Abstract
Formation of linolenic acid in vivo from various precursors [1- 14C]-2:0, -12:0, -16: 0, -18:0, -18:1, 18:2 in the cold resistant wheat cultivar Miranovskaja 808 and cold sensitive wheat cultivar Penjamo 62 was investigated at three different temperatures (+25, +5, and −6 °C). Both cultivars converted the offered precursors to linolenic acid only very slowly. Decreasing the experimental temperature brought about an increase formation of linolenic acid, however, Miranovskaja 808 being more successful than Penjamo 62. Comparison of the specific activities of linolenic acid at the “time of equal level of tissue labeling” revealed that Miranovskaja 808 formed 2 to 10 times faster linolenic acid from various precursors upon exposure to cold than Penjamo 62. Considering the low rate of formation of linolenic acid in leaves it appears probable that even the cold resistant cultivars are unable to increase the proportion of linolenic acid in their membranes fast enough to prevent the thermotropic phase transition from liquid crystalline to solid gel state at beginning of the onset of cold. It is suggested that rapid accumulation of hitherto unknown cryoprotective substance ( s) of lipidic nature precedes the accumulation of linolenic acid upon exposure of the seedlings to chilling temperatures.
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