The objective of this study was to answer the question of how the deacclimation process affects frost tolerance, photosynthetic efficiency, brassinosteroid (BR) homeostasis and BRI1 expression of winter oilseed rape. A comparative study was conducted on cultivars with different agronomic and physiological traits. The deacclimation process can occur when there are periods of higher temperatures, particularly in the late autumn or winter. This interrupts the process of the acclimation (hardening) of winter crops to low temperatures, thus reducing their frost tolerance and becoming a serious problem for agriculture. The experimental model included plants that were non-acclimated, cold acclimated (at 4 °C) and deacclimated (at 16 °C/9 °C, one week). We found that deacclimation tolerance (maintaining a high frost tolerance despite warm deacclimating periods) was a cultivar-dependent trait. Some of the cultivars developed a high frost tolerance after cold acclimation and maintained it after deacclimation. However, there were also cultivars that had a high frost tolerance after cold acclimation but lost some of it after deacclimation (the cultivars that were more susceptible to deacclimation). Deacclimation reversed the changes in the photosystem efficiency that had been induced by cold acclimation, and therefore, measuring the different signals associated with photosynthetic efficiency (based on prompt and delayed chlorophyll fluorescence) of plants could be a sensitive tool for monitoring the deacclimation process (and possible changes in frost tolerance) in oilseed rape. Higher levels of BR were characteristic of the better frost-tolerant cultivars in both the cold-acclimated and deacclimated plants. The relative expression of the BRI1 transcript (encoding the BR-receptor protein) was lower after cold acclimation and remained low in the more frost-tolerant cultivars after deacclimation. The role of brassinosteroids in oilseed rape acclimation/deacclimation is briefly discussed.

• Keywords
• brassinosteroid insensitive 1, brassinosteroids, dehardening, delayed chlorophyll fluorescence, frost tolerance, homocastasterone, photosystem I, photosystem II, prompt chlorophyll fluorescence, stress tolerance,
• MeSH
• Acclimatization physiology   MeSH
• Brassica napus * genetics   MeSH
• Brassinosteroids MeSH
• Photosynthesis MeSH
• Homeostasis MeSH
• Cold Temperature MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Brassinosteroids MeSH

The objective of our study was to characterise the growth of tomato seedlings under various light spectra, but special attention has been paid to gaining a deeper insight into the details of photosynthetic light reactions. The following light combinations (generated by LEDs, constant light intensity at 300 μmol m-2 s-1) were used: blue/red light; blue/red light + far red; blue/red light + UV; white light that was supplemented with green, and white light that was supplemented with blue. Moreover, two combinations of white light for which the light intensity was changed by imitating the sunrise, sunset, and moon were also tested. The reference point was also light generated by high pressure sodium lamps (HPS). Plant growth/morphological parameters under various light conditions were only partly correlated with the photosynthetic efficiency of PSI and PSII. Illumination with blue/red as the main components had a negative effect on the functioning of PSII compared to the white light and HPS-generated light. On the other hand, the functioning of PSI was especially negatively affected under the blue/red light that was supplemented with FR. The FT-Raman studies showed that the general metabolic profile of the leaves (especially proteins and β-carotene) was similar in the plants that were grown under the HPS and under the LED-generated white light for which the light intensity changed during a day. The effect of various light conditions on the leaf hormonal balance (auxins, brassinosteroids) is also discussed.

• Keywords
• Solanum lycopersicum L., auxins, brassinosteroids, light spectral composition, photosynthesis, plant growth,
• MeSH
• Brassinosteroids metabolism   MeSH
• Chlorophyll metabolism   MeSH
• Photosynthesis * radiation effects   MeSH
• Photosystem I Protein Complex metabolism   radiation effects   MeSH
• Photosystem II Protein Complex metabolism   radiation effects   MeSH
• Indoleacetic Acids metabolism   MeSH
• Plant Leaves growth & development   metabolism   radiation effects   MeSH
• Metabolome MeSH
• Spectrum Analysis, Raman MeSH
• Plant Growth Regulators metabolism   MeSH
• Seedlings growth & development   metabolism   radiation effects   MeSH
• Solanum lycopersicum growth & development   metabolism   radiation effects   MeSH
• Light MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Brassinosteroids MeSH
• Chlorophyll MeSH
• Photosystem I Protein Complex MeSH
• Photosystem II Protein Complex MeSH
• Indoleacetic Acids MeSH
• Plant Growth Regulators MeSH