The effect of phenylurea with reported cytokinin-like activities on seed germination, seedling growth, activities of antioxidant enzymes, polyphenol, peroxidase, indoleacetic acid oxidase, and total phenolic compounds, flavonoids was investigated in stressed barley seedlings. The application of phenylurea decreases the activity of peroxidase, indoleacetic acid oxidase and increases the activity of polyphenol oxidase with decrease in total phenolic compounds and flavonoids and consequent increase in growth rate. Saline (NaCl) stress in barley seedlings causes an increase in total phenolic compounds, flavonoids and enhancement of peroxidase and indoleacetic acid oxidase activities and consequent decrease in growth rate. The adverse effect of salt stress on germination, antioxidant enzymes, phenolic compounds, flavonoids can partially be rectified by phenylurea.Keywords: barley; phenylurea; salt stress; antioxidant enzymes; polyphenol oxidase; peroxidase; indoleacetic acid oxidase; phenolic compounds; flavonoids Environmental stresses are thought to result in the production of active oxygen in plant species, causing oxidative stress (Smirnoff 1993, Gossett et al. 1994, Hernandez et al. 1999). The ability of higher plants to scavenge the toxic active oxygen seems to be a very important determinant of their tolerance to environmental stress. The primary compounds of components of this antioxidant system include carotenoids, flavonoids, phenolic compounds as well as antioxidant enzymes such as catalase, peroxidase, polyphenol oxidase and indoleacetic acid oxidase.Phenolic compounds and flavonoids are among the most influential and widely distributed secondary products in the plant kingdom. Many of them play important physiological and ecological roles, being involved in resistance to different types of stress (Delalonde et al. 1996, Rice et al. 1998, Ayaz et al. 2000.Salinity stress can reduce cytokinin export from the root to the shoot in many plants (Rao and Rao 1985, Kuiper et al. 1988, 1990). An adequate cytokinin supply is essential for normal plant development; it can explain why exogenous applications of cytokinin can overcome the effect of salinity stress on the growth of wheat seedlings (Naqui et al. 1982, Roth 1987.In our study we used phenylurea because we believed that phenylurea application is likely to be a commercially viable way of reducing the effects of salinity stress compared with other synthetic cytokinins or kinetin. It is water soluble but it is little known about the response of phenylurea metabolism during stress. Therefore, the present study was undertaken to examine the effect of different levels of phenylurea on germination, seedling growth, phenolic compounds, flavonoids and antioxidant enzymes in barley grown under salinity stress.
MATERIAL AND METHODSThe plant material was Hordeum vulgare L. (Giza 123 variety), an important crop grown in Egypt. Seeds were kindly supplied by the Egyptian Ministry of Agriculture. Selected seeds of uniform size were sterilised with 0.1% mercuric chl...
