• Energy Research

AbstractTo avoid photodamage, photosynthetic organisms have developed mechanisms to evade or dissipate excess energy. Lumen overacidification caused by light‐induced electron transport triggers quenching of excited chlorophylls and dissipation of excess energy into heat. In higher plants participation of the PsbS protein as the sensor of low lumenal pH was clearly demonstrated. Although light‐dependent energy quenching is a property of all photosynthetic organisms, large differences in amplitude and kinetics can be observed thus raising the question whether a single common mechanism is in action. We performed a detailed study of PsbS expression/accumulation in Chlamydomonas reinhardtii and investigated its accumulation in other algae and plants. We showed that PsbS cannot be detected in Chlamydomonas under a wide range of growth conditions. Overexpression of the endogenous psbs gene showed that the corresponding protein could not be addressed to the thylakoid membranes. Survey of different unicellular green algae showed no accumulation of anti‐PsbS reactive proteins differently from multicellular species. Nevertheless, some unicellular species exhibit high energy quenching activity, suggesting that a PsbS‐independent mechanism is activated. By correlating growth habitat and PsbS accumulation in different species, we suggest that during the evolution the light environment has been a determinant factor for the conservation/loss of the PsbS function.

Several plants and invertebrates interact and communicate by means of volatile organic compounds (VOCs). These compounds may play the role of infochemicals, being able to carry complex information to selected species, thus mediating inter- or intra-specific communications. Volatile organic compounds derived from the wounding of marine diatoms, for example, carry information for several benthic and planktonic invertebrates. Although the ecological importance of VOCs has been demonstrated, both in terrestrial plants and in marine microalgae, their role as infochemicals has not been demonstrated in seagrasses. In addition, benthic communities, even the most complex and resilient, as those associated to seagrass meadows, are affected by ocean acidification at various levels. Therefore, the acidification of oceans could produce interference in the way seagrass-associated invertebrates recognize and choose their specific environments. We simulated the wounding of Posidonia oceanica leaves collected at two sites (a control site at normal pH, and a naturally acidified site) off the Island of Ischia (Gulf of Naples, Italy). We extracted the VOCs and tested a set of 13 species of associated invertebrates for their specific chemotactic responses in order to determine if: a) seagrasses produce VOCs playing the role of infochemicals, and b) their effects can be altered by seawater pH. Our results indicate that several invertebrates recognize the odor of wounded P. oceanica leaves, especially those strictly associated to the leaf stratum of the seagrass. Their chemotactic reactions may be modulated by the seawater pH, thus impairing the chemical communications in seagrass-associated communities in acidified conditions. In fact, 54% of the tested species exhibited a changed behavioral response in acidified waters (pH 7.7). Furthermore, the differences observed in the abundance of invertebrates, in natural vs. acidified field conditions, are in agreement with these behavioral changes. Therefore, leaf-produced infochemicals may influence the structure of P. oceanica epifaunal communities, and their effects can be regulated by seawater acidification.

AbstractOcean acidification is an emerging problem that is expected to impact ocean species to varying degrees. Currently, little is known about its effect on molecular mechanisms induced in fleshy macroalgae. To elucidate genome wide responses to acidification, a transcriptome analysis was carried out on Sargassum vulgare populations growing under acidified conditions at volcanic CO2 vents and compared with populations in a control site. Several transcripts involved in a wide range of cellular and metabolic processes were differentially expressed. No drastic changes were observed in the carbon acquisition processes and RuBisCO level. Moreover, relatively few stress genes, including those for antioxidant enzymes and heat‐shock proteins, were affected. Instead, increased expression of transcripts involved in energy metabolism, photosynthetic processes and ion homeostasis suggested that algae increased energy production to maintain ion homeostasis and other cellular processes. Also, an increased allocation of carbon to cell wall and carbon storage was observed. A number of genes encoding proteins involved in cellular signalling, information storage and processing and transposition were differentially expressed between the two conditions. The transcriptional changes of key enzymes were largely confirmed by enzymatic activity measurements. Altogether, the changes induced by acidification indicate an adaptation of growth and development of S. vulgare at the volcanic CO2 vents, suggesting that this fleshy alga exhibits a high plasticity to low pH and can adopt molecular strategies to grow also in future more acidified waters.