Water Shortage-Caused Changes in Endogenous Brassinosteroid Contents in Maize Leaves Depend on the Brassinosteroid Type and Occur Already at the Beginning of the Stress Period

Abstract Brassinosteroids (BRs) have been shown to play an important role in plant response to drought. Our goal was to determine whether the profile of various endogenous BRs changes already during the first indistinctive signs of drought stress, and whether these changes remain the same with the continuation of drought period. Such quantification of individual BRs representing all three main structural groups (C 28 -, C 27 - and C 29 -BRs), together with some of their immediate precursors has not been performed before. We examined BR contents in leaves of young maize plants exposed to very mild water shortage (70% soil field capacity) and more pronounced water shortage (30% soil field capacity). The results indicated that endogenous BR levels change with time, with various BR types behaving differently. Dynamic changes in the levels of individual BRs and their biosynthetic precursors were induced already by very mild stress and depended on the specific BR type/biosynthetic pathway. This could indicate that even at the very beginning of water shortage, plants intensify BR biosynthesis using various pathways (contents of 6-deoxo BRs from the C 28 group increased by 20–80% compared to control, contents of a C 27 -group representative increased by 70% and contents of some C 29 -BRs increased by 40%). This could enable plants to prepare for necessity to increase amounts of most biologically active BRs during potential drought continuation.