Insight into Hormonal Homeostasis and the Accumulation of Selected Heat Shock Proteins in Cold Acclimated and Deacclimated Winter Oilseed Rape (Brassica napus L.)

The aim of the current work was to characterize disturbances in the hormonal balance and changes in the accumulation of the protective heat shock proteins (HSP) as a result of deacclimation in a few cultivars of oilseed rape. Samples for both analyses were collected from plants that had not been acclimated (before cold acclimation-control), cold acclimated (at 4 degrees C d/n, three weeks) and then deacclimated at 16/9 degrees C d/n (one week). The tested hormones included abscisic acid, jasmonic acid, salicylic acid, gibberellins, auxins and cytokinins (including their precursors, intermediates and conjugates). Unambiguous results were obtained for a stress hormone, abscisic acid, whose concentration increased in the leaves of all of the tested cultivars during cold acclimation while it strongly decreased during deacclimation. Deacclimation resulted also in an elevated level of the typical growth hormones. As a result of cold acclimation, the accumulation of protective proteins such as cytoplasmic HSP70 and HSP90 increased in three of the four tested cultivars. The HSP content most often decreased in the deacclimated plants compared to the cold-acclimated plants. The hormonal and protein changes are discussed relative to the frost tolerance changes of the tested cultivar.