Estimating heat tolerance of plants by ion leakage: a new method based on gradual heating

Abstract

Heat tolerance of plants related to cell membrane thermostability is commonly estimated via the measurement of ion leakage from plant segments after defined heat treatment. To compare heat tolerance of various plants, it is crucial to select suitable heating conditions. This selection is time-consuming and optimizing the conditions for all investigated plants may even be impossible. Another problem of the method is its tendency to overestimate basal heat tolerance. Here we present an improved ion leakage method, which does not suffer from these drawbacks. It is based on gradual heating of plant segments in a water bath or algal suspensions from room temperature up to 70-75°C. The electrical conductivity of the bath/suspension, which is measured continuously during heating, abruptly increases at a certain temperature T (within 55-70°C). The T value can be taken as a measure of cell membrane thermostability, representing the heat tolerance of plants/organisms. Higher T corresponds to higher heat tolerance (basal or acquired) connected to higher thermostability of the cell membrane, as evidenced by the common ion leakage method. The new method also enables determination of the thermostability of photochemical reactions in photosynthetic samples via the simultaneous measurement of Chl fluorescence.

Special issue in honour of Prof. Reto J. Strasser - Analysis of K- and L-band appearance in OJIPs in Antarctic lichens in low and high temperature

“…The other two species showed slightly higher but still low termostability. The similarly low value of TF (of about +40.5°C) reflecting a relatively low heat stability of thylakoid membranes and primary photosynthetic processes has been found for some species of higher plants including Arabidopsis thaliana (Ilík et al 2018). The measurement of conductivity changes during linear heating of the lichens did not provide convincing results.…”

“…Thermostability measurements: Thermostability of lichen thalli was measured by a PlanTherm PT 100 instrument (Photon Systems Instruments, Drásov, Czech Republic) that allows estimation of heat stability of samples. The instrument combines the measurement of ion leakage-dependent changes in electrical conductivity of heated sample with ChlF signal measurement (Ilík et al 2018). The instrument consists of four main units: thermoregulation unit, conductivity probe unit, ChlF unit, and a mini-PC.…”

“…All data sets were plotted dependent on sample temperature (CTC -conductivity temperature curve, FTC -ChlF temperature curve). Critical temperatures TCOND and TF were estimated as described by Ilík et al (2018) and interspecific differences evaluated. In graph of the FTC, the TF roughly corresponds to temperature of intercept of a horizontal line at position of ChlF at room temperature with a line through a linear part of the ChlF increase to the first maximum of FTC (see e.g., Lazár and Ilík 1997).…”

“…A comparison of fluorescence temperature curves (FTCs) of the three lichen species confirmed the lower thermostability of X. elegans indicated by the results of OJIP measurements. The critical temperature TF, which is considered as an indicator of heat stability of thylakoid membranes (Ilík et al 2018), was in X. elegans about +40.5°C, whereas TF in the other two lichens was significantly higher [of about +42.5 and +44°C for U. antarctica and D. polyphyllizum, respectively (Fig. 4B insert)].…”

“…To analyse the effects of high temperature, we combined the OJIPs measurements with thermostability measurements. For the first time in the case of lichens, we applied a newly emerging method (Ilík et al 2018) based on ion leakage technique combined with ChlF measurements during linear heating.…”