Photocontrol of phenylalanine ammonia-lyase in barley seedlings treated with pyridazinone inhibitors of chloroplast development

Seedlings imbibed for 48 hr in aqueous solutions of the pre-emergent herbicide Sandoz 6706, or its presumably active conversion product Norflurazon, grow into albino plants in white light. Neither herbicide has any effect on PAL in dark grown barley shoots. In white light, however, pretreatment with 100 μM herbicide causes an increase in barley shoot PAL of about 50% over that found in untreated plants. Barley root PAL is stimulated by 0.1 μM Sandoz 6706 but inhibited by higher concentrations. Mung bean primary leaves show dose responses similar to barley roots. The herbicides have no effect in continuous red light, yet blue light is as effective as white light in eliciting PAL responses. The results are discussed in relation to the subcellular distribution of PAL.