The pattern of secondary root formation in curving roots of Arabidopsis thaliana (L.) Heynh.

Abstract. A gravitational stimulus was used to induce the curvature of the main root of Arabidopsis thaliana. The number of secondary roots increased on the convex side and decreased on the concave side of any curved main root axes in comparison with straight roots used as the control. The same phenomenon was observed with the curved main roots of plants grown on a clinostat and of mutant plants exhibiting random root orientation. The data suggest that the pattern of lateral root formation is associated with curvature but is independent of the environmental stimuli used to induce curvature.     

Stereological Implications of the Geometry of Cones

Given a cone around a curve β in IR³ it is shown that there is no relation between the curvature of β and the volume of the cone but, in contrast to the volume, the surface area of the cone depends, albeit rather weakly, on the curvature of β. The geometric meaning of the stereological formulae when applied to cones is considered and it is noted that stereological methods to estimate the surface area of a cone need to be extremely precise to provide information concerning curvature or tortuosity.     

Application of radiationless energy transfer for distance measurements across membranes

For several 2- or 3-dimensional configurations of stationary donors and acceptors on or near a spherical membrane shell the transition probabilities for radiationless energy transfer are calculated, using Förster's approximation obtained for Coulombic dipole-dipole interaction of the transition moments. It turns out that the difference in the refractive indices for membrane (lipid) and bulk phase (water) has only a small influence on the transition probabilities. Furthermore, the curvature of biological cell surfaces can be neglected, but affects the energy transfer across small vesicles. The ratio thickness/radius of small vesicles can be determined by measuring fluorescence quenching of excited donors by acceptors on the other side of the membrane.     

Circumnutation of Arabidopsis thaliana inflorescence stems

Time-lapse monitoring using infrared imaging revealed a distinct change in circumnutatory behaviour of Arabidopsis inflorescence stems by dark treatment, which drastically increased curvature and decreased nutation frequency. Re-irradiation during dark treatment had different effect on the nutation frequency and the curvature, suggesting that radiation condition controls them through different mechanism.