Rapid colour changes inEuglena sanguinea(Euglenophyceae) caused by internal lipid globule migration

Abstract

The accumulation of red pigments, frequently carotenoids, under chronic stress is a response observed in diverse kinds of eukaryotic photoautotrophs. It is thought that red pigments protect the chlorophyll located underneath by a light-shielding mechanism. However, the synthesis or degradation of carotenoids is a slow process and this response is usually only observed when the stress is maintained over long periods of time. In contrast, rapid colour changes have been reported in the euglenophyte Euglena sanguinea. Here we study the ecophysiological process behind this phenomenon through chlorophyll fluorescence, and pigment, colour and ultrastructural analyses. Reddening in E. sanguinea was due to the presence of a large amount of free and esterified astaxanthin (representing 80% of the carotenoid pool). The process was highly dynamic, shifting from green to red in 8 min (and vice-versa in 20 min). This change was not due to de novo carotenogenesis, but to the relocation of cytoplasmic lipid globules where astaxanthin accumulates. Thus, red globules were observed to migrate from the centre of the cell to peripheral locations when exposed to high light. Globule migration seems to be so efficient that other classical mechanisms are not operative in this species. Despite the presence and operation of the diadino-diatoxanthin cycle, non-photochemical quenching was almost undetectable. Since E. sanguinea forms extensive floating colonies, reddening can be observed at a much greater scale than at the cellular level and the mechanism described here is one of the fastest and most dramatic colour changes attributable to photosynthetic organisms at cell and landscape level. In conclusion E. sanguinea shows an extremely dynamic and efficient photoprotective mechanism, based on more on organelle migration than oncarotenoid 3 biosynthesis, which prevents excess light absorption by chlorophylls reducing the need for other protective processes related to energy dissipation.

Zeaxanthin, a Molecule for Photoprotection in Many Different Environments

“…This conversion cycle was initially termed the violaxanthin cycle. Since a special role emerged for zeaxanthin in allowing plants to cope with high light, this cycle is frequently referred to as the xanthophyll cycle, along with other xanthophyll cycles that interconvert xanthophyll epoxides to epoxide-free xanthophylls [17,[20][21][22][23]. In his foreword to a review on "In vivo functions of carotenoids in higher plants" [24], Norman Krinsky wrote, "Almost 40 years ago, David Sapozhnikov and his associates from Russia first described In his foreword to a review on "In vivo functions of carotenoids in higher plants" [24], Norman Krinsky wrote, "Almost 40 years ago, David Sapozhnikov and his associates from Russia first described the light-induced deepoxidation of the plant carotenoid epoxide, violaxanthin to non-epoxide derivatives, and the reversal of the process in the dark.…”

“…This conversion cycle was initially termed the violaxanthin cycle. Since a special role emerged for zeaxanthin in allowing plants to cope with high light, this cycle is frequently referred to as the xanthophyll cycle, along with other xanthophyll cycles that interconvert xanthophyll epoxides to epoxide-free xanthophylls [ 17 , 20 , 21 , 22 , 23 ].…”

Photosynthetic Physiology Comparisons between No Tillage and Sod Culture of Citrus Farming in Different Seasons under Various Light Intensities

“…Therefore, it is speculated that citrus grown in the fall and winter has a high photoprotection ability at high PPFD, and this hybrid may adjust the path of energy flow absorption using heat quenching. Laza-Martínez et al [42] revealed that xanthophyll cycle-associated photoprotection supports plant photosynthetic productivity and survival in environments with unique combinations of environmental factors. In our study, ETR was useful for the nondestructive estimation of Pn and NPQ, since these indices were significantly and positively correlated with ETR when exposed to 0~1200 PPFD (Figure 4) and 1200~2000 PPFD with SC (Figure 5B) and with NT in spring, fall, and winter (Figure 5A).…”

Effectiveness of different measures to control red bloom in carp ponds

“…Euglena sanguinea is a flagellated, unicellular algae found in high nutrient containing freshwaters (Ohio, 2013;Cimoli, 2014;Mandal et al, 2016Mandal et al, , 2018. The occurrence of red colour is due to presence of carotenoid astaxanthin pigments in the cytoplasm (Grung & Liaaen-Jensen, 1993;Gerber & Häder, 1994;Frassanito et al, 2008;Laza-Martínez et al, 2019, Zheng et al, 2020. The reddening process includes the relocation of cytoplasmic lipid globules where astaxanthin accumulates from the center of the cell to peripheral locations when exposed to high light (Laza-Martínez et al, 2019)frequently carotenoids, under chronic stress is a response observed in diverse kinds of eukaryotic photoautotrophs.…”

“…The occurrence of red colour is due to presence of carotenoid astaxanthin pigments in the cytoplasm (Grung & Liaaen-Jensen, 1993;Gerber & Häder, 1994;Frassanito et al, 2008;Laza-Martínez et al, 2019, Zheng et al, 2020. The reddening process includes the relocation of cytoplasmic lipid globules where astaxanthin accumulates from the center of the cell to peripheral locations when exposed to high light (Laza-Martínez et al, 2019)frequently carotenoids, under chronic stress is a response observed in diverse kinds of eukaryotic photoautotrophs. It is thought that red pigments protect the chlorophyll located underneath by a light-shielding mechanism.…”