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Freezing tolerance is essential for perennial plants and ability to adapt to extreme temperature is crucial for their survival in many environments. Freezing tolerance of hardened and unhardened plants of Dactylis glomerata and Lolium perenne varieties was probed by their quantum photosynthetic efficiency using the chlorophyll fluorescence technique. Quantum yield of photosystem II (PSII) electron transport (Φ PSII ), maximal (F m ') and steady-state (F s ) chlorophyll fluorescence yields of light-adapted samples were measured. Φ PSII depended on developmental phase, temperature and hardening process. A clear decline in PSII activity, especially after -10°C application was observed. Plant hardening during emergence phase had a positive impact on PSII activity, especially after -5°C application. After 72 h of -5°C temperature treatment, hardened plants showed quicker recovery of their photosynthetic apparatus (0.527-0.697) as compared to unhardened ones (0.224-0.330). Stress temperature of -10°C caused irreversible changes of photosynthetic apparatus of hardened and unhardened plants independently of growth phases (0.003-0.014). Φ PSII and F m ' parameters were strongly correlated with shoots survival under stress. Our results suggest that perennial plants' hardening allows them to survive low temperatures due inter alia enhancing their photosynthetic machinery performance.

Plant dehydrin proteins (DHNs) are known to be important for environmental stress tolerance and are involved in various developmental processes. Two full-length cDNAs JcDHN-1 and JcDHN-2 encoding two dehydrins from Jatropha curcas seeds were identified and characterized. JcDHN-1 is 764 bp long and contains an open reading frame of 528 bp. The deduced JcDHN-1 protein has 175 a.a. residues that form a 19.3-kDa polypeptide with a predicted isoelectric point (pI) of 6.41. JcDHN-2 is 855 bp long and contains an open reading frame of 441 bp. The deduced JcDHN-2 protein has 156 a.a. residues that form a 17.1-kDa polypeptide with a predicted pI of 7.09. JcDHN-1 is classified as type Y₃SK₂ and JcDHN-2 is classified as type Y₂SK₂ according to the YSK shorthand for structural classification of dehydrins. Homology analysis indicates that both JcDHN-1 and JcDHN-2 share identity with DHNs of other plants. Analysis of the conserved domain revealed that JcDHN-2 has glycoside hydrolase GH20 super-family activity. Quantitative real time PCR analysis for JcDHN-1 and JcDHN-2 expression during seed development showed increasing gene expression of both their transcript levels along with the natural dehydration process during seed development. A sharp increase in JcDHN-2 transcript level occurred in response to water content dropping from 42% in mature seeds to 12% in dry seeds. These results indicate that both JcDHNs have the potential to play a role in cell protection during dehydration occurring naturally during jatropha orthodox seed development.

Abstract:Effective microorganisms impact on photosynthetic activity of Arabidopsis plant grown under salinity stress conditions. Salinity is one of the main abiotic stressors which affects plant growth through various physiological processes such as photosynthesis. The aim of this work is to study the impact of salinity stress on Arabidopsis plants by evaluating plant growth rate and photosynthetic activity, while investigating the influence of effective microorganisms (EMs) with the objective to determine if EMs could alleviate the induced stress affiliated with salinity. Results showed that salinity negatively affects photosynthesis efficiency in Arabidopsis plants based on the data obtained from the measured chlorophyll fluorescence parameters. Additionally, application of EMs enhanced plant tolerance to counteract the induced stress. Effective microorganisms concentration of 10 mL/L suggested to bring about the best results. This work advocates, that quantum efficiency of photosystem II (PSII) is a reliable indicator for tolerance in Arabidopsis plants to salinity stress, the impact of which may be softened by the EMs.

The optimization of cultivation process and improving the yield of perspective energy crops in Europe could be one of the ways to overcome the problem of limited amount of conventional fuel. The aim of this work was to check if the use of JIP-test, as a noninvasive method for early detection of the changes in photosynthetic apparatus, can be applied to detect nutrients deficiency in miscanthus (Miscanthus × gigantheus Anderss.) plants. The experiment was performed in fully randomized design with the following experimental variants: CaNPK (full fertilization, control), NPK (without calcium), CaKN (phosphorus poor), CaPK (nitrogen poor), CaPN (potassium poor), and Ca (without NPK). Our results revealed that the reaction of photosynthetic apparatus of miscanthus plants grown under certain macronutrient deficiency was associated with exclusive significant modifications in the measured chlorophyll fluorescence signals, analysed further by JIP-test. Analysis of chlorophyll fluorescence induction curves discovered substantial deficiency of phosphorus and potassium ahead of the standard chemical method.