Abstract
Seagrass Cymodocea nodosa was sampled off the Vulcano island, in the vicinity of a submarine volcanic vent. Leaf samples were collected from plants growing in a naturally acidified site, influenced by the long-term exposure to high CO2 emissions, and compared with others collected in a nearby meadow living at normal pCO2 conditions. The differential accumulated proteins in leaves growing in the two contrasting pCO2 environments was investigated. Acidified leaf tissues had less total protein content and the semi-quantitative proteomic comparison revealed a strong general depletion of proteins belonging to the carbon metabolism and protein metabolism. A very large accumulation of proteins related to the cell respiration and to light harvesting process was found in acidified leaves in comparison with those growing in the normal pCO2 site. The metabolic pathways linked to cytoskeleton turnover also seemed affected by the acidified condition, since a strong reduction in the concentration of cytoskeleton structural proteins was found in comparison with the normal pCO2 leaves. Results coming from the comparative proteomics were validated by the histological and cytological measurements, suggesting that the long lasting exposure and acclimation of C. nodosa to the vents involved phenotypic adjustments that can offer physiological and structural tools to survive the suboptimal conditions at the vents vicinity.
Highlights
The Mediterranean submarine volcanic vents are natural sources of C O2 since this gas is the main component of the volcanic emissions that have been happening for hundreds of years, forming unique and extraordinary environments in which the relative abundance of dissolved inorganic carbon (Ci) species is altered by an increase in the partial pressure of C O2, with a consequent drastic reduction in seawater p H1,2
Comparative proteomics has been previously applied to seagrasses, revealing the protein molecular dynamics for surviving under various conditions[26,27,28,29,30] Since the amounts of protein and transcripts corresponding to the same gene are generally loosely c orrelated[31], the advantage offered by proteomics in the present study is to reveal changes in protein accumulation induced by high CO2 that cannot have been predicted from the previous transcriptomics investigation[24], contributing to elucidate the effects of a long-term exposure to naturally increased pressure of C O2 (pCO2)
Spite the same amount of leaf proteins loaded on each well, the band at 55 kDa, corresponding to the large subunit of RuBisCo, decreased in all replicates of plants living in high pCO2 with respect to those under normal pCO2 condition (Fig. 1)
Summary
The Mediterranean submarine volcanic vents are natural sources of C O2 since this gas is the main component of the volcanic emissions that have been happening for hundreds of years, forming unique and extraordinary environments in which the relative abundance of dissolved inorganic carbon (Ci) species is altered by an increase in the partial pressure of C O2 (pCO2), with a consequent drastic reduction in seawater p H1,2. An ecological assessment of Cymodocea nodosa at a shallow acidified site at Volcano Island (Italy) revealed that the meadow is negatively affected by the environmental conditions at the low pH site, as the plant’s density and biomass decreased[8,9]; authors reported a decrease in leaf area in plants acclimated to the CO2 vents This latter finding, along with similar studies, strongly suggests that the acclimation of seagrasses to the long-lasting high pCO2 concentration encompasses several physiological and morphological adjustments. These results support the suggestion that volcanic vents may not be ideal analogues for ocean acidification studies and that the observed effects on seagrasses are not merely due to the increased C O2 availability but are influenced by other environmental factors present at these sites[9]
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