Immunohistochemical localization of IAA and ABP1 in strawberry shoot apexes during floral induction

Abstract

By using an anti-indole-acetic acid (anti-IAA) monoclonal antibody and an anti-auxin-binding protein 1 (anti-ABP1) polyclonal antibody, IAA and ABP1 were immunohistochemically localized in strawberry (Fragaria ananassa Duch.) shoot apexes during floral induction. The spatial distribution patterns of endogenous IAA and ABP1 and their dynamic changes during floral induction were investigated. In addition, the affect of 1-N-naphthylphtalamic acid (NPA) on IAA distribution during floral induction was also analyzed. The results showed that IAA was present in the shoot apexes throughout the floral induction process, gradually concentrating in the shoot apical meristem (SAM). The distribution of ABP1 and its dynamic changes were similar to those of IAA. In addition, the ABP1 immune signal in SAM gradually increased as floral induction developed. On a morphological level, these results indicate both the spatial distribution and dynamic changes in endogenous IAA and ABP1 during the floral induction process. The close correlation found between IAA and ABP1 indicates that a cooperation occurs during the regulation of floral induction. The results also suggest that IAA was the significant agent for floral induction, and that SAM might be the place of the main action. Treatment with NPA during floral induction prevented the accumulation of IAA in the SAM, delayed the process of floral differentiation and induced an abnormal flower development. It is likely that IAA in the shoot apex is produced in young leaves and transported through the vascular tissues to the SAM and other places of function. Finally, an appropriate amount of IAA in the SAM and normal polar auxin transport are essential for floral induction and differentiation in strawberries.