Changes in proline and soluble sugars content during cold acclimation of winter rapeseed shoots in vitro

Low temperature is a major environmental stress for many crops worldwide. One of the most important agronomic traits in winter rapeseed (Brassica napus L.) is winter-hardiness or freezing tolerance, which can be enhanced by cold acclimation. Investigations were carried out in the laboratory of Agrobiotechnology of Lithuanian University of Agriculture. Changes in proline and soluble sugars levels in response to cold acclimation were monitored in vitro in winter rapeseed shoots. Shoots of varieties 'Insider', 'Siska', 'Valesca', 'Sunday' were acclimated at 4 degrees C for 7, 14, 21 and 28 days. The membrane injury for leaf discs was estimated by the electrolyte leakage test. Cold acclimation caused significant increase in proline and soluble sugars contents. Maximum proline level was achieved by 21 days of acclimation. The correlation between frost tolerance and proline accumulation in leaves of rapeseed shoots during cold acclimation in vitro offers the possibility of a rapid screening to cold tolerance of new winter rapeseed genotypes eliminating the need for a freezing treatment. The most intensive accumulation of soluble sugars takes place during the first two weeks, prolongation of acclimation time up to 21 days increases the amount of soluble sugars only in shoots of 'Insider'. The highly significant differences on freezing tolerance were found among tested rapeseed varieties. Across freezing treatments, 'Siska' had the least cold tolerance followed by 'Insider', 'Sunday' and 'Valesca'.