Microkinetics of Lamellar Crystallization in a Long Chain Polymer

The growth kinetics of single crystal lamellae grown from poly(isoprene) melts have been determined by thin film electron microscopy which also reveals the relevant microstructure. The growth rate of a continuous lamellar crystal is independent of the length of the crystal and (in the absence of crosslinks) depends only upon temperature and the chemical composition of the polymer. The temperature dependence is closely similar to that observed for bulk crystallization and spherulite growth, with a maximum crystallization rate around —24° C. The growth rate at a given temperature is extremely sensitive to the chemical composition of the poly(isoprene), being for a polymer containing 10 per cent trans-poly(isoprene) one thousandth of that for pure cis-poly(isoprene). Between these extremes the logarithm of the growth rate decreases linearly with increasing trans content. A similar effect is produced by the introduction of chemical crosslinks instead of trans units. These effects are attributed to a reduction in the probability of formation of the ‘secondary nucleus’, whose size can be calculated from the experimental data. The secondary nucleus is found to correspond to three molecular folds and this agrees well with an independent estimate obtained, by using thermodynamical theory, from the dependence of lamellar thickness on temperature.

INSTABILITY OF S MALE-STERILE CYTOPLASM IN MAIZE

A number of S male-sterile plants from several shrunken-2 inbred lines were crossed initially with an R138-TR inbred line pollinator carrying the nonrestoring genotype for S sterile cytoplasm. One such cross, involving a male-sterile female parent from inbred line M825, produced, unexpectedly, a number of male-fertile F1 progeny, along with the expected male-sterile off-spring. Pollen records of plants in F2, F3 and F4 progenies in the exceptional pedigree, and of a variety of testcross and backcross progenies from these male-fertile exceptions, indicate that the exceptional male fertility is not attributable to the action of either dominant or recessive nuclear restorer genes. They are, however, consistent with the hypothesis that the event responsible for the appearance of exceptional male-fertile offspring among progeny of the original cross involved a change from male-sterile to male-fertile condition in the cytoplasm of the male-sterile M825 plant involved as the female parent in this cross. It appears that this plant bore an ear in which there was a relatively early mutational event at the cytoplasmic level resulting in a chimera involving some kernels which carried S male-sterile cytoplasm, and others which carried the mutated fertile cytoplasmic condition. The finding of a number of additional ear chimeras supports this contention.—The evidence suggests that the change from sterile to fertile cytoplasm has occurred in a number of other instances. The male-sterile line M825 is especially prone to this change. These findings are of particular interest because it has heretofore been considered that both S and T types of male-sterile cytoplasm are highly stable.—The data presented here are not sufficient to support the notion that the exceptional event involves a qualitative change, analogous to gene mutation, in a cytoplasmic entity governing the expression of male fertility. It is equally plausible that the exceptional male fertility is the result of occasional transfer of normal cytoplasm through the male germ cells of maintainer parents.

Preservation of lipid reesterifying enzymes in the microsomal fraction of the rat jejunum

Studies were performed on methods of storage of rat jejunal tissue that would preserve activities of the lipid reesterifying enzymes, acyl CoA:monoglyceride acyltransferase and fatty acid CoA ligase. Storage at -80 degrees C of microsomes prepared from jejunal mucosa or storage of lyophilized microsomes at -20 degrees C was shown to preserve acyl CoA:monoglyceride acyltransferase very well for a matter of weeks. Preservation of fatty acid CoA ligase activity was adequate with either method, but results were not as good as for the transacylase enzyme.