scholarly journals Sensitivity of Antarctic freshwater algae to salt stress assessed by fast chlorophyll fluorescence transient

2013 ◽  
Vol 3 (2) ◽  
pp. 163-172 ◽  
Author(s):  
David Miguel Vilumbrales ◽  
Kateřina Skácelová ◽  
Miloš Barták
Keyword(s):  
Energy Transfer ◽  
Salt Stress ◽  
Chlorophyll Fluorescence ◽  
Electron Transport ◽  
Excitation Energy ◽  
Reaction Center ◽  
Excitation Energy Transfer ◽  
Ps Ii ◽  
Fluorescence Transient ◽  
Chlorophyll Fluorescence Transient

In this study, we investigated the effects of salt stress (2 mM NaCl) on excitation energy transfer from light harvesting complexes to photosystem II (PS II) in two Antarctic algal species: Klebsormidium sp. and Zygnema sp. Short-term salt stress led to a significant changes in the shape of chlorophyll fluorescence transient (OJIP). Analyses of the polyphasic fluorescence transients (OJIP) showed that the fluorescence yield at the phases J, I and P declined considerably with the time of exposition to salt stress. In both experimental species, OJIP transients reached lowest values of chlorophyll fluorescence signal after 30/60 min. of NaCl exposition. Then, OJIP shape and chlorophyll fluo-rescence showed species-specific recovery and rised towards original values (about 2/3 of untreated control). Analyses of chlorophyll fluorescence parameters derived from OJIPs showed that salt stress led to a decrease in the maximal efficiency of PS II photo-chemistry (FV/FM) in Zygnema sp. but not Klebsormidium sp. The results indicated that the probability of excitation energy transfer before and beyond QA, and the yield of electron transport beyond QA is limited by salt-induced stress in Zygnema sp. In addition, salt stress resulted in a decrease in the photosynthetic electron transport per PS II reaction center, but both increase and decrease in the trapping per PS II reaction center was found. Performace index (PIabs) was affected negatively in Zygnema sp. but possitively Klebsormidium sp. indicating that the latter species was more resistant to salt stress than Zygnema sp.

scholarly journals Methyl Jasmonate Protects the PS II System by Maintaining the Stability of Chloroplast D1 Protein and Accelerating Enzymatic Antioxidants in Heat-Stressed Wheat Plants

Antioxidants ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 1216
Author(s):  
Mehar Fatma ◽  
Noushina Iqbal ◽  
Zebus Sehar ◽  
Mohammed Nasser Alyemeni ◽  
Prashant Kaushik ◽  
...  
Keyword(s):  
Heat Stress ◽  
Chlorophyll Fluorescence ◽  
Electron Transport ◽  
Methyl Jasmonate ◽  
Reaction Center ◽  
D1 Protein ◽  
Fluorescence Induction ◽  
Chlorophyll Fluorescence Induction ◽  
Enzymatic Antioxidants ◽  
Ps Ii

The application of 10 µM methyl jasmonate (MeJA) for the protection of wheat (Triticum aestivum L.) photosystem II (PS II) against heat stress (HS) was studied. Heat stress was induced at 42 °C to established plants, which were then recovered at 25 °C and monitored during their growth for the study duration. Application of MeJA resulted in increased enzymatic antioxidant activity that reduced the content of hydrogen peroxide (H2O2) and thiobarbituric acid reactive substances (TBARS) and enhanced the photosynthetic efficiency. Exogenous MeJA had a beneficial effect on chlorophyll fluorescence under HS and enhanced the pigment system (PS) II system, as observed in a JIP-test, a new tool for chlorophyll fluorescence induction curve. Exogenous MeJA improved the quantum yield of electron transport (ETo/CS) as well as electron transport flux for each reaction center (ET0/RC). However, the specific energy fluxes per reaction center (RC), i.e., TR0/RC (trapping) and DI0/RC (dissipation), were reduced by MeJA. These results indicate that MeJA affects the efficiency of PS II by stabilizing the D1 protein, increasing its abundance, and enhancing the expression of the psbA and psbB genes under HS, which encode proteins of the PS II core RC complex. Thus, MeJA is a potential tool to protect PS II and D1 protein in wheat plants under HS and to accelerate the recovery of the photosynthetic capacity.

Photosynthesis

2009 ◽  
pp. 573-587
Author(s):  
Julia Adolphs
Keyword(s):  
Energy Transfer ◽  
Excitation Energy ◽  
Reaction Center ◽  
High Efficiency ◽  
Excitation Energy Transfer ◽  
Photosynthetic Reaction Center ◽  
Photochemical Reactions ◽  
Light Harvesting Complexes ◽  
Transition Energies ◽  
Local Transition

This chapter introduces the theory of optical spectra and excitation energy transfer of light harvesting complexes in photosynthesis. The light energy absorbed by protein bound pigments in these complexes is transferred via an exciton mechanism to the photosynthetic reaction center where it drives the photochemical reactions. The protein holds the pigments in optimal orientation for excitation energy transfer and creates an energy sink by shifting the local transition energies of the pigments. In this way, the excitation energy is directed with high efficiency (close to 100 %) to the reaction center. In the present chapter, this energy transfer is studied theoretically. Based on crystal structure data, the excitonic couplings are calculated taking into account also the polarizability of the protein. The local transition energies are obtained by two independent methods and are used to predict the orientation of the FMO protein relative to the reaction center.

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