The Effect of pH on the Action of Respiratory Inhibitors in Avena fatua Seeds

The effects of pH on the action of sodium azide, a cytochome-oxidaseinhibitor, and salicylhydroxamate (SHAM), an alternative respirationinhibitor, on the respiration of dormant seeds of wild oat (Avenafatua L.; line AN-51) were studied. While pH had little effecton seed respiration in controls, it strongly affected the activityof azide. One mM azide inhibited seed respiration at pH5, butstimulated it at pH 7. SHAM (10 mM) completely inhibited thestimulation of respiration by 1 mM azide in an unbuffered medium,but failed to do so when the medium was buffered at pH 7. Inunbuffered medium, 10 mM SHAM actually augmented the stimulationof respiration by 0.25 mM azide to the same degree as when theazide solution was acidified to mimic the pH change incurredwith dissolution of 10 mM SHAM. These results suggest that theinhibitory effect of SHAM on the action of azide in an unbufferedsystem may in part be due to its acidification of the incubationmedium rather than by the inhibition of alternative oxidase.Lower pH favours the formation of the undissociated hydrazoatemolecules causing greater inhibition of cytochrome-oxidase andother azide-sensitive enzymes. Avena fatua L, wild oat, seed dormancy, azide, salicylhydroxamate     

Hrip1, a novel protein elicitor from necrotrophic fungus,Alternaria tenuissima,elicits cell death,expression of defence‐related genes and systemic acquired resistance in tobacco

Here, we report the identification, purification, characterization and gene cloning of a novel hypersensitive response inducing protein secreted by necrotrophic fungus, Alternaria tenuissima, designated as hypersensitive response inducing protein 1 (Hrip1). The protein caused the formation of necrotic lesions that mimic a typical hypersensitive response and apoptosis‐related events including DNA laddering. The protein‐encoding gene was cloned by rapid amplification of cDNA ends (RACE) method. The sequence analysis revealed that the cDNA is 495 bp in length and the open reading frame (ORF) encodes for a polypeptide of 163 amino acids with theoretical pI of 5.50 and molecular weight of 17 562.5 Da. Hrip1 induced calcium influx, medium alkalinization, activation of salicylic acid‐induced protein kinase and several defence‐related genes after infiltration in tobacco leaves. Cellular damage, restricted to the infiltrated zone, occurred only several hours later, at a time when expression of defence‐related genes was activated. After several days, systemic acquired resistance was also induced. The tobacco plant cells that perceived the Hrip1 generated a cascade of signals acting at local, short, and long distances, and caused the coordinated expression of specific defence responses in a way similar to hypersensitivity to tobacco mosaic virus. Thus, Hrip1 represents a powerful tool to investigate further the signals and their transduction pathways involved in induced disease resistance in necrotrophic fungi.     

The inhibition of molting fluid enzymes of Pod borer,Helicoverpa armigera (Hubner) by an aspartic protease inhibitor: Its effects on insect development

In this study, the inhibition of molting fluid enzymes from Helicoverpa armigera by an aspartic protease inhibitor, Alkalophilic Thermophilic Bacillus Inhibitor (ATBI) purified from Bacillus sp. is reported. The in vitro experiments showed 80% inhibition (IC₅₀= 48 µM) of hemoglobin hydrolyzing and 95% inhibition (IC₅₀= 35 µM) of chitin hydrolyzing activity from molting fluid by ATBI (IC₅₀ value is the ATBI concentration for 50% inhibition of total enzymatic activity). The treatment of H. armigera larvae with 400 µM ATBI recorded 20% larval mortality, 27.77% deformed pupae and 12.22% deformed adults. The LC₅₀ value (Concentration of ATBI calculated to give 50% mortality) calculated for insect population was found to be 330.06 µM. Similarly, significant variations in mean larval and pupal weight, no. of eggs laid per female and percent hatching of eggs were observed at higher concentrations of ATBI. The results may provide the basis for the selection of non-host inhibitors to develop a H. armigera insecticide formulation.     

Inhibition of Gibberellic Acid-induced Starch Mobilization by Salicylhydroxamic acid in Avena fatua L. Seed

Inhibition of GA₃-induced endosperm mobilization in Avena fatuaL. by salicylhydroxamic acid (SHAM), a widely used alternativerespiration inhibitor, was studied. SHAM strongly inhibitedthe GA₃-induced release of reducing sugars in the incubationmedium by 3 mm de-embryonated endosperm segments; at 4 mM SHAM,GA₃-induced sugar release was inhibited by 66–79 per cent.Extracts prepared from segments incubated in 0.05 mM GA₃ with2, 5 and 10 mM SHAM showed 30, 53 and 71 per cent lower -amylaseactivity, respectively, compared to the GA₃-alone treatment.Addition of SHAM (0.5–5 mM) during the enzyme assay hadno effect on the activity of -amylase. Thus, the inhibitionof starch mobilization in endosperm by SHAM is due to inhibitionof the production and not the activity of -amylase. The inhibitionof Avena fatua seedling growth by SHAM reported earlier may,in part, be due to its effect on endosperm mobilization. Since (1) Avena fatua seeds have been shown to have little orno SHAM-sensitive respiration, and (2) concentrations of SHAMnecessary for inhibiting endosperm mobilization were significantlyhigher than those generally necessary for inhibiting alternativerespiration, the inhibition of endosperm mobilization by thiscompound does not appear to involve its effect on alternativerespiration. Avena fatua L., wild oat, -amylase, endosperm, gibberellic acid, salicylhydroxamic acid, seed     

Genetic mapping and QTL analysis of agronomic traits in Indian <Emphasis Type="Italic">Mucuna pruriens</Emphasis> using an intraspecific F<Subscript>2</Subscript> population

Mucuna pruriens is a well-recognized agricultural and horticultural crop with important medicinal use. However, antinutritional factors in seed and adverse morphological characters have negatively affected its cultivation. To elucidate the genetic control of agronomic traits, an intraspecific genetic linkage map of Indian M. pruriens has been developed based on amplified fragment length polymorphism (AFLP) markers using 200 F ₂ progenies derived from a cross between wild and cultivated genotypes. The resulting linkage map comprised 129 AFLP markers dispersed over 13 linkage groups spanning a total distance of 618.88 cM with an average marker interval of 4.79 cM. For the first time, three QTLs explaining about 6.05–14.77% of the corresponding total phenotypic variation for three quantitative (seed) traits and, eight QTLs explaining about 25.96% of the corresponding total phenotypic variation for three qualitative traits have been detected on four linkage groups. The map presented here will pave a way for mapping of genes/QTLs for the important agronomic and horticultural traits contrasting between the parents used in this study.     

Differential Response of Pure Lines of Avena fatua L. to Substituted Phthalimides: Germination and Endosperm-mobilization Studies

The germination and endosperm-mobilization responses of twogenetically pure lines (AN-51 and Mont 73) of Avena fatua (wildoat) to gibberellic acid (GA₃, ) and three substituted phthalimides(experimental compounds AC-92, 803, AC-94, 377 and AC-99, 524)were studied. The line AN-51 showed a much greater responseto GA₃, in terms of the percentage and the rate of stimulationof germination, than Mont 73. These lines also differed significantlyin their response to AC-94, 377 and AC-99, 524. The relativegermination response of the two lines to these phthalimideswas very similar to that for GA₃. The phthalimide AC-94, 377was more effective at stimulating germination than AC-99, 524,whereas AC-92, 803 had little or no effect. Salicylhydroxamate,an inhibitor of alternative respiration, did not inhibit theAC-94, 377-induced germination. Like GA₃, AC-94, 377 induced -amylase production and the releaseof reducing sugars by 3 mm endosperm segments. GA₃, was mosteffective at inducing endosperm mobilization, followed by AC-94,377, AC-99, 524 and AC-92, 803, respectively. The line AN-51showed a significantly greater response to both AC-94, 377 andGA₃, than Mont 73. It is concluded that: (1) genetically pure lines of wild oatsdiffer in their response to substituted phthalimides - the lineAN-51 being more responsive than Mont 73, (2) the phthalimideAC-94, 377 is the most effective at inducing germination andAC-92, 803 the least, (3) like GA₃, phthalimides induce endospermmobilization and pure lines differ in the degree of this response,and (4) salicylhydroxamate-sensitive respiration is not necessaryfor the stimulation of germination by AC-94-77. The similaritiesin the effects of AC-94, 377 and GA₂, (two structurally dissimilarcompounds), and in the relative response of the two lines tothese chemicals may provide a useful system for the investigationof wild oat seed physiology. The differential susceptibilityof pure lines to phthalimides also indicates that use of thesecompounds to deplete wild oat seed banks may increase the proportionof less responsive biotype(s) in field populations. Wild oats, weed seed bank, dormancy, germination, endosperm mobilization, -amylase, Avena fatua, phthalimides, gibberellic acid     

Action of Respiratory Inhibitors on Seed Germination and Oxygen Uptake in Avena fatua L.

The effects of sodium azide, potassium cyanide (cytochrome oxidaseinhibitors), and salicylhydroxamic acid (SHAM; an alternativerespiration inhibitor) on germination and respiration of Avenafatua L. seeds were studied. Azide and cyanide released seeddormancy at similar concentrations and treatment durations.Cyanide, however, stimulated germination of seeds with littleafter-ripening, whereas azide had no effect under similar conditionsunless the seeds were after-ripened for several months; theduration of after-ripening required for seeds to respond toazide varied with seed batch. There was also a greater lag priorto germination in the case of azide, compared to cyanide treatedseeds. SHAM inhibited the stimulation of germination and respirationby azide, but not by cyanide. Furthermore, respiration induced by azide or cyanide could notbe inhibited by the subsequent application of SHAM. These findingssuggest that the respiration stimulated by azide and cyanideis not alternative (SHAM-sensitive) and, therefore, this respiratorypathway cannot be involved in the stimulation of germinationby cytochrome oxidase inhibitors. While embryos excised fromcontrol, azide or cyanide pretreated seeds had the capacityto perform alternative respiration, the actual contributionof this pathway was negligible. A large proportion of respirationof embryos excised from azide or cyanide pretreated seeds wasresidual, i.e. insensitive to both SHAM and cyanide. Alternative respiration, azide, cyanide, dormancy, salicylhydroxamic acid, wild oats     

In defence of model‐based inference in phylogeography

Recent papers have promoted the view that model‐based methods in general, and those based on Approximate Bayesian Computation (ABC) in particular, are flawed in a number of ways, and are therefore inappropriate for the analysis of phylogeographic data. These papers further argue that Nested Clade Phylogeographic Analysis (NCPA) offers the best approach in statistical phylogeography. In order to remove the confusion and misconceptions introduced by these papers, we justify and explain the reasoning behind model‐based inference. We argue that ABC is a statistically valid approach, alongside other computational statistical techniques that have been successfully used to infer parameters and compare models in population genetics. We also examine the NCPA method and highlight numerous deficiencies, either when used with single or multiple loci. We further show that the ages of clades are carelessly used to infer ages of demographic events, that these ages are estimated under a simple model of panmixia and population stationarity but are then used under different and unspecified models to test hypotheses, a usage the invalidates these testing procedures. We conclude by encouraging researchers to study and use model‐based inference in population genetics.