Mona Knop

Glycoside carbamates from benzoxazolin-2(3H)-one detoxification in extracts and exudates of corn roots

Zea mays was incubated with the natural phytotoxin benzoxazolin-2(3H)-one (BOA) to investigate the detoxification process. A hitherto unknown detoxification product, 1-(2-hydroxyphenylamino)-1-deoxy-beta-gentiobioside 1,2-carbamate (3), was isolated and identified. A reinvestigation of known BOA detoxification products by NMR methods led to the finding that the structure of benzoxazolin-2(3H)-one-N-beta-glucoside (1) first reported from Avena sativa has to be revised. In fact, the correct structure is that of the isomeric 1-(2-hydroxyphenylamino)-1-deoxy-beta-glucoside 1,2-carbamate 2, which is structurally related to 3. It was now shown with a synthetic mixture of 1 and 2 that 1 underwent spontaneous isomerization to form 2 in solution. Thus, N-glucosylation of BOA in the plant led finally to the carbamate 2. In contrast to BOA-6-O-glucosylation, BOA-induced N-glucosylation appears first after 6-8 h of incubation. As soon as N-glucosylation is possible, BOA-6-O-glucoside is not further accumulated, whereas the amount of glucoside carbamate increases continuously during the next 40 h. Synthesis of gentiobioside carbamate seems to be a late event in BOA detoxification. All detoxification products are released into the environment via root exudation.

Allelopathic Monoterpenes Interfere with Arabidopsis thaliana Cuticular Waxes and Enhance Transpiration

Exposure to the allelopathic monoterpenes camphor (100 mg / 10 L) and menthol (50 mg / 10 L) for 24 h enhanced transpiration of Arabidopsis thaliana fully developed rosette leaves similar to de-waxing. As ascertained by ESEM analyses the leaf surfaces were spotted with platelet like structures which seem to be partly mixed with the lipophilic epicuticular layers. The structures are supposed to contain the condensed monoterpenes, which could be identified by GC. Long term exposure (more than 48 h) to 100 mg / 50 mg killed the plants by desiccation, a 24 h exposure caused necrotic spots that became visible one to two days after the treatment. Examinations of the stomatal apertures indicated that monoterpenes induced stomatal opening followed by extreme swelling and a final break down of the protoplasts. Exposure of Arabidopsis thaliana to volatiles of Mentha piperita, Lavandula latifolia and Artemisia camphorata resulted in a dramatic increase of the stomata aperture but swelling of the protoplasts was less exhibited. In contrast to de-waxing, expression of the fatty acid condensing enzyme encoding CER6 gene and de novo synthesis of CER6 protein was not induced after 24 h of exposure to the monoterpenes. The aim of the study was to demonstrate that the lipophilic layers of the leaf surface and the stomata are primary targets of monoterpene allelopathic attack. Enhanced transpiration results from a combination of affected lipophilic wax layers and a disturbed stomata function.

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

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

How Doratomyces stemonitis copes with Benzoxazolin-2(3H)-one (BOA), its derivatives and detoxification products

Summary.Doratomyces stemonitis (Hyphomycetales, Dematiaceae) is a saprotrophic fungus belonging to the mycobiota of the cereal rhizosphere. The fungus is able to metabolize benzoxazolin-2-(3H)-one and a variety of its derivatives including higher plant detoxification products, microbial degradation products and the chemically rather stable 2-amino-(3H)-phenoxazin-3-one. D. stemonitis can use all of these compounds as sole C-sources but their utilization, especially that of microbial degradation products and 2-amino-(3H)-phenoxazin-3-one, seems to be highly energy consuming, resulting in slow mycelium growth and a change of colony morphology. Benzoxazolin-2-(3H)-one derived compounds induce the synthesis of different isoforms of a glycosylated protein with sequence homologies to the endo-1,3-β-glucanase Asp f2, an allergen from Aspergillus fumigatus and other Asp f2-like proteins e.g., from Verticillium dahliae or PRA1 antigen from Candida albicans. The induction of the protein is regarded as a stress response.