Iron Deficiency Induces a Partial Inhibition of the Photosynthetic Electron Transport and a High Sensitivity to Light in the Diatom Phaeodactylum tricornutum

Abstract

Iron limitation is the major factor controlling phytoplankton growth in vast regions of the contemporary oceans. In this study, a combination of thermoluminescence (TL), chlorophyll fluorescence, and P700 absorbance measurements have been used to elucidate the effects of iron deficiency in the photosynthetic electron transport of the marine diatom P. tricornutum. TL was used to determine the effects of iron deficiency on photosystem II (PSII) activity. Excitation of iron-replete P. tricornutum cells with single turn-over flashes induced the appearance of TL glow curves with two components with different peaks of temperature and contributions to the total signal intensity: the B band (23°C, 63%), and the AG band (40°C, 37%). Iron limitation did not significantly alter these bands, but induced a decrease of the total TL signal. Far red excitation did not increase the amount of the AG band in iron-limited cells, as observed for iron-replete cells. The effect of iron deficiency on the photosystem I (PSI) activity was also examined by measuring the changes in P700 redox state during illumination. The electron donation to PSI was substantially reduced in iron-deficient cells. This could be related with the important decline on cytochrome c6 content observed in these cells. Iron deficiency also induced a marked increase in light sensitivity in P. tricornutum cells. A drastic increase in the level of peroxidation of chloroplast lipids was detected in iron-deficient cells even when grown under standard conditions at low light intensity. Illumination with a light intensity of 300 μE m-2 s-1 during different time periods caused a dramatic disappearance in TL signal in cells grown under low iron concentration, this treatment not affecting to the signal in iron-replete cells. The results of this work suggest that iron deficiency induces partial blocking of the electron transfer between PSII and PSI, due to a lower concentration of the electron donor cytochrome c6. This decreased electron transfer may induce the over-reduction of the plastoquinone pool and consequently the appearance of acceptor side photoinhibition in PSII even at low light intensities. The functionality of chlororespiratory electron transfer pathway under iron restricted conditions is also discussed.

The lipid biochemistry of eukaryotic algae

“…the major lipid droplet protein or DGAT) was increased [426]. Effects of Fe-deficiency in Phaeodactylum tricornutum were coincident with a partial deficiency of photosynthetic transport and a high sensitivity to light [429].…”

Diurnal regulation of photosynthetic light absorption, electron transport and carbon fixation in two contrasting oceanic environments

“…Sakshaug et al, 1997). Micro-nutrient limitation, most notably iron, has also been shown to exert a significant effect on light-dependent photosynthetic responses (Greene et al, 1991(Greene et al, , 1992Roncel et al, 2016;Schuback et al, 2015). Here, we examine potential iron-dependent effects by comparing absolute values and diurnal periodicity of components of the photosynthetic process between the high productivity coastal waters of OCE17 and the iron-limited NE subarctic Pacific (OSP14, Schuback et al, 2016).…”

Arbuscular Mycorrhizal Symbiosis Mitigates Iron (Fe)-Deficiency Retardation in Alfalfa (Medicago sativa L.) Through the Enhancement of Fe Accumulation and Sulfur-Assisted Antioxidant Defense

“…Apart from it, chlorophyll synthesis and photosynthesis parameters remarkably improved in leaves of alfalfa, suggesting that AMF supplementation restored the Fe balance in alfalfa plants even though plants were cultivated on Fe-deficient conditions. Fe deficiency changes the structure of thylakoid membrane resulted in a decline of PS-II efficiency in plants [27][28][29] and interferes chlorophyll biosynthetic pathway dependent on Fe containing enzymes [30,31]. Chlorophyll a fluorescence has been used as a powerful tool for studying photosynthetic systems in plants exposed to different abiotic stresses [32].…”