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Managing secondary dryland salinity: Options and challenges   总被引:1,自引:0,他引:1  
Salt occurs naturally at high levels in the subsoils of most Australian agricultural land. As a result of clearing native vegetation, groundwater tables have risen, mobilising the stored salt and causing adverse impacts on farmland, infrastructure, water resources, and biodiversity. The main action required to prevent groundwater tables from rising is establishment of perennial plants, either herbaceous (pastures or crops) or woody (trees and shrubs). Recent technical and economic research has emphasised how difficult it will be to establish sufficient perennials to get control of groundwater tables. Where watertables are already shallow, the options for farmers are salt-tolerant plants (e.g. saltbush for grazing) or engineering (e.g. deep open drains). The existing options for farm-level salinity management are reviewed, with mixed but somewhat disappointing findings regarding their suitability for addressing salinity. However, there are also a number of good prospects for development of new and better options for plant-based management of salinity, and these are described.  相似文献   
105.
The molecular weight pattern and the stage-specific activities of chitinases from the blowfly Lucilia cuprina, the tick Boophilus microplus and the intestinal nematode Haemonchus contortus were examined. Chitinolytic enzymes could be detected in all parasite species tested, but the activity was different between the stages. Highest chitinolytic titers were found in blowfly pupae (83 kDa, 118 kDa), hatching larvae of ticks (58 kDa, 94 kDa) and nematode eggs (43 kDa). Leaves from ethylene-treated bean plants Phaseolus vulgaris expressed two basic Class I chitinases (Ia, Ib) of 34 kDa, differing in their amino acid sequences at residue 33 and 34 (Ia: glycine, proline; Ib: lysine, aspartic acid). Inhibitor studies with blowfly pupae revealed that allosamidin (IC50=0·32 (±0·02) μM ) was by far the best inhibitor when compared with various amino sugar derivatives. This compound also inhibited chitinases from tick larvae (IC50=0·69(±0·10) μM ) and nematode eggs (IC50=0·048(±0·0045) μM ) specifically. Whereas Class Ia chitinase from bean leaves was inhibited only up to 18% by 10 μM allosamidin, it had an IC50 of 1(±0·14) μM for the Ib type, which is the first plant chitinase described to be highly sensitive to allosamidin.  相似文献   
106.
The cyclic depsipeptide PF1022A, given orally to mice, showed very good anthelmintic activity against Heligmosomoides polygyrus and Heterakis spumosa at 50 mg kg−1. In vitro, PF1022A was very active against Trichinella spiralis and had good activity against Nippostrongylus brasiliensis at 1 μg ml−1. An 18-membered enniatin analogue, JES 1798, showed good activity only against N. brasiliensis at 10 μg ml−1. The optical antipode of PF1022A had poor activity even at 100 μg ml−1. The effects of PF1022A on the membrane potential and input conductance of somatic muscle of Ascaris suum were examined using a two-microelectrode current-clamp technique. PF1022A did not antagonize the effects of the selective nicotinic agonist levamisole. PF1022A and an analogue, JES 1798, but not the PF1022A antipode, produced a small time-dependent increase in input conductance associated with no potential change. The increase in input conductance did not occur in the Cl-free bathing solution, suggesting that the increase in input conductance was mediated by Cl ions. The addition of high concentrations of Ca2+ to the preparation after the addition of PF1022A did not lead to production of Ca2+-activated Cl channels, suggesting that its mode of action was not that of a Ca2+ ionophore. The mechanism by which the cyclic depsipeptide might increase the Cl conductance is discussed.  相似文献   
107.
A GC-MS method capable of completely separating the four pairs of diastereoisomers of cyfluthrin is presented and the method used to show that isomerisation of the cyfluthrin enantiomers occurs in methanol. This methanol-induced isomerisation could also be demonstrated by bioassays using water fleas. The biological activities of the various cyfluthrin isomers contained in the commercial products cyfluthrin and beta-cyfluthrin were assayed using several strains of lepidopteran larvae including Plutella xylostella, Heliothis virescens and Spodoptera frugiperda. With the susceptible strains, the efficiencies of the isomers mixtures of cyfluthrin and beta-cyfluthrin were shown to obey the rules of additivity. However, in tests with a resistant strain of P. xylostella originating from Thailand, the ‘inactive’ isomer III acted synergistically with the active isomer IV. Resistance factors in strains of H. virescens and P. xylostella were found to be higher with cis than with trans isomers. This probably contributes to the superior action of cyfluthrin and beta-cyfluthrin against various pests of agricultural importance since the commercial products contain a high content of trans isomers (‘high trans pyrethroids’).  相似文献   
108.
The calcium channel and the ‘calcium release channel’ of muscle membrane of the cockroach Periplaneta americana have been characterized. Biological assays with calcium channel blockers and ryanodine on different insects and acari revealed pronounced insecticidal effects with ryanodine, but not with calcium channel blockers, at concentrations between 0·1 and 300 μg ml−1. Skeletal muscle membranes derived either from the tubular network or from the sarcoplasmatic reticulum of P. americana were characterized with respect to the binding of the dihydropyridine (DHP) [3H]isradipine (PN 200-110), the phenyl-alkylamine [3H]verapamil and the alkaloid [3H]ryanodine. Preliminary binding studies with the benzothiazepine [3H]diltiazem suggest a low-affinity binding site with a IC50 value of 3·3 μM . All binding sites tested were sensitive to treatment with proteinase K. Optimal conditions for binding of the radioligand ryanodine revealed the highest specific binding at pH 8 and at calcium chloride concentrations between 100 and 500 μM . EGTA at 10 μM abolished 95% of the ryanodine binding. Binding studies with calcium channel binding sites revealed a pronounced effect of low Ca2+ concentrations on specific isradipine binding, whereas verapamil and diltiazem binding were only reduced by the presence of 200 μM EGTA. With respect to high Ca2+ concentrations, specific binding of diltiazem, isradipine and verapamil was reduced by 73, 40 and 20%, respectively, at 5 mM Ca2+. Radioligand binding experiments showed high-affinity binding sites for ryanodine and isradipine. KD values of 0·95 nM (Bmax=550 fmol mg−1 protein) and 0·75 nM (Bmax=213 fmol mg−1 protein) were determined respectively. A lower-affinity binding site was identified in binding studies with verapamil (KD=7·4 nM and Bmax=27 fmol mg−1 protein). [3H]isradipine displacement studies with several dihydropyridines revealed the following ranking of affinity: nitrendipine>isradipine>Bay K8664≪nicardipine. Displacement of [3H]verapamil binding by effectors of the phenylalkylamine binding site showed that bepridil and S(-)verapamil had the highest affinities of the compounds tested followed by (±)verapamil, nor-methylverapamil and R(+)verapamil.  相似文献   
109.
A muscarinic acetylcholine receptor (mAChR) has been demonstrated and partially characterized in larvae of the cattle tick Boophilus microplus. Its properties are compared with mAChR from an epithelial cell line from the dipteran insect Chironomus tentans. Competition studies with cholinergic ligands of different specificity revealed the muscarinic nature of the cholinergic receptors investigated in both species. In homogenates from tick larvae, specific binding sites for [3H]quinuclidinyl benzilate (QNB) with high affinity (1·2±(0·13) nM ; Bmax 22·5 pmol mg protein−1) were detected that do not bind nicotinic compounds specifically. The estimated IC50 values for nicotine, imidacloprid and α-bungarotoxin were all in the mM range. Additionally, with tick larvae, high-affinity nicotinic binding sites were detected with [3H]nicotine which could be displaced by high concentrations of imidacloprid or QNB. The estimated IC50 values for nicotine, α-bungarotoxin, imidacloprid and QNB were 43(±8) nM , 0·8(±0·2) μM , 2·8(±0·6) μM and 78(±1·9) μM , respectively. With homogenates of the non-neuronal insect cell line from C. tentans, only high-affinity binding sites for [3H]QNB were found. Muscarinic antagonists selectively displaced [3H]quinuclidinyl benzilate (QNB) binding to tick larvae homogenates. The mAChR of B. microplus preferred pirenzepine (IC50 2·13(±1·02) μM ) among different subtype-specific mAChR antagonists (4-DAMP had IC50 49·9(±9·13) μM and methoctramine had IC50 121(±14·2) μM ) indicating a type of binding site similar to the vertebrate M1 mAChR subtype. The tick muscarinic receptor seems to be a G-protein-coupled receptor, as concluded from the 4·8-fold reduction in receptor affinity for binding of the muscarinic agonist oxotremorine M upon treatment with the non-hydrolysable GTP-analogue γ-S-GTP. Binding data for the agonists oxotremorine M (IC50 71·3(±19·6) μM ) and carbachol (IC50 253(±87·1) μM ) parallel the biological efficacy of these compounds, in that, while oxotremorine M showed some activity against ticks, carbachol was ineffective.  相似文献   
110.
The heading date is an important trait for determining regional and climatic adaptability in rice. To expand the adaptability of the indica rice cultivar ‘IR64’, we pyramided multiple early or late heading quantitative trait locus (QTLs) in the ‘IR64’ genetic background by crossing previously developed near-isogenic lines (NILs) with a single QTL for early or late heading. The effects of pyramiding QTLs were observed in three different climatic zones of the Philippines, Madagascar, and Japan. The early heading pyramiding lines (PYLs) headed 6.2 to 12.8 days earlier than ‘IR64’ while the late heading PYLs headed 18.8 to 27.1 days later than ‘IR64’. The PYLs tended to produce low grain yield compared to ‘IR64’. The low yield was not improved by combining SPIKE, which is a QTL that increases the number of spikelets per panicle. Conversely, ‘IR64-PYL(7+10)’ carrying Hd5 and Hd1 headed earlier, produced more tillers, and more panicles per m2 than ‘IR64’, and mitigated the yield decrease in early heading. These results suggest that the effects of pyramided QTLs on heading date were consistent across various environments and PYLs could be used to enhance the adaptation of ‘IR64’ in other rice growing environments.  相似文献   
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