Impact of sulfur starvation in autotrophic and heterotrophic cultures of the Extremophilic Microalga Galdieria Phlegrea (Cyanidiophyceae)

In plants and algae, sulfate assimilation and cysteine synthesis are regulated by sulfur (S) accessibility from the environment. This study reports the effects of S deprivation in autotrophic and heterotrophic cultures of Galdieria phlegrea (Cyanidiophyceae), a unicellular red alga isolated in the Solfatara crater located in Campi Flegrei (Naples, Italy), where H2S is the prevalent form of gaseous S in the fumarolic fluids and S is widespread in the soils near the fumaroles. This is the first report on the effects of S deprivation on a sulfurous microalga that is also able to grow heterotrophically in the dark. The removal of S from the culture medium of illuminated cells caused a decrease in the soluble protein content and a significant decrease in the intracellular levels of glutathione. Cells from heterotrophic cultures of G. phlegrea exhibited high levels of internal proteins and high glutathione content, which did not diminish during S starvation, but rather glutathione significantly increased. The activity of O-acetylserine(thiol)lyase (OASTL), the enzyme synthesizing cysteine, was enhanced under S deprivation in a time-dependent manner in autotrophic but not in heterotrophic cells. Analysis of the transcript abundance of the OASTL gene supports the OASTL activity increase in autotrophic cultures under S deprivation

Suitability of Solanum lycopersicum L. 'Microtom' to be grown in Bioregenerative Life Support Systems: exploring the effect of high-LET ionising radiation on photosynthesis, leaf structure and fruit traits.

The realisation of manned Space exploration requires the development of Bioregenerative Life Support Systems (BLSSs). In such self-sufficient closed habitats, higher plants have a fundamental role in air regeneration, water recovery, food production and waste recycling. In the Space environment, ionising radiation represents one of the main constraints to plant growth. In this study, we explore whether low doses of heavy ions, namely Ca 25 Gy, delivered at the seed stage, may induce positive outcomes on growth and functional traits in plants of Solanum lycopersicum L.'Microtom'. After irradiation of seed, plant growth was monitored during the whole plant life cycle, from germination up to fruit ripening. Morphological parameters, photosynthetic efficiency, leaf anatomical functional traits and antioxidant production in leaves and fruits were analysed. Our data demonstrate that irradiation of seeds with 25 Gy Ca-ions does not prevent the achievement of the seed-to-seed cycle in 'Microtom' and induces a more compact plant size compared to control. Plants germinated from irradiated seeds show a better photochemical efficiency than control, likely due to the higher amount of D1 protein and photosynthetic pigments content. Leaves of these plants also show smaller cells with a lower number of chloroplasts. The dose of 25 Gy Ca-ions is also responsible for positive outcomes in fruits: although developing a lower number of berries, plants germinated from irradiated seeds produce larger berries, also richer in carotenoids, ascorbic acid and anthocyanins, than control. These specific traits may be useful in the view of 'Microtom' cultivation in BLSSs in Space in so far as the crewmembers could benefit from fresh food richer in functional compounds directly produced onboard. This article is protected by copyright. All rights reserved