Cell and Tissue Journal

Abstract Aim: The first location of cold stress effect on PSII in plants and algae is not fully clear. Therefore, the effect of low temperature (8°C) on the activity of different parts of PSII were investigated in D. salina as plant model system is investigated using chlorophyll a fluorescence kinetics.
Material and methods: In this study unicellular green alga, D. salina, 200 UTEX strain was used. The Algae were cultured in the medium containing 1M of NaCl at 8°C or 25°C in triplicates. Then the parameters of Chl-a fluorescence was measured in various interval after cold stress.
Result: The results showed that at temperatures 8°C, the rate of parameters FV/Fo, φPo, ψo, φEo, φRo and PIABS in the species D.salina were decreased in comparison with the control (25°C). Whereas, the rate of parameters φDo and ABS/RC were decreased.
Conclusion: According to the results, decreasing of efficiency of water-splitting complex under low temperature stress probably has a significant effect on electron transport to the PSII electrons acceptors and creates imbalance in activity of PSII electron transport chain. The effect of cold stress on water-splitting complex, in turn, seems to decrease the rate of electron transport to Pheophytin and QA and from QA to QB, plastoquinone pool and finally reduction of end acceptor at photosystem I electron acceptor side. It could be finalized that the water-splitting complex is the first site that is affected by cold stress in PSII of D.salina cells.
 
 

Abstract Aim: Plants face many stresses in nature and have different defense mechanisms against stress. Rice is a cold sensitive plant and its product considerably decreases under cold stress. Since rice is an important crop, recognizing the tolerant cultivar and their defense mechanism against low temperature seems necessary.
Materials and Methods: In the present study anatomic and morphological features of tolerant (Onda) and sensitive (Nemat) rice varieties were studied at the germination phase under low (10, 15^°C) and room temperature (25^°C) for a period of of 8 days.
Results: Results show that dry weight, length of the hypocotyl and radicle of both Onda and Nemat cultivars under stress were decreased. The decrease was greater in the Nemat cultivar than the Onda cultivar. In addition, anatomic features of both cultivars under cold stress underwent some changes including increase of thickness of suberin layers and decrease of the amount of aeranchyma tissues.
Conclusion: Changes observed in the two varieties of rice were towards increasing resistance to low temperature stress. The Onda variety had a more suitable defense mechanism compared to the Nemat variety.