The effect of ionic stress on photosynthesis in Dunaliella tertiolecta

Abstract

A comparison of the effects of ionic stress and an uncoupler on long-term fluorescence transients (the 'Kautsky effect') in the green alga Dunaliella tertiolecta indicated that the large quenching induced by ionic stress was caused by a pH gradient across the thylakoid membrane. This possiblity was given support by the increase in the slow phase of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in algae subjected to ionic stress. Low-temperature fluorescence emission spectra indicated that salt stress enhanced photosystem-I emission in the dark, and a comparison of simultaneous emissions at 695 and 720 nm at room temperature indicated a further increase in photosystem-I emission during the fluorescence transients. Taken together with the decrease in the fast phase of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in stressed algae, our results indicate that ionic stress stimulates cyclic electron flow, and that non-cyclic flow is inhibited. The effect of sucrose-induced osmotic stress was similar to, but less marked than, the effects of NaCl and KCl; the effect of decreasing the external salinity was small.

Responses of photosystems I and II of Acutodesmus obliquus to chemical stress caused by the use of recycled nutrients

“…The same trend was demonstrated in unicellular algae under the effect of nitrogen starvation (Berges et al 1996) and heavy metal pollution (cadmium) in Chlorella pyrenoidosa (Wang et al 2013). Several other stresses also disturb quantum yield of PS II including hyperosmotic stress in Chlamydomonas reinhardtii (Endo et al 1995), ionic stress in Dunaliella tertiolecta (Gilmour et al 1985) as well as high light conditions that lead to photoinhibition of C. reinhardtii (Lidholm et al 1987), and chronic photoinhibition in Dunaliella salina (Neidhardt et al 1998). In all these cases, PS I-driven cyclic electron flow might play a key role to survive under stress conditions, e.g., as shown for desiccation tolerance (Gao et al 2011;Gao and Wang 2012) and is potentially the energy supplier for the microalgae cell without PS II activity to biodegrade toxicants (Papazi and Kotzabasis 2013) and eventually restore PS II activity.…”

Functional aspects of secondary carotenoids in Haematococcus lacustris (Girod) Rostafinski (Volvocales)

“…Considering suggestions given in the literature (Droop, 1954;Gilmour et al, 1985), the results might be summarized in the hypothesis that the SC accumulation in H. lacustris is related to a transformation of the photosynthesis from a more ' reductive ' type (linear electron transport, production of NADPH and reducing power for nitrogen assimilation, protein synthesis) to a more ATP-producing type (increase of photophosphorylating activity, synthesis and accumulation of carbohydrates, lipids and further storage products). A similar interpretation was given by Falk & Palmqvist (1992) concerning the induction of the COj-concentrating mechanism in Chlamydomonas reinhardtii: Increase of CO2 utilization efficiency during this process was maintained by the synthesis of 'extra' ATP due to cyclic photophosphorylation at the expense of a reduced light utilization efficiency and decreased noncyclic electron transport, most probably due to the reduced energy flow through PS II (cf.…”

Melting out of sea ice causes greater photosynthetic stress in algae than freezing in1

“…At the cellular level, salinity changes can result in a wide range of physiological impacts, including cell rupture, reduced photosynthesis, and damage to enzymes. For example, if a cell does not have the photosynthetic activity to generate sufficient ATP/NADPH to maintain membrane‐bound ionic pumps (which prevent uncontrolled entry of ions into the cell), then damage will occur to sensitive membranes/metabolic sites, and the cell will die (Gilmour et al. 1985, Maxwell et al.…”