On the relation between auxin transport and auxin metabolism in explants of Coleus

Summary Transport and metabolism of naphthylacetic acid, labelled with ¹⁴C or with ³H, were studied by means of the liquid scintillation counting technique in combination with thin layer chromatography.The amounts of radioactivity reaching the receiver blocks as well as the loss from donor blocks greatly depended on the donor concentration. The relative amounts in receiver blocks increased with decreasing auxin concentrations in donor blocks. This phenomenon may be ascribed to the low immobilization capacity of the tissue at very low auxin concentrations.The relative amounts of radioactivity lost from donor blocks increased with decreasing auxin concentrations in donor blocks.Different characteristics of auxin transport can be explained by assuming a movement in symplast or in apoplast. During transport in the symplast the auxin is immobilized. Auxin immobilization governs many characteristics of auxin transport and could have a regulating effect on the free auxin content in plant tissues.     

Changes in canine latissimus dorsi muscle during 24 wk of continuous electrical stimulation.

To study functional, structural, and biochemical adaptations to electrical stimulation of striated muscle in a large animal, the canine latissimus dorsi (LD) muscle was conditioned continuously for 24 wk with an increasing number of pulse bursts (burst duration 250 ms, burst frequency 30 Hz). Force measurements in vivo after 12 wk showed a significant decrease in the ripple, the ratio of interstimulus to peak force amplitude, from 0.94 +/- 0.03 to 0.13 +/- 0.08 (SE; n = 8, P less than 0.05), indicating reduction in contractile speed. Also the steep part of the force-frequency relation shifted to lower frequencies. A significant change in fiber-type composition was seen with both enzyme- and immunohistochemistry, manifested by an increase of type I fibers from 29.5 +/- 2.9 to 83 +/- 8% (SE; n = 8, P less than 0.05). During this period a transient rise in the number of type IIc/Ic fibers (from 3 to 10%) was seen. In the stimulated muscle, capillary-to-fiber ratio increased from 1.9 +/- 0.4 to 2.7 +/- 0.1 (P less than 0.05). A significant increase in mitochondrial volume was also seen, especially in the peripheral part of the fiber. Both creatine kinase and lactate dehydrogenase revealed a significant decline in activity within 12 wk. At the same time a shift in lactate dehydrogenase-isozyme pattern was observed toward the cardiac composition. No additional changes occurred after 12 wk of stimulation, indicating that conversion of the canine LD muscle was complete within this period.