Oxidation of paraffins by plant tissues.

Paraffins are fotund in almost every organism, plants (2), animals (13), and microorganismiis (14). The most common biological source of paraffins appears to be the surface lipids of plants (2), the chain length of the most abulndant paraffin being most often C., or C.:. These natural paraffins cant be readily catabolized by soil organisms (5) and to a limited extent bv an,inlals (6). The mechaniislm of paraffin oxidation was elucidated with bacteria ('12) aand with enzvmes isolated from themii (4, 15, 16). Young leaves of maniy plants readily synthesize paraffins from fatty acids (8). Experiments on the time course of incorporation of labeled substrates into paraffins of Brassica oleracea failed to show ,any turnover, possibly becautse the paraffins are ejected onto the surface of the leaves as soon as thev are synthesized (7). Attempts to show catabolicnm by providing C., paraffin to excised leaves, leaf tissue slices, or leaf honmogenates failed. The extremelv low solubilitv of these very long paraffins. andl the resulting lack of uptake made it almost impossible to find out whetlher plants poFsess the capacity to oxidize their natural paraffinis. In order to circunmvent these problems a muchl smaller paraffin, hexadecane-1-14C, was used as substrate. This communicationi describes experimental results wvhich slhow that lplants do possess the ability to oxidize the terminal methyl carbon of this paraffini to a carboxVl group. Hexadecane-1-_4C (47.2 mlc/mmole, Nuclear-Clhicago) contained polar impuirities and was therefore purified by column chromatography oni activated SilicAR cc-4 100 to 200 meslh (MIallinckrodt Chemical Works. St. Louis, Missouri ) Nvith hexane as the solvent (9). The purified heixadecane-1-'4C contained no radiochellmical iml)uritv as determined by thinl-layer clhromlatograp)hy. A sample of this labeled l)araffin ( 50 /sc) was dissolved in 4 to 5 mil ethyl ether and 3 (drol)s of Tween-20 were added. The etlier was eval)orated wvithi a streamn of nitrogen, and the residcue slhakell with 10 nil of water to give a stablc emulsion of the paraffin. Yooung leaves of broccoli, pea and tobacco, second from the apex and not fully expanded. were sliced (2 X 10 mm) witlh a razor blade. These slices when incubated with the purified lhexadecane, p)roduced radioactive lipids more polar than paraffin as sllon in table I. Althouglh Table I. Oxidationi of IJc.adecaitc-1-14C by, Leaf Sliccs of Broccoli, Pea, anzd Tobacco In experiment 1, 1 g of leaf slices was incubated with 2 X 106 cpm hexadecane-1-14C for 4 hr at 300 in 3 ml water. In experiment 2, 3 g of pea hypacotyl slices were incubated with 4 X 106 cpm hexadecanie-1-14C for the periods indicated at 300 in 3 ml water. At the end of the incubationl period, tissue slices were ground in a 2:1 nmixture of chloroform and methanlol, anid the total lipids extracted as described before (9). Aliquots of the total lipids were chromatographed on silica gel G plates with hexane as the developing solvent in an unlined tank. Only paraffins migrated with the solvent front. The oxidationi products such as fatty alcohols, acids and phospholipids remainied at the origin. The radioactivity in this fraction is shown in the table.