5. DISTRIBUTION OF PHOSPHOLIPIDS
255
amount, and quite possibly the composition, varies with the source, time
of harvest, and other factors. Accordingly, the establishment of species
differences presents a formidable problem. In general, however, those
seeds that have a high oil content also have a high phospholipid concentration. Soybean, cottonseed, and peanuts all have from 2 to 3.5%
phosphoHpids whereas the seeds of those plants that are generally not
used as a commercial source of oil (excluding the legumes) have less
than Yfc. Wittcoff (133) gives further information on the phospholipid
content of seeds.
There is no information on the distribution of all the different phosphoHpids of a given seed or indeed of the exact nature of all the seed
phosphoHpids. Early workers differentiated the phosphoHpids only on
the basis of cephalin and lecithin fractions. Choline and ethanolamine
are widely distributed, and phosphatidylcholine and phosphatidylethanolamine have been isolated from soybean (134, 135). Although serine
has been found in the phosphoHpids of peanuts (136), wheat and rye
germs (137), and soybeans (138), phosphatidylserine has not been isolated. There is some evidence that serine may be present as part of a
complex phosphoinositide (136). Phosphatidylinositol has been isolated
from peas (139), soybeans (30, 140), and wheat germ (141). It is also
apparent that a lysophosphatidylinositol is present in soybeans (32).
The presence of more complex phosphoinositides in maize and soybeans
is indicated by the work of Carter et al. (10) and in peanuts by Malkin
and Poole (142). The structure of the compound isolated by Carter et
al. has already been given in Fig. 4. This lipid probably accounts for
the galactose, mannose, and arabinose reported in the inositides of corn
and soybean by Scholfield et al. (143). The structure of the inositide
isolated from peanuts by Malkin and Poole is not fully defined; however,
it is probably a N-glycosyl derivative of the ethanolamine ester of
phosphatidylinositol phosphate. The glycosyl unit contains L-arabinose
and D-galactose in a molar ratio of 2:1. Phosphatidic acid, which has
been reported to occur in wheat germ (144) and soybeans (138) may
be produced by enzymatic hydrolysis during isolation.
The evidence of Lovern (145) for the occurrence of plasmalogen in
seed phosphatides has been further substantiated by the reported identification of choline, ethanolamine, and inositol plasmalogens in peas
(13).
B. VEGETATIVE TISSUES
The enzymatic degradation of plant phosphoHpids to phosphatidic
acid during isolation has been established by Hanahan and Chaikoff
(146, 147). Their data on phosphoHpids isolated from carrot roots and
255
amount, and quite possibly the composition, varies with the source, time
of harvest, and other factors. Accordingly, the establishment of species
differences presents a formidable problem. In general, however, those
seeds that have a high oil content also have a high phospholipid concentration. Soybean, cottonseed, and peanuts all have from 2 to 3.5%
phosphoHpids whereas the seeds of those plants that are generally not
used as a commercial source of oil (excluding the legumes) have less
than Yfc. Wittcoff (133) gives further information on the phospholipid
content of seeds.
There is no information on the distribution of all the different phosphoHpids of a given seed or indeed of the exact nature of all the seed
phosphoHpids. Early workers differentiated the phosphoHpids only on
the basis of cephalin and lecithin fractions. Choline and ethanolamine
are widely distributed, and phosphatidylcholine and phosphatidylethanolamine have been isolated from soybean (134, 135). Although serine
has been found in the phosphoHpids of peanuts (136), wheat and rye
germs (137), and soybeans (138), phosphatidylserine has not been isolated. There is some evidence that serine may be present as part of a
complex phosphoinositide (136). Phosphatidylinositol has been isolated
from peas (139), soybeans (30, 140), and wheat germ (141). It is also
apparent that a lysophosphatidylinositol is present in soybeans (32).
The presence of more complex phosphoinositides in maize and soybeans
is indicated by the work of Carter et al. (10) and in peanuts by Malkin
and Poole (142). The structure of the compound isolated by Carter et
al. has already been given in Fig. 4. This lipid probably accounts for
the galactose, mannose, and arabinose reported in the inositides of corn
and soybean by Scholfield et al. (143). The structure of the inositide
isolated from peanuts by Malkin and Poole is not fully defined; however,
it is probably a N-glycosyl derivative of the ethanolamine ester of
phosphatidylinositol phosphate. The glycosyl unit contains L-arabinose
and D-galactose in a molar ratio of 2:1. Phosphatidic acid, which has
been reported to occur in wheat germ (144) and soybeans (138) may
be produced by enzymatic hydrolysis during isolation.
The evidence of Lovern (145) for the occurrence of plasmalogen in
seed phosphatides has been further substantiated by the reported identification of choline, ethanolamine, and inositol plasmalogens in peas
(13).
B. VEGETATIVE TISSUES
The enzymatic degradation of plant phosphoHpids to phosphatidic
acid during isolation has been established by Hanahan and Chaikoff
(146, 147). Their data on phosphoHpids isolated from carrot roots and