INFLUENCE OF THE TRIAZOLE GROWTH RETARDANT BAS 111..W ON PHYTOHORMONELEVELS IN SENESCING INTACT PODS OF OILSEED RAPE

Foliar treatment of oilseed rape plants (Brassica napus L.ssp. napus c v. Linetta) with the growth retardant BAS 111..W at the 5th leaf stage delayed pod senescence during early maturation. Changes of immunoreac tive cytokinin- and abscisic acid (ABA)- like substances and of the et hylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and its m alonyl-conjugate (MACC) were determined in intact whole pods. When com pared with control plants, higher levels of total chlorophyll correlat ed with four-fold and three-fold increases of trans-zeatin riboside- a nd dihydrozeatin riboside-type cytokinins, respectively, in the pods o f plants treated with 0.25 mg BAS 111..W per plant. Isopentenyladenosi ne-type cytokinins and ACC and MACC contents remained virtually unchan ged, whereas ABA levels dropped considerably below those of controls ( 60% reduction). However, when analysed at late pod maturity, BAS 111.. W treatment no longer affected the total chlorophyll content, or the l evels of cytokinins, ABA, ACC and MACC. We hypothesize that the retard ant-induced changes in the hormonal status of the pods, favouring the senescence-delaying cytokinins as opposed to abscisic acid, could cont ribute to the developmental delay.