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Recent studies have demonstrated that exogenous polyamines have protective effects under various stress condition. A broader understanding of the role of the polyamine pool fine regulation and the alterations of polyamine‐related physiological processes could be obtained by comparing the stress effects in different genotypes. In this study, the impact of pre‐treatment with putrescine in response to osmotic stress was investigated in the drought‐tolerant Katya and drought‐sensitive Zora wheat (Triticum aestivum) cultivars. Photosynthetic performance, in vivo thermoluminescence emission from leaves, leaf temperature, polyamine and salicylic acid levels, contents of osmoprotectants, and activities of antioxidant enzymes in the leaves were investigated not only to reveal differences in the physiological processes associated to drought tolerance, but to highlight the modulating strategies of polyamine metabolism between a drought‐tolerant and a drought‐sensitive wheat genotype. Results showed that the tolerance of Katya under osmotic stress conditions was characterized by higher photosynthetic ability, stable charge separation across the thylakoid membrane in photosystem II, higher proline accumulation and antioxidant activity. Thermoluminescence also revealed differences between the two varieties − a downshift of the B band and an increase of the afterglow band under osmotic stress in Zora, providing original complementary information to leaf photosynthesis. Katya variety exhibited higher constitutive levels of the signaling molecules putrescine and salicylic acid compared to the sensitive Zora. However, responses to exogenous putrescine were more advantageous for the sensitive variety under PEG treatment, which may be in relation with the decreased catabolism of polyamines, suggesting the increased need for polyamine under stress conditions. [ABSTRACT FROM AUTHOR]

Oxidizing agents, notably hydrogen peroxide (H2O2), are increasingly used in a number of applications. Their manner of action on algae was investigated in this work. Different concentrations of H2O2 and silver ions were applied to the algal cultures to follow the effect of their action in antarctic and mesophilic isolates of the green alga Chlorella vulgaris. Oxidative stress-induced physiological responses manifested by changes in the photosynthetic apparatus and antioxidant enzymes were estimated. The algae from the antarctic region appeared to be less resistant to oxidative stress than their mesophilic counterparts, concerning growth after treatment with higher concentrations of the reagent. The increased concentration (0.05%) lead to raise of activity and isoenzyme number of catalase (CAT) in both C. vulgaris strains. The isoenzyme activity of peroxidase (POX) decreased and disappeared in the antarctic isolate. At the same time the highest concentration (0.08%) provoked restoration of POX activity in the mesophylic one. Decrease in superoxide dismutase (SOD) activity was registered and this effect was more intensive in the moderate and fast mobile isoenzymes. Isoenzyme profile at 0.08% reagent concentration for the mesophylic isolate was similar with this at 0.05% for the antarctic isolate and a fourth isoenzyme appeared. [ABSTRACT FROM AUTHOR]