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The occurrence of senescence (Evans blue staining) and programmed cell death (Hoechst staining/TUNEL reaction) was studied in the colonial cyanobacteria Anabaena flos-aquae and Microcystis flos-aquae during the late summer bloom in a eutrophic lake. Algae were analysed over a seven-day period (three sampling days) within mixed phytoplankton samples obtained from the upper epilimnion (trawl-net sample) and lower epilimnion (sediment-trap sample). Death of Anabaena in the trawl-net population was attributed to widespread infection by a chytrid fungus, resulting in breakdown and positive Evans blue staining of most filamentous colonies. Associated akinetes were a mixture of senescent cells (30% of total, Evans blue stained) and viable cells (unstained) plus a few dead cells (no contents). Sedimentation resulted in loss of filamentous colonies, leaving groups of akinetes with about 30% nonviable cells (senescent and dead). Over the sampling period, 20–50% of Microcystis colonies in the trawl-net samp...

Synchrotron-based Fourier-transform infrared (FTIR) microspectroscopy was used to distinguish micropopulations of the codominant algae Microcystis aeruginosa (Cyanophyceae) and Ceratium hirundinella (Dinophyceae) in mixed phytoplankton samples taken from the water column of a stratified eutrophic lake (Rostherne Mere, UK). FTIR spectra of the two algae showed a closely similar sequence of 10 bands over the wave-number range 4000–900 cm−1. These were assigned to a range of vibrationally active chemical groups using published band assignments and on the basis of correlation and factor analysis. In both algae, intracellular concentrations of macromolecular components (determined as band intensity) varied considerably within the same population, indicating substantial intraspecific heterogeneity. Interspecific differences were separately analysed in relation to discrete bands and by multivariate analysis of the entire spectral region 1750–900 cm−1. In terms of discrete bands, comparison of individual...