Potassium channel currents in intact stomatal guard cells: rapid enhancement by abscisic acid

Evidence of a role for abscisic acid (ABA) in signalling conditions of water stress and promoting stomatal closure is convincing, but past studies have left few clues as to its molecular mechanism(s) of action; arguments centred on changes in H⁺-pump activity and membrane potential, especially, remain ambiguous without the fundamental support of a rigorous electrophysiological analysis. The present study explores the response to ABA of K⁺ channels at the membrane of intact guard cells ofVicia faba L. Membrane potentials were recorded before and during exposures to ABA, and whole-cell currents were measured at intervals throughout to quantitate the steady-state and time-dependent characteristics of the K⁺ channels. On adding 10 M ABA in the presence of 0.1, 3 or 10 mM extracellular K⁺, the free-running membrane potential (V _m) shifted negative-going (–)4–7 mV in the first 5 min of exposure, with no consistent effect thereafter. Voltage-clamp measurements, however, revealed that the K⁺-channel current rose to between 1.84- and 3.41-fold of the controls in the steady-state with a mean halftime of 1.1 ± 0.1 min. Comparable changes in current return via the leak were also evident and accounted for the minimal response inV _m. Calculated atV _m, the K⁺ currents translated to an average 2.65-fold rise in K⁺ efflux with ABA. Abscisic acid was not observed to alter either K⁺-current activation or deactivation.These results are consistent with an ABA-evoked mobilization of K⁺ channels or channel conductance, rather than a direct effect of the phytohormone on K⁺-channel gating. The data discount notions that large swings in membrane voltage are a prerequisite to controlling guard-cell K⁺ flux. Instead, thev highlight a rise in membranecapacity for K⁺ flux, dependent on concerted modulations of K⁺-channel and leak currents, and sufficiently rapid to account generally for the onset of K⁺ loss from guard cells and stomatal closure in ABA.     

Genetic analysis of risk in clonal populations of forest trees

Summary A major concern arising from the culture of clonally propagated crops of forest trees is risk of catastrophic loss due to an agent or event not anticipated at the time of population establishment. Since danger of such a catastrophe depends to some degree on the genetic variability within clonal mixtures, attention has been focused on the number of clones needed to keep the risk of catastrophic loss below specified levels. In this paper, we describe a genetical analysis of susceptibility to a destructive agent and the effect that frequency of genes for susceptibility have on the number of clones needed to effectively manage this risk. As a part of the analysis, parameters representing the minimum unacceptable mortality rates in plantations () and acceptable levels of risk () are defined, and their effects on the number of single-pair matings needed for the production of clonal stock are evaluated. Dominance and recessive gene action models for a single two-allele genetic locus are investigated. Probabilities for plantation failure are functions of the gene frequency for the allele conferring susceptibility. These functions converge to zero for allele frequencies less than but to one for frequencies greater than or equal to . This convergence is periodic rather than monotonie, since probabilities for plantation failure increase rather than decrease over restricted ranges of increasing numbers of clones. Recessive and dominance gene actions are found to have different effects on the minimum number of clones needed to attain acceptable risk levels. For conditions in which substantial numbers of clones are required, selecting multiple clones per mating is an effective method for reducing the number of matings necessary to achieve acceptable risks.Paper No. 12480 of the Journal Series of the North Carolina Agriculture Research Service, Raleigh, NC 27695-7643, USA     

Neuronal Activation Regulates the Expression of Opioid Receptors: Possible Role of Glial-Derived Factors and Voltage-Dependent Ion Channels

The previous observation that a continuous chemical depolarization of aggregating rat brain cells with KCl alters the expression of opioid receptors was examined in more detail. In contrast to its significant and converse effect on forebrain and hindbrain cells cultured in serum-containing medium, KCl had only a small and transient effect in serum-free cultures of both types. The basal receptor density in serum-free cultures was similar to the receptor density in KCl-treated serum-containing cultures, but medium conditioned by glial cells restored partially the effect of KCl in serum-free cultures. The effect of KCl in serum-containing forebrain cultures was enhanced by the voltage-dependent calcium channel blocker verapamil, and magnesium and cadmium had a similar, though smaller, effect. The sodium channel activator veratridine had a profound and dose-dependent inhibitory effect on the expression of the receptors in forebrain and hindbrain cultures, and tetrodotoxin blocked the veratridine effect. Information about the selectivity of the effect of neuronal activation on the various opioid receptor subtypes was obtained with the neuroblastoma X glioma hybrid M8 cells that possess only delta type opioid receptors. A Scatchard analysis of [3H]etorphine binding to these cells has shown that depolarization increased the Bmax, but had little, if any, effect on the affinity (KD) of the ligand to the receptors. The significance of depolarization and voltage-dependent sodium and calcium channels on the expression of different opioid receptor subtypes is discussed.     

Effect of Adenosine and Intracellular GTP on KATP Channels of Mammalian Skeletal Muscle

We investigated the action of adenosine and GTP on K_ATP channels, using inside-out patch clamp recordings from dissociated single fibers of rat flexor digitorum brevis (FDB) skeletal muscle. In excised patches, K_ATP channels could be activated by a combination of an extracellular adenosine agonist and intracellular Mg²⁺-ATP and GTP or GTP-γ-S. The activation required hydrolyzable ATP and could be partially reversed with Mg²⁺, suggesting that it may involve a G-protein dependent phosphorylation of K_ATP channels. We found that K_ATP channels of the rat FDB could not be activated by Mg²⁺-ATP alone or by Mg²⁺-ATP in the presence of extracellular adenosine. Patches whose channel activity had been `rundown' by Ca²⁺ could not be recovered by adenosine, GTP or Mg²⁺-ATP. K_ATP channels activated by adenosine receptor agonists had a similar ATP sensitivity to those under control conditions; but adenosine appears to be able to switch these K_ATP channels from an inactive to an active mode. Received: 29 December 1995/Revised: 22 March 1996     

Nitrogen losses from perennial grass species

Nitrogen losses from plants may occur through a variety of pathways, but so far, most studies have only quantified losses of nutrients by above-ground litter production. We used ¹⁵N pulse labelling to quantify total nitrogen losses from above- and below-ground plant parts. Using this method we were able to include also pathways other than above-ground litter production. To test the hypothesis that species from nutrient-poor habitats lose less nitrogen than species from more fertile soils, six perennial grasses from habitats with a wide range of nutrient availability were investigated: Lolium perenne, Arrhenatherum elatius, Anthoxanthum odoratum, Festuca rubra, F. ovina and Molinia caerulea. The results of an experiment carried out in pots in a green-house at two fertility levels show that statistically significant losses occur through pathways other than above-ground litter production. In the low fertility treatment, most (70%) losses from L. perenne occurred by litter production, but in Ar. elatius, F. rubra, F. ovina and M. caerulea, more than 50% of labelled N losses took place by root turn-over, leaching or exudation from roots. When nutrient supply increased, the ¹⁵N losses in above-ground dead material increased in all species and in Ar. elatius, A. odoratum and F. rubra the ¹⁵N losses via other pathways decreased. Ranked according to decreasing turnover coefficient the sequence of species was: L. perenne, A. odoratum, F. rubra, F. ovina, Ar. elatius, M. caerulea. These results suggest that species adapted to sites with low availability of nutrients lose less nitrogen (including above- and below-ground losses) than species adapted to more fertile soils.     

Halcyon days with Bill Arnold

The circumstances that led to the discovery that plants luminesce after they are illuminated are described, as are other discoveries that would not have been possible were it not for the fortuitous association I had with my dear and most admirable friend, W.A. Arnold, to whom this special issue is dedicated.     

Maintenance of Weight Loss: A Needs Assessment

This study identified facilitators and obstacles to maintenance of weight loss following a very-low-calorie-diet and behavior modification program. A survey was mailed to a random sample of 178 program completers and received a 61% response rate; the most frequent follow-up period was more than 2 years. Twenty-nine percent reported weighing the same (within 10 lbs) or less than the end of their participation in the treatment program (maintainers), while 71% reported their present weight was a mean of 65% higher than their initial weight loss (regainers). Maintainers were significantly more likely to report engaging in regular aerobic exercise, attending a maintenance support group, and confidence in their ability to manage their weight in the future, while regainers were more likely to report stress and motivation as frequent weight management obstacles. Respondents consistently identified the need for low/no cost ongoing support. Maintainers and relapsers reported similar challenges in managing their weight, yet with different results, suggesting the need to identify subgroups for which different post-treatment support options could be applied.     

Combined Drug Treatment of Obesity

Pharmacological treatment of obesity has been neglected as a viable therapeutic option for many years. Recent long term studies with combinations of obesity drugs gives promise that drugs may play a role in weight maintenance, which classically has been the most difficult aspect of treating obesity. Currently available obesity drugs include centrally acting adrenergic agents and serotonin agonists. Drugs still in development include a lipase inhibitor that produces fat malabsorption, a combined adrenergic-serotonergic reuptake inhibitor, various gut-central nervous system peptides, and a number of beta-3 agonists. Any of these obesity drugs given alone produces modest weight loss, and for most, weight loss continues for as long as medication is given. The most successful drug regimens to date are combinations of phentermine and fenfluramine or of ephedrine, caffeine, and/or aspirin. The former combination produces reduction in body weight and complications of obesity for 2 to almost 4 years in clinical trials to date. More research is needed to document long term efficacy and particularly the long term safety of these and other combinations.     

羊草草地枯枝落叶中N,P,K变化动态

羊草草地枯枝落叶中Ｎ、Ｐ、Ｋ变化动态郭继勋,祝廷成（东北师范大学国家草地生态工程实验室,长春１３００２４）ＤｙｎａｍｉｃｓｏｆＮ,ＰａｎｄＫｉｎｌｉｔｔｅｒｓｏｎＡｎｅｕｒｏｌｏｐｉｄｉｕｍｃｈｉｎｅｎｓｅｇｒａｓｓｌａｎｄ．￥ＧｕｏＪｉｘｕｎａｎｄ...     

Induction of paternal genome loss by the paternal-sex-ratio chromosome and cytoplasmic incompatibility bacteria (Wolbachia): A comparative study of early embryonic events

Paternal genome loss (PGL) during early embryogenesis is caused by two different genetic elements in the parasitoid wasp, Nasonia vitripennis. Paternal sex ratio (PSR) is a paternally inherited supernumerary chromosome that disrupts condensation of the paternal chromosomes by the first mitotic division of fertilized eggs. Bacteria belonging to the genus Wolbachia are present in Nasonia eggs and also disrupt paternal chromosome condensation in crosses between cytoplasmically incompatible strains. Cytoplasmic incompatibility Wolbachia are widespread in insects, whereas PSR is specific to this wasp. PGL results in production of male progeny in Nasonia due to haplodiploid sex determination. The cytological events associated with PGL induced by the PSR chromosome and by Wolbachia were compared by fluorescent light microscopy using the fluorochrome Hoescht 33258. Cytological examination of eggs fertilized with PSR-bearing sperm revealed that a dense paternal chromatin mass forms prior to the first metaphase. Quantification of chromatin by epifluorescence indicates that this mass does undergo replication along with the maternal chromatin prior to the first mitotic division but does not replicate during later mitotic cycles. Contrary to previous reports using other staining methods, the paternal chromatin mass remains condensed during interphase and persists over subsequent mitotic cycles, at least until formation of the syncytial blastoderm and cellularization, at which time it remains near the center of the egg with the yolk nuclei. Wolbachia-induced PGL shows several marked differences. Most notable is that the paternal chromatin mass is more diffuse and tends to be fragmented during the first mitotic division, with portions becoming associated with the daughter nuclei. Nuclei containing portions of the paternal chromatin mass appear to be delayed in subsequent mitotic divisions relative to nuclei free of paternal chromatin. Crosses combining incompatibility with PSR were cytologically similar to Wolbachia-induced PGL, although shearing of the paternal chromatin mass was reduced. Wolbachia may, therefore, block an earlier stage of paternal chromatin processing in the fertilized eggs than does PSR. © 1995 Wiley-Liss, Inc.