Detoxification of allelochemicals-The case of bezoxazolin-2(3H)-one(BOA)

Abstract

Why studying detoxification processes in allelopathy? This question seems to be important, as in the relevant literature possibly existing mechanisms of detoxification that allow plants to diminish or to escape from harmful effects caused by allelochemicals are seldom, if ever mentioned. An objection might be that allelopathic interactions themselves are not unequivocally proven under field conditions, detoxification events not all the more. Others may oppose that detoxification eliminate allelopathic interactions and one can question whether those interactions are still allelopathic ones or not. However, the idea of using allelochemicals as natural herbicides in sustainable agriculture that can replace or reduce the application of synthetic compounds must be regarded in a much more detailed way when detoxification can appear under certain circumstances and perhaps just with the most noxious weeds. It is well known that many synthetic herbicides underlay effective detoxification in numerous crops and weeds (Coleman et al. 1997; Schulz and Friebe, 1999). Why should allelochemicals be excluded from those mechanisms? Detoxification may be an explanation for the well known phenomenon of species dependent sensitivity to allelochemicals (Einhellig, 1995). The higher sensitivity of dicotyledonous species in comparison to monocots was often observed, but the molecular reasons were unclear. Different sensitivity of species were found, for instance, with juglone and benzoxazinoids, such as DIBOA (2,4-dihydroxy-2H- 3 ecochemical interactions at the end of this paper for formula of all allelochemicals and detoxification products mentioned in the text). We assume a considerable participation of detoxification processes in the resistance of species against allelochemicals and the development of those pathways might be regarded as an aspect of co-evolution. A still theoretical consequence of sensitive and resistant species can be a shift in the composition of species in given plant communities when aggressive neophytes with a high allelopathic potential invade, or, on the other hand, support of the establishment of balanced plant communities where members are also physiologically adapted to each other. It is not a new idea that beside all other factors physiological, biochemical and genetic adaptation of plants to each other may play a role in plant communities (Boas, 1935). Studying detoxification mechanisms under field conditions is at least difficult as no clear experimental concepts can be realized, e.g., several, perhaps unknown allelochemicals can be absorbed and may interact in the plant cell, involvement of microorganisms stays obscure, the plant material is not homogeneous and other imponderables have to be taken in account. Working with model systems has the advantage of working under defined conditions, e.g., controlled application of one allelochemical, use of identical developmental stages of the plant material, reduced or none contamination with soil particles etc. This allows an easier isolation of detoxification products and performance of biochemical studies. With model systems, the plasticity of plant detoxification capacities can be elucidated. Whether they will occur or what for reactions will be realized under natural conditions is another question, the potency, however, is fixed in the genomes of the species.