The Auxin Transport Inhibitor N-(1-Naphthyl)phthalamic Acid Elicits Pseudonodules on Nonnodulating Mutants of White Sweetclover.

The collection of symbiotic (sym) mutants of white sweetclover (Melilotus alba Desr.) provides a developmental sequence of mutants blocked early in infection or nodule organogenesis. Mutant phenotypes include non-nodulating mutants that exhibit root-hair deformations in response to Rhizobium meliloti, mutants that form ineffective nodules lacking infection threads, and mutants that form infection threads and ineffective nodules. Mutant alleles from both the sym-1 and the sym-3 loci exhibited a non-nodulating phenotype in response to R. meliloti, although one allele in the sym-1 locus formed ineffective nodules at a low frequency. Spot-inoculation experiments on a non-nodulating allele in the sym-3 locus indicated that this mutant lacked cortical cell divisions following inoculation with R. meliloti. The auxin transport inhibitor N-(1-naphthyl)phthalamic acid elicited development of pseudonodules at a high frequency on all of the sweetclover sym mutants, including the non-nodulating mutants, in which the early nodulin ENOD2 was expressed. This suggests that N-(1-naphthyl)phthalamic acid activates cortical cell divisions by circumventing a secondary signal transduction event that is lacking in the non-nodulating sweetclover mutants. The sym-3 locus and possibly the sym-1 locus appear to be essential to early host plant responses essential to nodule organogenesis.

Cytokinin action is coupled to ethylene in its effects on the inhibition of root and hypocotyl elongation in Arabidopsis thaliana seedlings.

Cytokinins have profound effects on seedling development in Arabidopsis thaliana. Benzyladenine (BA) inhibits root elongation in light- or dark-grown seedlings, and in dark-grown seedlings BA inhibits hypocotyl elongation and exaggerates the curvature of apical hooks. The latter are characteristic ethylene responses and, therefore, the possible involvement of ethylene in BA responses was examined in seedlings. It was found that the inhibitory effects of BA on root and hypocotyl elongation were partially blocked by the action of ethylene inhibitors or ethylene-resistant mutations (ein1-1 and ein2-1). Ethylene production was stimulated by submicromolar concentrations of BA and could account, in part, for the inhibition of root and hypocotyl elongation. It was demonstrated further that BA did not affect the sensitivity of seedlings to ethylene. Thus, the effect of cytokinin on root and hypocotyl elongation in Arabidopsis appears to be mediated largely by the production of ethylene. The coupling between cytokinin and ethylene responses is further supported by the discovery that the cytokinin-resistant mutant ckr1 is resistant to ethylene and is allelic to the ethylene-resistant mutant ein2.

Five Nodulation Mutants of White Sweetclover (Melilotus alba Desr.) Exhibit Distinct Phenotypes Blocked at Root Hair Curling, Infection Thread Development, and Nodule Organogenesis.

In an effort to obtain a developmental sequence of mutations in the Rhizobium-legume interaction within a single legume species, we have characterized the early events of nodule development in 10 nodulation mutants of sweetclover, Melilotus alba Desr. cv U389, representing five genetic loci. Both seed and root exudates from all of the sweetclover mutants induced expression of the nod genes of Rhizobium meliloti. Mutants in three loci were blocked in the early stages of root hair curling. Of these, a mutant in the sym-3 locus exhibited root hair deformations in response to inoculation with R. meliloti but produced no nodules or emerging nodule primordia, suggesting a blockage in the signal transduction events leading to nodule organogenesis. In contrast, mutants in both the sym-1 and sym-5 loci formed ineffective nodules in response to inoculation but differed slightly in the type of root hair response observed. None of these three early mutants formed infection threads. Infection threads were observed in mutant sym-2 as well as in ineffective nodules. Mutant sym-4 also formed infection threads but lacked nodules. The phenotypes observed for mutants from these five loci suggest that a secondary receptor or signal produced by the plant is required for nodule development.

ATP promotes the appearance of two DNA-binding forms of the Ah receptor.

Following the binding of a specific ligand such as 2,3,7,8-tetrachlorodibenzo-p-dioxin, mild heating has previously been shown to convert cytosolic aryl hydrocarbon (Ah) receptor to two DNA-binding forms: peak I, which appears to be an Ah receptor monomer; and peak II, which is larger and resembles nuclear Ah receptor. In rat liver cytosol pretreated with charcoal-dextran, and heated briefly at 22 degrees C, the addition of a physiological (3 mM) concentration of ATP substantially increases the formation of both peak I and peak II receptor. On more extended incubation in the presence of ATP most of the Ah receptor converts to the tighter binding peak II form. The ATP analog 5'-adenylylmethylene diphosphonate (AMPPCP) stimulates the appearance of both DNA-binding forms as effectively as ATP does. In cytosol separated from low molecular weight components by gel filtration prior to incubation, ATP substantially stimulates the appearance of peak II receptor. ATP also increases the amount of peak II receptor formed when peak I receptor is incubated with unlabeled charcoal-treated cytosol. Thus, ATP promotes both the release of Ah receptor monomer from the 9 S complex which cannot bind DNA and the subsequent conversion of that monomer to a form similar or identical to nuclear Ah receptor.

Nucleoside triphosphates promote the transformation of Ah receptor to its DNA-binding form.

When it is bound to a specific ligand such as 2,3,7,8-tetrachlorodibenzo-p-dioxin, mild heating can convert the Ah (aryl hydrocarbon) receptor into a form capable of binding DNA. We found that physiological (1-3 mM) levels of ATP substantially increased the transformation of the receptor to its DNA-binding form. GTP, UTP and CTP had similar effects. ADP also promoted this transformation, but was less effective than ATP at low concentrations. Pyrophosphate too promoted transformation, but AMP had little effect. The process did not require nucleotide hydrolysis, since non-hydrolysable analogues of ATP such as adenosine 5'-[beta gamma-imido]triphosphate were nearly as effective as ATP itself. Inhibitors of ATP-stimulated proteases did not significantly affect the ability of ATP to promote receptor transformation, which suggests that the effect of ATP was not mediated by these proteases.

Intervention rates in spontaneous term labour in low risk nulliparous women.

This study analyses retrospectively the outcome of labour in 3,058 consecutive low risk nulliparous women in spontaneous labour at term in public and private care at the Mater Mothers' Hospital, Brisbane, Queensland. Differing rates of spontaneous, instrumental or Caesarean deliveries were found between the public and private cohorts (spontaneous vaginal delivery 73.7% public, 48.6% private; instrumental 17.9% public, 35.4% private; Caesarean section 8.4% public, 16% private). These differences were all highly statistically significant (p less than .001). Other statistically significant differences were evident in durations of labour and second stage of labour. Demographically the 2 groups were dissimilar, illustrated by differences in age distribution. Correcting for age difference failed to account for the differences in frequency of delivery methods between the private and public groups.