Mass-spectrometric analysis of chlorophyll degradation products in medicinal plants during leaf senescence

Chlorophyll is the most abundant pigment in the kingdom of higher plants. During leaf senescence, chlorophyll is released from the photosystems and degraded to linear tetrapyrroles, referred to as phyllobilins (PBs) in analogy to the bile pigments. Recently, pharmacological activities have been reported for a series of PBs.

The aim of this study was to investigate the appearance of PBs during leaf senescence in Melissa officinalis, Mentha x piperita, Salvia officinalis, Alchemilla vulgaris and Malva sylvestris. Senescence was induced, and chlorophyll contents of methanolic extracts were analyzed using UV/Vis-spectroscopy. Decrease in chlorophyll was moderate with 35% in mallow and sage, 40% in lemon balm. A more complete breakdown was observed in peppermint and lady's mantle, decreasing about 60–80%. Qualitative analysis of phyllobilins in Lamiaceae species was performed using high-resolution mass-spectrometry, applying a MS/MS-method with an inclusion-list containing 65 PBs. With decrease in chlorophyll, the number of phyllobilins increased in senescent mint (four to ten) and sage (three to seven). In yellow leaves of lemon balm, the number of phyllobilins increased from six to eight, showing a higher number already in the pre- senescence. Fourteen different PBs were identified in the three Lamiaceae, while four occurred in all three species. Such a pattern was suspected, as they belong to the same plant family ([Fig. 1]).

Fig. 1 Phyllobilins act as bioactive phytochemicals.

In conclusion, this study shows that medicinal herbs contain phyllobilins already in green stages. PB content and diversity increase at the onset of senescence, highlighting the potential of these phytochemicals for medical applications.

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Artikel online veröffentlicht:
16. November 2023