Effect of 3-Amino-1,2,4-Triazole on Histidine Metabolism in Algae

Growth of Chlorella vulgaris and Prototheca zopfii is inhibited by treatment with 3-amino-1,2,4-triazole. Growth of these 2 algae in the presence of amino triazole is accompanied by the accumulation in the culture media of the dephosphorylated histidine precursor, imidazoleglycerol. The addition of histidine to the culture media in the presence of amino triazole restored the normal growth rates of these organisms and reduced the accumulation of imidazoleglycerol. These data suggest that amino triazole inhibits the synthesis of histidine by interfering with the activity of the enzyme, imidazoleglycerol phosphate dehydrase.     

Regulation of ascorbate peroxidase activity in dark-grown radish cotyledons by a catalase inhibitor, 3-Amino-1,2,4-Triazole

The present study was performed to see the physiological role of cytosolic ascorbate peroxidase (APX) and its relationship to other enzymes involved in the H₂O₂ scavenging metabolism, and also to elucidate the regulation of APX expression in dark-grown radish (Raphanus sativus L. cv Taiwang) cotyledons. To do so, 3-amino-l,2,4-triazole (aminotriazole), a known specific inhibitor of catalase, was used to simulate a catalase-deficient phenomenon in cotyledons. Aminotriazole, in very low concetration (10^-4 M), inhibited remarkably the development of catalase activity in cotyledons during dark germination. This inhibition of catalase by aminotriazole, however, did not result in any significant changes in the growth response and the H₂O₂ level of developing cotyledons. In addition, the development of guaiacol peroxidase (GPX) activity was also not significantly affected. Unlike GPX, cytosolic APX activity was induced rapidly and reached a 1.7-fold increase in aminotriazole treated cotyledons at day 7 after germination. However,in vitro incubation of cytosolic APX preparation from cotyledons with aminotriazole did not result in any significant change in activity. One cytosolic APX isozyme (APXa) band involved in this APX activation was predominantly intensified in a native polyacrylamide gel by activity staining assay. This means that this APXa isozyme seems to play a key role in the expression of cytosolic APX activity. On the other hand, 2-day-old control seedlings treated with exogenous 1 mM H₂O₂ for 1 h showed a significant increase of cytosolic APX acitivity even in the absence of aminotriazole. Also, 2 μM cycloheximide treatment substantially inhibited the increase of APX activity due to aminotriazole. Based on these results, we suggest that a radish cytosolic APX could probably be substituted for catalase in H₂O₂ removal and that the expression of APX seems to be regulated by a change of endogenous H₂O₂ level which couples to APX protein synthesis in a translation stage in cotyledons.     

The in Vivo and in Vitro Inhibition of Catalase from Leaves of Nicotiana sylvestris by 3-Amino-1,2,4-Triazole

Seedlings of tobacco (Nicotiana sylvestris) were treated in vivo with 0.03 to 20 millimolar 3-amino-1,2,4-triazole (aminotriazole). There was a rapid loss of catalase (EC 1.11.1.6) activity over the first 5 hours followed by a slower decrease for the next 4 hours to a level that was 15 to 20% of the initial activity, with little or no change for periods up to 3 days. Fifty percent loss of catalase activity occurred at 0.10 to 0.15 millimolar inhibitor (18-hour incubation). The isozymes of tobacco catalase differed in sensitivity to the inhibitor. Enhanced-peroxidatic catalase (EP-CAT) (Havir EA, McHale NA, [1989] Plant Physiol 91: 812-815) decreased 35% under conditions in which the major isozyme decreased 85%. The resistance to aminotriazole inhibition demonstrated in vivo by EP-CAT was also observed in vitro. The times for 50% inhibition at 0.67, 3.33, 5.0, 10.0, and 15 millimolar aminotriazole were 15, 5, 2.6, 2.5, and 1.5 minutes, respectively, for the major isozyme of catalase and 60, 18.5, 5.1, 4, and 3.0 minutes, respectively, for EP-CAT. Increasing H₂O₂ concentration did not change the sensitivity of EP-CAT to aminotriazole. The major form of catalase contained 4.0 ± 0.4 moles of heme per mole enzyme and EP-CAT 3.4 ± 0.3. Thus, the resistance of EP-CAT to aminotriazole is probably not due to lowered affinity for H₂O₂ or alteration in heme content but to structural changes that impair inhibitor binding.     

Mowing during rainfall enhances the control of Cirsium arvense

Pastoral farmers in New Zealand have described dramatic demises in populations of the weed Cirsium arvense (L.) Scop., a perennial herb indigenous to Eurasia, following its mowing during rainfall. To test the hypotheses (1) that the mowing of C. arvense during rainfall increases the control of this weed and (2) that the causal organism in this ‘mowing-in-the-rain’ effect is the vascular wilt fungus Verticillium dahliae, two series of field experiments were carried out in C. arvense-infested pastures in New Zealand, one in autumn 2008 (Experiment series 1, 9 farms), and another in spring/summer 2008–2009 (Experiment series 2, 12 farms). The effect of mowing in the rain as compared to mowing in the dry was to reduce the % ground cover of the thistle in the spring following treatment by 21 and 32% in Experiment series 1 and 2, respectively. Correlations of this ‘rain versus dry’ effect with the incidence of V. dahliae in the subterranean parts of C. arvense shoots sampled in each of the two field experiment series provided no statistical evidence that the effect increased with V. dahliae incidence. Thus these experiments provide no support for the hypothesis that V. dahliae is the biological mechanism for the ‘mowing-in-the-rain’ effect. Nevertheless, they do support mowing during rainfall as a simple and effective management tactic for C. arvense.     

Establishing systemic rust infections in Cirsium arvense in the field

An existing method to induce systemic rust infections in creeping thistles (Cirsium arvense) using an insect vector, the weevil Ceratapion onopordi, was successfully applied in the field. Urediniospores of Puccinia punctiformis were experimentally transmitted to naturally grown thistles, to our knowledge for the first time resulting in systemically infected shoots in an established thistle population.     

Effects of pasture competition and specialist herbivory on the performance of Cirsium arvense

Combining specialist herbivory with interspecific plant competition can be an effective means of controlling pasture weeds. Cirsium arvense (Canada thistle, Californian thistle, creeping thistle) is one of the worst weeds of pastoral production systems in New Zealand (NZ). The oligophagous leaf-feeding beetle, Cassida rubiginosa, was recently released in NZ for control of C. arvense. To assess the impact of this biocontrol agent we conducted an outdoor potted-plant experiment with low and high densities of Cassida larvae combined with different levels of interspecific competition from typical NZ pasture species. Secondly, we carried out a field-release experiment to quantify the impact of high densities of Cassida under more natural conditions. Interspecific competition reduced all measured plant parameters of C. arvense except mean shoot height and base diameter. Herbivory by Cassida only reduced root biomass, and showed a weak additive response when combined with competition. All other measured parameters of C. arvense showed a substitutive response, with competition being the only factor having a significant impact on the weed. There were no significant synergistic interactions with competition and herbivory on C. arvense. Interestingly, the number of root buds per plant was significantly greater in the presence of herbivory by Cassida, suggesting that C. arvense may compensate for defoliation. Similar to the potted-plant experiment, Cassida had no significant effect on shoot growth and development in the field-release experiment. The results of this study indicate that competition from typical NZ pasture species is a more important factor than herbivory by Cassida, and unless Cassida reaches outbreak densities, it will likely have an insignificant impact on this weed.     

Effect of Application Time on the Efficacy of Sclerotinia sclerotiorum as a Mycoherbicide for Cirsium arvense Control in Pasture

An experiment was conducted in sheep-grazed pasture in three regions of New Zealand over three years to evaluate the effect of application time on the efficacy of a dry granule myceliumon-wheat formulation of Sclerotinia sclerotiorum for the biological control of Cirsium arvense . At each site, the experimental mycoherbicide was applied to a previously untreated plot in each month of the year for three years at a dose of 50 g m -2 . Applications made during the spring and early summer months of October, November and December significantly reduced the ground cover of C. arvense for 67, 67 and 44%, respectively of these applications. Reduced ground covers ranged from 38 to 81% of the cover on untreated plots. Applications in late summer and autumn were less effective. Correlations of ground cover by C. arvense with climate parameters suggested that free moisture promoted treatment efficacy, but that intense rainfall after treatment reduced efficacy through wash off. The importance of leaf wetness for the efficacy of the mycoherbicide was confirmed by comparing disease development and mortality in C. arvense shoots with and without enhanced moisture levels under field conditions. A water miscible formulation applied as a slurry was less dependent upon leaf wetness than the dry granule formulation.     

Anatomical Injury Induced by the Eriophyid Mite Aceria anthocoptes on the Leaves of Cirsium arvense

Anatomical injury of the leaves of the invasive species, Cirsium arvense (L.) Scop., caused by the eriophyid mite Aceria anthocoptes (Nal.), which is the only eriophyid mite that has been recorded on C. arvense worldwide, is described. The injury induced by the mite feeding on the leaves of C. arvense results in visible russeting and bronzing of the leaves. Other conspicuous deformations are folding and distortion of the leaf blade and curling of leaf edge, as well as gradual drying of leaves. The anatomical injury of the mature leaves of field-collected plants was limited to the epidermis of the lower leaf surface. However, on young leaves of experimentally infested plants, rust mite injuries extend to epidermal cells on both leaf surfaces and to those of deeper mesophyll layers. On these leaves, lesions on the lower leaf surface even affected the phloem of the vascular bundles. Leaf damage induced by A. anthocoptes is discussed with regard to the mite’s potential as a biological control agent of C. arvense.