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Query: UMLS:C0240066 (iron deficiency)
 7,156 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In this review we give an overview on the adaptational responses of photosystem (PS) II and PSI in cyanobacteria to iron starvation, mainly summarizing our results with the mesophilic Synechococcus elongatus PCC 7942. We also discuss this process with respect to the strong interrelationship between iron limitation and oxidative stress that exists in cyanobacteria as oxygenic photosynthetic organisms. The adaptation of the multiprotein complexes PSII and PSI to iron starvation is a sequential process, which is characterized by the enhanced expression of two major iron-regulated proteins, IdiA (iron deficiency induced protein A) and IsiA (iron stress induced protein A). Our results suggest that IdiA protects the acceptor side of PSII against oxidative stress under conditions of mild iron limitation in a currently unclear way, whereas prolonged iron deficiency leads to the synthesis of a chlorophyll a antenna around PSI-trimers consisting of IsiA molecules. The physiological consequences of these alterations under prolonged iron starvation, as shown by acridine yellow fluorescence measurements, are a reduction of linear electron transport activity through PSII and an increase of cyclic electron flow around PSI as well as an increase in respiratory activity. IdiA and IsiA expression are mediated by two distinct helix-turn-helix transcriptional regulators of the Crp/Fnr family. IdiB positively regulates expression of idiA under iron starvation, and Fur represses transcription of isiA under iron-sufficient conditions. Although both transcriptional regulators seem to operate independently of each other, our results indicate that a cross-talk between the signal transduction pathways exists. Moreover, IdiA as well as IsiA expression are affected by hydrogen peroxide. We suggest that due to the interdependence of iron limitation and the formation of reactive oxygen species, peroxide stress might be the superior trigger that leads to expression of these proteins under iron starvation. The modifications of PSII and PSI under iron starvation influence the redox state of redox-sensitive components of the electron transport chain, and thus the activity of metabolic pathways being regulated in dependence of the redox state of these components.
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PMID:Adaptation of the photosynthetic electron transport chain in cyanobacteria to iron deficiency: The function of IdiA and IsiA. 1503 75

To learn more about the adaptive response of Synechococcus elongatus PCC 7942 to iron starvation and the role of DpsA, presumably a protein protecting chromosomal DNA against oxidative damage, we performed a comparative analysis of S. elongatus PCC 7942 wild-type and a DpsA-free mutant, called K11. Relative to wild-type, the DpsA-free mutant had significantly higher amounts of phycocyanin and allophycocyanin, even upon iron limitation. While the Photosystem I activity in mutant K11 remained high under iron deficiency, the Photosystem II activity dropped severely with respect to wild-type. The DpsA content in wild-type was already fairly high under regular growth conditions and did not significantly increase under iron deficiency nor in the presence of 0.3 mM 2'2'-dipyridyl in iron-sufficient BG11 medium. Nevertheless, the absence of DpsA in K11 resulted in a significantly altered transcriptional/translational activity of genes known to be involved in adaptation to iron starvation. The amount of isiA/B transcript was about two-fold lower than in wild-type, resulting in a lower 77 K chlorophyll a fluorescence at 685 nm, implying a lower concentration of Photosystem I-IsiA supercomplexes. While in wild-type idiA, idiB, and irpA transcripts were highly up-regulated, hardly any were detectable in mutant K11 under iron limitation. The concentration of mapA transcript, however, was greatly increased in K11 compared to wild-type. Measurements of acridine yellow fluorescence with intact wild-type and K11 cells revealed that iron deficiency caused an increased contribution of cyclic electron transport to membrane energisation and ATP synthesis being in agreement with the formation of the Photosystem I-IsiA supercomplex. In addition, mutant K11 had a much higher respiratory activity compared to wild-type under iron limitation.
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PMID:Adaptation to iron deficiency: a comparison between the cyanobacterium Synechococcus elongatus PCC 7942 wild-type and a DpsA-free mutant. 1624 95