Analysis of elevated temperature-induced inhibition of photosystem II using chlorophyll a fluorescence induction kinetics in wheat leaves (Triticum aestivum)

Wheat is the major crop plant in many parts of the world. Elevated temperature-induced changes in photosynthetic efficiency were studied in wheat (T. aestivum) leaves by measuring Chl a fluorescence induction kinetics. Detached leaves were subjected to elevated temperature stress of 35 degrees C, 40 degrees C or 45 degrees C. Parameters such as Fv/Fm, performance index (PI), and reaction centre to absorbance ratio (RC/ABS) were deduced using radial plots from fluorescence induction curves obtained with a plant efficiency analyser (PEA). To derive precise information on fluorescence induction kinetics, energy pipeline leaf models were plotted using biolyzer hp3 software. At 35 degrees C, there was no effect on photosynthetic efficiency, including the oxygen-evolving complex, and the donor side of PSII remained active. At 40 degrees C, activity was reduced by 14%, while at 45 degrees C, a K intermediate step was observed, indicating irreversible damage to the oxygen-evolving complex. This analysis can be used to rapidly screen for vitality and stress tolerance characteristics of wheat growing in the field under high temperature stress.