Relation between phytohormone level and vascular bridge differentiation ingraft union of explanted internode autografting

Development of the graft union of explanted internode autografting of cucum ber ( Cucumis sativus Linn.) cultured in vitro is regulated by plant hormon es exogenously added to the media. The levels of auxin (indole-3-acetic aci d, IAA) and zeatin plus zeatin riboside (Z + ZR) in graft unions and in 4 p arts of the graft union have been analyzed by ELISA assay. Results show tha t vascular bundle regeneration in the graft union is co-regulated by IAA an d Z + ZR. Differentiation of vascular bridge across the graft interface req uires higher level of [AA and IAA/ (Z + ZR) ratio than that of anastomosing bundle, indicating that plant hormones are limiting and controlling factor s for the development of graft union.