Further Evidence for an Elongation-Decarboxylation Mechanism in the Biosynthesis of Paraffins in Leaves

Publisher Website
Google Scholar
Abstract
In isolated tobacco [Nicotiana tabacum] leaves L-valine-U- C gave rise to labeled even-numbered isobranched fatty acids containing 16-26 C atoms and iso C29, iso C31, and iso C33 paraffins. L-Isoleucine-U-14C on the other hand produced labeled odd-numbered anteiso C17 to C27 fatty acids and anteiso C30 and C32 paraffins. Trichloroacetic acid inhibited the incorporation of isobutyrate into C20 and higher fatty acids and paraffins without affecting the synthesis of the C16 and C18 fatty acids. Thus the very long branched fatty acids are biosynthetically related to the paraffins. In Senecio odoris leaves acetate- 1-14C was incorporated into the parffins (mainly n-C3l) only in the epidermis, although acetate was readily incorporated into fatty acids in the mesophyll tissue. Similarly only the epidermal tissue incorporated acetate into fatty acids longer than C18 suggested that the epidermis is the site of synthesis of both paraffins and the very long fatty acids. In broccoli [Brassica oleracea var. italica] leaves n-C12 acid labeled with 14C in the carboxyl carbon and 3H in the methylene carbons was incorporated into C29 paraffin without the loss of 14C relative to 3H. Since n-C18 acid is known to be incorporated into the paraffin without loss of carboxyl C these results suggest that the condensation of C12 acid with C18 acid is not responsible for n-C29 parffin synthesis in this tissue. Thus all the experimental evidence thus far obtained strongly suggests that elongation of fatty acids followed by decarboxylation is the most likely pathway for paraffin biosynthesis in leaves.