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

Abstract

We examined the morphology and pigment composition of zooxanthellae in corals subjected to normal temperature (27°C) and thermal stress (32°C). We observed several normal and abnormal morphological types of zooxanthellar cells. Normal cells were intact and their chloroplasts were unbroken (healthy); abnormal cells were shrunken and had partially degraded or broken chloroplasts, or they were bleached and without chloroplasts. At 27°C, most healthy zooxanthellar cells were retained in the coral tissue, whereas shrunken zooxanthellae were expelled. Under thermal stress, the abundance of healthy zooxanthellae declined and the proportion of shrunken/abnormal cells increased in coral tissues. The rate of algal cell expulsion was reduced under thermal stress. Within the shrunken cells, we detected the presence of a chllike pigment that is not ordinarily found in healthy zooxanthellae. Analysis of the absorption spectrum, absorption maxima, and retention time (by HPLC) indicated that this pigment was 13 2 , 17 3 -cyclopheophorbide a enol (cPPB-aE), which is frequently found in marine and lacustrine sediments, and in protozoans that graze on phytoplankton. The production of cPPB-aE in shrunken zooxanthellae suggests that the chls have been degraded to cPPBaE, a compound that is not fluorescent. The lack of a fluorescence function precludes the formation of reactive oxygen species. We therefore consider the formation of cPPB-aE in shrunken zooxanthellae to be a mechanism for avoiding oxidative stress.

Response of Subtropical Coastal Sediment Systems of Okinawa, Japan, to Experimental Warming and High pCO2

“…The HPLC system was equipped with a ZORBAX Eclipse Plus C8 column (2.1 × 50 mm; Agilent Technologies, Santa Clara, CA, USA). Pigments were extracted using a combination (1:3) of dry sediment and acetone (90% final concentration; Alsterberg et al, 2011), sonicated for 15 min, and maintained overnight in the dark at −30 • C. Extracts were filtered using a syringe filter (0.2 µm, Millex-LG; Millipore, Bedford, MA, USA; Suzuki et al, 2015) and 1.0 mL of each extract was mixed with 0.2 mL of deionized water (Milli-Q water, Millipore) immediately before injections (Zapata et al, 2000) in the HPLC system. Separated pigments were detected spectrophotometrically using a photodiode array detector (SPD-M30AD; Shimadzu, Kyoto, Japan) with an optical resolution of 1.2 nm across the 320-720 nm bandwidth.…”

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

“…Number in each star or diamond denotes the total number of species examined in the present study and/or previously reported (listed in Supplementary Table S2). Numbers with asterisks are data from previous reports [8, 12–14]. Among the nine MEAs, Archaeplastida examined in the present study consists exclusively of phototrophs, whereas Amoebozoa and Opisthokonta consist exclusively of heterotrophs.…”

“…We also conducted experiments on 112 unialgal cultures (UCs), and accumulation of CPE was found to be common among algae containing secondary chloroplasts, including chlorarachniophytes, phototrophic dinoflagellates (dinophytes) [12–14], haptophytes, and phototrophic euglenids (euglenophytes; Fig. 1, Fig.…”

“…Their secondary and tertiary chloroplasts derived from a red alga were acquired independently in each clade [26]. We and previous works [13, 14] identified accumulation of cPPB- a E, a chlorophyll- a -derived CPE, in UCs of some of these phototrophs.…”

“…The ubiquity of CPEs suggests that CPE-accumulating chlorophyll catabolism (CACC) contributes greatly to the turnover of chlorophylls in aquatic environments, in which ~50% of global primary production takes place [11]. However, accumulation of CPEs has to date been reported in cultures including only single strains representing each of four major eukaryotic assemblages (MEAs): Rhizaria, Alveolata, Stramenopiles, and Haptista [8, 12], along with enigmatic occurrences in several strains of dinoflagellates [13, 14]. The distribution of the potential for CACC and the role of this process in aquatic chlorophyll degradation in certain organismal groups are still largely unknown.…”