Expression of genes for acyl-desaturases in response to temperature changes in potato cells

The maintenance of a proper physical state and fluidity of cellular membranes is essenti al for plant growth and, ultimately, plant survival under fluctuating environmental temperatures. One of the most common adaptive mechanism to temperature stress is the change in the level of unsaturation of membrane lipids. Changes in lipid unsaturation extent is controlled by the activity of a set of desaturases , which catalyze the introduction of a double bond between two carbon of the fatty acid acyl chain. We have cIoned cDNAs and genomic clones encoding a 9 and 12-desaturases of Solanum commersonii, a cold tolerant wild potato species. Expression of both desaturase genes was down-regulated by a gradual up-ward shift of the growth temperatures (from 28 up to 37°C) of a potato celI suspension culture, but not when temperature was increased abruptly (heat shock). Upon cold-acclimation (4°C/l5 d), transcription of the 12-desaturase was increased in the cold-tolerant potato species, but not in S. tuberosum, the cultivated species that is known to be unable to cold- acclimate. This finding confirm the increase in linoleic acid (18:2) of plasma membrane prepara- tions reported for S. commersonii upon cold-acclimation. These results demonstrate that the expression of this class of genes is temperature-dependent and that the changes in gene expression observed may account at least partialIy for the variation in the level of membrane lipid unsaturation induced by changes in growth temperatures.