Response of brassinosteroid-treated oilseed rape cotyledons to infection with the wild type and HR-mutant of Pseudomonas syringae or with P. fluorescence Andrzej Skoczowski • Anna Janeczko • Ga ´bor Gullner • Istva ´n To ´bias • Andrzej Kornas • Bala ´zs Barna ISBC XVI Conference Special Issue Ó Akade ´miai Kiado ´, Budapest, Hungary 2010 Abstract The aim of the study has been to determine the protection effect of brassinosteroid (BR 27 ) in oilseed rape cotyledons against infection by an incompatible wild type of, a hypersensitive response mutant of and saprophytic Pseu- domonas bacteria. In this paper, membrane permeability, PSII efficiency and metabolic activity were analysed. The following strains of Pseudomonans were used: P. syringae pv. syringae (Ps), P. syringae pv. syringae hrcC mutant (Pm) and P. fluorescence (Pf). The study was carried out using two cultivars of spring oilseed rape (Brassica napus L.): ‘Li- cosmos’ and ‘Huzar’. Pre-treatment of cotyledons with BR 27 caused about 50–70% increase in ion leakage for both cul- tivars. However, BR 27 significantly decreased ion leakage from cotyledons inoculated with Ps in both cultivars. Infection with Ps and Pf caused disturbances of energy flow in PSII by lowering its efficiency in rape cotyledons. We noted insignificant impact of 24-epibrassinolide on PSII efficiency if compared to absolute control, but generally it had a positive effect in plants infected with bacteria. The values of heat flow in all treatments, except for cotyledons infected with Ps, decreased during 20 h after inoculation. However, the curves of heat flow for Ps-infected cotyledons showed a completely different pattern with at least two peaks. BR 27 pre-treated cotyledons infected with Ps had higher heat flow in comparison to Ps infected ones. BR 27 treatment did not change specific enthalpy of cotyledon growth (Dgh) for both cultivars if compared with absolute control. However, infection with Ps markedly increased Dgh values by about 200% for both cultivars. We suggested protective action of BR 27 in oilseed rape cotyledons after bacterial infection with Pseudomonas. Keywords Brassica napus Á 24-Epibrassinolide Á Isothermal calorimetry Á Membrane permeability Á Pathogenesis Á PSII efficiency Abbreviations AC Absolute control ABS Energy absorption BRs Brassinosteroids BR 27 24-Epibrassinolide cfu Colony forming unit DIo Energy dissipation ETo Energy flux for electron transport F v /F m Maximum quantum yield of PSII HR Hypersensitive response Ps Pseudomonas syringae pv. syringae Pm Pseudomonas syringae pv. syringae hrcC mutant Pf Pseudomonas fluorescence RCs PSII reaction centres TRo Energy flux for trapping Dgh Specific enthalpy of growth Introduction The discovery of a new naturally occurring plant growth regulator, a polyhydroxylated steroid lactone with high A. Skoczowski (&) Á A. Janeczko Franciszek Go ´ rski Institute of Plant Physiology, Polish Academy of Sciences, ul. Niezapominajek 21, 30-239 Krakow, Poland e-mail: amskoczowski@gmail.com G. Gullner Á I. To ´bias Á B. Barna Plant Protection Institute, Hungarian Academy of Sciences, Herman Otto u ´t 15, 1525 Budapest, Hungary A. Skoczowski Á A. Kornas Institute of Biology, Pedagogical University, ul. Podbrzezie 3, 31-054 Krakow, Poland 123 J Therm Anal Calorim DOI 10.1007/s10973-010-1204-z