Abstract

In-vitro cultured microshoots of two Persian walnut cultivars differed in rooting response following induction with auxin (3 mg dm^-3 IBA). Microcuttings of the cultivar ‘Sunland’ rooted well (66%) with a mean of 2.81 roots per shoot, while ‘Howard’ microshoots rooted poorly (29%) and produced only 1.6 roots per shoot. Because no exclusive order for the progress of phenolic changes during root emerging response was seen, no exact relationship was found between phenolic contents and rooting ability of these cultivars. The activity and isoenzymatic patterns of antioxidant enzymes were estimated using spectrophotometery and native PAGE. The differing activity patterns for peroxidase and polyphenol oxidase during root development may be useful as reliable and successful markers for the physiological processes of rooting. Maximum peroxidase activity was observed on day 35 of shoot culture during the initiation phase of rooting, and was correlated with the rooting ability of genotypes. ‘Sunland’, the most easily rooted cultivar, exhibited a greater increase than the more difficult to root ‘Howard’ cultivar. Polyphenol oxidase activity maximized on the 28th day and then declined to a minimum on day 49 in both cultivars, but the magnitude of change in ‘Sunland’ was consistently greater throughout the root development period. These results show that peroxidase and polyphenol oxidase activities are involved in defining the beginning and the length of particular phases of walnut rooting.

Key words: Persian walnut, peroxidase, polyphenol oxidase, phenolic compounds, root response, in-vitro culture.