Strigolactones in an experimental context

Strigolactones (SLs) have become intensively studied phytohormones in recent years. Their role in the regulation of various development processes and stress responses have been established. The biosynthetic and signalling pathways have been gradually described in Arabidopsis, rice, maize, tomato, pea etc. The conserved SL production and function are supported by the identified orthologs of crucial enzymes across the plant kingdom. Using phylogenetic studies orthologs were identified in moss Physcomitrella as well as poplar tree. Extremely low concentrations of endogenous SLs, together with their instability, cause problems with their detection, even if using advanced analytical methods of liquid chromatography-tandem mass spectrometry. To overcome this drawback, synthetic SL analogues were prepared and widely used. The most common is rac-GR24, a racemic mixture of two enantiomers. Recently, it was discovered that rac-GR24 stimulated not only SL but also a parallel karrikin signalling pathway. To ascertain specific SL effects, mutant plants or naturally occurring SLs need to be used. Nonetheless, there is little consensus about SL application which makes it difficult to compare the results of different studies.Moreover, many analogues are being readily synthesised each year. In this review, we aimed to describe the conserved role of MAX/D/RMS genes in SL biosynthesis and signalling with attention to their orthologs in other species. We also tried to emphasise the importance of relevant experimental conditions. It is necessary to take into consideration plant species and age, duration of exposure and SL concentration. Many observed SL effects on plant physiology were found to be concentration dependent.