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چکیده
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Quantitative and qualitative changes in total leaf soluble proteins were determined in a spring (cv. Kohdasht) and 2 winter (cvs. Sardari and Norstar) cultivars of wheat (Triticum aestivum L.) exposed to 4°C for 5 weeks. Seedlings were grown in a controlled growth room for 14 d at 20°C and then transferred to 4°C for 35 d (cold treatment), or else they were maintained continuously at 20°C (control treatment). Plants were sampled on days 2, 14, 21 and 35 of exposure to 4°C for either total leaf fresh weight or chlorophyll fluorescence (Fv/Fm) measurements. Leaf proteins were extracted and their concentration was either determined by a colorimetric method, or size-fractionated on SDSPAGE. Clear cold-induced 2-fold increases in proteins quantity occurred after 48 h in the 4°Ctreatment in the leaves of both winter wheat cultivars but such response was not detected in the spring cultivar. The electrophoretic protein patterns showed between-cultivar and betweentemperature treatment differences. Six new cold-induced polypeptides (20, 24, 67, 72, 97 and 104 kDa) were detected for a period of time at 4°C regardless of cultivar. With increasing cold exposure time, the winter cultivars tended to produce more HMW polypeptides in their leaves than the spring cultivar. The Fv/Fm ratio reduced markedly at 4°C compared to 20°C in the cultivars. A significant negative linear Fv/Fm-protein relationship was detected only in Norstar at 4°C. To examine the vernalization saturation, the 14 d-old seedlings were exposed to 4°C for either 7, 14, 24 or 35 d, followed by returning to 20°C until the flag leaf emergence. The non-vernalized seedlings were maintained continuously at 20°C. The final leaf number (FLN) decreased until days 24 and 35 in Sardari and Norstar cultivars, respectively, showing the vernalization saturation at these times. No clear changes were detected in the FLN of Kohdash cultivar, demonstrating no vernalization requirement for this cultivar.
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