Photoacoustic and fluorescence measurements of the chilling response and their relationship to carbon dioxide uptake in tomato plants

The response of tomato plants to various chilling treatments was studied using two approaches for the measurement of photosynthetic activity. One involved the use of a portable fluorometer for the measurement of in-vivo chlorophyll fluorescence, while the other employed a newly introduced photoacoustic system which allowed changes in oxygen evolution to be followed in a leaf disc. A strong correlation was found between results obtained by each system and those obtained by a conventional open gas-exchange system for the determination of CO₂ uptake. Both systems of measurements could readily distinguish between the effects of chilling in the dark (at 3° C for 18 h) and chilling at high photon flux density (2000 mol m^-2 s^-1 for 5h at 5° C). Chilling in the dark had practically no effect on the quantum yield of oxygen evolution, chlorophyll fluorescence or CO₂ uptake, while chilling at excessively high photon flux density resulted in a sharp reduction (50–70%) in the quantum yields obtained. The results support the view that photosystem II cannot be the primary site of damage by chilling in the dark, although it is significantly affected by chilling at high light intensity.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PA photoacoustic - PFD photon flux density - PSII photosystem II     

The natural enemies of the armored scale lady-beetleChilocorus bipustulatus [Col. Coccinellidae]

The most common parasite ofC. bipustulatus larvae and pupae in Israel isH. flaminius [Hym., Encyrtidae]. A theory of the survival of hyperparasites through a mechanism which prevents overlapping of appearance was presented. The parasites, predators and pathogens which were found as well as those reviewed in the literature explain the low value ofC. bipustulatus in biological control of scale-insects in groves.

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Résumé Le parasite le plus commun des larves et des nymphes deC. bipustulatus en Israel estHomalotylus flaminius (Encyrtidae). Il a été montré expérimentalement que deux autres espèces,Achrysopophagus aegyptiacus etPachyneuron siculum, sont des hyperparasites des larves deH. flaminius. Il est présenté une théorie de la survie des hyperparasites à l'aide d'un mécanisme qui empêche les chevauchements d'apparition. Les autres hyménoptères parasites nouveaux, les fourmis les fourmilions et les champignons pathogènes ont une importance secondaire dans la réduction des populations deC. bipustulatus. Les parasites, prédateurs et pathogènes que nous avons trouvés aussi bien que ceux mentionnés dans la littérature expliquent la faible valeur deC. bipustulatus pour la lutte biologique contre les cochenilles en vergers.

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Research financed in part by grant No. FG.-Is-227, U.S.D.A.     

Antigen-binding receptors on T cells from long-term MLR. Evidence of binding sites for allogeneic and self-MHC products

Antibody inhibition of radiolabelled stimulator membrane vesicle binding by T blasts activated in the mixed lymphocyte reaction (MLR) was used to identify responder-cell determinants involved in the binding phenomenon. Antisera or monoclonal antibodies against Thy-1, Lyt-1, Lyt-2 and Ly-6 antigens were not inhibitory. However, antibodies against heavy-chain V region (V_H) determinants strongly inhibited vesicle binding by both primary and longterm MLR blasts. Anti-Ia (both alloantisera and monoclonal reagents) caused inhibition of antigen binding by primary MLR blasts only. T blasts from long-term MLR lines were neither Ia-positive, nor susceptible to blocking of antigen binding with anti-Ia. However, these cells were capable of specifically absorbing soluble syngeneic Ia material, with the concomitant appearance of vesiclebinding inhibition with anti-Ia sera. Acquisition of syngeneic Ia by T blasts was effectively blocked with the anti-V_H reagent. Passively bound self-Ia did not interfere with vesicle binding in the absence of anti-Ia. These results strongly suggest the existance of specific self-Ia acceptor sites closely linked to the receptors for stimulator alloantigens on T cells proliferating in MLR. A receptor model based on these findings is briefly discussed.Abbreviations used in this paper B10 C57BL/10 - Con A concanavalin A - FcR Fc receptor - FCS fetal calf serum - H heavy chain - Ia I-region associated antigen - Ig immunoglobulin - LPS lipopolysaccharide - Lyt T-lymphocyte differentiation antigen - MHC major histocompatibility complex - MLR mixed lymphocyte reaction - PM plasma membrane - T thymus derived - Tcr T-cell receptor - V variable region of Ig     

Breeding tomatoes for salt tolerance: inheritance of salt tolerance and related traits in interspecific populations

Summary Interspecific segregating populations derived from a cross between tomato (Lycopersicon esculentum) cv M82-1 -8 (M82) and the wild species L. pennellii accession LA-716 (Lpen716) were used to study the genetic basis of salt tolerance and its implications for breeding. BC₁ (M82 x (M82 x Lpen716)) and BC₁ S₁ (progenies of selfed BC₁ plants) populations were grown under arid field conditions and irrigated with water having electrical conductivities of 1.5 (control), 10 and 20 dSm^-1. The evaluation of salt tolerance was based on total fruit yield (TY), total dry matter (TD) and TD under salinity relative to the control (RD). Sodium, potassium and chloride concentrations were measured in the leaves and stems. The methods for estimating heritability were adapted to BC₁ plants and BC₁S₁ families. TY, TD and RD had heritability estimates of 0.3–0.45, indicating that salt tolerance can be improved by selection. Genetic correlations between traits indicated that high yield may be combined with salt tolerance and that ion contents are not likely to provide an efficient selection criteria for salt tolerance. Genetic correlations between performances under various salinity levels suggested that similar mechanisms affect the responses to salinity treatments of 10 and 20 dSm^-1. Responses to paper selection confirmed that salt tolerance of the tomato may be improved by selection, and that this selection should be based on dry matter and yield parameters under salinity.Passed away May 1986     

Effect of substance P and eledoisin on K+ efflux, amylase release and cyclic nucleotide levels in slices of rat parotid gland.

The undecapeptides, substance P and eledoisin, caused a rapid, concentration-dependent increase in K+ efflux and amylase release from parotid tissue slices. The effects were not blocked by beta-adrenergic, alpha-adrenergic, or cholinergic antagonists. Incubation buffer calcium was required for stimulation of K efflux and amylase release. The action of the undecapepides was independent of any effects on parotid cyclic AMP or cyclic GMP levels. Since the actions of the undecapeptides were Ca2+ dependent and no effects on cyclic nucleotide levels were discerned it was concluded that Ca2+ plays a primary role in agonist regulation of K+ efflux from the parotid.     

Theoretical study of flow,pressure and solute concentration in double membrane systems

A model system consisting of two rigidly held membranes in series was investigated through the application of the Kedem and Katchalsky thermodynamic single membrane flow equations. This analysis results in predictions of the steady state flow properties as well as values for the solute concentration and pressure of the internal compartment when the system is under the influence of a constant solute concentration or hydrostatic pressure gradient. It is demonstrated that although the flow properties and internal compartment pressure are complicated functions of the membrane permeability coefficients and driving gradient across the system, the relationships are greatly simplified by the explicit appearance of the internal compartment steady state solute concentration in the equations. It is shown that the steady state volume flow rate depends on the absolute value of the solute concentration in the external compartments, as well as the solute concentration gradient across the system. The properties of non-linear dependence of volume flow on concentration gradient, and rectification of volume flow are discussed and shown to be independent properties of the system. For the system under the influence of a solute concentration gradient, the internal compartment pressure can be greater or less than the ambient pressure, and depends mainly on the order in which the membranes are encountered by the volume flow. These properties are qualitatively correlated with certain available experimental observations in biological systems.     

Mechanotransduction through the cytoskeleton

We constructed a model cytoskeleton to investigate the proposal that this interconnected filamentous structure can act as a mechano- and signal transducer. The model cytoskeleton is composed of rigid rods representing actin filaments, which are connected with springs representing cross-linker molecules. The entire mesh is placed in viscous cytoplasm. The model eukaryotic cell is submitted to either shock wave-like or periodic mechanical perturbations at its membrane. We calculated the efficiency of this network to transmit energy to the nuclear wall as a function of cross-linker stiffness, cytoplasmic viscosity, and external stimulation frequency. We found that the cytoskeleton behaves as a tunable band filter: for given linker molecules, energy transmission peaks in a narrow range of stimulation frequencies. Most of the normal modes of the network are spread over the same frequency range. Outside this range, signals are practically unable to reach their destination. Changing the cellular ratios of linker molecules with different elastic characteristics can control the allowable frequency range and, with it, the efficiency of mechanotransduction.     

mTOR generates an auto-amplification loop by triggering the βTrCP- and CK1α-dependent degradation of DEPTOR

DEPTOR is a recently identified inhibitor of the mTOR?kinase that is highly regulated at the posttranslational level. In response to mitogens, we found that DEPTOR was rapidly phosphorylated on three serines in a conserved degron, facilitating binding and ubiquitylation by the F box protein βTrCP, with consequent proteasomal degradation of DEPTOR. Phosphorylation of the βTrCP degron in DEPTOR is executed by CK1α after a priming phosphorylation event mediated by either the mTORC1 or mTORC2 complexes. Blocking the βTrCP-dependent degradation of DEPTOR via βTrCP knockdown or expression of a stable DEPTOR mutant that is unable to bind βTrCP results in mTOR inhibition. Our findings reveal that mTOR cooperates with CK1α and βTrCP to generate an auto-amplification loop to promote its own full activation. Moreover, our results suggest that pharmacologic inhibition of CK1 may be?a viable therapeutic option for the treatment of cancers characterized by activation of mTOR-signaling pathways.