High-temperature induced chlorophyll fluorescence changes in barley leaves Comparison of the critical temperatures determined from fluorescence induction and from fluorescence temperature curve

Abstract

The shape of the chlorophyll fluorescence induction curve (FIC) measured using a plant efficiency analyser (PEA, Hansatech, England) is characterised by several peaks signed from the shortest time as O, J, I and P. High-temperature stressed plants show a change of the shape of FIC and also a new peak K appears between the O and J peaks. Using a well defined linear heating regime applied to barley leaves, we determined the temperature of K peak appearance (T_K) from FIC, as the heat stress parameter. We compared it with the parameter of photosystem II inactivation (T_C) which was determined from high-temperature fluorescence increase in fluorescence temperature curve (FTC). With increasing time of high-temperature incubation the value of T_C rose, which reflects acclimation process, and was accompanied with the rise of T_K parameter. A good correlation between these two parameters upon the progressive high-temperature incubation was found. Further, we compared and discussed the high-temperature induced changes of the $\text{F}{}_{\mathrm{<mtext>V</mtext>}}\text{F}{}_{\mathrm{<mtext>P</mtext>}}$ ratio determined from FIC and $\text{M1}\text{F(T30)}$ ratio determined from FTC. A good correlation between these parameters was found too. The relationship between the four parameters is an evidence that both FTCs and FICs can be used for evaluation of changes in thylakoid membrane caused by high temperature stress.