New rust resistance specificities associated with recombination in the Rp1 complex in maize.

We address the question of whether genetic reassortment events, including unequal crossing over and gene conversion, at the Rp1 complex are capable of generating novel resistance specificities that were not present in the parents. Some 176 events involving genetic reassortment within the Rp1 complex were screened for novel resistance specificities with a set of 11 different rust biotypes. Most (150/176) of the events were susceptible to all tested rust biotypes, providing no evidence for new specificities. Eleven events selected as double-resistant recombinants, when screened with the 11 test biotypes, showed the combined resistance of the two parental types consistent with a simple recombination and pyramiding of the parental resistances. Nine events selected either as having partial resistance or complete susceptibility to a single biotype possessed resistance to a subset of the biotypes that the parents were resistant to, suggesting segregation of resistance genes present in the parental Rp1 complex. Four events gave rise to novel specificities being resistant to at least one rust biotype to which both parents were susceptible. All four had flanking marker exchange, demonstrating that crossing over within the Rp1 complex is associated with the appearance of new rust resistance specificities.

Calcium transport across avian uterus. III. Comparison of laying and nonlaying birds.

Transepithelial calcium fluxes were measured across isolated uterus of laying, nonlaying, and molting quail under conditions where no electrochemical difference existed across the tissue. Net uterine transfer of calcium in molting and nonlaying birds occurs in the secretory direction and is approximately one-fifth the value obtained for laying birds. The carbonic anhydrase enzyme activity of uteri from laying birds is twice that of uteri from molting birds and five times greater than that of uteri from nonlaying birds. When measured in the presence and absence of 2-mercaptoethanol or dithiothreitol, no statistical difference exists in uterine carbonic anhydrase activities of laying birds or the inhibitory effect of acetazolamide. These results indicate that nonlaying and molting quail secrete calcium at a rate much lower than that of laying quail and that net uterine transfer of calcium exhibits varing degrees of dependence on bicarbonate ion in laying, nonlaying, and molting birds. Carbonic anhydrase data sugges that the activtiy of this enzyme in the quail uterus may be related to uterine calcium secretion.