Comparison of different methods to evaluate tissue damage in response to leaf dehydration in Quercus ilex L. and Q. faginea Lam.

Determination of the point of critical damage in plant organs is crucial to elucidate the causes of plant mortality, but the different methodologies to quantify such damage have not been previously compared under the same experimental conditions. Here, we tested different indicators to evaluate damage in leaves of Quercus faginea and Q. ilex; in the latter case, 1- and 2-year-old leaves were included. The damage indicators were relative electrolyte leakage (REL), rehydration capacity (evaluated as the percentage loss of rehydration capacity; PLRC), chlorophyll fluorescence (maximum quantum yield of PSII; F/F), and the viability marker triphenyltetrazolium chloride (TTC). These damage indicators were evaluated in different sets of detached leaves for each species and leaf age dehydrated on the lab bench. Electrolyte leakage and PLRC showed a gradual response to decreasing relative water content, whereas F/F and TTC showed a threshold-like response, especially in the case of Q. faginea. Electrolyte leakage and TTC did not show differences between species and/or leaf ages. Measurement of F/F in dehydrating leaves proved to be the most straightforward, rapid and precise method for damage quantification, allowing for the differentiation in dehydration tolerance between Q. ilex and Q. faginea.