Effect of exogenous proline and de-acclimation treatment on cold tolerance in Brassica napus shoots cultured in vitro

Abstract

Winter rapeseed (Brassica napus L.) is one of the most important oil crop in Lithuania. Winter hardiness is a complex trait limiting cultivation of winter rapeseed in the region of temperate climate. Changes in cold tolerance in response to exogenous proline and de-acclimation treatment were monitored in vitro in winter rapeseed shoots. The experiments were performed during 2009-2010 in the laboratory of Agrobiotechnology of Aleksandras Stulginskis University. Shoots of cultivar ‘Sunday’ were acclimated at 4°C for 14 days and subjected to de-acclimation under temperatures of 18/16ŗC, photoperiod 16/8 h (day/night) for 1, 3, 5 and 7 days. The membrane injury for leaf discs under freezing stress (at -10°C for 24 h) was estimated by the electrolyte leakage test. Exposure of cold-acclimated shoots to normal growth temperature (18/16ŗC) significantly reduced cold tolerance as well as soluble sugars and proline contents. The degree of cold tolerance of the shoots was substantially decreased with increasing de- acclimation duration. Exogenous proline caused significant increase endogenous proline content in winter rapeseed shoots. The addition of exogenous proline to culture medium resulted in significant increase in rapeseed shoots cold tolerance. On the medium supplemented with exogenous proline after 7 days of de-acclimation electrolyte leakage of proline-treated shoots was 4.2-17.88% lower in comparison with non-treated shoots.