MODIFICATION OF PHYTOSTEROL PROFILES AND IN-VITRO PHOTOSYNTHETIC ELECTRON-TRANSPORT OF GALIUM-APARINE L. (CLEAVERS) TREATED WITH THE FUNGICIDE, EPOXICONAZOLE

Foliar application of the triazole fungicide, epoxiconazole, retarded the growth of Galium aparine L. (cleavers). GC-MS and GC analysis clea rly indicated that phytosterol biosynthesis in stem and leaflet tissue was significantly affected by this treatment. For example, in leaflet tissues, 125 g al ha(-1) (field rate) caused reductions in campestero l and sitosterol of 81% and 75% respectively. C14-methyl phytosterols such as 14 alpha-methylergost-8-enol, obtusifoliol and dihydroobtusifo liol were detected in treated tissues indicating that epoxiconazole in hibits the cytochrome P-450 dependent obtusifoliol 14 alpha-demethylas e. In addition, ratios of campesterol to sitosterol were reduced. Stig masterol was not detected in control or treated tissues. Preliminary d etermination of photosynthetic characteristics of isolated thylakoids from treated plants indicated that electron transport and oxygen evolu tion were impaired by epoxiconazole and these effects were dose-relate d. Ten days after treatment, oxygen evolution from thylakoids (determi ned as electron flow from water to ferricyanide) isolated from control plants was 24.2 mu mol mg(-1) chl h(-1), whilst treatment with 125 g and 250 g ai ha(-1) reduced this rate to 15.2 mu mol and 8.2 mu mol mg (-1) chl h(-1), an inhibition of 37 and 67% respectively. These result s suggest that epoxiconazole influences thylakoid integrity and functi on in addition to phytosterol biosynthesis in G. aparine.