Brassinosteroids, de-etiolation and the re-emerging art of plant hormone quantification.

An increase in the use of molecular techniques has provided a significant insight into the function of genes, and how they are regulated and interact. However, in the field of plant hormone physiology, the increased use of these techniques has been accompanied by a reduction in the direct measurement of plant hormone levels by physiochemical methods. Instead, the transcript (mRNA) levels of genes involved in hormone metabolism are often used to predict endogenous hormone levels. The validity of this approach was recently tested by comparing the expression of a range of genes involved in BR synthesis, catabolism and perception, with the actual endogenous BR levels in pea seedlings grown under different light conditions.1,2 Based on this comparison, we now argue that gene expression analysis alone is not always a reliable indicator of endogenous hormone levels.