The aim of our work was to examine the suitability of chemically induced osmotic stress by polyethylene glycol (PEG) for drought stress experiments based on key physiological parameters of apple (Malus domestica Borkh.) leaves. In this context, we hypothesized that PEG-induced osmotic stress influences the plant physiology in a similar manner as physical water deficit. Both PEG and water shortage induced changes in relative water content (RWC), proline and chlorophyll contents, thickness of leaf cross sections, net photosynthesis rate, and chlorophyll fluorescence. However, there was no clear relationship between the values recorded from PEG and drought treatments. In summary, we confirm that PEG might be used to induce drought-like physiological changes, but it cannot be considered as an unconditional equivalent for natural drought, particularly in long-term studies.
The aim of our study was to identify appropriate multiparametric fluorescence ratios to evaluate the response of tomato (Solanum lycopersicum) genotypes to salinity. In this context, we hypothesized that the fluorescence indices BFRR_UV, FLAV, NBI and SFR provided by the multiparametric fluorescence technique reveal the impact of salinity on tomato leaves. For this purpose, the tomato genotypes H-2274, Harzfeuer and Rio Grande were grown in the greenhouse under standard or saline conditions. As reference measurements, we recorded the maximum photochemical efficiency of photosystem II (Fv/Fm) via pulse-amplitude-modulated (PAM) chlorophyll fluorescence (ChlF) and analyzed the concentrations of sodium (Na), potassium (K), magnesium (Mg), proline and chlorophyll (Chl). In general, "Harzfeuer" showed a more pronounced response to salinity, as revealed by the increase in Na and proline as well as the decrease in K concentration. Significant differences between the control and the salt treatment were also assessed with Fv/Fm. The ratios BFRR_UV, FLAV, SFR_G and NBI_G increased significantly in the salinity-exposed plants. These ratios, compared with Fv/Fm, also provide precise but more rapid information about the impact of salinity on tomato leaves. On this basis, we demonstrate that the multiparametric fluorescence indices provide a valuable, rapid and practical tool for the in situ monitoring of the physiological status of plants exposed to salinity.
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