The distribution and kinetics of release of radiocalcium in tendon and skeletal muscle

The distribution of Ca(45) in frog (Rana pipiens) sartorius muscle, after 4 hours' exposure to Ringer's solution containing radiocalcium, has been analyzed by observing the kinetics of escape of the radioisotope into a non-radioactive Ringer's solution with calcium present or absent and by assuming that the tendon of Achilles is a satisfactory model of the extent of the uptake and release of Ca(45) by the interstitial connective tissue (c.t.). In a Ringer's solution containing 1 mM/liter calcium, the exchangeable calcium distribution in micromoles per gram wet weight is as follows: (a) Aqueous phase of c.t. space: 0.16; (b) bound to c.t.: 0.16; (c) bound to surface of fibers: 0.13, of which 0.03 is displaced only by self-exchange, whereas the rest, as in c.t., can be displaced by other ions; and (d) in myoplasm: 0.33. The kinetics of Ca(45) exit suggests that in infinite time of exposure to Ca(45) the myoplasmic component would rise to 0.85. In the muscles, the half-time of the quickly emerging Ca(45) averages about 3 minutes, whereas the time constant of the slowly released component is about 500 minutes. In the tendons the percentage rate of escape falls exponentially, the half-time of emergence being about 10 minutes.     

Does Late-acting Self-incompatibility (LSI) Show Family Clustering? Two More Species of Bignoniaceae with LSI:Dolichandra cynanchoides and Tabebuia nodosa

By means of hand pollination experiments and fluorescence microscopythe breeding systems and pollen tube growth were studied inDolichandra cynanchoides and Tabebuia nodosa, two bignoniaceousspecies of the Chaco woodland of NE Argentina. Both speciesabscised all selfed pistils within 4–8 d although selfpollen tubes grew successfully to the ovary and penetrated manyovules. Both species therefore show ‘late-acting self-incompatibility’(LSI) or ‘ovarian sterility’ (OS) type control ofselfing. LSI-OS has been reported in 17 species of the Bignoniaceae,and is also clustered in families such as the Bombacaceae-Sterculiaceae,Fabaceae and Myrtaceae. The implications of such family clusteringare discussed, with regard to current hypotheses for the actionof LSI-OS phenomena. Copyright 1999 Annals of Botany Company Bignoniaceae, Dolichandra cynanchoides, Tabebuia nodosa, Chaco, late-acting self-incompatibility, ovarian sterility.