Cell and Tissue Journal

Abstract Aim: The aim of this study was to investigate the effect of cold temperature and cold water stresses on chlorophyll fluorescence parameters in different rice genotypes. Material and Methods: Six rice genotypes including Koohsar, Shiroodi and Tarom Hashemi cultivars as well as PSB44, RI96 and IR752 lines were grown under hydroponic conditions. After two weeks, plants were kept as control (28 ^°C), cold temperature stress (8 ^°C) and cold water stress (8 ^°C) then chlorophyll fluorescence parameters were measured. Results: Cold temperature stress significantly reduced some of the measured parameters including variable fluorescence (Fv), maximum photochemical quantum yield of photosystem II (Fv/Fm), effective photochemical quantum yield of photosystem II [Y(II)], photochemical quenching coefficient (qP) and electron transport rate (ETR); while significantly increased quantum yield of regulated non-photochemical [Y(NPQ)], quantum yield of non-regulated non-photochemical[Y(NO)], non-photochemical quenching (NPQ) and Non-photochemical quenching coefficient (qN). Whereas cold water stress had significantly affected minimum fluorescence (Fo), maximum fluorescence (Fm), Fv and ETR. Inaddition PB44 line and Tarom Hashemi cultivar in cold temperature stress and RI752 and PB44 lines in cold water stress had the minimum change in fluorescence parameters. Conclusion: cold temperature stress was more effective than cold water stress. In cold temperature stress, PB44 and Tarom Hashemi were most tolareant genotypes while RI96, IR752 and Shiroodi were the most susceptible genotypes. In cold water condition, RI752 and PB44 were the most tolerant genotypes while IR96 and Shiroodi genotypes were the most susceptible genotypes.

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.