Comparative analysis of the effects of homocastasterone and two derivatives on shoot and main root elongation of tomato plantlets

- The effect of 28-homocastasterone and two synthetic derivatives were evaluated on tomato plantlets.
- Enhancement in the main root elongation was found for plantlets treated with 5fluoro-homocastasterone.
- 5fluoro-homocastasterone and 5 hydroxy-homocastasterone significantly enhanced shoot elongation, though significantly less than HCS and epi-BL did.

Brassinosteroids (BRs) comprise a specific class of low-abundance plant steroids of ubiquitous occurrence in plants. Molecular genetic analysis of mutants defective in BRs biosynthesis or response has demonstrated that the ability to synthesize, perceive and respond to BRs is critical for normal plant growth. In this work, the structure-activity relationships of two synthetic derivatives of 28-homocastasterone (28-HCS) were evaluated on tomato plantlets using the native 28-HCS and epibrassinolide (epi-BL) as control. Progressive enhancement in the main root elongation was found for plantlets treated with increased doses of 5α-fluoro-28-homocastasterone (5F-HCS) within the 0.5-4 μg shoot−1 range. When compared to epi-BL, to the parental 28-HCS and to a mono 5-hydroxy HCS derivative (5OH-HCS), no difference between 5F-HCS and the other BRs, towards stimulation of main root elongation, was found when these BRs were applied at a dose of 2.0 μg per plantlet. Both, 5F-HCS and 5OH-HCS significantly enhanced shoot elongation, though significantly less than HCS and epi-BL did. Besides provinding an insight into the morphological responses of tomato plantlets to application of 28-HCS derivatives, these results also demonstrate that the 5F-HCS-induced stimulation of main root elongation might be useful to improve the plants's nutrient and especially water uptake, particularly under water deficit, besides improving anchorage.