Organization of cortical microtubules at the plasma membrane in Arabidopsis

 To understand the role of microtubules in the regulation of cell elongation, we characterized microtubule patterns in fass, a cell shape mutant of Arabidopsis thaliana (L.) Heynh. Examining microtubule patterns via immunocytochemistry, we found that fass cells were able to organize their microtubules into mitotic spindles and phragmoplasts. During interphase or preprophase, fass cells had cortical microtubules, verified by transmission electron microscopy, but these microtubules were not organized into the cortical array or preprophase band. Using chromatin condensation and tubulin localization on the nuclear envelope as preprophase stage markers, we found that although fass cells lacked the preprophase band and cortical array, their cell division cycle appeared normal. To pinpoint the defect in fass cells, we delineated the sequential events leading to cortical array formation in Arabidopsis cells and found that fass cells initiated and recolonized cortical microtubules in the same manner as wild-type cells, but failed to order them into the cortical array. Taken together, these results suggest fass cells are impaired in a component of the microtubule organizing center(s) required for the proper ordering of cortical microtubules at the plasma membrane. Received: 23 August 1996 / Accepted: 25 September 1996     

中华绒螯蟹卵子皮层反应的初步研究

中华绒螯蟹每个成熟卵的皮层内约有１２３０００枚皮层颗粒。皮层颗粒略呈球形,直径约０．４μｍ,外围一层薄膜,内含酶多种以及粘多糖,蛋白质等。受精时,一个真正起受精作用的精子穿入卵质膜以后,近穿入下的皮层颗粒破裂,随即破裂由近及远,迅速有序地向四周蔓延,播及全卵的所有皮层颗粒。全部皮怪颗粒因破裂而排出的内含物大部分和卵膜内层组合成坚厚的受精巢,用耿防阻多精受精。同时排出的内含物还引起卵子渗透压的骤升,     

Effect of cytokinins on the photosynthetic apparatus in water-stressed and rehydrated bean plants

Effects of the cytokinins 6-benzylaminopurine (BAP) and N-2-chloro-4-pyridyl-N′-phenylurea (4-PU-30) on the photochemical activity, oxygen flash yields, and thermoluminescence in bean plants under a water stress were studied. The cytokinins increased the photochemical (Hill reaction) activity and thermoluminescence "B"-band in control as well as in stressed and rehydrated plants, while the oxygen flash yields were affected only in the stressed and rehydrated plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Acetylethylcholine Mustard on [3H]Quinuclidinyl Benzilate Binding and Acetylcholine Release in Rat Brain Synaptosomes

The effects of acetylethylcholine mustard and its aziridinium derivative (AMMA) on acetylcholine (ACh) release and [3H]quinuclidinyl benzilate (QNB) binding were studied in rat cortical synaptosomes. After incubation for 5 min at 37 degrees C, AMMA reduced [3H]QNB binding with an IC50 of 9 microM. Following incubation for 5 min with 50 microM AMMA and washing, there was a 62% reduction in the [3H]QNB binding capacity with no change in the KD value for the remaining receptors, a result indicating the irreversibility of the AMMA binding. AMMA and oxotremorine both reduced the basal and 30 mM K+-induced release of newly synthesized [3H]ACh in dose-dependent manners over a 2.5-min period. At identical 50 microM concentrations, AMMA produced a much longer inhibition of basal [3H]ACh release than oxotremorine did. The inhibition of basal and 30 mM K+-induced [3H]ACh release by AMMA (10-250 microM) was blocked by 2 microM atropine during a 2.5-min release incubation, but not during a 30-min release incubation. After synaptosomes were treated with 50 microM AMMA for 5 min and the unbound drug was washed out from the tissue, [3H]ACh release (basal and K+-induced) was reduced. AMMA (50 microM) reduced high-affinity choline uptake and ACh synthesis by greater than 90% in this tissue, but these effects did not account for the [3H]ACh release inhibition, because they were not atropine sensitive and hemicholinium-3 had no effect on [3H]ACh release under the conditions used in these studies, i.e., after extracellular [3H]choline was washed out. Taken together, these results suggest that AMMA may be an irreversible agonist at presynaptic muscarinic autoreceptors.     

Stimulation of γ-[3H]Aminobutyric Acid Release from Cultured Mouse Cerebral Cortex Neurons by Sulphur-Containing Excitatory Amino Acid Transmitter Candidates: Receptor Activation Mediates Two Distinct Mechanisms of Release

In primary cultures of mouse cerebral cortex neurons, sulphur-containing excitatory amino acids (SAAs; namely, L-cysteine sulphinate, L-cysteate, L-homocysteine sulphinate, L-homocysteate, S-sulphocysteine) at concentrations ranging from 0.1 microM to 1 mM evoked a saturable release of gamma-[3H]aminobutyric acid ([3H]GABA) in the absence of any other depolarizing agent. All SAAs exhibited essentially similar potency (EC50, 100-150 microM) in releasing [3H]GABA although a variable profile of maximal stimulatory effect was observed when compared with basal release. The intracellular accumulation of the lipophilic cation, [3H]tetraphenylphosphonium, was significantly reduced in the presence of all SAAs, thus verifying a depolarization of the neuronal plasma membrane. SAA-stimulated release of [3H]GABA was shown to comprise two distinct components, calcium-dependent and calcium-independent, which occur after activation of N-methyl-D-aspartate (NMDA) and non-NMDA receptors. Thus, all SAA-evoked responses were antagonized by the selective, competitive NMDA-receptor antagonist, 3-[(+/-)-2-carboxypiperazin-4-yl]propyl-1-phosphonic acid (IC50 range, greater than 50 microM) and the non-NMDA-receptor antagonist, 6,7-dinitroquinoxalinedione (IC50 range, 5-50 microM). Removal of magnesium ions from the superfusion medium caused a significant potentiation of SAA-evoked responses without having any effect on basal levels of [3H]GABA efflux, a result consistent with an involvement of NMDA-receptor activation. Calcium-independent release (i.e., that release remaining in the presence of 1 mM cobalt ions) was a distinct component but of smaller magnitude. Using 500 microM excitatory amino acid agonist concentrations, this component of release was (1) markedly attenuated by 15 microM SKF-89976-A, a non-transportable inhibitor of the GABA carrier, and (2) abolished when choline ions replaced sodium ions in the superfusion medium or when in the presence of excitatory amino acid receptor antagonists. These observations are clearly consistent with a receptor-mediated, depolarization-induced reversal of the GABA carrier.     

Regulation of Cyclic AMP Accumulation by Peptide Hormone Receptors in Immunocytochemically: Defined Astroglial Cells

Primary cultures of neonatal murine brain have been reported to express multiple receptors that regulate adenylate cyclase activity. Since for the most part these results were obtained with mixed cell cultures, it has been difficult to define receptor profiles for specific cell types. With this concern in mind a series of studies has been initiated designed to identify specific receptors present on highly purified, immunocytochemically defined astroglia derived from the cerebral cortices of neonatal rats. In this study the capacity of a variety of peptide hormones to regulate cyclic AMP metabolism in these cells was examined. Fibroblasts derived from the meninges represent a predictable source of contamination in primary CNS culture. Thus, to assign more clearly specific receptors to the astroglial cell population, receptor-mediated regulation of cyclic AMP accumulation was also examined in fibroblasts. Cyclic AMP accumulation in astroglia was stimulated by catecholamines (acting at beta 1-adrenergic receptors), prostaglandin E1, vasoactive intestinal polypeptide, alpha-melanocyte-stimulating hormone, and adrenocorticotropin. Bombesin, luteinizing hormone-releasing hormone, neurotensin, thyrotropin-releasing hormone, somatostatin, secretin, and vasopressin did not significantly increase cyclic AMP levels in these cultures. Catecholamines, acting at alpha 2-adrenergic receptors, and somatostatin inhibited agonist-stimulated cyclic AMP accumulation. In meningeal cell cultures catecholamines (acting at beta 2- and alpha 2-adrenergic receptors) and prostaglandin E1 regulated cyclic AMP levels. However, vasoactive intestinal peptide did not stimulate and somatostatin did not inhibit cyclic AMP accumulation in these cells.     

Freeze-fracture analysis of structural reorganization during meiotic maturation in oocytes of Xenopus laevis

Summary During meiotic maturation, the cortex of oocytes of Xenopus laevis undergoes structural reorganization, visualized in this study by freeze-fracture electron microscopy. In the full-grown but immature oocyte, annulate lamellae are dispersed throughout the subcortex of the egg, 5 to 20 m from the plasma membrane. The annulate lamellae consist of well-organized stacks of membrane with visible pores. Stimulation of meiotic maturation by progesterone leads to disruption of the annulate lamellae and formation of an elaborate cortical endoplasmic reticulum which surrounds the cortical granules and intertwines throughout the cortex of the mature egg. Pore-like structures similar to those previously observed in the subcortical annulate lamellae are observed in the mature cortical endoplasmic reticulum. The cortical endoplasmic reticulum is often in close apposition with the plasma membrane and with membranes of cortical granules, but no junctions are visualized. This study provides further evidence that the cortical endoplasmic reticulum develops during progesterone-stimulated meiotic maturation in vitro, and that the annulate lamellae are precursors to the cortical endoplasmic reticulum.     

Optimization of the bare platinum electrode as an oxygen measurement system in photosynthesis

This paper is concerned with the definition of the standard conditions required for optimum operation of the bare platinum electrode with photosynthetic samples. Experimental evidence shows the following: 1) Polarization circuits should have zero resistance; 2) The electrolyte layer between the electrodes should have a conductance higher than 54×10^{–6 –1} per mm² of platinum electrode area; 3) The electrodes should be polarized just before taking the measurements. All these facts can be interpreted in terms of phenomena occurring on the electrode: The adsorption of hydrogen on the electrode imposes the need for low resistances in the system, and oxygen consumption by the electrode is minimized by polarizing the electrodes as late as possible. This investigation increases the reliability of the bare platinum electrode and gives a basis for a comparison of the results from different experiments. Demonstrations of the pertinence of these conditions are made in our lab with the algae Dunaliella Tertiolecta.     

Nanosecond flash studies of the absorption spectrum of the Photosystem I primary acceptor Ao

Photosystem I particles devoid of the secondary electron acceptor A₁ were studied by nanosecond flash absorption. The primary radical pair (P-700⁺, A₀ ^-) decays with a half-time of 35 ns. The difference spectrum was measured (400–870 nm). After subtraction of the P-700⁺/P-700 difference spectrum, the A₀ ^-/A₀ was obtained. It includes bleachings centered at 690 and 430 nm, and broad positive bands in the near infra-red and the blue-green. This spectrum is consistent with A₀ being chlorophyll a absorbing at 690 nm.