PHOTOINDUCED EFFECTS OF POLYCYCLIC AROMATIC-HYDROCARBONS ON BRASSICA-NAPUS (CANOLA) DURING GERMINATION AND EARLY SEEDLING DEVELOPMENT

It has recently been demonstrated that light dramatically enhances the toxicity of polycyclic aromatic hydrocarbons (PAHs) to the duckweed L emna gibba L,. G-3 (L. Ren, X.-D. Huang, B. J. McConkey, D. G. Dixon, and B. M. Greenberg, 1994, Ecotoxicol. Environ. Saf. 28, 160-171). To extend this research to terrestrial plants, Brassica napus L. (oil see d rape) seeds were germinated in the presence of three PAHs; anthracen e (ANT), benzo[a]pyrene (BAP), and fluoranthene. The chemicals were ap plied both in intact form and following photomodification in UV-B radi ation; toxicity was assessed in simulated solar radiation (SSR), a lig ht source with a visible light:UV-A:UV-B ratio similar to that of sunl ight. Germination efficiency, root and shoot growth, and chlorophyll c ontent, measured after 6 days of exposure, were used as toxicity endpo ints. Intact and photomodified PAHs had little impact on shoot fresh w eight or chlorophyll content, but markedly inhibited root fresh weight , with the photomodified PAHs having greater impacts than the intact P AHs. The decline in root fresh weight was not attributable to a declin e in germination frequency or delayed germination. However, the seedli ngs produced shorter roots in the presence of either intact or photomo dified PAHs. To explore the role of actinic radiation on PAH toxicity, seedlings were incubated in SSR, visible light and darkness with eith er intact or photomodified PAHs. Inhibition of root growth was only ac hieved by the intact chemicals if actinic radiation was present. Howev er, with photomodified ANT or photomodified BAP, root fresh weight acc umulation was inhibited in SSR, visible light and darkness. Thus, inta ct PAHs are hazardous to terrestrial plants in the presence of light, but once the compounds are photomodified, actinic radiation is no long er an absolute requirement for phytotoxic activity. (C) 1996 Academic Press, Inc.