1. FATTY ACID OCCURRENCE AND DISTRIBUTION
23
the fat content. The increase in iodine value of the oil during ripening
was attributed to desaturation of the fatty acids.
Grindley, using cottonseed (122), was the first to describe the quantities of fatty acids and other constituents on a per seed basis. In
these seeds saturated, oleic, and linoleic acids all continue to increase
in weight during ripening. Any increase in unsaturation may thus be
interpreted as an increase in synthesis of unsaturated acids rather than
a desaturation of saturated acids. Similar results were obtained by
Simmons and Quackenbush (123), using Lincoln soybeans. No evidence for dehydrogenation of saturated fatty acids was found either in
the oil analyses or in the tests of the tissues for dehydrogenase activity.
In another experiment excised stems bearing pods and leaves supplied
with C
14 -labeled sucrose were used (124). After 2 days 56% of the total
radioactivity was present in oleic acid, which constituted about onethird of the total, while linoleic acid, which was also present in similar
amounts, contained but 18% of the total activity. Five days after withdrawal, the total activity in the oleic fraction doubled, linoleic showed
a fourfold increase, and linolenic a sevenfold. Since the relative percentages of different fatty acids had not changed, the evidence, contrary to that earlier obtained, suggested the possibility of some conversion of oleic acid to the other acids.
Climatic conditions have been found to influence the content of
more unsaturated fatty acids, as shown by Painter and Nesbitt (125) for
linseed oil. Similar observations have been made on other unsaturated
oils, notably sunflower seed oils. Using seeds taken from field trials in
diverse regions of the Australian Commonwealth, Budge and co-workers
(126) found that the oils from the Northern Territory contained 3136% linoleic acid as compared with 65% in the most southerly latitudes.
The mechanism of the formation of fatty acids in higher plants has
not been studied so extensively as in animals. However, Newcomb and
Stumpf (127) showed that slices of peanut cotyledons synthesize radioactive long-chain fatty acids from C
14 acetate. Subsequently Gribble
and Kurtz (128) made in vitro cultures of developing flax seeds with
the addition of acetate-1-C
14 . The individual fatty acids, including palmitic/stearic, oleic, linoleic, and linolenic, when degraded showed much
more radioactivity in first and third carbon atoms than in the second
and fourth. The results are thus consistent with those for animal tissues
in respect of the formation of fatty acids by "head to tail" condensation of acetate.
Further evidence of the nature of the fatty acid synthesis in higher
plants has been obtained by Stumpf and Barber (129), who found that
particles from avocado fruit mesocarp incorporate C
14 -labeled acetate
23
the fat content. The increase in iodine value of the oil during ripening
was attributed to desaturation of the fatty acids.
Grindley, using cottonseed (122), was the first to describe the quantities of fatty acids and other constituents on a per seed basis. In
these seeds saturated, oleic, and linoleic acids all continue to increase
in weight during ripening. Any increase in unsaturation may thus be
interpreted as an increase in synthesis of unsaturated acids rather than
a desaturation of saturated acids. Similar results were obtained by
Simmons and Quackenbush (123), using Lincoln soybeans. No evidence for dehydrogenation of saturated fatty acids was found either in
the oil analyses or in the tests of the tissues for dehydrogenase activity.
In another experiment excised stems bearing pods and leaves supplied
with C
14 -labeled sucrose were used (124). After 2 days 56% of the total
radioactivity was present in oleic acid, which constituted about onethird of the total, while linoleic acid, which was also present in similar
amounts, contained but 18% of the total activity. Five days after withdrawal, the total activity in the oleic fraction doubled, linoleic showed
a fourfold increase, and linolenic a sevenfold. Since the relative percentages of different fatty acids had not changed, the evidence, contrary to that earlier obtained, suggested the possibility of some conversion of oleic acid to the other acids.
Climatic conditions have been found to influence the content of
more unsaturated fatty acids, as shown by Painter and Nesbitt (125) for
linseed oil. Similar observations have been made on other unsaturated
oils, notably sunflower seed oils. Using seeds taken from field trials in
diverse regions of the Australian Commonwealth, Budge and co-workers
(126) found that the oils from the Northern Territory contained 3136% linoleic acid as compared with 65% in the most southerly latitudes.
The mechanism of the formation of fatty acids in higher plants has
not been studied so extensively as in animals. However, Newcomb and
Stumpf (127) showed that slices of peanut cotyledons synthesize radioactive long-chain fatty acids from C
14 acetate. Subsequently Gribble
and Kurtz (128) made in vitro cultures of developing flax seeds with
the addition of acetate-1-C
14 . The individual fatty acids, including palmitic/stearic, oleic, linoleic, and linolenic, when degraded showed much
more radioactivity in first and third carbon atoms than in the second
and fourth. The results are thus consistent with those for animal tissues
in respect of the formation of fatty acids by "head to tail" condensation of acetate.
Further evidence of the nature of the fatty acid synthesis in higher
plants has been obtained by Stumpf and Barber (129), who found that
particles from avocado fruit mesocarp incorporate C
14 -labeled acetate