Movement of Pulses of Labeled Auxin in Corn Coleoptiles

The transit of indole-3-acetic acid through 20-mm sections of corn coleoptiles can be separated from processes involved in the uptake of auxin by the section and the exit of auxin from the section. Aerobic sections are supplied with an exogenous source of (14)C IAA for a limited time, and after the source is removed, a pulse of (14)C IAA moves down at 12 to 15 mm/hour. After transfer to nitrogen, movement of the pulse at the aerobic rate persists for about 10 minutes; thereafter drops to only 1 to 2 mm/hour and remains at this level during the next 4 hours. Within 2 hours, 70% of the total (14)C in aerobic sections has moved 10 mm or more down the section from the position of the initial peak, whereas after the same time in nitrogen less than 10% of the total (14)C has moved as far.During the migration down the coleoptile, the peak of radioactivity becomes broader and less distinct. This dispersion is more rapid in aerobic than anaerobic sections, but appears to be nonpolar and to occur along the existing concentration gradients. Diffusion probably contributes to this dispersion.In both inhibited and uninhibited sections, the movement of the peak, in contrast to its dispersion, is A) polar (downward) and B) independent of existing concentration gradients. Thus transit within the section possesses the fundamental properties of the overall transport system. The reduced amount of transport in inhibited sections is more likely maintained by glycolysis than by a low level of aerobic respiration dependent on the residual oxygen in the tissue.     

The elimination and differentiation of chromosomes in the germ line of sciara

The germ line chromosomes of S. coprophila have been followed from the time of origin of the germ cells up to the time of meiosis in the male and up to first larval molt in the female. The mechanism which prevents the accumulation of L (limited) chromosomes in the germ line is a unique process of chromosome elimination: it occurs in male and female embryos after the germ cells have migrated from the pole plasm to the definitive gonad site, and it involves the movement of whole L chromosomes through the nuclear membrane into the cytoplasm. The extra paternal X chromosome is eliminated from the germ cells at the same time and in the same manner. Following this elimination there is a cytological differentiation of the chromosomes remaining inside the nucleus. First, the 4 paternal homologues of the regular complement undergo a loosening of coils and become light-staining whereas the maternal homologues remain condensed like the L's. Next, the L chromosomes undergo a process of extreme attenuation and dispersion following which they return to the condensed state. H³-thymidine autoradiography on gonial and premeiotic cells in the testis reveals that the L chromosomes undergo DNA replication at the end of the S period, also that there are asynchronies in DNA synthesis among the regular chromosomes. The phenomena of differential chromosome staining and asynchronous DNA replication are considered in the light of current theory regarding heterochromatization and gene inactivation, also in relation to the phenomenon of chromosome imprinting encountered in this genus.The studies reported here were supported by the National Science Foundation grants GB-42 and GB-2857, and in part by Contract No. AT-(40-1)-2690 under the Division of Biology and Medicine, U.S. Atomic Energy Commission.Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, in the Faculty of Pure Science, Department of Botany, Columbia University. This work was carried out in the laboratory of Professor J. Herbert Taylor and has been supported in part by U.S. Public Health Training Grant No. 2 T 1-GM-216-05. Grateful acknowledgement is made to Professor Spencer W. Brown, Department of Genetics, University of California, Berkeley, in whose laboratory the final studies were completed.     

Survey for mitochondrial-desmosome complexes in differentiating epithelia

Summary Mitochondria are frequently found to be closely associated with the plaques of desmosomes in a variety of columnar or cuboidal epithelia of fetal or early postnatal mammals (mouse, rat, human being). The organs in which mitochondrial-desmosome complexes were found include stomach, small intestine, pancreas, kidney, epididymis, seminal vesicle, coagulating gland, thyroid gland. The association has not been observed in simple squamous epithelium (vascular endothelium). Mitochondria lie quite close to desmosomes in the stratum spinosum of stratified squamous mucous epithelium of fetal animals and also to axo-dendritic synapses in still poorly differentiated central nervous system. Mitochondria have also been detected close to attachment sites in ectoderm of the early frog gastrulae. Here there is as yet no visible plaque material.We suggest that the mitochondria may provide energy or some chemical for the formation of the plaque. This hypothesis does not explain why the complexes are not found in poorly differentiated epithelia from older animals.Dedicated to Professor Berta V. Scharrer on her 60th birthday, with affection and admiration. — This study was supported by U.S.P.H.S. research grants NB-05219 and GM-10757 from the National Institutes of Health.