EARLY TOXIC EFFECTS OF ZINC ON PSII OF SYNECHOCYSTIS AQUATILIS F. AQUATILIS (CYANOPHYCEAE)¹

Abstract

Zinc toxicity on photosynthetic activity in cells of Synechocystis aquatilis f. aquatilis Sauvageau was investigated by monitoring Hill activity and fluorescence. The oxygen-evolving activity decreased to about 80% of the initial value after exposure to 0.1 mM ZnSO 4 for 1 h. The PSII activity was inhibited by 40% in the presence of zinc concentrations ranging from 0.5 to 5.0 mM, suggesting that the metal effect is limited by zinc uptake. The fluorescence capacity (F max -F/F max ) decreased from 0.57 to 0.35 and 0.20 in Zn-treated cells for 15 and 60 min, respectively, thus providing evidence for rapid inactivation of electron transport at PSII. Zinc treatment promoted a rapid increase in PSII fluorescence that was counteracted by addition of 1,4-benzoquinone, indicating that electron transfer at the reducing side of the PSII reaction center is arrested by zinc. Furthermore, a decline in the fluorescence yield could be observed after 1 h of zinc treatment as well as when Zn-treated cells were excited in presence of 3-(3 0 ,4 0 -dichlorophenyl)-1,1-dimethylurea. Under these conditions, zinc did not affect energy transfer from phycobilisomes to PSII, and the gradual quenching of PSII fluorescence may be due to a decrease in electron flow on the donor side of PSII. However, the 20% increase in the minimal fluorescence intensity (F o ) in parallel to the absence of changes in the maximal fluorescence intensity (F max ), observed in the first hour of zinc treatment, could also suggest a metal-induced decline in the energy transfer from PSII-chl a antenna to the PSII reaction center.

Heavy Metals Effect on Cyanobacteria Synechocystis aquatilis Study Using Absorption, Fluorescence, Flow Cytometry, and Photothermal Measurements

“…3, Table 1) and decrease the emission under stronger stress (higher concentration). A similar effect of fluorescence fluctuations as a function of the incubation time was reported for cyanobacteria affected by Zn ions [5].…”

“…This group includes 53 naturally existing chemical elements (among them As, which is a semimetal). Many heavy metals play essential roles for living photosynthetic organisms, and a very low concentration of their ions is required for optimum growth in distinct culture media [5]. Most of the chemical elements often occur as cations able to form complex molecules and show activity in redox reactions.…”

Pulverização foliar com nitrogênio e zinco em milho (Zea mayz L.) “safrinha” em Confresa (MT)

“…Viana e Kiehl (2010) observaram, com adição crescente de nitrogênio ao solo para cultivo de trigo, aumento da concentração da clorofila foliar promovido pela maior concentração de nitrogênio no tecido. Santos (2014) observou que os teores de clorofila "a" e "b" são reduzidos em excesso ou deficiência de zinco foliar, sendo que nessas condições o elemento poderá inibir o transporte de elétrons no fotossistema II (CHALOUB et al 2005).…”

Chl-a fluorescence parameters as biomarkers of metal toxicity in fluvial biofilms: an experimental study

“…binding at their native sites on the water oxidizing complex (Rashid et al, 1994). Based on algal monocultures, Zn toxicity is reported at very different concentrations depending on the species tested and the biomarker assessed: Chaloub et al (2005) found Zn toxicity on cyanobacteria cultures between 30 and 332 mg l -1 , and Posthuma et al (2001) describe an EC 50 of 15 lg l -1 in Selenastrum capricornutum. Cd is considered as an important contaminant of natural waters because of its high toxicity at low concentration (Deckert, 2005).…”