Chlorophyll fluorescence, dark respiration and metabolomic analysis of Halodule pinifolia reveal potential heat responsive metabolites and biochemical pathways under ocean warming.

Seagrasses are submerged marine angiosperms often prone to various biotic and abiotic stress factors in the marine environment. Our study investigated the response, adaptation and underlying tolerance mechanism of tropical seagrass Halodule pinifolia upon temperature stress (24°, 29°, 37°, and 45 °C) and evaluated the effect of temperature stress on net photosynthesis (ΔF/F') and dark respiration (F/F). In this study, metabolomic analysis of seagrass H. pinifolia upon heat stress has been performed using GC-MS based omics approach. As a result, the net photosynthetic efficiency (ΔF/F') was found significantly decreased upon heat stress, while the dark respiration rate was increased to 2.903 mg O/g FW h and 3.87 mg O/g FW h as compared to the control (24 °C), respectively. Metabolomic analysis showed heat stress could cause large metabolite variations with respect to sugar, amino acids and organic acids. Interestingly, three thermo-protective metabolites such as trehalose (sugar), glycine betaine (amino acid) and methyl vinyl ketone (organic acid) were profiled from H. pinifolia (45 °C) and is the first report on the occurrence of glycine betaine and methyl vinyl ketone from seagrasses and other aquatic species so far. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis demonstrated H. pinifolia exposed to heat stress lead to intense biochemical changes and caused significant variations in the heat responsive metabolic pathways. The present findings would facilitate the further research on identifying gene to metabolite networks for an effective management of seagrass conservation by genetic manipulation.