Two synthetic brassinosteroids, 24-epibrassinolide (24-epiBR) and 2o,3a,l7P-trihydroxy-5cu-androstan-6-one (THA-BR), exhibit different effects on growth of tobacco callus tissue. When added to a culture medium containing growth-limiting amounts of auxin, 24-epiBR reduced and THA-BR increased the fresh weight yield of tissue up to 53% and 207%, respectively, after 6 weeks of cultivation. The stimulatory and inhibitory effects of the two brassinosteroids on tissue growth occurred over a broad range of concentrations without a pronounced maximum corresponding to the 'yes or no' type of response. Different effects of 24-epiBR and THA-BR on tissue growth were inversely proportional to the content of endogenous cytokinins. Maximum contents of predominant cytokinins N6-(A=-isopentenyl)adenine (iP) and trans-zeatin (Z) in tissues supplied with 24-epiBR in growth-inhibiting concentrations were up to 3.7 fold and 3.4 fold higher, respectively, as compared to tissues grown on media containing growth-stimulating concentrations of THA-BR. Stimulation of tissue growth by THA-BR correlated with content of endogenous IAA and an inverse correlation was found between the content of endogenous IAA and cytokinins in tissues supplied with 24-epiBR. THA-BR exhibited weak cytokinin-like activity in a bioassay based on stimulation of growth of lateral buds of pea while 24-epiBR was inactive. Results indicate that the qualitatively different effects of the two brassinosteroids on growth of tobacco tissue may reflect their different influence on content of endogenous cytokinin.Abbreviations: BR(s) = brassinosteroid(s); 24-epiBR = 24-epibrassinolide; THA-BR = 2a,3a,l7/3-trihydroxy-5cu-androstan-6-one; CK(s) = cytokinin(s); iP = N6-(A=-isopentenyl)adenine; [9R]iP = N6-(A=-isopentenyl)adenosine; Z = trans-zeatin, [9R]Z = ribosyl-trans-zeatin; ABA = abscisic acid; IAA = indole-3-acetic acid; NAA = naphtalene-1 -acetic acid; DEAE cellulose = diethylaminoethyl cellulose; HPLC = high performance liquid chromatography; ELISA = enzyme linked immuno-sorbent assay
Using several extraction methods including the QuEChERS approach, samples of both model and natural sediments were prepared. For the isolation of the target group of pesticides, two variants of two complementary extractions had to be used. Resulting extracts were analysed with LC/MS/MS. Selected methods furnishing the best results were validated in the terms of linearity and repeatability. Their limits of detection ranged from 0.1 to 2 ng/g, their limits of quantification from 1 to 6 ng/g and their recovery percentage varied between 46 % and 102 %.
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