Antioxidant enzyme activity and osmolyte content in winter cereal seedlings under hardening and cryostress

Activities of antioxidant enzymes and the osmolyte contents in seedlings of winter rye (Secale cereale L.), soft (Triticum aestivum L.) and durum (T. durum L.) wheat, and barley (Hordeum vulgare L.) grown at 20A degrees C (control) or after 7-day cold hardening at 2A degrees C and/or 5-hour freezing at -6A degrees C were investigated. It was found that nonhardened rye seedlings differed from those of other cereals by their ability to survival after freezing at -6A degrees C and higher activity of guaiacol peroxidase (GPO) and high content of proline. Hardening induced the increase in the frost tolerance of all cereals under study, and the resistance of rye and soft wheat was found to be significantly higher than that of durum wheat and barley. Rye and soft wheat exhibited more profound tolerance to oxidative damages as well, and it was expressed in lesser increase in the MDA content after freezing. In the course of hardening, detectable increase in the activities of GPO and catalase (CAT), as well as the contents of proline and soluble carbohydrates, was observed in seedlings of all cereals under study. In barley, the activity of superoxide dismutase (SOD) increased to the highest extent under these conditions. After freezing of both hardened and nonhardened seedlings, higher activities of all tested antioxidant enzymes were revealed in rye and soft wheat as compared to those in durum wheat and barley. In this case, hardened rye and soft wheat seedlings after freezing displayed increased content of proline. All these results lead to the conclusion that the high content of proline and activity of GPO observed in rye seedlings may determine their increased constitutive frost tolerance, whereas high tolerance of hardened soft wheat seedlings is primarily associated with accumulation of low-molecular-weight protectors, such as sugars and proline, and, to some extent, with the increased activity of antioxidant enzymes.