The health and existence of coral reefs are in danger by an increasing range of environmental and anthropogenic impacts. The causes of coral reef decline include worldwide climate change, shoreline development, habitat destruction, pollution, sedimentation and overexploitation. These disasters have contributed to an estimated loss of 27% of the reefs. If the current pressure continues unabated, the estimated loss of coral reef will be about 60% by the year 2030. Therefore, the present study was aimed to analyze the enzymes involved in stress induced by coral pathogen and its resistance. We focused on the enzymes involved in melanin synthesis pathway (phenoloxidase (PO) and peroxidases (POD)) and free radical scavenging enzymes (super oxide dismutase (SOD), catalase (CAT)) and glutathione peroxidase (Gpx) in selected scleractinian corals such as
The coral holobiont is comprised not only of coral animal and endosymbiotic dinoflagellates (zooxanthellae) but also of microbial communities such as bacteria, archaea, and fungi as well as numerous viruses [
Prophenoloxidase is an important enzyme and a key component of innate immunity system of corals [
Six different coral specimens were collected from three different locations, that is, from villundi theertham (lat.: 9°17′33.81′′N, long.: 79°12′ 46.69′′E), Pamban (lat.: 9°17′1.21′′N, long.: 79°12′44.20′′E), and Olaikuda (lat.: 9°18′30.12′′N, long.: 79°20′ 4.44′′E) of the Palk Bay, southeast coast of India. Specimens were collected during low tide in the early morning in the month of April 2012. These were identified based on the morphological features and keys observed during collection of samples. The identified corals were (1)
The coral samples were crushed using sterile sea water and the homogenate was obtained by centrifugation at 15,000 RPM for 15 minutes to separate the supernatant and pellets. The supernatant thus obtained was considered as substrate for the analysis of protein and enzyme activities of coral host [
Peroxidase activity was assayed spectrophotometrically (SPECRTA max M2e) at 470 nm using guaiacol as a phenolic substrate with hydrogen peroxidase [
Quantification of SOD activity was based on the ability of SOD to inhibit the reduction of NBT by superoxide [
Catalase activity was estimated by the method described by Aebi, 1984 [
Glutathione peroxidase (GPx) activity was determined using a slightly modified protocol of Rotruck et al.
Data were analyzed by one-way analysis of variance (ANOVA) with the Graph-Pad Prism 5 software and the least significant differences were compared at
Phenoloxidase activity of both zooxanthellae and coral tissues of six healthy coral samples collected from the Palk Bay was presented in Figure
Phenoloxidase activity of coral tissue and zooxanthellae (
The phenoloxidase activity of coral tissues of six different corals such as
Peroxidase (POD) activity of both zooxanthellae and coral tissues of six different coral species is presented in Figure
Peroxidase activity of coral tissue and zooxanthellae (
The peroxidase activity of coral tissues of six different coral species such as
Significant increase in peroxidase activity was observed in zooxanthellae extracts when compared with coral tissue extracts of all coral samples except
The three major antioxidant enzymes are the superoxide dismutase (SOD) which produces H2O2 by converting
Superoxide dismutase activity of both zooxanthellae and coral tissues of six different coral species is presented in Figure
SOD activity of coral tissue and zooxanthellae of 6 coral species (
SOD activity of coral tissues of
SOD activity of
Catalase (CAT) activities of zooxanthellae and coral tissues of six different coral species have been presented in Figure
Catalase activity of coral tissue and zooxanthellae (
Similarly, CAT activity of coral tissues of
Comparing CAT activity between coral zooxanthellae and coral tissues of the six different species, it was observed that, except
Like SOD and CAT activities, glutathione peroxidase (GPx) activities of both zooxanthellae and coral tissues of six different corals were also estimated and presented in Figure
Glutathione peroxidase activity of coral tissue and zooxanthellae (
The zooxanthellae of
Similar to GPx activity of zooxanthellae, the GPx activity of coral tissues has been presented in Figure
The GPx activities of both zooxanthellae and the coral tissues of
As phenoloxidase plays a vital role in defensive mechanism of invertebrates, the presence of PO activity in all 6 coral species indicates the presence of baseline level of antimicrobial defense [
Peroxidase activity induction includes oxidation of substrates and cytotoxic molecules [
The maximum catalase activity was observed in zooxanthellae compared to coral tissue. This may be due to the conversion of superoxide ion produced during photosynthesis into hydroxyl ion which was denoted by the increase in GPx and SOD activity, which in turn resulted in hydrogen peroxide free radical in the zooxanthellae. Hence, the increase in CAT activities was observed as a result of increased H2O2 concentrations in the zooxanthellae [
Glutathione peroxidase (GPx) plays a vital role in cleaving H2O2 as a compensatory mechanism under severe oxidative challenge where the catalase activity may be inhibited [
The present study focused on the enzymes involved in the coral resistance among the selected coral species of the Palk Bay region, southeast coast of India. The results of this study described that the corals
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors are grateful to the Department of Marine and Coastal studies, Madurai Kamaraj University, for providing laboratory facilities. The financial support from UGC-BSR is also acknowledged.