Abstract
Although the appearance of coloured chlorophyll degradation products of higher plants is well known, knowledge about such compounds produced and released particularly by planktonic algae is still limited. Colourless conditioned media (CM) obtained from autotrophic cultures of unicellular green alga Desmosdemus subspicatus turn red after acidification. The accumulation of red pigments in the medium and the growth rate of algae were inversely correlated. The red, crude solution isolated from CM by dialysis and ion exchange chromatography, and next purified by means of high-performance liquid chromatography, appeared to be a mixture of three compounds with characteristic UV/VIS absorption maxima near 330 and 505 nm. Electrospray ionization (ESI) mass spectrometry analysis revealed that the molecular mass of the most polar and most abundant compound was 637 Da and molecular masses of two other ones were 641 and 607 Da. Addition of 15 N isotope to the culture medium and subsequent mass spectrometry measurements revealed the occurrence of four nitrogen atoms per each molecule. The data suggest that red pigments isolated from algal-conditioned media are chlorophyll degradation compounds, the production of which depends on light intensity, and are released mainly during the stationary phase of growth.
Highlights
The degradation path of chlorophyll during developmental processes in higher plants, such as leaf senescence or fruit ripening, is nowadays well elucidated
We present the evidence that red pigments observed in conditioned media of the chlorococcalean green microalga Desmodesmus subspicatus are chlorophyll catabolites
The production of various chlorophyll catabolites (NCC) in many species of higher plants is well documented (Hörtensteiner and Kräutler 2011). It is well-known that these colourless catabolites of the porphyrin moiety can readily decompose to rust-coloured materials within a few minutes when exposed to air, acidic solvents and daylight
Summary
The degradation path of chlorophyll during developmental processes in higher plants, such as leaf senescence or fruit ripening, is nowadays well elucidated (for a review, see for example Kräutler 2014). Nonfluorescent chlorophyll catabolites (NCCs) may spontaneously decompose to rust coloured material, especially in daylight and acidic or oxidizing environment (Bortlik et al 1990; Moser et al 2008). In such conditions, dehydrogenation may occur at the C20 meso bridge and at the saturated C15 meso position. As a result, red-shifted absorption is observed with a maximum at around 500 nm
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