Abstract: Histological characters and the modification of endogenous IAA and ABA during the rhizogenesis of walnut shoots were investigated with in vitro cultivar of Xinzaofeng (Juglans regia L. ). It was identified that the adventitious root primordia of in vitro shoot originated from the vascular cambium cells, especially, the cross areas of cambium and pith ray and they started to differentiate at the 6th dayand lasted to the 10th day. Ifthe shoots were cultured in the root inducingmedium for 12 days, led to not only descend of rooting rate, but also the damaged plantlets, showing black shoot tips, callus of stem base, and leaf senescent. However, if they were transferred into the medium without hormone in time, the root p rimordial p rotruded the epidermis and developed normally after 5 days culture. Itwas also found that when the adventitious root primordia formed and lengthened, endogenous IAA concentration reach the peak and ABA was still increasing. The rate of IAA
and ABA was maximum before the adventitious root primordium forming, after wards, it decreased. The research not only confirmed that the two step smethod is reasonable for walnut rhizogenesis; but also expounded the mechanism of the hormone regulation during the induced rooting on the physiological level.

Key words: Walnut, In vitro shoot, Hormone, Adventitious root, Histology and morphology