Use of different fluorometric systems in the determination of fluorescence parameters from spinach thylakoid membranes being exposed to atrazine and copper

Abstract

Sensitivity of photosystem II fluorescence parameters, as indicators of atrazine and copper inhibitory effects, were investigated by using LuminoTox, Pulse Amplitude Modulated (PAM) and Plant Efficiency Analyzer (PEA) fluorometric systems. Inhibition of Photosystem II was induced when samples of spinach thylakoid membranes were treated with atrazine or copper sulphate for 15 min. In those samples we investigated the change of the following fluorescence parameters: For PAM and PEA, the maximal variable fluorescence as F_V , the basal quantum yield of nonphotochemical processes in PSII as the ratio F_O /F_M , the relationship between photochemical and concurrent nonphotochemical processes within PSII as the ratio F_V /F_O and the maximum quantum yield as the ratio F_V /F_M . For the LuminoTox, the evaluation of the parameters [F ₂ − F ₁, F ₂/F ₁, (F ₂ − F ₁)/F ₁ and (F ₂ − F ₁)/F ₂] was based on two fluorescence yields F ₁ and F ₂ measured under low- and high-light intensities, respectively. We found the change in sensitivity of the inhibitory response (Ir) to be caused either by the specific optical mode of the fluorometric system or by differences in inhibitory mechanism between atrazine and copper. The sensitivity order of EC-50% of Ir was for atrazine: Ir_{( F 2− F 1)/ F 1} (LuminoTox) > Ir _{FO / FM} (PAM) > Ir _{F 1/ F 2} (LuminoTox) > Ir _{F 2− F 1} (LuminoTox) > Ir _{F V / F O} (PAM) > Ir_{( F 2− F 1)/ F 2} (LuminoTox) > Ir _{F V / F O} (PEA) > Ir _{F O / F M} (PEA) > Ir _{F V / F M} (PEA) > Ir _{F V / F M} (PAM) and for copper: Ir _{F 2− F 1} (LuminoTox) > Ir _{F O / F M} (PEA) = Ir _FV (PEA) > Ir _{F V / F O} (PEA) > Ir _{F 1/ F 2} (LuminoTox) > Ir_{( F 2− F 1 )/ F 1} (LuminoTox) > Ir _{F V} (PAM) > Ir _{F O  / F M} (PAM) > Ir _{F V / F O} (PAM) > Ir _{F V / F M} (PEA) > Ir_{( F 2− F 1 ) / F 2} (LuminoTox). Study of these Ir, based on fluorescence parameters, may provide useful indication for the practical approach in the evaluation of atrazine and copper phytotoxicity.

Keywords:

• Copper
• atrazine
• photosystem II
• chlorophyll fluorescence

Acknowledgement

This research was financed in part by a grant from the Natural Science and Engineering Council of Canada (NSERC) attributed to R. Popovic.