ABSTRACT
Measurements of the thrust and forward impulse of a simulated fish tail and mathematical modeling indicate that the propulsive forces of fast-start swimming can be optimized by three different effects: (i) exactly inverting the tail tip vortex that is generated with the initial stroke, (ii) using a moderately flexible tail, and (iii) introducing a specific delay between the initial stroke and the return stroke. Experiments were performed with a new computer-controlled fish-tail simulation apparatus, and the results confirm the theoretical predictions of a previous study.
ABSTRACT
The antibacterial effect of the soybean phytoalexin glyceollin was assayed using a liquid microculture technique. Log-phase cells of Bradyrhizobium japonicum and Sinorhizobium fredii were sensitive to glyceollin. As revealed by growth rates and survival tests, these species were able to tolerate glyceollin after adaptation. Incubation in low concentrations of the isoflavones genistein and daidzein induced resistance to potentially bactericidal concentrations of glyceollin. This inducible resistance is not due to degradation or detoxification of the phytoalexin. The inducible resistance could be detected in B. japonicum 110spc4 and 61A101, representing the two taxonomically divergent groups of this species, as well as in S. fredii HH103, suggesting that this trait is a feature of all soybean-nodulating rhizobia. Glyceollin resistance was also inducible in a nodD1D2YABC deletion mutant of B. japonicum 110spc4, suggesting that there exists another recognition site for flavonoids besides the nodD genes identified so far. Exudate preparations from roots infected with Phytophthora megasperma f. sp. glycinea exhibited a strong bactericidal effect toward glyceollin-sensitive cells of B. japonicum. This killing effect was not solely due to glyceollin since purified glyceollin at concentrations similar to those present in exudate preparations had a much lower toxicity. However, glyceollin-resistant cells were also more resistant to exudate preparations than glyceollin-sensitive cells. Isoflavonoid-inducible resistance must therefore be ascribed an important role for survival of rhizobia in the rhizosphere of soybean roots.
Subject(s)
Benzopyrans/pharmacology , Isoflavones/pharmacology , Rhizobiaceae/drug effects , Rhizobium/drug effects , Symbiosis/drug effects , Benzopyrans/metabolism , Cell Division/drug effects , Cell Survival/drug effects , Dose-Response Relationship, Drug , Drug Resistance, Microbial , Genistein , Pterocarpans , Glycine max/metabolismABSTRACT
A rotating spiral scanner interrupts an incident light beam for time intervals which are proportional to the position of the beam. This produces an electrical signal via a photodetector system which is independent of beam intensity. The device was used to measure the relative change in sarcomere spacing during the initial development of tension in a contracting frog sartorius muscle.
ABSTRACT
A water cell has been developed as an attenuator for 1.315-microm radiation, providing a variable transmission with a dynamic range of typically 10(3). The filter was used to determine the linear range of a photoresistor.