No abstract

P. 1993. Synergisticactivationof plasma membrane H*-ATPase in Arabidopsis thaliana cells by turgor decrease and hy fusicoccin. -Physiol. Plant. 87: 592-600.The regulation of the H*-ATPase of plasma memhrane is a crucial point in the integration of transport processes at this memhrane. In this work the regulation of H^-ATPase activity induced by changes in turgor pressure was investigated and compared with the stimulating effect of fusicoccin (FC). The exptisure of cultured cells of Arabidopsis thaliana L. {eeotype Landsberg 310-14-2) to media containing mannitol (0.15 or 0.3 M) or polyethylene glycol 6(K» (PEG) (15.6% or 22% w/v) resulted in a decrease in the turgor pressure of the cells and in a strong stimulation of H* extrusion in the incuhation medium. The osmotica-induced H^ extrusion was (1) inhibited by the inhibitor of plasma membrane H^-ATPase, erythrosin B (EB), (2) dependent on the external K* concentration, (3) associated with a net K* influx, and (4) lead to an increase of cellular malate content. These results show that the reduction of external osmotic potential stimulates the activitv of plasma membrane H*-ATPase. The effect of mannitol was only partially inhibited by treatments with cycloheximidc (CH) and cordycepin, which block protein and mRNA synthesis, respectively. All the effects of osmotica were qualitatively and quantitatively similar to those induced by 5 \iM FC. However, when FC and mannitol (or PEG) were fed together, their effects on H* extrusion appeared synergistic, irrespective of whether FC was present at suboptimal or optimal concentrations. This behaviour suggests that the modes of actionofFC and of the osmotica on H'-ATPase activity differ at least in some step(s).

The regulation of the H+‐ATPase of plasma membrane is a crucial point in the integration of transport processes at this membrane. In this work the regulation of H+‐ATPase activity induced by changes in turgor pressure was investigated and compared with the stimulating effect of fusicoccin (FC). The exposure of cultured cells of Arabidopsis thaliana L. (ecotype Landsberg 310–14‐2) to media containing mannitol (0. 15 or 0. 3 M) or polyethylene glycol 6000 (PEG) (15. 6% or 22% w/v) resulted in a decrease in the turgor pressure of the cells and in a strong stimulation of H+ extrusion in the incubation medium. The osmotica‐induced H+ extrusion was (1) inhibited by the inhibitor of plasma membrane H+‐ATPase, erythrosin B (EB), (2) dependent on the external K+ concentration, (3) associated with a net K+ influx, and (4) lead to an increase of cellular malate content. These results show that the reduction of external osmotic potential stimulates the activity of plasma membrane H+‐ATPase The effect of mannitol was only partially inhibited by treatments with cycloheximide (CH) and cordycepin, which block protein and mRNA synthesis, respectively. All the effects of osmotica were qualitatively and quantitatively similar to those induced by 5 μM FC. However, when FC and mannitol (or PEG) were fed together, their effects on H+ extrusion appeared synergistic, irrespective of whether FC was present at suboptimal or optimal concentrations. This behaviour suggests that the modes of action of FC and of the osmotica on H+‐ATPase activity differ at least in some step(s)

Intrathoracic, totally ectopic goiters are rare, but have to be considered as a diagnostic possibility in all mediastinal masses. The displacement of the thyroid tissue inferiorly in connection with the embryogenesis of the heart and the large vessels explains the aetiology of the disease. Ectopic goiters are often asymtomatic or oligosymptomatic. They may be classified into two groups according to their location in the anterior or posterior mediastinum. The diagnostic procedures include standard X-ray and CT scan imaging, eventually combined with radionuclide scintigraphy. Once the diagnosis of a intrathoracic goiter is obtained the treatment is surgical (unknown dignity, risk of compression or other symptoms). The approach of choice is through a median sternotomy in case of a anterior location and a posterolateral thoracotomy in case of a posterior location. We discuss the diagnostic and therapeutic approach in 2 patients with mediastinal goiters--one located in the anterior and one in the posterior mediastinum.