Abstract
Thidiazuron (TDZ) is a diphenylurea synthetic herbicide and plant growth regulator used to defoliate cotton crops and to induce regeneration of recalcitrant species in plant tissue culture. In vitro cultures of African violet thin petiole sections are an ideal model system for studies of TDZ-induced morphogenesis. TDZ induces de novo shoot organogenesis at low concentrations and somatic embryogenesis at higher concentrations of exposure. We used an untargeted metabolomics approach to identify metabolites in control and TDZ-treated tissues. Statistical analysis including metabolite clustering, pattern and pathway tools, logical algorithms, synthetic biotransformations and hormonomics identified TDZ-induced changes in metabolism. A total of 18,602 putative metabolites with extracted masses and predicted formulae were identified with 1412 features that were found only in TDZ-treated tissues and 312 that increased in response to TDZ. The monomer of TDZ was not detected intact in the tissues but putative oligomers were found in the database and we hypothesize that these may form by a Diels–Alder reaction. Accumulation oligomers in the tissue may act as a reservoir, slowly releasing the active TDZ monomer over time. Cleavage of the amide bridge released TDZ-metabolites into the tissues including organic nitrogen and sulfur containing compounds. Metabolomics data analysis generated six novel hypotheses that can be summarized as an overall increase in uptake of sugars from the culture media, increase in primary metabolism, redirection of terpene metabolism and mediation of stress metabolism via indoleamine and phenylpropanoid metabolism. Further research into the specific mechanisms hypothesized is likely to unravel the mode of action of TDZ and to provide new insights into the control of plant morphogenesis.
Highlights
Thidiazuron (TDZ; N-phenyl-N -l,2,3-thidiazol-5-ylurea) is an N,N -diphenylurea derivative that was originally developed as a cotton defoliant (SN 49537; Figure 1) [1,2]
About 2200 metabolites were common to all samples representing primary metabolites required for cell viability (Supplementary Table S3). 1412 features were identified which were present only in TDZ-treated tissues and were not present in African violet petioles grown on basal medium, 312 of these were found to increase with TDZ treatment (Supplementary Table S3)
Important features identified by Variable Importance in Projection (VIP) scores are those with the highest peak intensities
Summary
Thidiazuron (TDZ; N-phenyl-N -l,2,3-thidiazol-5-ylurea) is an N,N -diphenylurea derivative that was originally developed as a cotton defoliant (SN 49537; Figure 1) [1,2]. Products containing TDZ alone or in combination with ethephon, diuron, glyphosate or protoporphyrinogen-(IX) oxidase (PPO) inhibitors are widely used in modern agriculture. The commercial products Adios (Arysta LifeScience), FreeFall SC (NuFarm Americas Inc.) and others containing TDZ are used to induce senescence of cotton leaves allowing for the large-scale harvest of cotton. Proposed mechanisms of action include crosstalk with cytokinins [3] or increased levels of ethylene relative to auxin in leaf petioles. Synthetic Biotransformations 16 of 35 2 of 28. I‘nPaacdkdhitaimon’sto Trtihuemlpikhe’ly[1p2–re1s5e]n, acendofinTcDreZasdeimyieerldcoinnjpuegaarte(sP.(Tcaalblelrey3an) amcavss‘Hesocsouni’siasntedn‘tPwacikthhathme’sfoTrrmiuamtiopnh’o)faTnDdZ cutcruimmebresrw(CeruecuidmeinstsiafiteivdaiLn.T) [D1Z5,-1t6re].ated tissues (Supplementary Figure S5)
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