Comparative morphoanatomy and phycochemical screening of three selected Gracilaria (Rhodophyta) species from Sri Lanka

Abstract

Gracilaria is the largest genus of the red algal family Gracilariaceae. A comparative morphoanatomical study was undertaken of three selected Gracilaria species: G. hikkaduwensis (endemic to Sri Lanka); G. corticata; and G. canaliculata with investigation of phycochemicals and pigments. Samples were collected from Koggala, Sri Lanka. Following the morphoanatomical study, crude extracts were prepared by macerating the thalli in methanol: dichloromethane, followed by rota-evaporation. Phycochemicals were tested using standard methodologies. Ethyl acetate extraction was performed to obtain chlorophyll a and carotenoids. Phycobiliproteins were extracted and quantified by ultraviolet–visible spectrometry. G. hikkaduwensis had toothed apices which distinguish this from G. corticata and G. canaliculata with rounded apices in vegetative thalli. G. corticata had markedly compressed axes distinguishing it from G. canaliculata with cylindrical axes further confirmed species level identity. Phycochemical analysis indicated the presence of alkaloids, glycosides, saponins, amino acids, phenols, tannins, steroids and flavonoids. However, terpenoids were only present in G. hikkaduwensis. The highest phenolic content (2.02 ± 0.11 mg GAE g‒1) is present in G. corticata and lowest (1.36 ± 0.08 mg GAE g‒1) in G. hikkaduwensis. The highest flavonoids content (1.52 ± 0.01 mg QUE g‒1) was in G. hikkaduwensis and the lowest (1.02 ± 0.01 mg QUE g‒1) in G. corticata, respectively. Pigment analysis revealed the highest chlorophyll a (6.2 μg g‒1) in G. canaliculata while the lowest (1.9 μg g‒1) in G. hikkaduwensis. The highest carotenoids content (0.8 μmol g‒1) was reported in G. corticata, while the lowest (0.3 μmol g‒1) was in G. canaliculata. Individual phycobiliproteins (phycoerythrin, phycocyanin, and allophycocyanin) were recorded spectrophotometrically as 0.25 mg g‒1, 0.14 mg g‒1 and 0.18 mg g‒1, respectively. This study provides the first report on phycochemical screening of the endemic algae G. hikkaduwensis. These results together with those of G. corticata and G. canaliculata can be used as baseline data in further research on these species.

Keywords

• Carotenoids
• flavonoids
• Gracilaria
• morphoanatomy
• phycochemicals
• Sri Lanka