chloroplast dimensions for individual cells (small circles) are distributed over a range spanning the two-fold increase in volume and surface that accompanies chloroplast duplication during cellular growth. Inserts show an overlay transmission and chlorophyll autofluorescence image (top) and the respective three-dimensional chloroplast reconstruction (bottom). The left insert illustrates an iron-limited cell close to dividing with two nearly duplicated chloroplasts. Note the characteristic increase in vesiculation of the cellular interior at low-iron. An iron-replete cell at the beginning of its cell cycle (shortly after division) contains four chloroplasts (right insert). CP, chloroplast; U, cell at the beginning of its cell cycle ('unit cell'); V, vesicle.