It is well established that auxins play a central role in the formation of adventitious rooting, which is essential for micropropagation. Recent studies with walnut (Juglans regia L.) have pointed to significant effects of endogenous free IAA levels on this phenomenon. In the present study, a comparative analysis of the adventitious rooting of microcuttings of two variety groups of Juglans regia L. (easy-to-root and difficult-to-root varieties) was carried out on Vermiculite-DKW medium and in this period, the endogenous IAA content and Peroxidase (POX) enzyme activity- isoenzymes that also participate in IAA catabolism- was assayed every 7 day. Parameters for determination of rooting capacity were the percent rooting, number of roots per rooted cutting and length of roots. Results showed that, as it has been determined before, the maximum concentration of endogenous auxin was required during the induction phase of rooting. Noticeable aspect in this survey was that varieties with difficulty to root- Howard and Kerman Varieties- had lower increase of endogenous IAA levels during this phase of root formation than the other varieties- Sunland and Chandler. POX enzyme showed the similar pattern of activity along rooting formation of all the varieties with the minimum level of activity observed in the induction phase and the maximum one in the initiation phase. Besides, there was a significant difference in changes of POX activity between two types of walnut varieties according to root ability. It is confirmable that there was a reverse relationship between endogenous IAA content and POX activity changes during the root development of all the samples and walnut varieties with better root capacity were clearly showed this opposite relationship.

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