Risk Management by Organisms of the Phototoxicity of Chlorophylls

Abstract

. His research interests span from the elucidation of photosynthetic energy and electron transfer in a molecular level using natural systems and artificial models to the construction of photoactive nano(bio)devices. AbstractThe phototoxic effects of chlorophylls on the cells of organisms have been debated for decades. The extreme phototoxicity of uncontrolled chlorophylls and the concomitant need for rapid elimination of chlorophylls in cells have again attracted attention since the robust processes of higher plants for their catabolism during senescence have been clarified (e.g., autumnal tints). Recently, another type of chlorophyll catabolism has been identified in aquatic microbes that digest algae. Both of these processes involve the detoxification of chlorophylls: the former degrading them into colorless compounds in multiple steps and the latter rapidly converting them into colored but nonphotosensitive molecules. In this paper, we describe various ways that organisms circumvent the phototoxicity of chlorophylls, emphasizing the costs of the adaptive mechanisms against this risk to biological processes.

Finding of 132, 173‐cyclopheophorbide a enol as a degradation product of chlorophyll in shrunk zooxanthellae of the coral Montipora digitata

“…(, ) found that herbivorous protozoa produce cPPB‐ a E when they graze on and digest microalgae. cPPB‐ a E is generated from pyropheophytin a (Kashiyama and Tamiaki ). Several types of phytoplankton are also able to generate cPPB‐ a E (Kashiyama et al.…”

Assessment of the impact of chlorophyll derivatives to control parasites in aquatic ecosystems

“…In 2014, Kashiyama and Tamiaki (2014) published a review, which described various strategies by which organisms avoid phototoxicity of chlorophylls, emphasizing the costs of adaptive mechanisms against this risk of these biological processes. The objective of the present study was to evaluate the potential risk of environmental toxicity caused by the application of chlorophyll to control pest organisms in aquatic systems.…”

Taming chlorophylls by early eukaryotes underpinned algal interactions and the diversification of the eukaryotes on the oxygenated Earth

“…The observed phylogenetic ubiquity of CACC among eukaryotes strongly indicates that the acquisition of CACC was a key evolutionary step that led to the diversity of extant eukaryotes. CACC is a “rate-emphasizing” process [6] that is rapid and requires no substantial biochemical cost and thus advantageous in digestive processing of algal materials. On the other hand, another “quality-emphasizing” process [6], such as the phyllobilin/PAO pathway, is rigorously but only slowly degrading chlorophylls with substantial biochemical costs (i.e., in the consumption of reducing cofactors and ATP); hence, it is less suited for algivorous processing.…”

“…However, the elevated p O 2 conditions of the modern world are a major potential source of oxidative stress (if not death) to organisms. Moreover, molecular oxygen is even destructive when it is photosensitized by “phototoxic” biomolecules, such as chlorophylls [6].…”