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     

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     

The first genetic map of pigeon pea based on diversity arrays technology (DArT) markers

With an objective to develop a genetic map in pigeon pea (Cajanus spp.), a total of 554 diversity arrays technology (DArT) markers showed polymorphism in a pigeon pea F₂ mapping population of 72 progenies derived from an interspecific cross of ICP 28 (Cajanus cajan) and ICPW 94 (Cajanus scarabaeoides). Approximately 13% of markers did not conform to expected segregation ratio. The total number of DArT marker loci segregating in Mendelian manner was 405 with 73.1% (P > 0.001) of DArT markers having unique segregation patterns. Two groups of genetic maps were generated using DArT markers. While the maternal genetic linkage map had 122 unique DArT maternal marker loci, the paternal genetic linkage map has a total of 172 unique DArT paternal marker loci. The length of these two maps covered 270.0 cM and 451.6 cM, respectively. These are the first genetic linkage maps developed for pigeon pea, and this is the first report of genetic mapping in any grain legume using diversity arrays technology.     

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     

Comparison of [14C]oryzalin Uptake in Root Segments of a Sensitive and a Resistant Species

Uptake of the dinitroaniline herbicide oryzalin (3,5-dinitro-N⁴,N⁴-dipropylsulfamlamide) and its effect on root growth werestudied using 5 mm corn (Zea mays L.) and pea (Pisum sativum)root apices. Pea root growth was much less susceptible to oryzalinthan corn root growth. Uptake studies showed that pea root apicesalso accumulated much less [¹⁴C]oryzalin and had a lower bindingaffinity for this herbicide. [¹⁴C]oryzalin was not metabolizedin root apices from either species. Thus, the differential susceptibilityto oryzalin in the case of corn versus pea can be explained,at least in part, by differences in oryzalin uptake and accumulationby roots. Oryzalin, dinitroaniline herbicides, Zea mays, Pisum sativum     

Gene effects for specific leaf area and harvest index in three crosses of groundnut (Arachis hypogaea)

Groundnut productivity is low in the semi‐arid tropics mainly because of drought caused by low and erratic rainfall. Genotypes that have ability to use limited available water efficiently are required to enhance productivity of the crop. In groundnut, water use efficiency (WUE) is correlated with specific leaf area (SLA). The latter can be used as a surrogate trait for selecting for WUE. Partitioning of assimilates as measured by the harvest index (HI) has the greatest effect on pod yield. In order to improve SLA and in turn WUE and HI, a good knowledge of genetic systems controlling the expression of these traits is essential for the choice of an efficient breeding procedure. This study was conducted to investigate inheritance of SLA and HI in three crosses involving Chico, TMV 2 NLM, and ICGV 86031 groundnut genotypes. The study included parents, F1, F2, and backcross generations. Generation means analysis indicated that the additive effects were more important than the dominance effects in the expression of SLA and HI. In addition to additive and dominance effects, additive × additive type of epistasis, which can be fixed in groundnut (a self pollinated crop), was also significant for SLA in all the three and for HI, in two crosses. The selection for SLA and HI can be effective in early generations in some crosses and to exploit the additive × additive type of interaction, it can be done in large populations of later generations.     

Shoot and Plantlet Formation in Organ and Callus Cultures of Albizzia lebbek Benth

Plantlets were produced in vitro from root and hypocotyl explantstaken from seedlings of the tree legume, Albizzia lebbek. Theseexplants formed shoots when cultured with 5.0 mg l^–1 kinetinand 1.0 mg l^–1 IAA in MS medium. Shoots were also inducedin large numbers from callus treated with benzylaminopurine.About 20 per cent of the shoots rooted and were grown into plants. Albizzia lebbek Benth, tree legume, hypocotyl, root, in vitro cultures, shoot-plantlet induction     

Some Biochemical Changes Associated with Paclobutrazol-Induced Adventitious Root Formation on Bean Hypocotyl Cuttings

Phaseolus vulgaris hypocotyl cuttings were placed in solutionscontaining either 0 (controls) or 43 µM paclobutrazolfor 24 h after which they were placed in peat– perlitefor 8 d. Paclobutrazol more than doubled the number of rootsformed on the cuttings but did not affect individual root length.Compared with controls, treated cuttings exhibited increasedactivities of catalase, peroxidase, polyphenol oxidase, malatedehydrogenase, protease and RNase in the base of the cuttings.These enhanced enzyme activities were particularly evident between3 and 5 d after excision. The largest paclobutrazol-inducedpromotion of enzyme activity occurred with malate dehydrogenasewhich was increased more than 2-fold compared with the controls.In contrast, paclobutrazol reduced amylase activity in comparisonto controls, suggesting that this enzyme may not be directlyrelated to root formation. These data indicate that the enhancementof adventitious root formation by paclobutrazol is accompaniedby changes in the activities of a number of enzymes which havepreviously been postulated to be involved in rooting. However,these changes in activity are generally greatest later in therooting period, suggesting that they may be involved in thedevelopment rather than the initiation of roots. Enzyme activity, growth regulator, Phaseolus vulgaris L., rooting