Cellular actin patterns in heterocysts passing through four modes of cell death.

<p>(<b>A–D</b>) Healthy heterocyst displaying phalloidin stained (PS) actin seen as a meshed network covering the cell (arrows), and a strong blue and red fluorescence of DNA (DAPI) and autofluorescing (AF) photosynthetic pigments, respectively. (<b>E–H</b>) An apoptotic-like heterocyst with a shrunken cytoplasm (long arrows) and a polygonal partly disorganized actin pattern (short arrow) and weaker DAPI- and autofluorescence. (<b>I–L</b>) An autophagic-like heterocyst with a retracted cytoplasm but with an intact plasma membrane (short arrow) and a condensed but mostly retained actin pattern (long arrow) and strong DAPI- and autofluorescence. (<b>M–P</b>) A necrotic-like heterocyst with a disruptered cell wall and plasma membrane (black arrow) resulting in leakage of cellular contents (DNA and pigments), and a more or less disrupted actin (long white arrow). (<b>Q–T</b>) An autolytic-like degraded heterocyst lacking most cellular inclusions including the actin network. A, E, I, M and P, bright field; B, F, J, N and R, phalloidin staining; C, G, K, O and S, DAPI-DNA staining; D, H, L, P and T, pigment autofluorescence. Scale bars: 1 µm.