The steady state levels of sunflower transcripts, detected with heterologous probes to either the Â9, the Al2 or the Àlb desaturase, were determined in embryos and vegetative tissues at different stages. The presence of Â15 gene transcript was limited to the leaves. Transcripts of À9 and the Â12 genes were detected in embryos between 12 and 20 DAp, and as few as traces in the other tissues examined. The accumulation of Â9 gene transcript precedes that of the À12 gene. The levels of mRNA accumulation in CANpS, a line with normal levels of oleic acid, and a high oleic acid line (Hoc) were compared after standardization of signal intensities. Âg mRNA accumulation was slightly higher in HOC than in CANpS. In contrast, Â12 mRNA accumulation wâs significantly reduced in HOC than in CANP3. The HOC mutation is correlated with a reduction in the steady state level of a putative seed-specific ^12 gene. We also observed that the Â9 and Â12 nRNA accumulate to higher levels in developing seeds maintained at 26.C dav/22"C night than at 2O'C dayl18"C night. From a genomic library, 2 arld, 4 clones carrying homologous sequences to the a9 and the a12 desaturases, respectively, were used for amplification with primers unique to each desaturase. This allowed us to have a clear identification for each desaturase. Moreover, such an ag desaturase fragment was amplified in 12 different wild species covering most of the Helianthus genus. sequence variability revealed a mixture of two À9 sequences in all the species of He&anthus