Response of brassinosteroid-treated oilseed rape cotyledons to infection with the wild type and HR-mutant of Pseudomonas syringae or with P. fluorescence

The aim of the study has been to determine the protection effect of brassinosteroid (BR27) in oilseed rape cotyledons against infection by an incompatible wild type of, a hypersensitive response mutant of and saprophytic Pseudomonas 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.): 'Licosmos' and 'Huzar'. Pre-treatment of cotyledons with BR27 caused about 50-70% increase in ion leakage for both cultivars. However, BR27 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. BR27 pre-treated cotyledons infected with Ps had higher heat flow in comparison to Ps infected ones. BR27 treatment did not change specific enthalpy of cotyledon growth (Delta gh) for both cultivars if compared with absolute control. However, infection with Ps markedly increased Delta gh values by about 200% for both cultivars. We suggested protective action of BR27 in oilseed rape cotyledons after bacterial infection with Pseudomonas.