The synthesis of amylase in parotid glands of young and old rats

The age-related changes in the rate of synthesis of total and secretory proteins were examined in parotid glands of young (2 months) and old (24 months) rats. The differences in the rate of incorporation of radioactive leucine into acid-insoluble proteins of the gland indicate that the rate of protein synthesis declines with age in this gland. To determine whether the rate of synthesis of secretory proteins changes with age in this gland, the rates of incorporation of [3H]leucine into amylase, a major secretory protein of the gland, were compared by radioactivity determinations. For this comparison, amylase was precipitated with glycogen after incubating the gland slices in the presence of the labeled amino acid. The study shows that rate of synthesis of amylase declines significantly with age in this gland. The possible relationship between the decline in protein synthesis and the reduced level of secretory activity of the gland due to aging is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25584/1/0000128.pd

Substitutes for genome differentiation in tuber-bearing Solanum: interspecific pollen-pistil incompatibility, nuclear-cytoplasmic male sterility, and endosperm.

The cultivated potato, Solanum tuberosum L. (2n=4x=48), has a very large number of related wild and cultivated tuber-bearing species, widely distributed in the Americas. These species, grouped in 16 taxonomic series, range from the diploid to the hexaploid level. Polyploid species are either disomic or polysomic. Sexual polyploidization via genetically controlled 2n gametes has played a major role in their evolution. Species are separated in nature by geographical and ecological barriers. However, there are several examples of sympatric species that share the same niches but do not readily cross (i.e. the diploids S. commersonii and S. chacoense, in certain areas of Argentina). External barriers are, therefore, not sufficient to explain species integrity. In addition, there are no strong evidences indicating that genome differentiation is important in the group. Thus, evidences are presented in this review to support the assertion that interspecific pollen-pistil incompatibiliy, nuclear-cytoplasmic male sterility and endosperm are major forces that strengthen the external hybridization barriers allowing, at the same time and under specific circumstances, a certain amount of gene exchange without jeopardizing the integrity of the species