DIM-RED-LIGHT-INDUCED INCREASE IN POLAR AUXIN TRANSPORT IN CUCUMBER SEEDLINGS - I - DEVELOPMENT OF ALTERED CAPACITY, VELOCITY, AND RESPONSETO INHIBITORS

We have developed and characterized a system to analyze light effects on auxin transport independent of photosynthetic effects. Polar transp ort of [H-3]indole-3-acetic acid through hypocotyl segments from etiol ated cucumber (Cucumis sativus L.) seedlings was increased in seedling s grown in dim-red light (DRL) (0.5 mu mol m(-2) s(-1)) relative to se edlings grown in darkness. Both transport velocity and transport inten sity (export rate) were increased by at least a fatter of 2. Tissue fo rmed in DRL completely acquired the higher transport capacity within 5 0 h, but tissue already differentiated in darkness acquired only a par tial increase in transport capacity within 50 h of DRL, indicating a d evelopmental window for light induction of commitment to changes in au xin transport. This light-induced change probably manifests itself by alteration of function of the auxin efflux carrier, as revealed using specific transport inhibitors. Relative to dark controls, DRL-grown se edlings were differentially less sensitive to two inhibitors of polar auxin transport, N-(naphth-1-yl) phthalamic acid and 2,3,5-trrioodoben zoic acid. On the basis of these data, we propose that the auxin efflu x carrier is a key target of light regulation during photomorphogenesi s.