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Effects of putrescine (Put) and high temperature (HT) on the responses of wheat (Triticum aestivum L.) seedlings or developing grains were studied in six wheat cultivars (PBW 343, C 273, C 306, PBW 550, PBW 621 and HD 2967) raised in the laboratory (25°C or 32°C) in Petri dishes for seven days or in the field under normal (November) and late (December) planting conditions. High temperature significantly reduced root/shoot lengths and dry weights of all the six cultivars, whereas Put ameliorated this effect by increasing these attributes. C 306 and C 273 showed higher root/shoot lengths and dry weights over PBW 550, PBW 621. High temperature significantly increased the activities of ascorbate peroxidase, guaiacol peroxidase, superoxide dismutase and catalase in correspondence with an increase in membrane injury index (MII) and thiobarbituric acid reactive substances (TBARs) and H2O2 contents. Application of Put under HT further elevated activities of these enzymes whereas MII and contents of TBARs, H2O2 were reduced. In fact, Put treated seedlings performed better in terms of antioxidant response under HT than seedlings in absence. Various morpho-physiological parameters like plant height, peduncle length, 1000 grain weight and the number of grains per year were decreased in the late sown crop. However, Put application under HT stress increased these parameters. Overall, it appears that upregulation of the antioxidant system by Put in wheat cultivars contributes to the better protection and membrane integrity in the root, shoot and grains against HT through reduced MII and TBARs contents. [ABSTRACT FROM AUTHOR]