Because of their unique tolerance to desiccation, the so-called resurrection plants can be considered as excellent models for extensive research on plant reactions to environmental stresses. The vegetative tissues of these species are able to withstand long dry periods and to recover very rapidly upon re-watering. This study follows the dynamics of key components involved in leaf tissue antioxidant systems under desiccation in the resurrection plant Haberlea rhodopensis and the related non-resurrection species Chirita eberhardtii. In H. rhodopensis these parameters were also followed during recovery after full drying. A well-defined test system was developed to characterise the different responses of the two species under drought stress. Results show that levels of H₂O₂ decreased significantly both in H. rhodopensis and C. eberhardtii, but that accumulation of malondialdehyde was much more pronounced in the desiccation-tolerant H. rhodopensis than in the non-resurrection C. eberhardtii. A putative protective role could be attributed to accumulation of total phenols in H. rhodopensis during the late stages of drying. The total glutathione concentration and GSSG/GSH ratio increased upon complete dehydration of H. rhodopensis. Our data on soluble sugars suggest that sugar ratios might be important for plant desiccation tolerance. An array of different adaptations could thus be responsible for the resurrection phenotype of H. rhodopensis.

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Radiation mutagenesis has been used in sustainable agriculture as a tool for increasing plant variability and providing new lines for selection. This necessitates a comparison, by using suitable stress markers, of the newly created lines with some well-established varieties, which are stress tolerant or susceptible. Drought is one of the most frequently encountered stresses with deleterious effects on plant performance and crop yield. Winter wheat seedlings (soil cultures at 3–4th leaf stage) from one mutant line (M181/1338K), one drought-tolerant (Guinness) and one sensitive variety (Farmer) were subjected to severe drought stress by water withholding, followed by recovery. Changes in leaf protein profiles, the amount of Rubisco large subunit (RLS), some specific chloroplast proteins such as Rubisco binding protein (RPB), Rubisco activase (RA), the chaperone subunit clpA/C of clp protease, as well as the activities of exo- and endo-proteases were analyzed. At the protein level, some differences were found in the drought response of genotypes – stability of RLS and RBP in M181/1338K and Guinness, diminution of RLS and increase in RBP in Farmer. RA presented strong up-regulation at recovery in Guinness but decreased in content under drought in M181/1338K and Farmer. Increase in ClpA/C level was found in all compared varieties under stress. Strong increase in total proteolytic activity was detected under drought only in Farmer. Inhibitory analysis revealed a predominance of cysteine and serine protease types. Aminopeptidase activities remained higher at recovery in M181/1338K and Farmer. Results are discussed in terms of genotype-linked different stress coping strategies.

The effect of the sources of nitrogen nutrition (nitrogen fixation or nitrate assimilation) and a gradual water stress on the relative water content, total fresh and dry biomass production, leaf growth, and changes in the total soluble protein spectra were studied. The plants were cultivated as soil cultures in a naturally illuminated greenhouse. Comparative studies were carried out with respect to well-watered, control plants. Nitrogen-fixing control and drought plants had relatively smaller root development but be�er relative water content and large leaf area on the last sampling day than nitrate-fed soybean plants. Water deficit effects on plant biomass at the end of the period studied (21 days) were independent on the nitrogen source. There was no qualitative difference in the total soluble protein spectra of nitratefed and nitrogen-fixing soybean leaves neither with the progress of development nor under drought conditions. But there was a difference in response to drought in termostable proteins of nitrate-fed and nitrogen-fixing plants. The quantity of termostable proteins in inoculated control plants was lower in some degree compared to uninoculated ones. In inoculated plants the water stress caused an increase in the amount of soluble termostable proteins.

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The effects of different salt concentration treatment of soybean plants and the occurrence of salinity stress have been assessed from a comparative analysis of remotely sensed groundbased spectral reflectance data and biochemical parameters. The contents of phenols, proline, malondialdehid, hydrogen peroxide, thiol groups, and chlorophyll a and b have been determined. The soybean plants were grown under controlled conditions as water cultures on Helrigel nutrient solution. Salinity was performed at the stage of 2 nd to 4 th trifoliate expanded leaves by adding of NaCl in the nutrient solution in concentrations 40 mM and 80 mM. The leaf spectral reflectance was measured in laboratory in the visible and near infrared spectral ranges using a fibre-optic multichannel spectrometer. An algorithm based on multivariate statistical analysis of the leaf reflectance spectra was developed. It includes Student's t-criterion, discriminant analysis and derivative analysis. The spectral intervals of interest were the green, red, red-edge and near infrared ranges of the spectrum. Statistically significant differences at p<0.05 were found between the leaf spectral reflectance data of control and treated plants at 80 mM NaCl in all of the ranges examined with the exception of the near infrared range. No statistically significant differences were established at 40 mM NaCl treatment. Some of the biochemical parameters (proline, malondialdehid, thiol groups) were found at salinity treatment by 40 mM NaCl to increase in value more than 10% while the chlorophyll a and b concentrations decreased more than 20%. This trend was preserved for the 80 mM NaCl treatment as the corresponding parameters changed by about 45% on average, which is symptomatic for the stressed plants.

The influence of the environmental stress factors, salinity and enhanced UV-B radiation, on young nitrogen fixing soybean plants (Glycine max L.) was investigated by using hyperspectral reflectance data. Soybean is the leading oilseed crop produced and consumed worldwide. The soybean plants were grown in a growth clamber as water cultures on Helrigel nutrient solution. Three day's seedlings were inoculated with suspension of Bradyrhizobium japonicum strain 273. Salinity was performed at growth stage of 2 nd -4 th expanded leaves by adding of NaCl in the nutrient solution in concentrations 40 mM and 80 mM. Plants were divided into six groups. The first three groups consisted of untreated (control) and treated only with two NaCl concentrations plants. The other three groups (control and salinized) on the 14 th day after the treatment were illuminated for four hours with UV-B radiation at intensity 64.4 μmol m -2 s -1 . Spectral reflectance was registered by a portable fiber-optic spectrometer in the visible and near infrared (NIR) spectral ranges (450-850 nm). Data were subjected to statistical analysis through the Student's t-criterion in four spectral ranges: green, red, red-edge and NIR (520-580 nm; 640-680 nm; 690-720 nm; 720-780 nm). The results from spectral reflectance and biochemical analysis (evaluated stress markers) revealed that both treatments (salinity and salinity + UV-B radiation) bring the plants to stress and to decline of the biological nitrogen fixation. The UV-B treatment decreases the salinity action and partly restores the physiological state of the plants.