In the recent studies of the ridges in the Indian Ocean, it was found that the compensation depth of isostasy became shallow with mean ascending speed of about 1mm/year. “Bubble Model” and “Two Layers Model” were proposed. For the better understanding of the upward movement of low density material, we studied the relation between gravity anomaly and topography for the Hawaiian Ridge. The ridge has two topographic highs having different wave length: about 1, 700km and 350km. As for the topography of wave length of more than 1, 000km, calculated depth of compensation is about 80km. The depth is nearly the same with the depth of the boundary between lithosphere and asthenosphere given from difference between observed gravity anomaly and that calculated from the crustal velocity structure. On the other hand, the depth of compensation for the topography of wave length of about 350km is 40km, assuming Airy's isostasy. This gravity effect is equivalent to that of the structure at two different depths: 10km (depth to the Moho) and 80km, where the contribution of the Moho for the isostatic achievement is about 60% and the contribution of the deep boundary is 40%. The result coincides with the velocity structure below the Islands of Hawaii. Though the results are for the ridge or the seamount of hot spot origin, we suspect that the model can apply to the case of the formation of an island arc.
Phytoplasma-infected paulownia tissue cultures showing typical witches'-broom symptoms were heat-treated at 35°C in a growth chamber for five weeks. Then the meristem tissues were excised and cultured in MS medium at 25°C. Untreated comparable infected paulownia tissue cultures were maintained at 25°C as control. The treated paulownia plantlets were symptomless and grew vigorously with healthy appearance. The total DNAs were extracted from both treated and untreated tissue cultures. After amplification by polymerase chain reaction (PCR), no phytoplasmas were detected in 94% of the meristem cultures from the treated plantlets and in all of healthy control cultures using universal primers. A very faint DNA band was observed in 6% of the meristem cultures. A specific, prominent DNA fragment was amplified from DNA samples of the diseased cultures. The results showed that the phytoplasma-free paulownia plantlets could be obtained by selecting meristem cultures through PCR-based phytoplasma DNA detection after the heat treatment of infected tissue cultures.
A synaptic spinule formed on the postsynaptic membrane in the cat superior cervical ganglion (SCG) in vivo was electron microscopically studied. When the preganglionic nerve fiber was tetanically stimulated at 10Hz for more than 10 seconds, a post-tetanic potentiation (PTP) was electrophysiologically detected and maintained up to 30min. Concurrently with PTP, a small process, termed as synaptic spinule, was generated as a small projection standing out from the postsynaptic dendritic membrane with a straightly extended contour. The spinule produced a break at about a middle point of the postsynaptic density (PSD) and divided it into two parts forming a perforated synapse. Then, the spinule increased in size, invaginated into the cytoplasm of the nerve terminal, and subdivided the presynaptic terminal bag into two compartments. Each of the compartments retained a morphology of an active synaptic site with a cluster of synaptic vesicles associated with a presynaptic active zone standing opposite to the one part of the subdivided PSD. The longer the tetanic stimulation in period, the more the synapses with the spinule increased in number. In addition to this, a few spinules (multiple type of spinule) were often formed after the stimulation of 1min and more than two compartments were generated in a single nerve ending. The present observations have suggested that the synaptic spinule is a morphological representation of the “synaptic plasticity” which is electrophysiologically displayed as the PTP in cat SCG in vivo.
We reinvestigated the involvement of the nicotinic-acetylcholine receptor in catecholamine secretion from chick adrenal chromaffin cells. Nicotine (10-8-10-4M), as well as methacholine, caused a dose-dependent increase in the cytosolic concentration of Ca2+ and catecholamine secretion from freshly isolated adrenal chromaffin cells. The effects of acetylcholine (10-4M) were effectively inhibited by both hexamethonium (10-4M) and atropine (10-5M), and almost completely blocked by both antagonists. The results suggest the existence of functional nicotinic receptors, which mediate Ca2+ mobilization and catecholamine secretion, in chromaffin cells of chick adrenal glands.