Cytoplasmic Alkalization and Cytoplasmic Streaming Induced by Light and Histidine in Leaf Cells of Egeria densa: in vivo 31P-NMR study

Rotational streaming of the cytoplasm including chloroplastswas induced by L-histidine, as well as by light, on the anticlinalface of leaf cells of Egeria densa. In the case of treatmentwith L-histidine some of the chloroplasts remained stationaryon the periclinal face of cells after rotational cytoplasmicstreaming was initiated. However, these chloroplasts were easilydislodged and translocated to the centrifugal end of the histidine-treatedcells by application of a centrifugal force that barely affectedthe location of chloroplasts in cells incubated in the darkwithout L-histidine. This result indicates that the anchoringof chloroplasts was weakened by L-histidine. Thus only the releaseof chloroplasts from anchoring was not enough for initiationof their streaming. The cytoplasmic pH (pH_c) and vacuolar pH(pH_v) were noninvasively monitored by in vivo ³¹P-nuclear magneticresonance (NMR) spectroscopy. Compared with the dark controlvalue, both illumination and treatment with L-histidine increasedthe pH_c by 0.3 units. In contrast, pH_v changed only a littlewith both illumination and treatment with L-histidine. Releaseof chloroplasts from anchoring and initiation of cytoplasmicstreaming are discussed in relation to the increase in pH_c inducedby both light and L-histidine. ⁴ Present address: Department of Cell Biology, National Instituteof Agrobiological Resources, Kannondai, Tsukuba, Ibaraki, 305Japan ⁵ Present address: Marine Biotechnology Institute Co., Ltd.,Head Office, 2-35-10 Hongo, Bunkyo-ku, Tokyo, 113 Japan (Received July 16, 1990; Accepted December 20, 1990)     

Deficient polymerization in vitro of a point-mutated beta-actin expressed in a transformed human fibroblast cell line

HUT-14 cells, tumorigenic human fibroblasts, express a mutant beta-actin which has a single amino acid substitution at position 244 (glycine to aspartic acid), in addition to normal beta- and gamma-actin. In order to characterize the biochemical function of the mutant beta-actin, actins were extracted and purified from HUT-14 cells. The partially purified actin fraction contained beta-, gamma-, and mutant beta-actins in the ratio of 1:1:1, the same ratio as in the cells. When the actin of this fraction was purified through a polymerization step, mutant beta-actin was always less incorporated into actin filaments than beta- and gamma-actin. When the polymerization ability of purified HUT-14 actins was examined by sedimentation technique, it was lower than those of muscle and of cytoplasmic actins from another human cell line (HUT-11) which expresses only normal beta- and gamma-actin, in the ratio of 2:1. The deficient polymerization of mutant beta-actin was also observed by examining the ratio of beta-, gamma-, and mutant beta-actins incorporated into actin filaments. The ratio of mutant beta-actin in polymerized actins under all conditions examined was always less than that before polymerization. These results indicate that the single amino acid substitution at position 244 caused the reduction of incorporation of the mutant beta-actin into actin filaments in vitro.     

Cytoplasmic Ca2+ has No Effect on the Excitability of Chara Plasmalemma

Internodal cells of Chara australis were subjected to two consecutiveintracellular perfusions with a Ca²⁺-free EGTA medium whichdisintegrated the tonoplast within about 10 minutes and thenwith a Ca²⁺-buffered medium. All perfusion media usually contained1 mM ATP. To stop the electrogenic pump, the internode was depletedof intracellular ATP. The excitability of the plasmalemma wasnot significantly influenced by intracellular free Ca²⁺ concentrationsup to 10^–4 M. To trigger action potentials, minimum currentdensities of 1 to 2 µA cm^–2 had to be applied atall tested Ca²⁺ concentrations. In the absence of cytoplasmicATP, excitability was completely lost at all Ca²⁺ concentrations. ¹ Present address: Botanisches Institut der Universit?t Bonn,Venusbergweg 22, D-5300 Bonn, FRG. (Received September 22, 1984; Accepted March 6, 1985)     

Ionic Activity Gradients across the Surface Membrane of Cytoplasmic Droplets Prepared from Chara australis

The membrane potential and the ionic activity gradients of K⁺and Cl^– across the surface membrane of cytoplasmic dropletsprepared from Chara australis internodal cells, were measuredin high and low ionic strength bathing solutions using liquidion exchange microelectrodes selective for K⁺ and Cl^–.Our results indicate that K⁺ is close to electrochemical equilibriumwhereas Cl^– is not. ¹ Present address: ICI Japan, Palace Hotel Annex Building, Marunouchi,Tokyo, Japan.     

Development of human pancreas

The developmental sequence of human pancreatic secretory proteins has not previously been studied in detail. We applied immunohistochemistry to study 20 fetal and neonatal pancreas' (8th to 39th gestational weeks) using antisera against the following pancreatic secretory proteins: pancreatic secretory trypsin inhibitor (PSTI), serine proteinases (trypsin, chymotrypsin, and elastase I), and amylase. PSTI was first detected in developing buds of the pancreas during the 8th gestational week, and proteinases were observed in acinar cells during the 14th week of gestation. Immunoreactivity for both PSTI and proteinases was found in most acinar cells soon after their appearance. Immunoreactivity for amylase could not be detected in fetal or neonatal pancreas tissue. PSTI was also found in developing islets during the 14th gestational week, but the number of immunoreactive cells had decreased by term. Cells positive for serine proteinases were occasionally in contact with islets in second-trimester fetuses. In discussing these results, we give particular attention to the nonparallel appearance of secretory products in the fetal pancreas, and the significance of cells immunoreactive for secretory proteins in endocrine islets.     

Effects of haloperidol and sulpiride on dopamine-induced inhibition of nucleus accumbens neurons

Microiontophoretic study was performed to elucidate dopaminergic mechanism in the nucleus accumbens (Acc) of rats anesthetized with chloral hydrate. Iontophoretically applied dopamine produced an inhibition of glutamate-induced firing in 28 (62%) out of 45 Acc neurons tested. The dopamine-induced inhibition of 14 Acc neurons was clearly antagonized by simultaneous application of haloperidol, and a partial antagonism by sulpiride was observed in 3 out of 10 Acc neurons. These results indicate that dopamine produces an inhibition of the Acc neuron and that, compared to haloperidol, sulpiride is a less potent blocker of the postsynaptic dopamine receptor involved in the dopamine-induced inhibition.     

Possible roles of calcium and ammonium in the development of bitter pit in apple

Apple trees ( Malus pumila Mill . var. domestica Fuji/ Malus prunifolia rootstock) showed a high susceptibility to bitter pit when supplyed with ammonium salt instead of nitrate (control) in the nutrient solution. When apple fruit was affected by bitter pit, a lower calcium as well as a higher nitrogen and ammonium-nitrogen contents was observed in the fruit flesh near the calyx end. The activity of the mitochondrial Ca²⁺-uptake of the fruit flesh near the calyx end was higher when the tree was grown with ammonium salt than when grown with nitrate. Both the activities of succinate: cytochrome c oxidoreductase and the mitochondrial Ca²⁺-uptake per g of tissue were higher in affected fruit than in healthy fruit. Each of chlorpromazine, N-(6-aminohexyl)-5-chloro-l-napthalenesulfonamide (W-7) and N-(6-aminohexyl)-l-naphthalenesulfonamide (W-5), calmodulin antagonists, was infiltrated into the fruit for 20 min under reduced pressure (about 1 × 10⁴ Pa). Few days later, numerous bitter pit-like spots were observed in both fruit treated with W-7 and chlorpromazine, while only a few spots were observed after the infiltration with W-5, a less potent calmodulin antagonist. A possible mechanism for the occurrence of bitter pit is discussed.