Impact of heat and cold events on the energetic metabolism of the C3 halophyte Halimione portulacoides

According to the newest predictions, it is expected that the Mediterranean systems experience more frequent and longer heat and cold treatments events. Salt marshes will be no exception. Halimione portulacoides is a widely distributed halophyte highly adapted to harsh environments. Plants exposed to heat stress showed a reduction in the maximum electron transport rates and increase in the rate of RC closure, as indicated by the increase in M0. Alongside there was also a reduction in the quinone pool size while compared to the plants maintained in the control condition. In contrast plants exposed to low temperatures didn't show any signs of damage on the ETC. Heat-exposed individuals experienced a reduction of connectivity between the PS II antennae with simultaneous inhibition of the electron transport. This was more evident in the donor side of the PS II, Being this a consequence of the damages in the oxygen-evolving complex. Also if both PS I and PS II energy fluxes are observed, there are evident differences in the thermal tolerance of both photosystems. While compared to the control group, cold exposed plants showed an increased PS I efficiency (δR0) indicating a tolerance of this photosystem to low temperatures. Nevertheless, the excessive redox potential generated by light harvesting and inefficient processing was not dissipated correctly and consequently causing a oxidative stress situation. In the present study only heat exposed plants showed a significant activation of the xanthophyll cycle. Alongside with this mechanism and similarly to what was observed for cold treated plants, it could be observed an increase in auroxanthin content, an efficient energy quencher under stress conditions. The coupled activation of the xanthophyll cycle along with a higher auroxanthin synthesis suggests that heat-treated individuals had higher needs to dissipate excessive energy than the cells exposed to cold treatment. In both cases appears to exist an efficient ROS scavenging mechanism. According to our data, heat and cold treatment events can have serious impacts on H. portulacoides photobiology reducing its primary productivity. At the ecosystem level, these climatic events could pose a serious threat to the survival of this species in the new climatic reality that our planet is facing.

info:eu-repo/semantics/publishedVersion